# Preparing for REW+BFD



## Trekari (Jan 3, 2008)

In seeking out the best place for my subwoofer (i.e. the one that will require the least amount of EQ with the BFD), I was planning on putting my sub onto my couch and taking REW measurements at potential locations for the subwoofer.

However, where should I be placing the sound meter while doing this? I have a 12" downfiring subwoofer, so should the sound meter be placed on the floor, or 1" off the floor where the cone of the subwoofer normally rests?

Within the next few days, this thread will be turned into my REW measurements thread, once my BFD arrives 

-Jason


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## Wayne A. Pflughaupt (Apr 13, 2006)

Getting it close to where the driver “fires” into the room makes sense to me, but I’m sure as long as the mic is within a foot or so of your proposed location you’ll be fine.

Regards,
Wayne


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## Trekari (Jan 3, 2008)

Thanks for the reply Wayne. Keep your eyes peeled for what hopefully turns out to be decent pre-EQ waterfalls 

Also, is it possible to place the BFD directly on a wooden shelf as I asked in this thread here:

http://www.hometheatershack.com/for...8425-setting-up-speaker-system.html#post74968

My concern stems from the fact this is a rackmount device usually, but I've *never* used such equipment before and do not know if the chassis of the product is expected to be in a rackmount setup, or whether or not I would be posing any sort of a grounding/fire/safety hazard in placing it directly on the wooden shelf.

-Jason


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## Wayne A. Pflughaupt (Apr 13, 2006)

The rack-mounting feature basically means the unit is designed so that it can be fully supported by its faceplate. But it doesn’t have to be used that way. You can locate the BFD anywhere that suits your needs. You might want to add some stick-on rubber feet to the underside, since it doesn’t have any, to avoid scuffing your wood shelf.


http://www.radioshack.com/product/i...=rubber+feet&kw=rubber+feet&parentPage=search

Regards,
Wayne


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## OvalNut (Jul 18, 2006)

> You might want to add some stick-on rubber feet to the underside, since it doesn’t have any, to avoid scuffing your wood shelf.


D'oh! Boy, do I feel like Homer right now. That is a great simple idea Wayne. Thanks!

Tim
:drive:


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## Trekari (Jan 3, 2008)

Here are my REW graphs for 4 sub positions.

I was unable to get the input volume higher than -22dB during actual measurements. The measured -3dB according to JBL of my sub is 25Hz, but my graphs are way worse than that? 

How 'bad' do these actually appear? Subwoofer only was measured, the mains were completely disconnected.


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## brucek (Apr 11, 2006)

> I was unable to get the input volume higher than -22dB during actual measurements


Use a more sensitive scale on the meter (as long as it doesn't clip during the measure - don't get so sensitive as to peg the needle).
Or you can measure at 80dB to increase the input level.



> The measured -3dB according to JBL of my sub is 25Hz, but my graphs are way worse than that?


Do a near field measurement with the sub in the middle of the room to check the actual speakers response with minimal room influence.



> How 'bad' do these actually appear?


Are they filtered responses or are they raw? 
BTW, if you want your filters to be sequencial, there is a "sort" button on the filter pop-up screen.
Overall the response looks great for a sub with a cutiff around 35Hz. 
It's nice to see at least one raw measure to evaluate better.

brucek


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## Trekari (Jan 3, 2008)

Those were raw feeds directly into the AUX connection of my Onkyo TXSR705. I had disabled Audyssey entirely before running these tests. 

Hopefully later today once my neighbors are gone I can run some more measurements, specifically the near-field one you asked for. (I live in a condo and as I'm sure you know, REW measuring is rather loud )

I'm rather confused about two things however.

1) Why is it my internal measurements/calibrations are just fine as far as signal levels, yet when I go to make an actual measurement, the levels are way low, despite not changing *anything* between the internal checks and measuring.

(I understand I can change the sensitivity of the sound meter, but it was already set to 80, which I thought was appropriate?)

2) The cabling I have is mini-stereo line out to dual RCA, converted to single RCA at the receiver end and input via the Right AUX channel. From the sound meter I have a Right-only RCA connected, going to the Right-only AUX2 connection on my X-Fi Platinum (which in this case is using an RCA line-level input on the front panel). Is this correct, or should the sound meter output be converted into a dual-mono signal?


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## brucek (Apr 11, 2006)

> 1) Why is it my internal measurements/calibrations are just fine as far as signal levels, yet when I go to make an actual measurement, the levels are way low, despite not changing *anything* between the internal checks and measuring.


That's because the _Check Levels_ routine in the Measurement screen and the _Check Levels_ routine in the Settings screen use different values to generate the pink noise for level setting.

The Check Levels routine in the the Settings screen uses the fact that you have the _*Check/Set levels with Subwoofer*_ pull-down selected to generate its test noise. It uses a pink noise low cut of 30Hz and a high cut of 80Hz. This is the energy band that you use to set the Check Levels in the settings screen. See the first attached pic below.

But then to double check and verify that the _*end frequency*_ of the sweep that you have selected in the Measurement panel matches that subwoofer setting, its Check Level routine uses the end frequency as the test pink noise hi-limit cutoff. So if you had 20KHz as the end frequency to measure for your sweep, you can see how the pink noise would be different (between the two Check Levels) and as such you would experience quite a different level. See the second attached pic where 200Hz is the end frequency and the hi-cut of the pink noise is 200Hz. In this case there will be a small difference in the check level result.

Set the End Frequency in the Measurement panel to 200Hz.................. it should be fine.....





















> I understand I can change the sensitivity of the sound meter, but it was already set to 80, which I thought was appropriate?


It is. I thought you might be using a higher one...



> 2) The cabling I have is mini-stereo line out to dual RCA, converted to single RCA at the receiver end and input via the Right AUX channel. From the sound meter I have a Right-only RCA connected, going to the Right-only AUX2 connection on my X-Fi Platinum (which in this case is using an RCA line-level input on the front panel). Is this correct, or should the sound meter output be converted into a dual-mono signal?


That all seems fine. The jacks on the soundcard are stereo, and we need to break them out into the two left and right channels as you've done. 
Then you use one of those broken out channels for the line-in from the mic and the line-out to the receiver. I use a Y-splitter at the receiver to feed left and right AUX in so I can have both mains playing when the time comes - but whatever.... 

brucek


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## Trekari (Jan 3, 2008)

Ok, here is a near-field measurement from the middle of my living room. Below the first graph (near-field) is a measurement from the left of the fireplace next to the dart throw-line. The purple dotted line is what I'd like to correct it to if that will not damage the subwoofer.

Below the purple graph is the waterfall from the current default position near my television. I appear to have the dreaded 'hum' problem? However it's only noticeable at high volumes so...hrm. **EDIT** Nevermind about the hum...it was my coax (television) cable being routed into the surge protector that was causing it.


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## brucek (Apr 11, 2006)

> The purple dotted line is what I'd like to correct it to if that will not damage the subwoofer.


You cannot add +10dB at 28Hz and expect good results. That much gain isn't a good idea. An EQ is better used to remove peaks. If your sub begins to drop off at 35Hz, then that's what it does. Throwing a bunch of gain at it won't solve the problem I'm afraid.

brucek


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## Trekari (Jan 3, 2008)

I guess I should hold off on purchasing a duplicate PB12 to get better sub response . The product literature doesn't specify a -3dB frequency, it simply states the frequency response is 25Hz-crossover setting.

After all this excitement with BFDs and REWs and HCFRs and $$$$ I come to find out my subwoofer, which I used to think was fairly good, is just **** at frequency response :'(

At least I have Comcast coming out tomorrow to fix their grounding problem for free 

-Jason


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## JohnM (Apr 11, 2006)

Where is the sub placed? Sub response specs are often "in-room" assuming some room gain, putting the sub by a wall or in a corner will extend the LF output.


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## brucek (Apr 11, 2006)

> I guess I should hold off on purchasing a duplicate PB12 to get better sub response


Adding a like or similar sub only adds headroom, not response extension...........


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## Trekari (Jan 3, 2008)

Wouldn't it add volume at the lower frequencies? Basically I would've been able to make more filters (cuts) on the range that is already reproduced appropriately, but the second sub would've added a few dB to the lower frequency range that the single sub currently drops off at.

Anyway...I'm impulsive and am looking into a much improved sub anyway


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## brucek (Apr 11, 2006)

If you had ten subs that dropped off at 35Hz, the response would still drop off at 35Hz......

Buy a sub that extends to 15Hz and you'll be happy... 

brucek


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## HClarkx (Nov 10, 2007)

brucek said:


> Adding a like or similar sub only adds headroom, not response extension...........


Bruce, I'm not sure I agree fully with this statement. If the response at the listening position is the same wherever you put the sub, then I agree. But, if the potential sub locations vary in the response they provide at the listening position, then there's an opportunity to have the two subs complement each other. I was able to do that. The result wasn't magical, but I did pretty much eliminate one peak and one dip and pick up a few db below 30 Hz from the combination. And, as you or others have mentioned, I got some headroom that allowed the low end to be EQ'd with less risk of exceeding Xmax (using Audyssey in my case).

It wasn't clear to me how Trekari put his sub in the listening position. I would think it would need to be upside down (it's down firing) and sitting on something to put the sound power out about where the head is positioned. Was that the case? Sitting lower, the sofa/chair would soak up some SPL and change the pattern.

Harrison


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## Trekari (Jan 3, 2008)

Actually I resorted to simply moving the subwoofer with the sound meter on a tripod at the couch.

However, having my delusions destroyed by seeing a frequency response graph of my subwoofer has made me decide I needed a better one anyways.

http://www.av123.com/products_product.php?section=subwoofers&product=15.1



Calling tomorrow to see about ordering one of those.

Other than that, my horrible hum has no solution. The cable company was here today and checked the outside ground (with me present) and even took a file and cleaned up all the connections from the ground block down the copper cable and into the earth stake.

My hum still exists without cheater plugs if the coax cable is plugged in. It makes no difference if I have the coax going into the surge supressor first and then to the tv or not.

I was thinking that one of these http://www.cs1.net/cables/products/jensen_transformers/VRD-1FF.htm put on the main coax line into my condo (right before the cable splitter sends the signal to all the rooms), would solve the problem in all rooms?

Any other advice to offer since the hum ONLY exists when coax is connected?


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## brucek (Apr 11, 2006)

> I was thinking that one of these


Give it a try and tell us how it works...............


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## Trekari (Jan 3, 2008)

I was more hoping for some sort of confirmation from those who know more than I do that the problem is 'definitely' a ground loop in my coax cable system before I spend $50.


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## HClarkx (Nov 10, 2007)

Trekari said:


> I was more hoping for some sort of confirmation from those who know more than I do that the problem is 'definitely' a ground loop in my coax cable system before I spend $50.


Trekari, this is probably not the correct thread for this subject, but I'm not adept at linking to other threads and such so maybe the staff can move this post to where it should be. Sorry.

I'm assuming that your electrical panel stake (or plumbing ground) and your CATV ground stake are some distance apart. That means that any stray earth currents (e.g., from nearby power lines) is causing a potential difference between the two grounds. The result is current from your electrical panel out the circuit to your HT equipment, through audio interconnect shields, and then through the TV coax shield to the CATV ground stake. 

If this is the case, most of the usual treatments such as putting all HT equipment on one dedicated circuit and such aren't going to help. One that might is linking all of the cases in your HT with an external ground wire might help. That will route the stray currents away from the interconnect shields. If that helps but does not fully solve the problem, then you at least know you are on the right track.

Interconnects that have the shield lifted at one end and the ground wire twisted with the "hot" wire can help. But, there will still be stray currents through your system.

I can only think of two ways to avoid those currents. One is to isolate the CATV coax at dc and low frequencies (which the device you are looking at presumably does). Another is to bring the potential of the CATV ground stake and your electrical panel to the same potential by running a wire between them. That should help but may not be a full solution because it will have impedance and won't bypass all of the current between the two ground points (some will still flow through your HT equipment).

Long story short, the CATV isolator does seem to have the best shot at solving the problem. I'd look for one for a couple bucks at Home Depot or Ace Hardware. If you have plenty of CATV signal strength, a cheap lossy one should work fine.

Good Luck,

Harrison


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## Wayne A. Pflughaupt (Apr 13, 2006)

Trekari said:


> I guess I should hold off on purchasing a duplicate PB12 to get better sub response


I suggest a consultation call with SVS. Something’s drastically wrong if your response is falling like a brick below 40 Hz with that sub. It got below 20 Hz in my cavernous room with no problem.


















Regards,
Wayne


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## HClarkx (Nov 10, 2007)

Wayne A. Pflughaupt said:


> I suggest a consultation call with SVS. Something’s drastically wrong if your response is falling like a brick below 40 Hz with that sub. It got below 20 Hz in my cavernous room with no problem.


I was thinking the same thing as Wayne. Before you invest in another sub, have you looked for room problems that could explain the absent low end? Is it missing all throughout the room? Is the room so large that you don't have any room gain to help out? (that would be a very large room). Are there any "cavities" or "traps" such as an opening to an adjacent room that would reflect back an out-of-phase wave at the problem frequency? Usually such reflections would create a narrower notch, but there are exceptions.

The test at the center of the room is a start, but isn't conclusive. You will have reflections from all four walls (depending on where you put the mic) that will still affect the apparent response.

The call to the Mfgr is an easy place to start, but unless the unit has a subsonic filter or a plugged port or something very wrong, it's hard to conceive of a problem that would roll it off with that shape.

Ideally, you would test it outdoors, placed face up in the middle of a field or against a wall where there are no reflections to cloud the result.

Good Luck
Harrison


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## Trekari (Jan 3, 2008)

Sorry, it isn't a SVS PB-12, it's a JBL 12" downfiring 250w version from 2000.


Anyway, I believe I've fixed my problem by moving some things around.

Before:











After:









Twin MFW-15s  I'll get some REW measurements once I can bring myself to lug my PC back out into the living room. And no, my house is not crooked - the tripod was.


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## HClarkx (Nov 10, 2007)

Trekari said:


> Sorry, it isn't a SVS PB-12, it's a JBL 12" downfiring 250w version from 2000.
> 
> Anyway, I believe I've fixed my problem by moving some things around.
> I'll get some REW measurements once I can bring myself to lug my PC back out into the living room. And no, my house is not crooked - the tripod was.


Should be interesting. Way cool setup!! Mine is somewhat similar but with the subs outside of the mains (left is a corner sub and right is a 2/3 along-the-wall sub) and two 15" Dayton RSS390-HF in each one, equalized by an Audyssey Sound EQ. I'm within +/- 5 db of flat from 20 to 100 with the Audyssey turned off and +/- 1 db at all three seats with the Audyssey turned on.

Enjoy.
Harrison


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## Trekari (Jan 3, 2008)

So..I set phase manually and then ran Audyssey today. Then I measured manually with my ratshack SPL meter and imported the data. Here is 10Hz-100Hz with Mains and both Subs active at listening position 1!

Corrected RS values are in the blue chart below. Not a bad starting place I think!


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## brucek (Apr 11, 2006)

> Then I measured manually with my ratshack SPL meter and imported the data.


Why????


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## Trekari (Jan 3, 2008)

Because it's a chore to move my computer tower into the living room, then find the mouse, keyboard, monitor, etc to go along with it.

My desk where all my computer cables go is not exactly accessible, so it truly is easier to measure manually. It might take more time, but it requires IMO less work.

THe only drawback I see so far is that I don't seem to have a way inside of REW to apply the RS calibration curve to what I manually import?


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## Trekari (Jan 3, 2008)

Ok..so I went back and re-tested the obvious problem area at 91-Hz or so.

With the RIGHT subwoofer firing along with the mains, I get
91Hz 69
92Hz 67
93Hz 65
94Hz 64

With only the LEFT subwoofer firing and the mains I get:
91Hz 66
92Hz 63
93Hz 63
94Hz 65

Is this a phase problem with the left subwoofer? I set the phase identically since they are equidistant from the listening position. All main speakers are Xover'd at 80Hz, and the "LFE" Xover is 90Hz. If this were a Xover problem, wouldn't it be logical to assume both subs would be equally affected?

**EDIT#2**

Apparently it was a phase problem. At the very least, reversing the phase of the second (LEFT) subwoofer then commencing playback with both enabled resulted in:

71, 70, 69, 68, 68 and 69dB readings from 91Hz through 96Hz. I'll report back with further testing after brucek admonishes me for doing this manually and tells me to haul my computer out into the living room no matter what I 'enjoy'


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## HClarkx (Nov 10, 2007)

Trekari said:


> Ok..so I went back and re-tested the obvious problem area at 91-Hz or so.
> 
> Is this a phase problem with the left subwoofer? I set the phase identically since they are equidistant from the listening position. All main speakers are Xover'd at 80Hz, and the "LFE" Xover is 90Hz. If this were a Xover problem, wouldn't it be logical to assume both subs would be equally affected?


Trekari, You certainly fixed the low-end with the new subs!!

The 91 Hz problem isn't due to phase difference between the two subs unless your mic was off to the left or right so that it was 6.15 feet further from one sub than the other. You will have a notch that moves in frequency and depth as you move away from the center line between the two subs. That's unavoidable. It will start at 0 db and increase in depth as you move off to the side and the frequency at which it occurs will drop. It won't get down into the sub range until you are several feet off to one side or the other. This is the same problem most dual-woofer center channel speakers have.

The above is based on ignoring reflections so may not be as obvious as I make it out to be. I.e., reflections will add their own notches and maybe mask the ones from the direct wave.

A question though, your green plot shows a 10-15 db notch while your per-speaker measurements indicate half that for one sub and nearly flat for the other sub. Something doesn't add up. Were the measurements take with the RS on a tripod and not moved?

Was the RS meter pointing straight up at a fixed position where your ears would be and with nothing else near it? That's important since the only way to make the mic omni-directional to sound coming from the subs and reflecting off the walls. It will be more sensitive to sound coming off the ceiling, but that's unavoidable.

Your ears are nearly omni-directional at sub frequencies so you want the mic to be omni-directional as well.

It would be interesting to see the plot with Audyssey turned off. The notch might be 10 db deeper. If so, that gives you some idea of what's causing the problem.

Audyssey will reduce the notch well if it appears at all measurement locations. If it's only at some measurement locations, those will be improved possibly with a bit of a peak introduced at the same frequency at other locations where there was no notch.

It would also be interesting to see the pattern at each of your seats. If the notch only affects some seats, you might not be able to improve it without degrading sound at other seats. Or moving subs or such.

Can you give us a floor plan of the room with all openings to other rooms shown? 

Long story short, it sure looks like you have a reflection problem. Are the subs both facing a back wall that is parallel to the wall they are on? If so, I'd bet you can measure the distance from your subs directly to the mic location and then from the subs to the back wall and then forward to the mic. The difference will be 6.15 feet. Either that or the distance from the subs to the ceiling and back down to the mic is 6.15 feet further than the direct path. Ditto for the left and/or right wall. The back wall will give a sharper, deeper notch than the ceiling and walls.

From this you can see some issues becoming evident. For instance, you don't want mid-room with a sub in front of you and a wall behind you. There are sub locations that will kind of spread out the reflections so that none of them are horrendous. The trick is keeping the subs and your mains equidistant from the prime seat, though adjusting sub phase carefully helps a lot.

Harrison


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## Trekari (Jan 3, 2008)

The RS meter was in fact mounted on a tripod and was not moved during any of the measurements. I was sitting in the seat to the right of it... but I was in that spot for *every* measurement.










The kitchen is open to the living room, with a 34" or so high counter behind the love seat. The 'hallway' going down is into the kitchen, and towards the front door.

The hallway going Left is towards the bedrooms.

The ceiling is a cathedral ceiling, with the sofa and TV being positioned directly underneath the apex, which is 11' high. The ceiling does not slope back down to 8' high until the sliding glass door and the bottom surround speaker (about 8" below that speaker, actually).

The mic was positioned on the center seat of the sofa - the wall to it's (on the image at least) down-left was perhaps 18" away, and the wall directly left of it is 1' behind the sofa.

Now that I have the new subs positioned in what I'm hoping can be a 'final' spot (ever try moving 130lb subs that are on spikes and discs?), I plan on doing some serious measuring work in the near future. I currently have another 1/4" TS to RCA cable pair coming along with a Y-adapter to split my sub pre-out to go into L and R inputs on the Behringer, then to each sub.

Thank god for you guys who know what you're talking about/doing. You know FAR more about audio and acoustics than I do, and I appreciate every input you offer, even if I don't necessarily like your replies 

**EDIT** And yes, the low end definitely got fixed  I should also mention (if it matters?) that EVERY speaker is actually aimed at the center listening area of the couch, including the subs.


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## HClarkx (Nov 10, 2007)

Trekari, Good information. Very helpful. 

The wall that is a foot behind the sofa can be a problem. It's not the cause of your 91 Hz dip because it's not 6 feet from the mic to the wall and back to the mic (is it?). I'm assuming it's more like 4 feet. That will give you notches at your ears at about 280 Hz, 560 Hz, 1120 Hz, 2240 Hz, 4480 Hz, etc. (assuming exactly 4 feet). Audyssey MultEQ may be taking good care of those higher frequencies even though it isn’t eliminating the more severe 91 Hz one.

If the back wall is found to be a problem, you might want to look into an ornamental wall-hanging or something like that (heavy, with some sound absorbing material behind it) for the wall behind the sofa to reduce sound reflections that bounce back and partly cancel the direct wave. Even if Audyssey MultEQ is taking care of this problem, it can be a bit more effective if the problem is reduced to start with.

Your ceiling might be the problem or much of it. If you trace lines from your subs to the ceiling and down to the sofa, one on either side of the ridge line, following the equal incidence/reflection angle theory, you will find that the ceiling is kind of focusing any sound reaching it directly from the subs back down to the sofa. That is, you are getting more SPL at the sofa from your ceiling than you would from a flat ceiling. If it's 6 feet further (or 9 feet further ... 0.5, 1.5, or 2.5 wavelengths at 91 Hz) via the ceiling than it is direct from the speakers to the sofa, I'd bet on that being the major contributor to your 91 Hz notch. Not easily fixed!!

The openings to the hall and kitchen are potential problems, but are unlikely to cause a sharp notch at just one frequency. At most they would cause some ups and downs across the sub range but only small ones. The left wall is a possible minor issue and might be contributing to the notch but alone isn't likely the cause (it’s weakened by the fireplace). 

I'm looking only at first reflections here ... the direct wave and the first reflection meeting at the sofa. Secondary reflections aren't likely to be all that damaging though they can aggravate a first reflection problem.

I’d measure all three seats. That will provide more info and maybe even cause you to decide to live with the problem.

How many mic locations are you measuring for the Audyssey MultEQ setup? You don't want to let the mic get too close to the back wall. Your ear location is as close as you want to get to the back wall in your case.

The subs don't need to be aimed at your center seat. The low frequencies flow out from the subs in all directions. You could turn your subs 90 degrees and hardly know the difference (though it might take a blind a/b comparison to prove that). The mains definitely should be canted in and pointing directly at your center seat. This is the best angle for most speakers. 

I’d go after more information to narrow down the problem, but I think if you want to solve it and don’t want to give up the fireplace or slider, you may end up thinking about moving the left sub to the left of the fireplace and move the right one a bit further to the right, maybe even to the corner near the kitchen (where the bookshelf is). The phase would need to be advanced a bit because they would be further from your seat, but you might lose that 91 Hz notch.

I’m still concerned about the green trace not matching your RS measurements. Can you clarify that?

I'm with you ... my subs are about 250 lbs and 43" tall ... hard to move and not many acceptable locations. I lucked out with a very agreeable wife and some available ideal locations.

Sorry about my writing problem.

Harrison


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## Trekari (Jan 3, 2008)

House is on tv right now (great show!) but I'll be back in a while to post more information.

For now, here is a link to photos of my current living room setup (just pretend the JBL sub isn't there )

http://www.hometheatershack.com/for...8425-setting-up-speaker-system.html#post74968

I'll answer your questions as best as I can when House is done. 

Thanks again for your time and help!


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## Trekari (Jan 3, 2008)

HClarkx said:


> Trekari, Good information. Very helpful.
> 
> The wall that is a foot behind the sofa can be a problem. It's not the cause of your 91 Hz dip because it's not 6 feet from the mic to the wall and back to the mic (is it?). I'm assuming it's more like 4 feet. That will give you notches at your ears at about 280 Hz, 560 Hz, 1120 Hz, 2240 Hz, 4480 Hz, etc. (assuming exactly 4 feet). Audyssey MultEQ may be taking good care of those higher frequencies even though it isn’t eliminating the more severe 91 Hz one.


**EDIT** It's actually more about 32-36" (I measured to the general area the tripod meter was at)



> If the back wall is found to be a problem, you might want to look into an ornamental wall-hanging or something like that (heavy, with some sound absorbing material behind it) for the wall behind the sofa to reduce sound reflections that bounce back and partly cancel the direct wave. Even if Audyssey MultEQ is taking care of this problem, it can be a bit more effective if the problem is reduced to start with.


Hopefully you've seen the links in the previous post. I DO have something on that back wall. I'm not sure it's enough (and of course we....ok, ok, you aren't sure what the problem is yet)...(of course I'm not offering any theories as I'm not qualified to do so, so you're the only intelligent one here)?




> Your ceiling might be the problem or much of it. If you trace lines from your subs to the ceiling and down to the sofa, one on either side of the ridge line, following the equal incidence/reflection angle theory, you will find that the ceiling is kind of focusing any sound reaching it directly from the subs back down to the sofa. That is, you are getting more SPL at the sofa from your ceiling than you would from a flat ceiling. If it's 6 feet further (or 9 feet further ... 0.5, 1.5, or 2.5 wavelengths at 91 Hz) via the ceiling than it is direct from the speakers to the sofa, I'd bet on that being the major contributor to your 91 Hz notch. Not easily fixed!!


I'm not sure where to measure since the ceiling is slanted, wouldn't that make it very difficult to determine the reflection point without a lot of trigonometry? I do understand the concept that it would act as a focus. The only way to solve something like that would be some serious acoustic treatment, since just hanging some decorative tapestries aren't enough to stop bass waves, right?



> The openings to the hall and kitchen are potential problems, but are unlikely to cause a sharp notch at just one frequency. At most they would cause some ups and downs across the sub range but only small ones. The left wall is a possible minor issue and might be contributing to the notch but alone isn't likely the cause (it’s weakened by the fireplace).


Hopefully you saw the other photos and you'll see that aside from hanging beads or a tapestry from the top of the hallway, there isn't much that can be done there without angering the landlords (parents).



> I’d measure all three seats. That will provide more info and maybe even cause you to decide to live with the problem.


I will get to that as soon as my other Behringer cables show up, that way I don't have to be setting up and taking down my computer multiple more times . If my cables get here, then whatever measurements and sub locations we come up with can immediately be used to apply filters to my 2496 so I can just take the PC out there one more time.



> How many mic locations are you measuring for the Audyssey MultEQ setup? You don't want to let the mic get too close to the back wall. Your ear location is as close as you want to get to the back wall in your case.


Well, this morning when I ran it (couldn't yesterday because it was VERY windy), I only used 3 positions, each on the 'ear' point of the sitting locations of the 3 cushions of the sofa. Speaking 2D, each position was equidistant laterally from the subs.

When I get this 'right' so to speak, and I know that I can move forward with final measurements, settings, locations, etc., I plan on taking 8 measurements from the entire couch area, including the coffee table.



> The subs don't need to be aimed at your center seat. The low frequencies flow out from the subs in all directions. You could turn your subs 90 degrees and hardly know the difference (though it might take a blind a/b comparison to prove that). The mains definitely should be canted in and pointing directly at your center seat. This is the best angle for most speakers.


Yea...well...they look intimidating that way!


> I’d go after more information to narrow down the problem, but I think if you want to solve it and don’t want to give up the fireplace or slider, you may end up thinking about moving the left sub to the left of the fireplace and move the right one a bit further to the right, maybe even to the corner near the kitchen (where the bookshelf is). The phase would need to be advanced a bit because they would be further from your seat, but you might lose that 91 Hz notch.


I can't give up the fireplace or even that side of the room. That's my dart board location - which makes it the third dart board location in that room. Parental landlords are getting ****** about the holes 

I COULD however, move one of the sub to by the love seat. I don't actually have a shelf over there now (again, hopefully you saw the photos). In fact...I still have my old JBL subwoofer that certainly could augment frequencies?



> I’m still concerned about the green trace not matching your RS measurements. Can you clarify that?


*shrug*

All I know is the original phase was 180 for both, and what I wrote down is exactly what was tested. And in fact, I'm dyslexic, sigh. Right meant Left in my chart and Left meant Right. (Corrected in this post)

LEFT subwoofer firing + mains:
91Hz 69
92Hz 67
93Hz 65
94Hz 64

RIGHT subwoofer firing + mains:
91Hz 66
92Hz 63
93Hz 63
94Hz 65

LEFT subwoofer (phase 180) + RIGHT subwoofer (phase 0) + mains:

91Hz 71
92Hz 70
93Hz 69
94Hz 68
95Hz 68
96Hz 70

Which fit into the values around them, as 90Hz was 69, 89Hz was 71 and 82Hz-88Hz were all 72.




> Sorry about my writing problem.
> 
> Harrison


I appreciate each and every answer, particularly where I learn things while reading them.


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## Trekari (Jan 3, 2008)

Ok, here goes. I know in my mind that these are significant.

http://www.hometheatershack.com/forums/rew-forum/8841-preparing-rew-bfd.html#post76177 

(from a few replies up, my 4 graphs)

Green is where the JBL was in the recent photo on the left side of the TV taken from the couch seat on a tripod.

Red was a mirror image of the previous setup, but on the right side of the TV instead of Left.

Teal was in the corner with the port facing against my kitchen wall. (The corner of the Love seat/kitchen counter/front wall).

Gold was taken in that exact corner as Teal but with the port firing against the front wall.

As you can see, each of those pairs of locations (similar) have different areas of frequency problems. But the first two, each right next to the TV, have problems at 91Hz.

THOSE measurements however were taken with ONLY the subwoofer (JBL) active. These results today had/have problems while the mains are on too.

I dunno..I'm tired and thinking outside my boundaries of qualified subjects to try and troubleshoot.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Trekari said:


> Because it's a chore to move my computer tower into the living room, then find the mouse, keyboard, monitor, etc to go along with it.
> 
> My desk where all my computer cables go is not exactly accessible, so it truly is easier to measure manually. It might take more time, but it requires IMO less work.


Understandable...

Why not just get a long extension cable for the mic and run it to your computer in the other room?

Regards,
Wayne


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## Trekari (Jan 3, 2008)

Do you know how many cable orders I've made in the past few weeks? hehe

I'd need an extension for both the ouput and the mic. I'm running out of dollars to buy things 

I'll be moving the PC as soon as my second set of Behringer cables arrives from BJC...I don't think they got them shipped out today


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## HClarkx (Nov 10, 2007)

32-36" .... that's 16" or 18" from the wall to your ears (and the RS meter). Or 32-36" round trip, right? 

You are right, if the back wall is a problem only at 198 Hz (assumes 34" round trip) that's easier to absorb than 20-100 Hz. But, a quick check around 198 Hz will tell you if you have a problem there ... one Audyssey isn't fully eliminating.

You're right, measuring the ceiling reflection isn't very easy ... and maybe not worth doing since there is no good solution if that is the problem and you don't want to move furniture. Your 91 Hz dip is fairly narrow ... you aren't losing much.

You didn't by any chance have to change the RS meter scale to capture that one low reading at 91 Hz did you? I've seen RS meters that don't give the same reading when you compare the low end of one scale with the high end of the next lower scale.

I'm curious. You have a receiver with MultEQ, right? Why do you need additional sub filtering. Especially if your Audyssey MultEQ has ALFC, it doesn't get any better than that.

With your seating Audyssey recommends a minimum of six readings, one at each of the three head positions and three more about 3' forward of those (I use 2 feet forward). I'd stay within that area with any additional readings. Personally, I use the extra readings at MY seat (the center one) to give it more weight.

I'm not sure you have a 91 Hz notch problem. If you get relatively flat with each sub individually, and both are similarly phased and a similar distance from the center seat, the combined subs should be relatively flat as well.

I'm at a loss to explain why you get more SPL with two subs than with either sub individually when one is run out-of-phase. I'm wondering if the phase switch on one of them is mis-wired. Very strange. In any event, both subs should be set at 0 degrees if that gives each a smooth blend with the mains.

I take it you don't have adjustable phase, just 0 or 180. In your situation both should always be 0 even if you move them left or right some distance. And, without adjustable phase, you probably want to leave them close to the mains if that doesn't give rise to any more than the narrow dip at 91 Hz.

But, if the green plot which shows a >10db dip at 91 Hz isn't right and your individual sub readings are, then I think we are chasing a ghost here and Your system is working very very well.

Harrison


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## HClarkx (Nov 10, 2007)

Trekari said:


> Do you know how many cable orders I've made in the past few weeks? hehe


Hmmm. Might have been cheaper to buy a used laptop!


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## Trekari (Jan 3, 2008)

32-36 round trip, yes.

Yes, I did have to change the sensitivity on the SPL meter.

I was thinking of using the Behringer (now that I've seen how Audyssey performs with a quality sub) to create a house curve and clean up any leftovers from Audyssey.

I will measure the individual subwoofers as soon as I get the motivation to go through the sine waves twice again, or my cables get here and I'll move the PC for a day of measurements.


Here is a corrected RS values graph

I also measured (corrected values here too):
11Hz 66dB
12Hz --not measured
13Hz 65dB
14Hz 69.3dB










Extra weighting for YOUR seat eh? How many people in your house know you did that?


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## HClarkx (Nov 10, 2007)

Tekari,

I'm not that familiar with the Behringer. It will be interesting to see what you can accomplish with it. 

If you just want the Behringer to help flatten the bass response, my instinct is to attack any problems you can with it, but then do the Audyssey room correction calibration with it in the circuit. The Behringer contribution won't be defeated by Audyssey. All that will happen is that any problems that Audyssey wasn't able to fully fix alone will probably become fixable by Audyssey because you've reduced them with the Behringer. Room treatments can have the same benefit (though room treatments to fix problems below about 200 Hz tend to be huge and very intrusive on room decor).

Doing a final setup with the Behringer in the circuit will also allow Audyssey to correct any time domain anomalies introduced by the Behringer filters. I'm assuming the Behringer unit provides just frequency response correction and thus will introduce some time domain distortion characteristic of such devices.

That said, I'm not sure the Behringer will be very helpful at achieving a flat response. Does it have the resolution to bring up your very narrow 90-95 Hz notch without putting shoulders on either side of it? Also, if the Audyssey version you have has ALFC, it has 512 terms in its Finite Impulse Response filter all crowded into the sub region. That provides very high resolution correction of both frequency and time domain anomalies. That's hard to beat.

You mention doing a house curve with the Behringer unit. In that case you would let Audyssey do the room correction and then apply Behringer afterward to tailor the bass to your personal liking. You would do this at the risk of degrading the even time-response provided by Audyssey. I've found that the bass tone control in my pre-pro does that very well and shapes the bass response so that it provides a correction for the ear's weaker response to lower frequencies when the volume is reduced, e.g., from 105 db to 80 db. Hopefully the DSP-based bass tone control is not introducing time-domain distortions. If it's well done it shouldn't.

Cool stuff. You really need that laptop!

Harrison


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## brucek (Apr 11, 2006)

> That said, I'm not sure the Behringer will be very helpful at achieving a flat response. Does it have the resolution to bring up your very narrow 90-95 Hz notch without putting shoulders on either side of it?


The behringer equalizer is definitely resolute enough to flatten and remove any modal resonance peak at the point of measurement. The filters effects are felt both in the frequency and time domain. The filter(s) address both the increased amplitude of the modal resonance and the longer decay time resulting in an elimination of the effects. REW is used to measure and design the filters to be used to flatten the subwoofers response, and many member here use the Behringer in conjunction with receiver/processor auto EQ systems.

These auto EQ systems are usually quite effective above the room modes ~100Hz. The auto EQ system is initially set up for the best response and then the REW is used to flatten the crossover region and remove resonant peaks in the low frequencies.

brucek


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## Trekari (Jan 3, 2008)

Brucek,

It is my understanding that whether I have filters engaged or not, that the Behringer adds 1ms processing time to the signal?

Therefore it shouldn't matter that I have no active filters if I run Audyssey with the Behringer in the loop, then start charting my frequency responses of the main speakers and subs in various combinations?

I plan on charting the main speakers by themselves at various crossover points until I get a nice flat graph, then charting the subs (individually) until I get nice response graphs from them at various xover points, then combining the two and making my house curve.

Hopefully this sounds like an appropriate procedure.


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## HClarkx (Nov 10, 2007)

brucek said:


> These auto EQ systems are usually quite effective above the room modes ~100Hz. The auto EQ system is initially set up for the best response and then the REW is used to flatten the crossover region and remove resonant peaks in the low frequencies.
> 
> brucek


I've seen your thoughts on this but haven't seen anything proving that the room decay is fully offset by the filter time response (i.e., that the two match). Is there some mechanical-electrical duality between a room and the filters that ensures a match? Also, can you refer me to tests that confirm the time components added by the filters correct room decay characteristics? 
But assuming that all works as advertised, why do you suggest the auto EQ systems in the receivers are beneficial only above ~100 Hz? 

I did have to move one of my subs to get rid of a 15 db null but once I had my combined subs within about +/- 5 db of flat, Audyssey brought me down to within a small fraction of a db when calibrating just one seat and within about +/- 1 db when calibrating three seats (i.e., no more than about 2 db difference between seats at any frequency). The later result obviously benefited from all three seats having nearly the same raw frequency response. This was the case down to 20 Hz (actually, the maximum 1 db deviation from flat occurred right at 20 Hz). 

My situation wasn't particularly challenging, but I got excellent frequency response room correction down to 20 Hz (without Audyssey's ALFC). I can only assume that the time domain correction was equally well done and that Audyssey's claims of decay time improvement also are effective. I don't have a way to test that. 

I've had the Sound EQ since they came out and have gone through different subwoofers and somewhat different room arrangements always with impressive results. 

Does REW provide room decay info? Maybe I should give it a try.

Harrison


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## Trekari (Jan 3, 2008)

REW does indeed provide a waterfall, decay, and impulse measurements in addition to the basic frequency graph you're accustomed to seeing.


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## HClarkx (Nov 10, 2007)

Trekari said:


> REW does indeed provide a waterfall, decay, and impulse measurements in addition to the basic frequency graph you're accustomed to seeing.


Cool. I will have to try it. Do you know if anybody has compared all three with Audyssey EQ turned off and then turned on?

Harrison


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## brucek (Apr 11, 2006)

> I've seen your thoughts on this but haven't seen anything proving that the room decay is fully offset by the filter time response (i.e., that the two match).


Take a peak at this waterfall thread I started a while ago. I tried to show experimentally how a filter counteracts a room mode.



> assuming that all works as advertised, why do you suggest the auto EQ systems in the receivers are beneficial only above ~100 Hz?


Purely anecdotal. Each time someone posts an "after auto eq" response graph, it shows a decent job except for low frequencies. That's my only proof. No doubt it's a foolish conclusion I've concocted.. 

brucek


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## Trekari (Jan 3, 2008)

Off-hand I don't know the answer to that.

However I plan on dialing in my audio system as good as I can get it. This thread (starting hopefully Friday morning) will start populating itself with various graphs. 

I will be happy to include a comparison between Audyssey on and off once I've got everything else all sorted out. 

I'm still very confused on the phase issue, but I will have REW help me figure out what is going on.

It makes NO sense to me whatsoever that the phase is 180 on one sub and 0 on the other, as they are *exactly* (no I'm not using that word lightly) equidistant from my main listening position as each other, as well as with the LCR speakers.

i.e. LCR are each *exactly* 126" to my ears (well, the space between them ), and the subs are each *exactly* 114" to my ears. However the 1ms processing time from the Behringer should add 12" to the perceived distance of each sub, which would bring them to exactly 10.5' as the LCRs are.



I'm going to hold off on calling AV123 to see if either of these subs might've been wired incorrectly and if so, how they plan on fixing that, until after I have REW graphs at various phases to show me what's up.

-Jason


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## HClarkx (Nov 10, 2007)

With the subs close to your mains, phase is quite important and you are right to worry about it. I know your subs lack continuous phase adjustment and I gather your receiver can't adjust sub distance separately from the mains and center (as is my case). As such, keeping the subs within a foot or so of the mains is highly desirable.

At 100 Hz a wavelength is 11.2 feet, so a foot one way or the other is not a major issue (about 36 degrees difference). But, any more than that will start showing a dip in the crossover region with the subs close to the mains. If you crossover lower, you have a bit more tolerance for distance errors.

Did Audyssey warn you of a sub being out-of-phase? It would likely do that only with one sub connected. With two connected (and one out-of-phase) it would probably find your subs weak and might not flag a phase problem.

Any REW comparison of the Behringer on/off (Audyssey off) would also be interesting.

Question. What is the background noise in your HT? Your readings at 60-70 db would be a bit close to the noise in my house. I try to keep readings above 80 db (with noise in the 40's). I think you want to be at least 30db above the noise to limit the effects of noise on your readings (your RS meter is listening to the noise as well as the subs/mains since it's capturing from 30Hz to 15kHz or something like that).

Finally, have you had someone switch one sub back and forth (0 to 180) while you are sitting in the middle seat listening to a bass-heavy track? 

Harrison

Also, 

Harrison


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## Trekari (Jan 3, 2008)

Actually they do have variable phase, and the Onkyo has separate distance settings for each channel. 

I'm unsure what the background noise in my condo is. When I'm doing REW, I turn off the HVAC entirely and wait until my refrigerator makes no noise. I wouldn't be surprised if my noise floor is actually very, very quiet when I'm measuring with intent.

Acoustically the subs are exactly the same distance as the mains, and I will make sure to check phase with frequency response graphs until one looks correct.

i.e. Frequency chart at 0 phase, 20, 40, 60, 80 and higher if need be until I find the flattest, and then I will dial it down as close as I possibly can.

After all, I didn't spend $1200 on these bad boys to have them sound awful


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## HClarkx (Nov 10, 2007)

Fast response ...... I hope you are getting some work done ... I need to soon.

I didn't follow your 20, 40, 60, 80 ... are these the choices on the sub variable phase control?

This leads me to ask one more question, can REW provide phase or "distance" at each of an array of sample frequencies?

Bruce, I'm sure you are right that if an auto EQ room correction system falls short, it's going to be below ~100 Hz and more often than not, rooms will have severe problems down there.

In a bit of experimenting with sub locations with a higher WAF rating, I did find some with a range of +10 to -15 db under 100 Hz that would take some powerful EQ to solve. And, frequencies at the peaks and valleys were different at each seat and no EQ system can solve that. 

Harrison


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## Trekari (Jan 3, 2008)

I have an analog phase control on each sub, variable from 0 to 180.

It simply has some dashes to represent where you are on the phase 'scale.' So the first big dash is 20 degrees, the second is 40, the third 60, etc. In between the big dashes...aw, here:

http://av123forum.com/showpost.php?p=484648&postcount=141


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## brucek (Apr 11, 2006)

> This leads me to ask one more question, can REW provide phase or "distance" at each of an array of sample frequencies?


You simple take multiple REW sweep measures from 0-200Hz with the sub and mains playing, and adjust the phase of the sub(s) until the crossover area provides a smooth transition.

Or you wait for the next version of REW in beta testing right now that has an RTA feature and adjust the phase live with the RTA running.



> I did find some with a range of +10 to -15 db under 100 Hz that would take some powerful EQ to solve. And, frequencies at the peaks and valleys were different at each seat and no EQ system can solve that.


It's not a perfect solution, but REW allows up to 8 sweeps to be averaged to produce a new response, that you then create your filters from for the BFD, and this gives a fairly good response over the measurement area.

brucek


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## HClarkx (Nov 10, 2007)

Trekari,

It just occurred to me that the dip you are worrying about in the 90-95 Hz region is right about where a crossover might fall. What is your mains-subs crossover set at?

If there is any phase problem between your subs and mains the dip should be wider, but still one has to wonder.


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## Trekari (Jan 3, 2008)

I had the xover on the fronts at 80Hz, and the sub crossover was set to 180 actually.

After my measurements of each front speaker/center on Friday I will set their xovers to where each makes sense and integrates with the subs the best.


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## Wayne A. Pflughaupt (Apr 13, 2006)

HClarkx said:


> I've seen your thoughts on this but haven't seen anything proving that the room decay is fully offset by the filter time response (i.e., that the two match).
> Also, can you refer me to tests that confirm the time components added by the filters correct room decay characteristics?


I haven’t seen any comprehensive in-room testing, other than Ethan Winer’s EQ vs. Bass Traps extravaganza. The test has some problems, though, mainly that the sheer number of measurements presented is mind numbing, and the guy who set up the equalizer did a really bad job of it. 

Ethan also did a simple evaluation of the effectiveness of the Audyssey MultEQ, which claims to reduce ringing. His conclusion was that it was a mixed bag as far as dealing with extended low frequency signal decay, aka “ringing” or “modal ringing.”

Since there seems to be a dearth of in-room time domain testing, other than these two, I’ve done some of my own (although I haven’t posted any results). After studying waterfalls ’til I’m bleary-eyed, I’ve found pretty much the same thing as Ethan, that _actual in-room measurements_ show that it’s a mixed bag using an equalizer as a fix for extended low frequency decay issues. 

I compared multiple waterfalls (as alluded to here, you won’t get a true picture from a single sweep) of equalized response using what I’ll call “modal filters,” that REW recommended to improve ringing (which is what REW does when you run the “Find Peaks” routine), to the “smoothing filters” I like to use (i.e., simply EQing out peaks and nulls with no regard for any effect on ringing). What was apparent was that the modal filters improved ringing for some peaks REW had identified, but for others there was no improvement at all. 

Even then, the improvement waterfalls did show for modal filters was only apparent in the short-duration 300 ms window. When the window was lengthened to 600 or 1000 ms, any advantage modal filters showed over smoothed fully vanished. The overall trend was that modal filters had the effect of quickly attenuating decay in the short term (compared to smoothing filters), but only down to a certain level. In the long term, both sets of filters were showing comparable results (this despite the fact that most of the smoothing filters were set for boost!). Which is to say, there was no reduction in ringing.

That’s one thing I have noticed here at the Shack where people (including myself) have posted graphs showing that an EQ filter improved ringing: They’ve all been short-duration 300 ms windows, not long-duration.

You can clearly see this “fast attenuation but only to a certain level” effect with the first set of comparison graphs from Ethan’s Audyssey evaluation - note the region between 56 and 20 Hz.










Ethan and John both maintain that narrow filters have the greatest effect on time domain. That’s one thing I have yet to evaluate at length, but intend to.

Regards,
Wayne


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## Trekari (Jan 3, 2008)

Well, it turns out that BJC was exceptionally slow in shipping my order.

Placed 2am Tuesday morning, is only supposed to ship out today. 

So unless I get the desire to do manual measurements, I won't be moving my PC into the living room until (at BEST) Friday, possibly Saturday, depending on when they arrive.

I plan on doing sweeps of all 7 speakers individually with and without Audyssey, so those of you interested in the benefits of Audyssey will want to stay tuned for another sample.

Secretly I'm also hoping that my in-room non-Audyssey sub response is a bit more suited for a house curve than the relatively flat post-Audyssey graph.  So I have my own reason for running the comparisons, hehe.


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## HClarkx (Nov 10, 2007)

Wayne A. Pflughaupt said:


> Ethan also did a simple evaluation of the effectiveness of the Audyssey MultEQ, which claims to reduce ringing. His conclusion was that it was a mixed bag as far as dealing with extended low frequency signal decay, aka “ringing” or “modal ringing.”


I recall the Ethan Winer monolog on his comparison of Audyssey and room treatments. Didn't Chris Kyriakakis of Audyssey take issue with his results and quite conclusively demonstrate that the Audyssey FIR filters do address decay? The Audyssey filters are FIR so it would seem they should.

It occurs to me that I said something stupid earlier about filters compensating room decay. One may want to adjust room decay but one doesn't want to eliminate it. Doing so would befuddle sensitive ears that expect a "real" room. I wonder though whether a filter that corrects a given peak or dip in frequency response will necessarily be altering the decay at those frequencies appropriately. I.e., is there a correlation between a dip in frequency response at a listening position and the room decay at that frequency. I'm thinking not. A reflection from a wall/ceiling near the sub can combine with the direct wave (as in Tekari's case) and cause quite a response dip, but that doesn't mean that there will be additional reflections that continue bouncing around the room at that frequency (that reflection may have come via the only solid surface in the room). If I'm right, any decay correction wouldn't necessarily be appropriate. 



> . . . . I’ve found pretty much the same thing as Ethan, that _actual in-room measurements_ show that it’s a mixed bag using an equalizer as a fix for extended low frequency decay issues.


Seems there's an opportunity for some definitive comparisons of Behringer, Audyssey, and other approaches.

I wonder though, the ear must deal frequently with variations in decay. Decay may not be much of an issue if the ear/brain takes care of it. Unless maybe the decay problem is severe. I mean a boomy room is a problem, but beyond that maybe decay isn't much of an issue.



> . . . . . What was apparent was that the modal filters improved ringing for some peaks REW had identified, but for others there was no improvement at all.


I think it's significant that you didn't find REW's recommendation to degrade decay. That would definitely be a negative result. At least if the improvement ranges from none to some, the results are in the right direction. But, fixing decay implies we know what decay is appropriate. Maybe we should to go london and measure the Philharmonic hall and then adjust our own decay to match it when we are listening to the London Philharmonic. Or maybe not, doesn't the recording already provide that effect? So what is the target? I think I've seen "desirable" HT decay times mentioned so presumably there or optimum ones (do they vary by music/movie type?). Can we actually hear the difference if the decay is in a credible range?



> That’s one thing I have noticed here at the Shack where people (including myself) have posted graphs showing that an EQ filter improved ringing: They’ve all been short-duration 300 ms windows, not long-duration.


My guess is that if the ear/mind can be troubled by inappropriate (?) ringing, it's probably the longer duration ringing that is problematic.



> You can clearly see this “fast attenuation but only to a certain level” effect with the first set of comparison graphs with Ethan’s Audyssey evaluation - note the region between 56 and 20 Hz.


I do see that. It would seem likely that the lower the frequency, the more difficult it is to control ringing. There's an awful lot of energy bouncing around to be controlled by a speaker cone. I mean after the bit of energy is sent out, additional energy has to be emitted to counter the ringing. Can a filter that only needs to make a small correction in frequency response at a certain listening position be expected to help much with a monster ringing problem at that frequency.



> Ethan and John both maintain that narrow filters have the greatest effect on time domain. That’s one thing I have yet to evaluate at length, but intend to.


I look forward to that. I may download REW, connect my Audyssey mic, and see what happens when I turn my Sound EQ on and off.

Best,
Harrison


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I think it's significant that you didn't find REW's recommendation to degrade decay.


Well, since REW only recommends cutting filters, there isn’t much chance that would happen!  However, I did notice some _sonic_ degradation with the modal filters (which were more numerous and narrower than I like to use). The uneven bass notes I complained about in the Hard Knee article returned. 



> Decay may not be much of an issue if the ear/brain takes care of it. Unless maybe the decay problem is severe. I mean a boomy room is a problem, but beyond that maybe decay isn't much of an issue.


To my ears it isn’t, at least not like long decay in the upper frequencies is.



> Can we actually hear the difference if the decay is in a credible range?


Supposedly you can with bass traps (although I’ve never heard them).

Here are a few more graphs, this time from Ethan’s Traps vs. EQ face-off (the ones added after the fact). Again, the equalizer was not adjusted properly, which may account for why we don’t see the “fast attenuation” effect. But one thing's for sure, looking at the Traps graph, I don’t think anyone can say they got they get that kind of reduction of decay from equalization (although I don't think I want 17 traps in my living room!).

























Regards,
Wayne


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## HClarkx (Nov 10, 2007)

Convincing enough. Do I read these as running out to 518ms? I vaguely recall 600ms being an appropriate decay rate. Does that ring a bell?

The 18-50 Hz range looks to be several seconds with traps and a bit less with the EQ. Higher frequencies are brought down very quickly by the traps and only modestly by the EQ. I wonder if the more uniform decay rate across the 18-322 region provided by the EQ isn't preferable to the longer decay at the low end and very short decay above about 50 Hz in the traps option. Does Ethan discuss that? If my recollection of 0.6 seconds is right, the EQ looks better. But, maybe that .6 isn't right.

I think I'm lucky. My room is large, well broken up, lots of random absorbing surfaces, few opposing sizable parallel surfaces, etc. But, I'll check it with REW as soon as I master it. Right now it's telling me my "input" is too low and I can't get it up.

If Audyssey does as well with decay as it does with frequency, I should be in good shape. Below are my before and after sub plots averaged across 10 measurement locations in a three-seat bubble. Each seat tested individually looks about the same before and after, so even though these are averages for the 10 measurement locations, they are representative of each seat. Vertical divisions are 5 db. Horizontal range is 20Hz and up.

Before:








After:









Harrison


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I wonder if the more uniform decay rate across the 18-322 region provided by the EQ isn't preferable to the longer decay at the low end and very short decay above about 50 Hz in the traps option. Does Ethan discuss that?


Don’t think so, but if I know Ethan, he’d prefer to have truncated decay all the way down to 0 Hz! One thing he did note, I think it was at an after-the-fact discussion thread at AVS, was that he didn’t use the correct traps for low frequencies – another sad shortcoming for what should have been a stupendous experiment. IIR most bass traps absorb to 70-80 Hz or so, but you can see the ones he was using were pretty much “done” by ~140 Hz.


Trekari, we’re not hijacking your thread here, just talking amongst ourselves here until you get back to us with your sweeps. 

Regards,
Wayne


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## HClarkx (Nov 10, 2007)

I've read that listening in a too-dead room can be disconcerting. I know being deep in a cave is an interesting experience. Presumably any room echos are on top of anything provided in the recording, so are "extra" but still expected by the ear/brain. This book provides some perspective. Note especially the top of page 26, though all of section 2.7 (starting on page 24) is interesting.

http://books.google.com/books?id=JIuIAVxeKdEC&pg=PA27&lpg=PA27&dq=room+decay+appropriate+seconds&source=web&ots=MtmeRkciPP&sig=Y7lx6LAyV7WiZ-42EXAkIDiTTF0#PPA27,M1

Harrison


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## Trekari (Jan 3, 2008)

I don't know where to start with this kind of problem :'(










The above graph is both subs active, phase 160 on the Right, 0 on the Left. No mains.
The Right sub Xover is set to 100, the L Sub is set to 80

No Audyssey, No BFD Filters.

Now:










The above graph is both subs set to Phase 0, no mains, direct input to Sub-In on the amplififer, no BFD, no Audyssey.


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## Trekari (Jan 3, 2008)

So...in order to remove that nasty dip at 81Hz, Ihad to move the sub up onto my couch. Does that mean it is my ceiling that is creating that null?

For instance, moving the R sub onto the top of the LSub produces:


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## HClarkx (Nov 10, 2007)

The phase numbers are very strange ... is this plot the result of trying to optimize the curve by changing them? That shouldn't be necessary with your sub locations. If there is any benefit to a phase difference, that difference should be only a few degrees, maybe 5 or 10 at the most.

What does the plot look like with both subs set to 0 degrees?

Harrison


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## Trekari (Jan 3, 2008)

The most recent 2 graphs in the previous post were Phase 0


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## HClarkx (Nov 10, 2007)

You inserted a new plot while I was typing ......

Re the new plot .... 

It doesn't look like you removed the notch, just moved it up 10 Hz. 

If you get that dip with both subs set to 0 phase (assuming no wiring errors) and in their correct positions (near the mains in your case) and working together, then it's probably there with either sub working individually (though that's worth confirming) and you are going to have to fix it with the BFD. I.e., it's a room problem that isn't going to be fixed with any reasonable sub relocations (unless you have some other locations that you'd be happier with from an aesthetics standpoint ... in which case you might want to try those locations).

Harrison


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## HClarkx (Nov 10, 2007)

Both phase 0 but with one on the sofa, right?

I don't think there's anything to be gained for you in moving the subs other than to desirable locations (next to the mains as before or further to the left and right).

I'd limit my testing to those positions.

Harrison


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## HClarkx (Nov 10, 2007)

Limit your phase adjustments to a few degrees one way or the other, but only for fine tuning (I mean very fine tuning). At this point if the phase adjustment helps the notch, it's probably going to create problems elsewhere so is not a good solution to the notch (and surely won't help measurably in any event).

Harrison


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## Trekari (Jan 3, 2008)

I suppose I should start with the basics.

Here is a plot of the LEFT subwoofer fed directly, Xover on the sub is 180, no mains, completely solo.










Now here is a graph of the R sub solo, no mains, Xover set to 180 also.










BOTH graphs show the subs in their aesthetically ideal position (where you've seen them in the photos) The only caveat is that the R sub is not on its spikes because I was moving stuff around and they make it harder 

Here is a graph of both subs, Phase ZERO, playing together.


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## HClarkx (Nov 10, 2007)

That's better. 

Both subs together look better than either alone. That's the way it's supposed to be. 

You do have that dip between 80 and 90. If audyssey doesn't take care of it, you can address it with BFD.

Hopefully Audyssey will minimize and smooth out the other minor deviations as well so that you can use the BFD just to create your house curve. 

Please do try the bass tone control in your receiver. You may find it does an excellent job of beefing up the lows to your preference. If it's like mine, it will. Mine pretty much compensates for the low-volume ear-sensitivity problem all humans have.

Harrison


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## Trekari (Jan 3, 2008)

Now, here is the LEFT channel included with both subs, Double-Bass in ON in my receiver, and the FRONT channels are set to full range.










Now let's turn Double-Bass off, leaving the front speakers as Full Range. NO change to the subs, still both set to Phase 0.


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## Trekari (Jan 3, 2008)

Now, let's put the crossover of the FRONT speaker at 80Hz, leaving the subs exactly as they were. (Phase 0, Xover 180)










As you can see, turning off double bass hurt things when implementing a legitimate crossover.

Now here is a graph with a 50Hz crossover with JUST THE LEFT main speaker and both subs in light green, versus adding the RIGHT main speaker in dark green.

Again, Light Green=Left main, 50Hz Xover, both subs.
Dark Green = both mains, 50Hz Xover, both subs.


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## Trekari (Jan 3, 2008)

The bass control on my receiver adjusts 50Hz in an unknown bandwidth. 

Upcoming I have more graphs with both mains at various crossovers with both subs still set to Phase 0, Xover 180.


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## HClarkx (Nov 10, 2007)

You are moving too fast for me. 

Is "double-bass" your receivers word for running the mains large AND sending content to the sub below the set crossover?

Clearly something is awry with your mains/sub.

I'd turn both subs off, set the mains to large, double-bass off, tone controls flat, and test both mains (individually). 

Once we see any problems with the mains alone, we can consider crossover and main/sub blending issues.

If the mains alone both look good, the next step will be the following....

Set mains small, sub xover off or at max frequency, receiver crossover at 80 Hz, both subs connected, double-bass off, tone controls flat, and then test with one main and then the other main. 

This will let us parse the pieces and maybe identify the issues. It sure seems that your subs need to (both) be set at 180 degrees. But, don't do that yet, do the above tests so we can be sure we are on the right track.

...... 50 Hz. Interesting. Mine is centered at 30 Hz and so drops off some at 20 but on the high side washes out at about 200 Hz.

Harrison


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## HClarkx (Nov 10, 2007)

..... more on the 50 Hz ........ I'd still try it ... with low enough Q it might sound pretty good. They probably center up at 50 to avoid bottoming out the sub drivers. This is not an issue for you (your neighbors wouldn't allow it).

Harrison


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## Trekari (Jan 3, 2008)

Now I'm unhappy.










The above graph includes speakers LCR+both subs at Phase 0, xover on subs 180, xover on mains 60, and xover on center 100

I arrived at those settings for Xovers via the following graphs.

MAIN SPEAKERS+SUBS!

Light Green=Double Bass
Red=50Hz xover
Gold=40
Purple 60
Blue 70
Dark Green 80


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## Trekari (Jan 3, 2008)

Ok..bbiab with individually tested mains.


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## Trekari (Jan 3, 2008)

CENTER only

Light Green Full
Red 40
Gold 50
Purple 60
Blue 70
Dark Green 80
Light Purple 90
Light Blue 100










Left Speaker only.

From top to bottom we have crossovers (subs turned off though) of:

Light Green Full
Red 40
Gold 50
Purple 60
Blue 70
Dark Green 80












RIGHT main speaker, same colors:
Light Green Full
Red 40
Gold 50
Purple 60
Blue 70
Dark Green 80










Finally, both main (L+R) without subs, same colors:

Light Green Full
Red 40
Gold 50
Purple 60
Blue 70
Dark Green 80











Left+Center+Right Xovers

Light Green Full
Red 40
Gold 50
Purple 60
Blue 70
Dark Green 80
Light Purple 90
Light Blue 100


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## Trekari (Jan 3, 2008)

Update:

I'm a complete idiot. I had my distances in the recever set to:

Left 10.5'
Center 10.5'
Right 10.5'
Subs 10.5'

Actual measured distances?:
Left 126"
Center 126"
Right 126"
Subs 114"

No, the Behringer adds 1ms=1ft delay, so I added 12" to my subs ACTUAL distance....

*smacks self* Since it adds delay, I should've SUBTRACTED the 12"...******

Upon setting the distances correctly...










LCR+Subs ...sigh. Now I need to work on the xover of the subs.


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## brucek (Apr 11, 2006)

> the Behringer adds 1ms=1ft delay, so I added 12" to my subs ACTUAL distance


Yes, that's correct. 

Since the BFD delays the signal by 12", you want to tell the processor that the sub is 12" further away and it will (in essence) advance the signal 12" sooner...

brucek


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## Trekari (Jan 3, 2008)

Then I'm at a loss as to what is wrong.

Do my LCR graphs by themselves look ok? I realize there are a few room problems..but in general? 

*frustrated*
Jason


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## HClarkx (Nov 10, 2007)

I mis-spoke I think (not unusual) .... I was hoping to see your mains alone with no crossover applied (I forgot to mention the crossover). That's what you want to look at (along with the subs alone and no crossover) to choose a crossover frequency for good blending. You can always correct problems with Audyssey or the BFD but it's nice to minimize problems before turning to them.

At this point I've been assuming the Behringer is bypassed. You don't want it in until you see what you've got to work with and what you can do without it.

Your last plot is encouraging though. What phase was dialed into the subs on that green trace with distances set correctly. And, what was the crossover frequency? You had the center and mains (and subs) running, so it's not all that helpful. You want to see subs alone, mains alone, and center alone. Then you choose crossovers from there.

But, I wanted to see the mains alone (no crossover) and the subs alone (no crossover) to see how they look in the potential crossover region. If both are flat, you can choose any crossover. If one has issues, you might minimize those by moving the crossover so that area is well down the crossover slope. Since your mains and subs are close together, they should look similar.

If the room issues between 60 and 120 are the same for the subs and mains, you can use any crossover you wish.

Incidentally, there are other considerations in choosing crossover frequencies. You take a load off of your mains by crossing over at a higher frequency. This allows you to run higher SPL with lower risk of damaging a main woofer and reduces somewhat the undesirable impacts of having higher frequencies sitting on top of lower frequencies in the main woofer. I forget what this issue is called .. maybe intermodulation distortion (IMD)? You also have lower risk of clipping in your mains amps since they are delivering less power. Clipping can destroy a tweeter.

The 12" error should have minimal effect below about 150 Hz.

Those "humps" above 100 Hz are disturbing, but Audyssey should smooth them out fairly well. At least the dip between 80 and 90 is gone.

I wouldn't turn Behringer or Audyssey on until you have done all you can without them.


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## HClarkx (Nov 10, 2007)

Trekari said:


> Then I'm at a loss as to what is wrong.
> 
> Do my LCR graphs by themselves look ok? I realize there are a few room problems..but in general?
> 
> Jason


Jason, I don't think anything is wrong. You just need to look at each speaker to be sure it's performing as expected and well enough, be sure phasing is correct, pick a crossover, turn Audyssey loose, iron out any remaining issues and set a house curve with the BFD.

I didn't look close at the 12" issue, glad Bruce caught it. 

Harrison


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## brucek (Apr 11, 2006)

> Do my LCR graphs by themselves look ok?


Can't see the graphs??


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## HClarkx (Nov 10, 2007)

Bruce, I think he's talking about his previous post ... 

Harrison


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## Trekari (Jan 3, 2008)

And my concern is that whenever I pick a crossover, my charts are terrible. It doesn't even seem like I can adjust the subs xover without something going completely haywire.


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## Trekari (Jan 3, 2008)

For instance, if you'd like to understand why I'm so angry right now...

In my LCR graphs I posted what the response is with each speaker set to full range.

I also posted what my sub responses are individually, and combined.

After running Audyssey, here are two examples.










How am I supposed to be anything other than angry right now? Red is phase 0, purple is phase 180.

*Keep in mind that without the mains at all, this was my subs response*


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## HClarkx (Nov 10, 2007)

By "subs crossover" you are talking about the crossover in your receiver/pre-pro, right? The crossover built into your sub should be turned off or set as high as possible and never touched again.

I don't think you've gotten the right measurements yet. Ideally you would do the following.

Left sub alone 
(sub enabled, no sub crossover, receiver xover as high as possible ... or better yet, plug the sub into your main output and set that main to large)

Right sub alone
(same as above)

Left main alone
(receiver set to large, no tone control, etc.)

Right main alone
(same as above)

Center alone
(same as above ... set to large, etc.)

Use all above results to assure all is well, no fatal room problems, etc. then choose crossover frequencies. Use 80 Hz unless there is compelling reason to do otherwise. **

Pair up the mains and subs (one main and its adjacent sub) and look for proper crossover performance.

Pair up other main and that same sub.

Check each main with the other sub.

Pair up the center and subs and look for proper crossover performance.

The above is mostly to check sub phasing which has been an issue for you. The simple tests above will define that problem once and for all.

Then you are ready to run Audyssey and play with the BFG.

** Your mains and subs are close together so you could use 100 or 120Hz. Think about that later.


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## Trekari (Jan 3, 2008)

I'll get the measurements tomorrow, but here is what I have to work with:

1) My receiver only has "LFE" crossover for the sub. That setting does NOT impact anything that is not delivered via an LFE channel. Currently and throughout all testing, I had that set to 120Hz.

The sub itself has a crossover that has been set to 180Hz for every measurement except where noted.

Pictures coming later, most of the information you've asked for I already posted in other graphs, but I'll post clarified ones in a few hours.


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## HClarkx (Nov 10, 2007)

I agree about LFE, but I would put the subs on a main channel set to large to be sure there is no crossover impact whatsoever.

But, doesn't your receiver have crossovers for the mains to sub, center to sub, etc.? That's what we are trying to avoid by using the mains channels with them set to large.

Hang in there, I don't think you have problems that Audyssey won't handle well. Just got to be sure phasing is correct. Can't tell that with LCR all running or similar.

Harrison


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## brucek (Apr 11, 2006)

> Do my LCR graphs by themselves look ok?


I can't see them...... here's what I see.

-------------------------------------









-------------------------------------


brucek


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## Trekari (Jan 3, 2008)

Left set to Full Range:
















Right set to Full Range:










Center set to Full Range:









Left Subwoofer by itself, LFE at 120Hz (doesn't matter) and Xover on sub maxed @ 180Hz










Right Subwoofer by itself, same settings as Left (120LFE, 180Xover on Sub)









Both subs together, LFE 120, 180Hz Xovers


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## Trekari (Jan 3, 2008)

brucek said:


> I can't see them...... here's what I see.
> 
> 
> brucek


Sorry, I was referring to the graphs located in this post, with the multiple crossover points charted.

http://www.hometheatershack.com/forums/77828-post79.html


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## HClarkx (Nov 10, 2007)

Jason,

Now we're talking! 

Your right sub performs better than your left, at least at the center seat where you were measuring. I'm tempted to suggest moving the left one over next to the right one, but I know that would be strange. But, it might be an interesting conversation piece.. "why are both of your subwoofers over there?" 

In my opinion, you have relatively good sub performance. The dips at 85 and 120Hz (both subs together) isn't wide enough to get very excited about. The dip up at about 130 Hz is pretty bad, but won't be a problem if you keep the crossover down around 100 Hz or less. Based on the subs, I'd use the tried-and-true 80 Hz crossover (isn't that Dolby's recommendation and also the THX standard?). You are better than +/- 4 db from 20 to 80. That's hard to beat.

As a wild guess, the ~85 Hz dip is your left wall and the 130 Hz dip is your ceiling. You have two reflected waves from your ceiling, twice what you would have with a flat ceiling, and that explains the deep notch at 130 Hz and the second low up at 180 Hz (you get a comb effect from any surface like that). But, this paragraph is just to help understanding, it doesn't change the next above recommendation.

Your combined sub test was a good idea. It shows 6db gain over either sub alone, so confirms that your two subs are in phase with each other. We wondered earlier if one of them was wired wrong.

Unfortunately, your mains suffer from some reflections as well. The deep dip at about 120 Hz in the left channel is probably that ceiling again. It's at a different frequency from the big sub dip because your mains are closer to the ceiling (further off the floor). I'm guessing the left main is closer to being right under the ridge.

It's not practical to crossover high enough to minimize the effect of that dip because you would just bring the similar but lower dip on the subs into play. That dip is very narrow and that's good. It is only really serious in the left main and that's good because at 120-150 Hz, most material is the same in both main channels so the right channel helps support the left with its lesser dip.

The +/- 8db variations in the mains above 120 Hz are unfortunate, but will be largely smoothed by Audyssey. At least one of them (one close to 200 Hz) is the reflection off the wall that is 16" behind your ears in the center and left seats. If your mic was 18" from the back wall, the dip would be exactly at 185 Hz. So, more sound absorbing material behind your head would help, but only with one of the dips that is visible on these charts. I say that because that dip will repeat as you go up in frequency, though at higher frequencies, the wall-hanging you mentioned is probably more effective.

The center is more problematic. It has a very deep notch up at about 150 Hz. That's the only one that gives me pause. It might be a combination of reflections (note the two close proximity dips). You might try putting the center above your TV if that's a credible option. That would worsen the refection off the back wall (direct wave hits the backwall closer to 90 degrees), but might move the one from the ceiling away from it. But, again, a complete dropout of 5 or 10 hz (the width of this notch) isn't much of a penalty. Also, Audyssey will help with it. Also, you will hear mostly voices in the center channel, and this is below the female voice range and at the low end of the male voice range so won't have much impact. Roucous sounds from movies that go to the center don't need to be perfect fidelity. So, you are home free on the center in my humble opinion.

I'd cross the center at 80Hz along with the mains. It's good for that in that it is fairly flat down to 50 Hz. The tiny notch at 60 isn't an issue, but will be comfortably below the crossover frequency (i.e., it will be well down the crossover skirt and so not an issue).

So, I think you've got a good system going. Now you've got to be sure the subs and mains are in phase and the receiver crossover is working well. Do that by setting the mains to small, setting the crossover at 80, enabling one or both subs and one main. Enabling both subs will put the subs 6 db above the main, but that's easy to take into account if you want to do that. I think I'd do that because you get smoother sub peformance with both enabled. I'd test each main individually with one or both subs. Don't drive both mains at the same time.

Then test the center paired with one or both subs and an 80 Hz crossover.

If all looks good, crank in the Audyssey and see what it can do. You will probably see significant improvement, but keep in mind that the Audyssey system is also improving decay and correcting time alignment which don't show up in frequency response plots (time does to some extent if it's really bad to start with). I.e., the Audyssey correction is doing more for you than we are measuring here (though you could go further with the waterfall plots and such). 

If you want to fine-tune the sub phase, you can play with that by changing the sub phase setting or the sub distance. That should have minimal effect as long as the subs are close to start with (they should be if the are not out by 180). Do that before you run Audyssey. Otherwise you would have to re-run the full Audyssey setup each time you make a sub phase change. 

It's late. At 66, I don't usually function very well this late. If anything above doesn't make good sense, let me know.

Keep up the good work Jason.

Harrison


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## Wayne A. Pflughaupt (Apr 13, 2006)

brucek said:


> I can't see them...... here's what I see.
> 
> -------------------------------------
> 
> ...


I can’t see them either, although a link to a picture in one of my e-mail notifications worked – strange... :huh: 

Regards,
Wayne


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## Trekari (Jan 3, 2008)

I received a PM suggesting that certain key members were not able to view my graphs and a question of whether I'd be willing to post them on a site other than comcast's personal web pages.

Hah! Like I'd refuse help in this problem! 

The graphs have been uploaded to HTS and are shown below in the following order:

Center Full Range
Left Main Full Range
Right Main Full Range
Left Sub by itself (Xover 180 on the sub, 120 in the receiver but that only affects LFE)
Right Sub by itself, same settings
Both Subs together, Phase 0


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## Trekari (Jan 3, 2008)

Harrison - I thank you for your post and helpful suggestions. 

I haven't forgotten about them, it's just a bit early in the morning to start running more sweeps


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## brucek (Apr 11, 2006)

Thanks, I can see those fine now. I have a few comments.

The mains and center measurements are taken at far too low a level. The measurements should all be taken with a target level of 75dB. The graphs should then be posted at the standard 45dB-105dB vertical scale. You see in the red plot for example where the signal has some sharp dips at about 30hz and then the signal starts to rise? It actually isn't rising, the signal is in the noise at that point. The rising portion is noise, not signal. So, take all measures at 75dB.

Personally, I see very little problem with your response(s). I am of the camp that I want to see the sub signal(s) alone with no mains, but I want it with the crossover engaged. The same holds for the mains. I wouldn't concern myself with measuring the center channel - it's mostly dedicated to voice any way. The prime concern is the subs and the mains and how they integrate together.

I don't understand your statement about the sub crossovers. The sub should be crossed over using the receivers bass management with the subs own filters bypassed or maxed with the dials...

brucek


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## HClarkx (Nov 10, 2007)

Bruce,

We pretty much covered the noise issue earlier. Jason is limited by neighbors so takes the tests with refer off and during quiet hours. Also, yes some dips are down in the noise, but the actual depth is academic. If Jason isn't going to attack them with room treatments, then the next step is to see what Audyssey can do with them and then go after anything that's left with the BFD. 

The LCR 30 Hz dips are interesting but academic because they are well below the crossover. 

The reason for the sans-crossover tests is that some confusing issues were arising with the receiver crossover engaged and these tests were explicitly run to isolate those problems.

With the filter-less plots we now know the raw speaker-room characteristics and can parse any new problems that arise with mains and sub coupled by the receiver crossover. If new problems arise with the speakers paired via the receiver crossover, and we suspect a crossover problem, Jason can then back off and test main and crossover and sub and crossover (with the same 80 Hz crossover setting) to further isolate the problem. However, that isolation will be pretty much academic if we've already decided the receiver crossover has a problem. If it's in the receiver we don't care whether it's high or low pass. Mostly though, we earlier saw results that indicated one sub might be of phase with all other speakers. The recent tests confirm that that isn't the case. So the first concern with the next test will be to assure that the subs are in phase with the mains.

I agree as indicated in my earlier post that the center is less an issue. But, as an interesting (I hope) side note, I've found that cleaning up the center with Audyssey quite noticeably improves intelligibility of voices, particularly when masked by background noise (coming from the center, mains, surrounds or sub). You'll find that sometime in your 50's, while your hearing doesn't degrade all that much according to tone tests, your ability to parse speech from background noise drops dramatically. It's normal, but having very clear speech helps combat that weakness (as does pushing up the center channel volume a bit).

Regards,
Harrison


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## Trekari (Jan 3, 2008)

WHile I wait for the postman to deliver the remaining cables I need...

Right Main+ Right Sub, Phase 0, Xover on Subwoofer maxed, using LFE input of Sub (so xover is bypassed on it anyway), LFE Xover in receiver is set to 120, Xover of MAINS are set to 120.


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## brucek (Apr 11, 2006)

Post graphs with a vertical scale of 45dB-105dB.

Why are you using a crossover of 120Hz instead of 80Hz?

brucek


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## Trekari (Jan 3, 2008)

Because 80 didn't look too great.. I'll post that too (blame REW for changing my scale on me all the time, my apologies).


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## HClarkx (Nov 10, 2007)

I agree, I'd stick with an 80 Hz crossover. But, are you sure the main amp is turned on?  Or is the sub gain pushed up too high?

Something is awry. Maybe crank down the sub gain until you are fairly flat from zero to 200 with the crossover set at 80 Hz. Push the receiver gain up to compensate for turning the sub gain down.

Harrison


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## Trekari (Jan 3, 2008)

Using the Aux input, my max speaker volume is about 72dB. I did in fact have the sub "pink noise" calibrated to about 73-74. However this needs clarification:

I calibrate my speaker volume using the internal Onkyo test tone inside it's "Speaker Level" settings page. Every satellite speaker is set to 75dB via that page. The sub was adjusted within that page as well to 73-74dB.

Using the AUX input, I am only able to produce (at max volume) 72dB using REWs speaker pink noise with the satellite speakers. The sub may have been a little hot, but not more than 1-2dB IMO.



Perhaps one of you can explain why you want me to use 80Hz? Here are my reasons for 120Hz at the moment.

1) I have two subwoofers, which means I can get a more flat response from those frequencies produced by the subs, than I can any other individual speaker.

2) I have a Behringer ready and waiting to use with the sub channel, whereas I cannot do any post-Audyssey EQ on any other channel.

3) The subs are right at the feet of the main speakers, so localization is not a big deal IMO?

It would seem wiser to me (I'm no expert) to use the subs to produce as much of the frequency response as they are capable of since I have the ability to correct the subs.

*EDIT*

Ok, I could see where localization could be an issue if only the Right main is supposed to have a 100Hz tone, whereas sending it to the subs would produce it on both sides of the TV.


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## HClarkx (Nov 10, 2007)

Jason, you make very good arguments for a 120 Hz crossover. Another is that the more load you can take off the mains, the better.

Your mains do have some ups and downs above 100 Hz that might be too much for Audyssey and I agree that if the BFD can handle them, that would be fine. In fact, that argues for an even higher crossover. I wouldn't question 180 Hz if it works. 

You do have a nasty 130 Hz dip in one of the subs that I'd be inclined to avoid. But, if that doesn't show up as much of a problem once you have combined the mains and subs, or the BFD can handle it, I'm with you.

I'd still be inclined to start with 80, see what you have to deal with there, look at 120 and see how that compares (you say it's better but I'd like to see it) and maybe try 160 or 180 to see if it gets even better.

It all depends on what Audyssey can clean up. Audyssey does have limits on what it can do, but within it's limits, it's very accurate (frequency and time domains especially). It's biggest advantage over the BFD is probably it's 10 ms time alignment capability. That can do wonders for blending a sub and main.

So, I guess if you really want to optimize the crossover choice, you would try 80, 120, 160 each with Audyssey run with all 8 measurements. That's a lot of work though.

A sequence of 80, 120, 160 with Audyssey off would be very interesting to see.

But, it needs to be with that massive upper-end roll-off fixed. I'm still not clear on what's going on there. Until you see fairly flat from 10 to 200 (and preferrably to 300), I wouldn't worry about optimizing the crossover.

Harrison


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## brucek (Apr 11, 2006)

> explain why you want me to use 80Hz? Here are my reasons for 120Hz


Anything over 80Hz results in localization of the sub. You really don't want that. The only reason to use a cross greater than 80 is when you have little satellites that can't handle low frequencies - not your case... use 80 or below.

brucek


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## Trekari (Jan 3, 2008)

Sorry, spent the day with friends. I'll get some graphs going again in the near future post-Super Bowl.

(I also kind of just want to enjoy what I have for a few days in between graphing sessions )


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## HClarkx (Nov 10, 2007)

Bruce makes a good point, but you will know if localization is a problem and can backtrack if that happens. But, since your subs are within a couple feet of your mains and inside of your mains, localization shouldn't be any worse than it would be with a large full range speaker with its big woofer on the bottom. I.e., any localization is unlikely.

Enjoy the Suberbowl.

Yes, do enjoy what you've got, it probably sounds a lot better than the plots would seem to indicate.

Incidentally, since your right sub performs a lot better than your left, and in fact better than both together (it's within +/- 4 db up to 100 Hz with one small exception), you could return the left sub and be quite happy. The second sub does add 6 db to your low end capability, but I'd guess just one sub could easily get you kicked out of the building if you really exercised it. But, I'm not suggesting you return one, just tossing out the possibility. Sharing the load on the two subs reduces risk of getting into any nonlinearity the subs may present as they are driven harder. And someday you might want that extra 6db. And two of them reduces the likelihood of localization (you might want to stick with 80 Hz crossover if you had just one).

Another thought. Some people argue for putting the second sub behind you or something close to that. I tried it and didn't like it (and it didn't equalize as flat). But, that's what they say. My son had an extra sub and put it next to his sofa pointing into his sofa. The sofa really shook on the lows. Kinda like those shaker things they make for sofas.

Harrison


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## brucek (Apr 11, 2006)

> localization shouldn't be any worse than it would be with a large full range speaker with its big woofer on the bottom. I.e., any localization is unlikely.


Full range speakers are in stereo, and create a soundfield. That's a big difference from a mono sub signal that is easily localized to a point source....



> you could return the left sub and be quite happy


Or simply co-locate them, which is one of the better methods of running two subs. Find the best spot for one sub and co-locate the second to increase the headroom.

brucek


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## Trekari (Jan 3, 2008)

Here is what I am working with for my listening area and possible reflection points:


Would either of these products be useful in correcting some of the problems REW has pointed out? Note that I cannot place something of these sizes below the shelf but above the couch, they'd have to go ABOVE the shelf with the photos on it.

http://www.gikacoustics.com/gik_244.html

http://www.gikacoustics.com/gik_242.html

Or in order to be useful, would these products need to be placed on the ceiling?


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## HClarkx (Nov 10, 2007)

brucek said:


> Full range speakers are in stereo, and create a soundfield. That's a big difference from a mono sub signal that is easily localized to a point source....


Good point.



brucek said:


> Or simply co-locate them, which is one of the better methods of running two subs. Find the best spot for one sub and co-locate the second to increase the headroom.


Also a good suggestion. THX reference is 105 db peak. Not many subs can do that in a room as large as Jason has (including kitchen and hallways). Also, you don't want to push the limits of a sub if you can avoid doing so. I have a 13,000+ cubic foot great room not including openings to kitchens and hallways and a large SPL-eating fireplace. My subs can each can do a theoretical 107 db at Xmax but I'm sure can't come close to 105 in that space. Hence I have four of them giving me theoretically another 12 db. That probably gets me close to 105 at the listening positions at Xmax. Because I found two good locations, I have two subs at each.

I'm sure Jason's neighbors would raise an eyebrow at this thread. I'm lucky, no neighbors.

Harrison


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## HClarkx (Nov 10, 2007)

Trekari said:


> Would either of these products be useful in correcting some of the problems REW has pointed out? Note that I cannot place something of these sizes below the shelf but above the couch, they'd have to go ABOVE the shelf with the photos on it. Or in order to be useful, would these products need to be placed on the ceiling?


I'm not an expert at room treatment, but from what I've read, a pair of 2x4 panels might be a drop-in-the bucket for a room as large as yours. If you think about sound (below about 200 Hz) spilling out into the room and going in all directions, you realize that you have hundreds of square feet of reflective surface sharing that SPL. Hence a considerable number of such panels might be needed and would have to be optimally located. A good room treatment solution can require a lot of panels and a lot of work finding the right placement. Understanding reflections gives one a head start, but there's still a lot of trial and error to identify the right locations and the surface area required and the frequency response characteristics of the panels. The professionals use software to get a starting point, but still have some trial and error work to do. I can see it now ... Jason to wife .... "hold it a foot more to the left and hold another one alongside it and let me run another frequency scan...". 

That said, a panel to quell the reflection off the back wall would definitely have to be centered right behind your head to be very effective.

Some of these panels on the ceiling strategically placed would also help. That placement could be estimated with the trigonometry you mentioned last week. A wild guess would be two panels on either side of the ridge.

I wouldn't give up on Audyssey and the BFD yet. They are a much more flexible and cost-effective solution. If they leave a significant problem or two that can be tied to a particular wall surface, then consider resorting to room treatment.

The price seems very good on these panels. Some are much more costly. I don't see any specs on them though I'm not sure there are standards by which to judge them in that industry.

Another thought occurs to me. One of Audyssey's strong points is that, while it can't fully smooth out huge peaks and dips, it can share what it can't smooth out fairly equally across the three seats. Tests at just one seat will tell you how well Audyssey can bring up a notch or shave a peak, but you really want to balance the notches and peaks (what's left of them) across the three seats. So, only a test with a full set of measurements will tell you the whole story.

Likewise, you don't want to be looking at just one seat when you work with room treatment. You want to consider all three and share the benefit.

The BFD as well needs to be set with all three seats in mind. If all three seats share the same notches and peaks, then you can improve all three quite well, but more likely there will be differences and you again will want to share the wealth. In a really bad stroke of luck, you will have a peak at one seat and a notch at another, both at the same frequency. All you can do with Audyssey or the BFD is balance them (10 db and 10 db rather than 15 db and 5 db). Room treatment probably has a better chance of addressing both, but only with a huge amount of work.

Harrison


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## Trekari (Jan 3, 2008)

If I had a wife, I wouldn't have the money to blow on my sound system 

Really though, I think I've reached a point where I'm going to break in a few new speakers (pics coming by Friday I'm thinking), run Audyssey with 8 measurements, set the BFD to create a house curve and call it good.

If room treatment was easier, or if my room would respond better to select treatments that don't include coating every possible reflection point, then I'd go that route.

But hey, at some point you have to just call it good and save the really expensive and time-consuming projects for a dedicated room.


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## HClarkx (Nov 10, 2007)

Trekari said:


> But hey, at some point you have to just call it good and save the really expensive and time-consuming projects for a dedicated room.


Yes, one can go nuts/overboard to little avail.

If you use REW again after you are all tuned up, don't sweat the narrow peaks and notches (mostly notches) .... unless they are horrendous (wide and deep), it's unlikely fixing them will improve the sound much. Better to spend the time listening than trying to fix a minor issue.

Please do try your tone control. Even with a 50 Hz center, it may have a low enough Q to provide a nice adjustable, remote-controlled loudness control. A base line and +6db bass boost REW recording will tell you what your bass tone control does for you (though your ears will tell you more ... whether you like it). It's an underutilized feature these days, especially for movies. 

A second use of the BFD could be for loudness. If you watch movies at typical home listening levels (about 85 db peak) you want an "equal loudness" boost to make a movie sound, at 85 db, like it does at 105 db reference level. I.e., to compensate for your ear/brain's loss of sensitivity as volume is reduced. There are adjustments for mid and high frequencies, but the low end is what most people notice.

frequency/db
20/6
30/5
40/4.5
50/3
60/2
70/2
80/2
90/1
100/0

This will make movies at home sound like they do in the theater without irritating the neighbors by playing at 105db.

Enjoy.

Harrison


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## Trekari (Jan 3, 2008)

New look


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## HClarkx (Nov 10, 2007)

Really really nice. In my wife's dreams mine would look so good. My subs (home made) have black grille cloth draped over the unfinished wood boxes.

Your center is very close to your mains in capability. That's rare and very good.

My center sits on a table as well. Though that's not necessarily problematic, I hope to move my components off to the side and put my center on a shelf under the TV so it has free air around it like the mains.

Your center and mains look to have enough woofer capacity to support an 80 Hz crossover (and that was confirmed by your REW tests). Or 120 if your prefer.

Enjoy.

Harrison


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## Trekari (Jan 3, 2008)

Sorry for the long absence - been doing some remodeling of the home.

The Center channel (and indeed all of the surround speakers you see) are completely sealed around the back. 

Coming up soon, I happen to finally have enough of an RCA cable I believe to do testing without moving my PC to the living room. I was hoping to wait until the next version of REW came out, but that seems to be a bit stalled.

As for my FEQ2496, I plan on using that to calibrate a flat response from the subwoofers, and THEN running Audyssey. The reason for that is when using my analog multichannel inputs, the Onkyo 705 doesn't do any processing of that audio. (No Audyssey, no crossovers, nothing) My recent adventure into surround sound music means that if I do the 2496 *first*, and then run Audyssey...whenever Audyssey is not able to be used (SACD playback, DVD-A, etc through the analog inputs), then I still have flat bass response.

Does anyone have suggestions on a house curve for multichannel music?


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## HClarkx (Nov 10, 2007)

Trekari said:


> Does anyone have suggestions on a house curve for multichannel music?


I can't help you with the house curve other than to suggest starting with flat and use your tone control to deviate from that and then pick a curve that kind of matches what you found desirable with the tone control. Or just try each one. Does the Onkyo let you try the different curves without completing the setup as the Sound EQ Pro does?

I suspect that your speakers, your room acoustics, the music you listen to, and your hearing might all influence the house curve you choose. I include speakers and room acoustics in the list because Audyssey doesn't 100% eliminate them from the equation.

Harrison


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## Trekari (Jan 3, 2008)

No, the Onkyo doesn't allow you to give trial listens to the curve. And in the EQ section, your only options are "Off, Manual 7-Band, or Audyssey."

On another note, I'm quite happy with how my room turned out. I think moving the couch forward gave enough room for the Surround Back speakers to work well.


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## HClarkx (Nov 10, 2007)

Trekari said:


> On another note, I'm quite happy with how my room turned out. I think moving the couch forward gave enough room for the Surround Back speakers to work well.


The room is very nice. I like it. I'd stuff a couple of throw pillows into the new bookshelf behind the sofa (right behind your head) when I'm doing serious listening. But then the question is whether to have them there or not when doing the BFD and/or Audyssey setup?

Harrison


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## Wayne A. Pflughaupt (Apr 13, 2006)

Nice looking room, Trekari! 

Re the house curve, never really thought about what it would take to do it with multi-channel. I’d say determine your needed slope with the usual method, but the tricky part might be blending with the mains. Offhand I’d say you might need to run the sub (EQ’d for a house curve, natch) a bit hotter than you would normally, since extra speakers are operating. On the other hand, it could be that the extra speakers running might make you inclined to run your overall volume levels a bit lower than usual, which would put you back where you started. Probably Harrison’s advice is best: Listen and let your ears decide.

Regards,
Wayne


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## Trekari (Jan 3, 2008)

Well, the BFD/Audyssey interaction came to a head last night while I listened to a SACD through my analog multichannel inputs on my Onkyo 705. Those inputs get no processing whatsoever and the high frequencies nearly drove me insane.

So  rather than use the Burr-Brown DACs in the upcoming Oppo 983 I wish to purchase, I will relagate myself to using HDMI PCM so that Audyssey can be applied and those ear-piercing high frequencies can be quelled.

I mean seriously, it was downright painful to try and listen to. I suppose room treatment would fix that problem, but for now I've got many long months of plasma donating to pay off what I've done thus far


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## HClarkx (Nov 10, 2007)

Trekari said:


> So  rather than use the Burr-Brown DACs in the upcoming Oppo 983 I wish to purchase, I will relagate myself to using HDMI PCM so that Audyssey can be applied and those ear-piercing high frequencies can be quelled.


I just bought the Oppo DV-981HD a month ago figuring it will hold me for a year or two until the Blu-HD battle is over ..... and suddenly Toshiba capitulates and now you are telling me there's a 983 coming? I always buy too soon. I bought an Intel E6850 CPU two weeks before the new 45nm E8400 came out for $50 less! I always buy too soon.

Is the 983 Blu-Ray or is it just an upgrade of the 981 (standard definition DVD)?

Harrison


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## Trekari (Jan 3, 2008)

The 983 is Oppo's last foray into the SD DVD market. It is using some crazy-good upscaler chipset that is equivalent in performance to a VP30 video processor.

It conveniently also does SACD and DVD-Audio


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## HClarkx (Nov 10, 2007)

Trekari said:


> The 983 is Oppo's last foray into the SD DVD market. It is using some crazy-good upscaler chipset that is equivalent in performance to a VP30 video processor.
> 
> It conveniently also does SACD and DVD-Audio


Whew. The Faroudja implementation in the 981 is downright amazing. The 983 will be icing on the cake! Very cool. I hope Oppo now goes to work on a good Blu-Ray unit.


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