# 2nd time around..measurements



## Mattlock (May 9, 2007)

Well after royally screwing up my first attempt at measurements....here's my 2nd attempt...

Sub only
700 liter sonosub, FI Q18 tuned to 13hz, powered by EP2500, with BFD1124.
Crossover set at 80.

First graph without filters
2nd...with filters...

any thoughts or suggestions....

Still alittle confused about setting the target..looks like they should match up to compare the filter effect? correct?

thanks
Matt


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## Otto (May 18, 2006)

Hi Matt,

You can overlay the plots on the same set of axes so they're easier to compare. In the filter window, there are tabs, and one is called "All Measured." Select that one and then you will be allowed to choose which of your (up to) nine measurements you want to overlay. 

I would probably push the output of the sub a little bit, such that you go above the target by 5 6dB or so. Then, you will be able to quash peaks more, such that you get a flatter response. This assumes you have the headroom, which you will with the EP2500 amp. Just turn the amp gain up a little and remeasure and refilter. 

I also like to apply some gain in the dips. Not too much, and I like to play with it manually, either on the front panel of the BFD or through REW and the MIDI download (either way is OK, but the point is it's me picking the filter values, and not REW).


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## Mattlock (May 9, 2007)

Otto said:


> Hi Matt,
> 
> You can overlay the plots on the same set of axes so they're easier to compare. In the filter window, there are tabs, and one is called "All Measured." Select that one and then you will be allowed to choose which of your (up to) nine measurements you want to overlay.
> 
> ...


Okay Otto, Since I set up my system with my amp gain at max, I assume I can adjust my SW output on my receiver to boost the output. I will also overlay and repost. I'll play around with some gains but from my understanding I should keep these on the lower side to prevent clipping???

thanks again for your suggestions. BTW...should my Target be the same for both measurements? seems logical but I have to manually adjust when I re-measure with filters. Make sense?


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## Otto (May 18, 2006)

Yeah, you can turn up the SW output on the receiver, or you can just turn up the volume knob on the receiver. Either way will work. I'd probably go with the master volume knob since it's easier.

I don't think that Target is super-important. I usually set it at the beginning and then just tweak till I get close to the desired curve. You're doing fine, and on the right track!


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

Matt,

IMO your response is highly problematic, to the point that it’s probably unequalizable. You have about a 30 dB or more differential between some of your peaks and depressions. That needs to be narrowed to something workable, i.e., ~15 dB or less. 

Often when we see response this bad, the problem is a bad sub location. Do you have any other placement options? I’d try a good corner (i.e., one with no unsealable openings in either wall), if you have one available.

Also, it appears you applied some equalization way up in the 130 Hz range. You don’t have your sub crossed over that high, do you? There’s usually no need to apply equalization above the crossover frequency.

Regards,
Wayne


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## Mattlock (May 9, 2007)

Wayne A. Pflughaupt said:


> Matt,
> 
> IMO your response is highly problematic, to the point that it’s probably unequalizable. You have about a 30 dB or more differential between some of your peaks and depressions. That needs to be narrowed to something workable, i.e., ~15 dB or less.
> 
> ...


Wayne,
thanks. I may be able to put the sub up front left next to picture...it's already wired. Challenge is I have my front speaker there as well. It may mean I have to reduce my screen little due to the diameter of this beast....see picture. Currently it is in rear behind the couch. (not in pic but there now) I'll play around with it and re-measure.


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## brucek (Apr 11, 2006)

Matt - some tips.......

Use logarithmic display and not linear display for your graphs. Press the Freq Axis icon in the top right corner of REW.

Use a vertical scale of 45dB-105dB and a horizontal scale of 15Hz -200Hz.

There is a Filter Sort icon on the Filters screen to order your filters from low to high. It's very useful.

brucek


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## Mattlock (May 9, 2007)

Wayne A. Pflughaupt said:


> Matt,
> 
> IMO your response is highly problematic, to the point that it’s probably unequalizable. You have about a 30 dB or more differential between some of your peaks and depressions. That needs to be narrowed to something workable, i.e., ~15 dB or less.
> 
> ...


Well,it looks like I limited to the rear. The speaker is simply too large to be moved up front (left). I can move around a little in the rear (to the left) so that it is right beside the cutout wall. Its only about 2 feet but can't hurt to try. 

more later


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## Mattlock (May 9, 2007)

brucek said:


> Matt - some tips.......
> 
> Use logarithmic display and not linear display for your graphs. Press the Freq Axis icon in the top right corner of REW.
> 
> ...


Will do brucek....thanks for the suggestions


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## Mattlock (May 9, 2007)

Wayne A. Pflughaupt said:


> Matt,
> 
> IMO your response is highly problematic, to the point that it’s probably unequalizable. You have about a 30 dB or more differential between some of your peaks and depressions. That needs to be narrowed to something workable, i.e., ~15 dB or less.
> 
> ...



Wayne....got a semi-random question for you. Does it make any sense for me to consider a 2nd sub up front if indeed I cannot get the peak/dip range shortened? Still learning here but somewhere I read that dual subs must be tuned the same (13hz) in my case so the point if probably moot because with 8.5feet ceilings I can only go so high with a narrower diameter...just thought I would ask....

Had this crazy idea....Was playing around with Sonosub.exe and it looks like I may be able to get a 24 inch diamter sonosub but the specs would have to be...500 liters, 6.5ft tall, port 8x40, which would give me a 13hz tune.....have I gone off the deep end?


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## Mattlock (May 9, 2007)

Here's my graph using the logarithmic display and changing my graph scales per Brucek. 

Anyone with more filter suggestions or other comments?

thanks


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## Jman (Jul 23, 2006)

Do you have any space for bass traps?


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## Mattlock (May 9, 2007)

Jman said:


> Do you have any space for bass traps?


hmmmm...not real sure....school me a little on what these could do for me?


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## brucek (Apr 11, 2006)

Matt, any chance you can show me your impulse response graph of your measurement?

brucek


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## Mattlock (May 9, 2007)

brucek said:


> Matt, any chance you can show me your impulse response graph of your measurement?
> 
> brucek


Bruce, 
Here is my impulse graph.....


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## brucek (Apr 11, 2006)

Just wanted to see where the noise floor was in relation to the signal.

Signal is ~40dB above the noise. Not great, but OK. Sometimes the response graph looks a bit like yours when there's a lot of noise....

Does your Check Levels routine work out OK for you when you're setting up?

brucek


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## Mattlock (May 9, 2007)

brucek said:


> Just wanted to see where the noise floor was in relation to the signal.
> 
> Signal is ~40dB above the noise. Not great, but OK. Sometimes the response graph looks a bit like yours when there's a lot of noise....
> 
> ...



think so but I'll double check....what could be the culprit on the noise?


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## Guest (Dec 30, 2007)

Matt.... Forget what I said to do yesterday by PM!


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

Matt, are you using both of these subs?








Regards,
Wayne


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## Mattlock (May 9, 2007)

Wayne A. Pflughaupt said:


> Matt, are you using both of these subs?
> 
> 
> 
> ...


no...just the big one....plan on selling the other


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

Mattlock said:


> Wayne....got a semi-random question for you. Does it make any sense for me to consider a 2nd sub up front if indeed I cannot get the peak/dip range shortened?


It may make things worse. You could do some checking using the SVS before you sell it, but don’t forget to level-match them first.



> I may be able to put the sub up front left next to picture...it's already wired. Challenge is I have my front speaker there as well. It may mean I have to reduce my screen little due to the diameter of this beast....see picture.


Maybe you could lay it on its side? You’d have to do something to keep it from rolling, of course. And make some kind of custom stand or wall mount for the left speaker...

Your before and after graph, does the “after” sound any better?

Regards,
Wayne


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## Mattlock (May 9, 2007)

Wayne A. Pflughaupt said:


> It may make things worse. You could do some checking using the SVS before you sell it, but don’t forget to level-match them first.
> 
> 
> Maybe you could lay it on its side? You’d have to do something to keep it from rolling, of course. And make some kind of custom stand or wall mount for the left speaker...
> ...


Havent really had time to do much comparison yet but will soon. These holiday plans just get in the way of more important things.. :bigsmile:


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## JohnM (Apr 11, 2006)

From the impulse response the distortion looks very high, getting on for 10% 2nd harmonic and several % 3rd harmonic. May want to check the sub isn't being driven too hard.


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## Mattlock (May 9, 2007)

JohnM said:


> From the impulse response the distortion looks very high, getting on for 10% 2nd harmonic and several % 3rd harmonic. May want to check the sub isn't being driven too hard.


John, what exactly would i be looking at or changing to reduce the sub strain?

thanks


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## JohnM (Apr 11, 2006)

Just lower volume - was the sub playing particualrly loud when generating that impulse response? Otherwise might just be the nature of the drive unit.


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## Mattlock (May 9, 2007)

JohnM said:


> Just lower volume - was the sub playing particualrly loud when generating that impulse response? Otherwise might just be the nature of the drive unit.



Actually it wasnt playing that loud. Another thought....could it be possible leakage around the top and bottom endcaps? I havent sealed it yet but to be honest they are very tight anyway..had to hammer down.... Another thought...my doors in my room rattle pretty loudly but this is probably a higher hz anyway....

thanks John for the thoughts
Matt


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## Mattlock (May 9, 2007)

Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....

Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?

thanks
Matt


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## MakeFlat (Mar 30, 2007)

Mattlock said:


> Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....
> 
> Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?
> 
> ...


That depends on the sub's power.

You can push the gain as long as you have the headroom. For the sake of explanation, let's just say that you have 6 dB headroom for the sub, like your loudest movie is 6dB below the power reserve of the sub. Then you can push 3dB and still maintain a 3dB headroom for the sub, just in case you happen to crank the avr volume control a little higher than normal.

A little boost is not going to cause an issue. If however, the boost does practically nothing, you may as well not apply the boost. That 49Hz dip is likely much deeper than visible on the graph, so it's not going to budge. The value of adding 6dB to a 16dB dip is questionable.


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## Jman (Jul 23, 2006)

Mattlock said:


> Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....
> 
> Question: I realize gains have to be used with caution but at what point (ie amount) is the gain considered "pushing the boundary of reasonableness"?
> 
> ...


Earlier I asked if you had room for bass traps. They'll reduce those deep/narrow nodes that you're getting. The problem with trying to fix deep notches with EQ is that it usually does little or nothing. That's the nature of room nodes. The traps reduce the room interaction, which are what cause them in the first place.

The front left and right corners would be a great place for 2 traps. Is that door at the front right used? You could also put one at the back where the sonosub is. The traps would need to be 2' wide and mounted at 45 degree angle at 2 boundaries like 2 walls, wall/ceiling, wall/floor.


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## DrWho (Sep 27, 2006)

It also looks like your sub is tuned too low, and the ports aren't being loaded fully. It's hard to tell from the pics, but the measurements indicate that the sub is about 6 feet tall? (on the inside) What's the internals of the sub look like?

Also, is your mic moving inbetween measurements? If you think about it, it doesn't make sense for your dips to move around in frequency (unless of course you move the mic around).


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## tnargs (Sep 7, 2006)

Mattlock said:


> ....Does it make any sense for me to consider a 2nd sub up front if indeed I cannot get the peak/dip range shortened?


It certainly makes sense. Research has shown that multiple subs, up to 4 or 5, increases the listening area that gets good (smooth) bass.

Arg
http://tnargs.googlepages.com/tnargsound


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## Mattlock (May 9, 2007)

tnargs said:


> It certainly makes sense. Research has shown that multiple subs, up to 4 or 5, increases the listening area that gets good (smooth) bass.
> 
> Arg
> http://tnargs.googlepages.com/tnargsound


I assume a 2nd sub would need to have the same tuning as my first? REad that somewhere....Obviously my original sub SVS PB12 isnt as low as my DIY (13hz) so I had planned on selling that and possible building a 2nd tuned to 13hz


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## Mattlock (May 9, 2007)

DrWho said:


> It also looks like your sub is tuned too low, and the ports aren't being loaded fully. It's hard to tell from the pics, but the measurements indicate that the sub is about 6 feet tall? (on the inside) What's the internals of the sub look like?
> 
> Also, is your mic moving inbetween measurements? If you think about it, it doesn't make sense for your dips to move around in frequency (unless of course you move the mic around).


Yes Sub is about 6 feet tall. The inside has a about 3 layers of 1/4 inch polyfill around the tube with more polyfill on the Top Endcap (opposite the driver) and also about 2-3 inches wrapped around the port. 

My mic has not moving during the testing. 

What suggestions do you have based on this info? I have not sealed by endcaps so I can get back inside fairly easily if I need to. 

thanks for the advice....as I am still learning


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## Mattlock (May 9, 2007)

Jman said:


> Earlier I asked if you had room for bass traps. They'll reduce those deep/narrow nodes that you're getting. The problem with trying to fix deep notches with EQ is that it usually does little or nothing. That's the nature of room nodes. The traps reduce the room interaction, which are what cause them in the first place.
> 
> The front left and right corners would be a great place for 2 traps. Is that door at the front right used? You could also put one at the back where the sonosub is. The traps would need to be 2' wide and mounted at 45 degree angle at 2 boundaries like 2 walls, wall/ceiling, wall/floor.


The door is used but I can look around and see about possibly adding some traps..Do you have any websites or pics of traps installed so I can get a feel for what you are describing?

I did a little searching around and several websites had the traps mounted vertically on walls or on the ceiling...I can certainly do that all over my theater...the 45 degree angle might be tough though.... 

Question: Would traps also help reduce the "Den shaking" that goes on right above my theater room which is in the basement?. Last night I had WOTW cranking and my lovely wife informed me that the effects upstairs were "ridiculous" :foottap: her.... :bigsmile: me




thanks
Matt


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## Jman (Jul 23, 2006)

The traps won't lessen transmission to other rooms. The reason for the 45 degree angle is to maximize the depth from boundary corner to the edge of trap. With a 2' wide trap, that gives you about an 18" depth. As you lessen the angle you get closer to what is just the thickness of the trap itself - i.e when you reach 0 degrees, your 3" thick trap only has a depth of 3" so now you're only absorbing down to ~200hz. With a depth of 18" you can get full absorption down to 100hz and still good performance below that.


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## clubfoot (Apr 12, 2007)

Mattlock said:


> Question: Would traps also help reduce the "Den shaking" that goes on right above my theater room which is in the basement?. Last night I had WOTW cranking and my lovely wife informed me that the effects upstairs were "ridiculous" :foottap: her.... :bigsmile: me
> 
> thanks
> Matt


You would need to at the very least, isolate the ceiling sheet rock from the floor above using something like sheet rock Z channels, and insulation between the ceiling joists. Of course if you secured the walls directly to the ceiling joists,...it's not going to make your wife very happy upstairs in WOTW


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## tnargs (Sep 7, 2006)

Mattlock said:


> I assume a 2nd sub would need to have the same tuning as my first? Read that somewhere....Obviously my original sub SVS PB12 isn't as low as my DIY (13hz) so I had planned on selling that and possible building a 2nd tuned to 13hz


Not necessarily needing the same tuning... after all, two different subs might even out the irregularities of each other. :unbelievable:

Recommended positioning for a 2-sub system is one centre front and the other centre rear, or one on the midpoint of each side wall.


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

Mattlock said:


> Here's my latest curve.....even though I tried different gains from 3 to 8 I really couldnt get much movement on the 49hz dip....


Hmm... Doesn’t look much different than the others. I take it you haven’t moved it? You might want to take a look at these two threads, where people with highly problematic response, due to unusual placement, realized instant improvement just by re-locating the sub to a good corner. Good chance it’ll eliminate your 49 Hz problem as well.

http://www.hometheatershack.com/forums/rew-forum/8339-i-think-i-have-problem.html#post70673

http://www.hometheatershack.com/for...vs-bass-traps-best-position-target-curve.html

Regards,
Wayne


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## DrWho (Sep 27, 2006)

Mattlock said:


> Yes Sub is about 6 feet tall. The inside has a about 3 layers of 1/4 inch polyfill around the tube with more polyfill on the Top Endcap (opposite the driver) and also about 2-3 inches wrapped around the port.
> 
> My mic has not moving during the testing.
> 
> ...


What are the dimensions on your port and where is the driver and port located in the enclosure?

The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.

Anyways, you're going to end up with a response that looks like this:








This should also be showing port resonances too, but I'm not sure exactly what size and tuning you have for your ports so it will probably be different. ****, it's a different driver too...only intended to demonstrate the effects of the cabinet and ports being "too large".

You probably won't be able to address the ports, but you could try to break up the standing waves inside the cabinet. The ~3" of absorption you have right now will only be good down to about 1kHz. You would need 3ft to be effective down to 90Hz (yikes). You wouldn't want to go that low anyway since it will effect the Q of the enclosure too.


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## Mattlock (May 9, 2007)

DrWho said:


> What are the dimensions on your port and where is the driver and port located in the enclosure?
> 
> The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.
> 
> ...


the port is an 8x26.75. The port (top) is exactly opposite the driver(bottom), ie sonosub design. My crossover is set at 80hz so my focus has been below 80hz.


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## DrWho (Sep 27, 2006)

Mattlock said:


> the port is an 8x26.75. The port (top) is exactly opposite the driver(bottom), ie sonosub design. My crossover is set at 80hz so my focus has been below 80hz.


That doesn't mean it's not going to be an issue...

Harmonic distortion will trigger the resonances, not to mention the crossover isn't instantaneous so you've still got the driver itself triggering them too. It's probably why your distortion measures so high. :yikes:


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## Mattlock (May 9, 2007)

Since my sub is too big to re-locate we moved my sitting area forward 3 feet, ran REW and applied some filters. My target needs to be raised but my curve is improving. 

I give credit to "Kbgl" who has been coming over and helping me out. He guessed that moving forward 3 feet would help based on his measurements and sure enough he was right. We tested it out with WOTW and I could definitely tell an improvement with the sounds in the lower range...I'm no audiophile with trained ears but I could tell the difference in the lower end stuff

Now I am dealing with the tempation to put a matching 2nd sonosub beside my current one...twins.... 1400 liters total... me :jump: wife :hissyfit:


The first graph is with the sitting area moved forward 3 feet.
The second is with sitting area in the original position (back 3 feet)

I am also wondering if I can get any benefit in the lower end (<80hz) with adding bass traps. Any thoughts on that? For budget reasons I may have to go with some DIY traps especially if I am remotely considering a 2nd sonosub :bigsmile: Got to spend my $$$ wisely. Of course I am now thinking with results I ought to focus on possibly a 2nd sub vs. traps....but I dont pretend to know all the advantages of traps. 


Matt


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## Jerm357 (May 23, 2006)

Now that looks much better. Are these new graphs raw or do you have Eq already applied to them?


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## Mattlock (May 9, 2007)

Jerm357 said:


> Now that looks much better. Are these new graphs raw or do you have Eq already applied to them?


EQ is applied on both...2nd one doesnt make much sense because the filter settings for the +3 feet position were left on and the couch was moved but it is very similar the curve.


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## SteveCallas (Apr 29, 2006)

HUGE improvement! If you can't move the sub, move your seat = brilliant :R I came across this thread late, but I want to comment on a few things I read.



DrWho said:


> It also looks like your sub is tuned too low, and the ports aren't being loaded fully.


Not at all. With the driver being used, the enclosure volume and tuning were chosen to yield a gently sloping low end that would mesh well with a bit of room gain. The valley in response in the low end was clearly a room effect, not subwoofer response related, as can be seen from his new measurement with the seat moved. The new measurement is a great example of how extended and powerful the in room low end will be with a LLT design. Mattlock is either using filters to go for a house curve or he is benefitting from strong low end gain to achieve that rising low end - either way, in nearly every case, the result is deep, flat, in room response.



> The 6 feet height of your cabinet is going to give you standing waves inside your enclosure. At 1/2 wavelength you're going to get the first null, which happens at ~95Hz...looks to be exactly around 98Hz or so from your measurements.


Again, not the case, that dip is merely another room related or phase issue. If you take a look at Ilkka's testing of a large and low tuned sub, you'll see that the FR is not affected in the least by any type of standing wave created inside a large enclosure. You do benefit from decreased harmonic distortion at that frequency, but it doesn't affect FR.



> This should also be showing port resonances too, but I'm not sure exactly what size and tuning you have for your ports so it will probably be different.


Port resonances will show up as a blip in the FR, but with his first resonance being ~250hz and a 24db/octave 80hz crossover in play, it's a non issue.



> It's probably why your distortion measures so high


:innocent: Nah. Though a different driver is being used (Fi Q18 vs TC2k 15), you can see again from Ilkka's measurements that that type of a design will keep distortion very low throughout the subwoofer range. These high excursion drivers sometimes have high inductance which can result in increased distortion as frequency rises, but with the 80hz crossover, distortion should be quite good at even spirited levels. 



Mattlock, are you using filters to achieve that rising low end?


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## Guest (Jan 4, 2008)

We tilted the response a bit using a very wide bandwidth filter out around 600 Hz. (Possibly more than necessary.) Also added a little boost to flatten it out a little between 10 and 20 hz. We only had about an hour to play with it, and we were both learning how to use the REW software. We made all the filter settings manually. This was the first measurement after we entered the eq filters.


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## Mattlock (May 9, 2007)

Steve,
Glad to see you chime in on some of the issues brought up....

Here are the filters we set

Freq Gain BW/60
21.25, 7, 7
27.28, 6, 4
39.15, -13, 12
51.30, -12, 10
64.70, 5, 10
81.00, -7, 7
604, -31, 72




Matt


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## Guest (Jan 4, 2008)

Matt....


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## Mattlock (May 9, 2007)

kbgl said:


> Matt....


Hey kbgl...u are killing me...the temptation is too great... So are you gonna help me explain to my lovely wife "why" I need a second one... I planted the seed yesterday with her...(oh I blamed it on you)..you know good cop bad cap...Hope you dont mind..

I must say things to look better in pairs !!!!!!!!!! As you know I have twin daughters so I took that approach with her but didnt get very far....


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## DrWho (Sep 27, 2006)

The room doesn't cause cancellations below the lowest modal frequency of the room...and you'd need a rather large room to have modal issues down to 20Hz (most rooms end around 30Hz, but there's no need for generalities when the specifics can be measured)


SteveCallas said:


> The valley in response in the low end was clearly a room effect, not subwoofer response related, as can be seen from his new measurement with the seat moved.





kbgl said:


> Also added a little boost to flatten it out a little between 10 and 20 hz.


Just as expected 



SteveCallas said:


> If you take a look at Ilkka's testing of a large and low tuned sub, you'll see that the FR is not affected in the least by any type of standing wave created inside a large enclosure. You do benefit from decreased harmonic distortion at that frequency, but it doesn't affect FR.


Ilkka's subwoofer is 3 ft tall, which pushes the first standing wave up to ~200Hz. It seems to me like you're trying to defend the LLT idea instead of interpreting the measurements.

Btw, the standing wave is an issue with floorstanding speakers too and also shows up on the measurements there.

****, you can see great correlation between my dirty prediction in Hornresp and the actual measured response provided. You can also see the unloading of the port when you factor in the distance between the active driver and the port in hornresp...Classical T/S simulation assumes that the port is right next to the active driver and that no delay happens...more accurate simulation takes into account the time-delay between the active and the port (which is rather large in this case). Moving the exit of the port closer to the active driver will improve the behavior (that way less EQ can be used and the distortion will be lower).



SteveCallas said:


> Port resonances will show up as a blip in the FR, but with his first resonance being ~250hz and a 24db/octave 80hz crossover in play, it's a non issue.


The port resonance isn't triggered by the active driver playing at the port resonance frequency...the fact that air moves through the port triggers the resonance. Try playing a 13Hz sine wave or whatever frequency the port is tuned at...you'll hear it singing the port resonance tone.

One last comment...distortion is loosely a function of bandwidth. Although IMD doesn't directly show up in THD measurements, you still see an increase in higher orders of distortion when the bandwidth of the system is increased (ie, lower port tunings). High orders of harmonic distortion happen to be the more audible and annoying type. And then when you've got weird anomalies happening within half an octave of the used bandwidth, you're going to trigger them with the raw distortion of the driver itself.

Anyways, I'm not trying to critique any design approach...it's just a matter of interpreting the measurements to identify what problems are being experienced and then addressing those problems directly - which is important here because EQ can never reduce distortion.


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## Mattlock (May 9, 2007)

The room doesn't cause cancellations below the lowest modal frequency of the room...and you'd need a rather large room to have modal issues down to 20Hz (most rooms end around 30Hz, but there's no need for generalities when the specifics can be measured)

Quote:
SteveCallas wrote: 
The valley in response in the low end was clearly a room effect, not subwoofer response related, as can be seen from his new measurement with the seat moved. 

Quote:
kbgl wrote: 
Also added a little boost to flatten it out a little between 10 and 20 hz. 

Just as expected 

Actually the first filter was set at 21.25. See graph below without filter, filter and predicted curves...Nothing boosting below 20hz..

Matt


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## DrWho (Sep 27, 2006)

I was originally referring to the boosting at 20Hz, which is apparently right at 21.5Hz. With better port loading, you would have less of a dip in that region. And by dip, I'm not referring to that narrow Q right at 21.5Hz, there is a wider Q which is also amplified by the influence of the room. After looking at literally thousands of these measurements, I have no doubt of what I'm seeing in the response...and the EQ curve just further confirms it.

If you're not convinced, take the sub outdoors and rule out the influences of the room. It'll be an eye opening experience.

****, the whole point of measuring is to see what's actually happening in the system. Is the goal here to get confirmation that your system sounds good, or are you trying to make things sound better?


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## Guest (Jan 4, 2008)

My mistake on the comment about flattening the response between 10 and 20. I was watching the graph while Matt made the adjustments. Without my glasses, I couldn't read the actual numbers off his laptop screen, and we were working fast trying to get done by 10:00pm. I was replying to Steve's question about the rising low end.

I think the tuning is fine. As with all things, there are trade-offs.


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## Jman (Jul 23, 2006)

DrWho said:


> If you're not convinced, take the sub outdoors and rule out the influences of the room. It'll be an eye opening experience.


He can measure nearfield to see the same thing. Personally I wouldn't make any boosts under ~25hz. Just asking for trouble when you crank it and the right (or wrong :R ) content hits the sub.


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## SteveCallas (Apr 29, 2006)

DrWho said:


> and you'd need a rather large room to have modal issues down to 20Hz (most rooms end around 30Hz, but there's no need for generalities when the specifics can be measured)


I could easily affect the measured <20hz response in both my old place and new place by opening/closing doors or measuring from different spots in the room. What the sub is outputting isn't changing, the variable being changed (one at a time) was volume being pressurized or location from which the measurement was taken. ****, we can clearly see differences in the <20hz response from two of Mattlock's own measurements with no filters in play. 



> Ilkka's subwoofer is 3 ft tall, which pushes the first standing wave up to ~200Hz.


Perhaps I am confusing this statement of his (which shows up in the distortion measurement) with a standing wave?


Ilkka said:


> DIY TC Sounds TC-2000 15" ported 270L
> The very much discussed “LLT”. Very good extension and frequency response for larger rooms. Small rooms may have too much low end gain. Quite strong port resonance at ~160 Hz. High max SPL at all frequencies. Low compression up to 110 dB. The 115 dB was terminated due to amp clipping – not woofer bottoming. Low overall distortion, though the upper end could be cleaner. *End cap to end cap resonance shows at ~75 Hz. *Very low group delay for a ported subwoofer. Good decay too. The enclosure is naturally huge.





> The port resonance isn't triggered by the active driver playing at the port resonance frequency...the fact that air moves through the port triggers the resonance. Try playing a 13Hz sine wave or whatever frequency the port is tuned at...you'll hear it singing the port resonance tone.


Interesting. Why then would the blip in the FR of Ilkka's sub show up at the first resonant frequency? At that high a frequency, there should be next to no air moving through the port, so what causes the blip? :scratch: I can't say I've ever heard my port sing a 300+hz tone whenever low frequency sine waves have been played through it. 



> Although IMD doesn't directly show up in THD measurements, you still see an increase in higher orders of distortion when the bandwidth of the system is increased (ie, lower port tunings).


When comparing the harmonic distortion by component measurements between the low tuned TC2k and small sealed TC2k - while two different samples of the same driver were being used - I'm not seeing the fruition of what you are describing unless you are only referring to measurements below the tuning frequency. 


I agree with Jman Mattlock, I don't see too much benefit in the low end boosting, just potential for trouble.


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## Mattlock (May 9, 2007)

SteveCallas said:


> I agree with Jman Mattlock, I don't see too much benefit in the low end boosting, just potential for trouble.


okay...I'll bring those down...

thanks


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## Mattlock (May 9, 2007)

Question: I'd be curious to know if anyone sees any material benefit/enhancement to my responses in the low end from using bass traps? Just curious....

Matt


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## Guest (Jan 5, 2008)

SteveCallas said:


> I agree with Jman Mattlock, I don't see too much benefit in the low end boosting, just potential for trouble.



I would at least halfway disagree Steve. The EQ added resulted in more output. This was a low spot in the response, not a null. We played WOTW with good strong LFE effects, but the sub level could have easily been reduced about 3 dB and it would have been fine. I've seen people crank the overall level up till the actors sound like they are shouting in order to get the effects to sound strong. Turning up the volume level 6 or 7 dB would not only boost the 21 Hz frequency, it would boost them all. 

On the other hand, I monitored the excursion during one of the demanding scenes, and it was getting a little close to what I would assume were its x-max figures. It might be a better compromise to move the couch back some and live with a slight notch at 50 hz, and have the additional headroom.

What are the x-max and x-mech figures for this driver?

I think I saw about 1 3/4" peak to peak excursion for a second or so. Couldn't see it real well, so I may be wrong.


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## Mattlock (May 9, 2007)

Well, I made more measurements and wanted to post for feedback...

Graph 1: Couch moved 2ft forward with no filters (sub in rear)

Graph 2: Couch moved 2ft forward with filters (sub in rear) 

(I pulled back on the gain for filters 1 and 2 from +5 and +7 to +3s on both)

Graph 3: Sub moved to front of room laying down with NO FILTERS (this is the only possible option and quite frankly it lwill most likely will get spousal disapproval in a big way) Actually I would have to remove the baseplate in order for it to fit between the walls and fireplace base and also be forced to reduce my screensize slightly....this thing is just huge 

Practically speaking is the differnce between 2&3 that big enough to warrant moving upfront and dealing with the aesthetic challenges????
How about I just work some more with my filters ?????????? 

The other option would be to put a smaller second sub up front but I assume that would have to be tuned pretty close to my current one??

I could probably get a 500 liter 24 inch sonosub (or box) put up front that would look much better..


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## Guest (Jan 5, 2008)

Try laying it down in the back of the room. I think the second curve looks pretty good as it is. 

You might try reducing the effect of the 604hz filter and see how it looks. Maybe -20 dB, or reduce the bandwidth of the 604 hz filter a little

What are the limits on excursion with this driver?


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## Mattlock (May 9, 2007)

xmax on the Q18 is 27mm


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## Guest (Jan 5, 2008)

Mattlock said:


> xmax on the Q18 is 27mm


So 2" peak to peak excursion should be no problem for this driver!


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## SteveCallas (Apr 29, 2006)

Graph 2 is good enough I'd say, I wouldn't worry too much about trying toget any flatter than that in your room. What I would do though is take that measurement again, this time with the mains in play. You'll want to make sure nothing changes dramaically down lo when the mains are in play, otherwise you'll want to change the filtering again.

As for bass traps, in order to affect frequencies below 80hz, the traps would have to be extremely thick. I doubt that is a realistic option. However, adding some absorption to the room in the form of pannels or corner traps should help the overall sound quality, even if it isn't really affecting the low end bass.


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## tnargs (Sep 7, 2006)

Mattlock said:


> ...The other option would be to put a smaller second sub up front but I assume that would have to be tuned pretty close to my current one??


I answered that in post 37.


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## Guest (Jan 7, 2008)

You might want to make a target rolloff of 24 dB / oct and see if you like it better than the 12 dB.


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## Guest (Jan 9, 2008)

JohnM said:


> From the impulse response the distortion looks very high, getting on for 10% 2nd harmonic and several % 3rd harmonic. May want to check the sub isn't being driven too hard.


How do you read that off of the impulse response?


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## Guest (Jan 9, 2008)

SteveCallas said:


> Again, not the case, that dip is merely another room related or phase issue. If you take a look at Ilkka's testing of a large and low tuned sub, you'll see that the FR is not affected in the least by any type of standing wave created inside a large enclosure. You do benefit from decreased harmonic distortion at that frequency, but it doesn't affect FR.
> 
> 
> Port resonances will show up as a blip in the FR, but with his first resonance being ~250hz and a 24db/octave 80hz crossover in play, it's a non issue.


I was wondering if a circular baffle inside the sub made from foam, or maybe peg board or MDF would be beneficial in breaking up some resonances.


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## JohnM (Apr 11, 2006)

kbgl said:


> How do you read that off of the impulse response?


The scaled down copies of the main impulse to the left of it are distortion artefacts. The first one (going left) is the 2nd harmonic, the next one is the third harmonic etc.


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## Guest (Jan 10, 2008)

JohnM said:


> The scaled down copies of the main impulse to the left of it are distortion artefacts. The first one (going left) is the 2nd harmonic, the next one is the third harmonic etc.



Like This?


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## JohnM (Apr 11, 2006)

That's them.


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