# Another Level Question (Newbie)



## rogerv (Nov 8, 2009)

Hi Everyone,

I'm working my way through the steps to use REW, and I've run into something that I don't understand. Here's a summary of where I'm at:

1) I have a Creative Labs "Blaster X-fi" external sound card. This card has separate right and left channels for line out. It has a single connector for line in. 

2) I'm using a Radio Shack digital SPL meter. 

I believe I have done the sound card calibration properly. I set up the cables as shown in the first attachment. 

On this picture, I ran the right line output from the sound card to the right side of the splitter plugged into the sound card's line in. I believe that this Radio Shack Connector splits out left and right signals from the single pin. The picture shows a second splitter which is identical to the one plugged into the sound card for reference. 

The second attachment is the sound card's uncorrected response. The corrected response is completely flat from 2 - 24Khz. I don't have a jpeg for this graph.

So am I on track as far as the setup and procedures for calibrating the sound card ? 

I think I have done all of the steps correctly, but when I go to the acutal measurment phase of the process, I'm running into something I don't understand, so I thought it's possible that I've done something wrong with these steps, and would be best to check.

*Measurement Phase:* 

My thought was that I would measure the subwoofer first on its own without involving the mains. My sub has a separate amplifier with line in connectors for signal, and a separate output level control. For REW, I took the Right Output from the sound card's line out and ran it into the sub's line in, and ran the SPL's output into the same right side connector that I used for the sound card calibration.

3) I ran the sound meter calibration procedure as described in the help files. For this, I played the subwoofer test tone, and set the numeric value on REW to match what was shown on my SPL meter. I adjusted the output at the sub's amp so that it read 75 db. 

4) Next I did a measurment. This is where I don't understand something.

5) I clicked on the measurement icon, set the start Freq to 15 HZ, and the End Freq. to 200 Hz. When I pressed the "check levels" button, I get a message that says "Level is Low". I'm not sure what level this message is referring to. Is it the output from the Line Out right channel, or is is the output from the sub that is low, or is it something else ? 

I was able to set the Level (dB FS) setting to make this message to go away. But when I did this, the measurements were all above the recommended 75 dB level. I don't seem able to find the right combination to make the "Level is Low" message go away while at the same time keeping the measured output at 75 dB. If anyone has any words of wisdom, I'd greatly appreciate it. 

Thanks In Advance 

Rog


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## brucek (Apr 11, 2006)

> So am I on track as far as the setup and procedures for calibrating the sound card ?


Yes, and the soundcard file is fine. BTW, there is no corrected and uncorrected soundcard file. They are identical - it's simply the soundcard calibration file.



> For REW, I took the Right Output from the sound card's line out and ran it into the sub's line in, and ran the SPL's output into the same right side connector that I used for the sound card calibration.


Yes, you can feed the sub by itself, but it's highly recommended to feed your receiver/processors AUX input instead. If you want left and right channels tested, use a Y-splitter at that point.

Set the receiver into stereo mode and set the crossover you would normal use. For sub only, shut off the mains speakers.

Connect your SPL meter to the line-in.

Then run the *Check Levels* routine and adjust your receivers volume to receive 75dBSPL at the listening position on the actual SPL meter. Set the input volume so the REW VU is about -12dB.

Then run the *Calibrate* SPL routine.

Then *Measure* from 0-200Hz.

brucek


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## Guiria (Jun 15, 2008)

I had this problem when I initially setup REW and it drove me crazy. I even ended up buying TrueRTA to use instead of REW but it was not the same. I finally figured out that changing from right to left (or left to right, I can't remember  Either way just choose the one that is not selected now) input in the REW settings fixed my problem and I no longer received the "level is low" message.

Good Luck. I can post some pics later if my description doesn't make sense but I'd have to bring my laptop home from work...


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## gperkins_1973 (Aug 25, 2008)

I was having the same problem last night. I can calibrate the spl to 75db but even with the soundcard input/output volume on max I could only get -35db levels. I changed my spl meter setting from 80db to 70db and didn't have a level problem but what I did find was that the headroom was clipping or going into the red. Total nightmare.

cheers
graham


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

rogerv said:


> 4) Next I did a measurment. This is where I don't understand something.
> 
> 5) I clicked on the measurement icon, set the start Freq to 15 HZ, and the End Freq. to 200 Hz. When I pressed the "check levels" button, I get a message that says "Level is Low". I'm not sure what level this message is referring to. Is it the output from the Line Out right channel, or is is the output from the sub that is low, or is it something else ?


I've had the same problem of late. Try ignoring the "Level is Low" and go ahead and take a measurement. Mine will come out fine despite the low level warning.

Another alternative is to use the RTA feature instead.

Regards,
Wayne


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## gperkins_1973 (Aug 25, 2008)

Wayne,

Yeh! your right when I went ahead and measured it had a headroom of 16db in green so I guess that's fine. Its was doing the levels on the speakers that was a pain. I set the spl meter to 80db on the knob, set the spl meter to read 75db, yet on REW is it was really low but when i switched it to 70db on the spl meter and then set the level to 75db it seemed fine, I could hit the 18db level easy but when i went to measure it was clipping. Is the procedure the same for subwoofers as to speakers or are the set ups different. C weighting was on and it was set to slow. Is this correct?

cheers

Graham


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

Yeah, keep the meter at the 80 range, C weighting at all times, be it subs or w/ mains. The fast/slow has no bearing, it's just for the meter's own display.

Regards,
Wayne


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## rogerv (Nov 8, 2009)

Thanks to everyone for the additional info and encouragement. :thankyou:

I have made some progress, and have gotten some measurements which I will upload in a second post. Here's some description of what I ran into while doing this (in case it's useful for anyone else). I'm still not sure what exactly was happening. I've got a suspicion about what was going on, but haven't gone back to reproduce the problem. Maybe someone knows off the top of their head.

*Problem #1: Bad hum from the speakers.*

I had a terrible hum whenever I selected the amp's connection from the soundcard. I couldn't make it go away, and initially thought it had something to do with cables and splitters or possibly the sound card itself. In troubleshooting this problem, I noticed that the power cord for the monitor was lying on top of the audio cable going to the amp. So, I unplugged the power cord to re-route it. The hum went away when I unplugged the monitor. After additional trouble shooting, I attributed the problem to either the LCD monitor that I was using (an IBM 19 inch LCD), or the digital cable coming out of the port replicator, or noise generated by the video card on the laptop's main board. Unplugging the monitor and using the laptop's display fixed it. The screen's a bit small, but I got rid of the hum.

*Problem #2: Output Displays All looked the Same. *

I really scratched my head on this one for quite a while. When I tried to make a measurement, I could hear the sweep tones generated in the speaker, but the generated results all looked like attachment #1. No matter what I did, it all looked the same. 

So, I went back and double-checked settings etc. In fiddling with the settings, I noticed that default output and input devices were selected in the sound card settings. I clicked on those, and re-selected something different (I think "speakers" for output and "Line In" for input.) I then ran the "check levels" from the soundcard settings.

Another measurement then produced normal-looking results. I shut down the p.c., and re-started it to see if something was being changed. REW now worked properly. My hunch right now is that when I disconnected the laptop from the sound card yesterday to put it back downstairs in my office that the that Windows re-assigned the default sound card to something else (probably internal speaker). I'm thinking through a test case where I can try and re-create this. But, that's the computer nerd in me. The audio nerd is just happy that it worked and that I got some measurements. 

Rog


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## rogerv (Nov 8, 2009)

*Another Newbies First Measurement*

Hi Everyone,

I was able to get everything working right (I think), and have some results to post. The crossover for the amp is set to 60 Hz. Attachment #1 shows the response which used 8 iterations of the test tones. 

I don't know what to make of the rather severe drop out around 110 Hz. The only thing that I could think of was that it might have something to do with the bass management system from the amp, or possibly something to do with the amp itself ?

So I re-ran the test with the sub disabled and only using the mains (second attachment). The drop out seems to have gone away. with the sub out of the picture. Would it be fair to say that since the drop out went away with only the mains involved that it's probably not room acoustics ?

Anyone have any thoughts about what might be going on, or other comments ? 

All I can say is that I sure love playing around with this stuff. I haven't had this much fun for a long time 

Rog


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## brucek (Apr 11, 2006)

> Would it be fair to say that since the drop out went away with only the mains involved that it's probably not room acoustics ?


No, it wouldn't be fair to say that. The sub and mains are in different physical positions in the room. They will most certainly suffer from different reflection cancellations from the room, since they are at different distances from the wall.

What the sub and mains are enjoying together is a room resonance at ~38Hz, evidenced by the shared peak at that frequency.

brucek


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## glaufman (Nov 25, 2007)

One thing I find curious is that the mains seem to be putting out so much energy below the crossover... did you disable the xover for the mains only scan?

To test, run a scan with just the sub. I would guess it won't show the same dip, in which case I would guess whatever energy it's putting out at that frequency is cancelling with that of the mains, i.e. a phase issue. But it's just a guess.


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

glaufman said:


> One thing I find curious is that the mains seem to be putting out so much energy below the crossover...


Yeah, no kidding. That's one of the worst mains peak I've ever seen!

Regards,
Wayne


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## rogerv (Nov 8, 2009)

Bruce,

Thanks for the reply. 

Maybe you can help me understand this better. I thought that if the crossover was set at 60 hz. that the sub would handle <= 60 Hz., and the mains would take everything else. Is this dip being caused by interactions between what the sub is putting out and what the mains are putting out ? How does that work ?

Please bear with me. I'm not very versed in a lot of these types of technical details. Feel free to refer me to some outside documentation or threads that I can read if that works better.

Regards,

Rog


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## rogerv (Nov 8, 2009)

Greg,

When I ran the mains only scan, I told the amp that there was no subwoofer. I set up the left and right speakers to full range. I think this eliminates all of the crossover processing, but maybe not. 

The mains are B&W 603's. The Amp is a Sunfire Ultimate Receiver II. Sub is a HSU TN1220 HO. 

I'll test the sub only tomorrow. (Gotta use the theater tonight) 

Rog


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## brucek (Apr 11, 2006)

> I set up the left and right speakers to full range.


Why? Don't you want to see the mains as they are used in your system with the crossover engaged.

brucek


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## glaufman (Nov 25, 2007)

rogerv said:


> When I ran the mains only scan, I told the amp that there was no subwoofer. I set up the left and right speakers to full range. I think this eliminates all of the crossover processing, but maybe not.


Yes, it would. But it's better to tell the amp (or processor) there IS a sub, and turn the sub off, so you get a better picture of what the mains are doing in the real world. Similar for the sub-only scan, don't tell the amp you've changed anything, but disconnect the mains to run the scan and see precisely the contribution from the sub.



> I'll test the sub only tomorrow. (Gotta use the theater tonight)


Always good to stop tweaking for a while and enjoy what you've got!:T


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## glaufman (Nov 25, 2007)

rogerv said:


> Maybe you can help me understand this better. I thought that if the crossover was set at 60 hz. that the sub would handle <= 60 Hz., and the mains would take everything else.


Basically true, but not quite. The crossover isn't a "brick wall" that stops precisely at 60Hz. Starting at a frequency just higher than the crossover point and moving lower, the crossover gently rolls off the mains as it gently rolls up the sub. If you started at a point just under the crossover and moved higher, you'd see the amp gently rolling off the sub and gently bringing up the mains. If you looked at the freq plot of the mains and the sub output of the amp (no acoustics involved) and overlayed them, you would see them crossing over each other at the point where you told the amp to set the crossover frequency (hence the name)... At this point, summing the individual contributions brings the combined response (assuming their in phase, and level matched, and...) back to flat. The point is that each one (sub and mains) put out useful and necessary sound energy for at least an octave above and below the crossover point respectively.



> Is this dip being caused by interactions between what the sub is putting out and what the mains are putting out ? How does that work ?


Possibly. To test this we run the individual scans, and if they're both clean, then there's an interaction between them. Simply put, if they're in phase they sum nicely. If they're out of phase, the cancel. Anything in between, and you get some portion of the cancelling effect. Sort of.



> Please bear with me. I'm not very versed in a lot of these types of technical details. Feel free to refer me to some outside documentation or threads that I can read if that works better.


No problem! We all start somewhere. I'm still learning from Wayne, Brucek, and everyone else here as well. :TThe pictures in this link might help:
http://en.wikipedia.org/wiki/File:Interference_of_two_waves.png


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## brucek (Apr 11, 2006)

> If you looked at the freq plot of the mains and the sub output of the amp (no acoustics involved) and overlayed them, you would see them crossing over each other at the point where you told the amp to set the crossover frequency


Something like this..........









brucek


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## rogerv (Nov 8, 2009)

Thanks to everyone for the additional explanation. It helped a lot, and I think I'm starting to get a handle on some of this. I think I understand now what I was supposed to do and what we're looking for. Here's my understanding of what everyone has said so far:

I want to capture the sweeps from the mains with bass management and without the subs contribution to look at the characteristics of the curve for the mains. Similarly, I want to look at the characteristics of the curve for the sub with bass management and without the mains contribution to look at it's curve. The combination of the two curves should provide additional information about how the two components are interacting and possibly either explain the drop out around 110 Hz., or point to where to gather additional diagnostic information. 

I understand now why everyone commented on how strange the curves for the mains looked. My thinking when I ran the mains without the bass management was that it would provide a base line of sorts that other measurements could be compared to. I've used a similar approach in some of the work that I've done in the past (software system integration testing). Probably the wrong approach for this situation, and I now recognize the differences between the two environments.

I have repeated the measurements, and have attached them to this post. I don't know if the attached are any better than the previous ones or not. There are four sweeps attached, which I have labeled on the graphs. The crossover for all four was set at 60 Hz. One is for the mains without the sub. I physically dis-connected the sub for this sweep. Two are for the sub without the mains. I have a switch on the sub's amp labeled "polarity." One sub sweep is with the polarity at zero, and the other is at 180. For both of these sweeps I disconnected both the left and right speakers. The final sweep is with the mains and sub, but with the "polarity" set to 180 on the sub's amp. The post that I put up yesterday was with this toggle set to zero, which is where I normally have it. 

It still looks like there's a high peak around 40 Hz even with the bass management engaged. It still may be the "worst ... ever seen" even though the peak is lower than what I posted yesterday. So I guess one of the outstanding questions is why the mains are generating so much energy below the crossover frequency. This is in addition to why we have such a severe drop out slightly above 110 Hz. 

A further piece of info is that I did do a number of sweeps on Thursday (which I didn't post) using different crossover frequencies. All of them show a peak at around this same 40 Hz. point. Some of them are a little narrower than others (I think), but I have no instances out of 12 measurements where this peak is not there. So, I don't know what might be causing this. 

Any comments are appreciated as always.

Thanks and Regards,

Rog


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## brucek (Apr 11, 2006)

> one of the outstanding questions is why the mains are generating so much energy below the crossover frequency.


Not an outstanding question really - it's your room. You have a nasty resonance at 38Hz. It's as simple as that. 

My office system has the same problem. I helped it somewhat by raising the crossover, and this offers more to the sub which has EQ on its path, but it still has that horrible peak. The sub enjoys the same peak, so when they combine with the mains it creates quite a horror show at that frequency. 

If you took your speakers outside and measured them a few feet away you would be amazed how perfect they are. It's always the room.

brucek


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## laser188139 (Sep 19, 2009)

You've identified one obvious question. It is very weird that the main only curve seems to show so much energy below the crossover. One would expect to see a curve dropping off at something like 12dB per octave beginning above the crossover. It looks a little like this above 80Hz, but then turns around and ramps up again below there. Almost as if the receiver sensed the sub was no longer connected and switched the mains to Large/Full Range. Or as if the natural rolloff of the mains is at 40Hz, and trying to pull the crossover up to 80Hz is leaving a lot of response in the mains below that. 

Equally curious, though, is the levels in the graphs. In the range above 150Hz, the response of the mains alone is about 20dB higher than the response when the sub is added. Now how does that make sense? Unless you recalibrated the volumes to different levels between taking the measures, or adjusted the graphs to measure the same value at the 40Hz peak. That might help explain why the graphs seem so confusing, that they are not really apples and apples comparisons changing only one variable. 

Bill


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## brucek (Apr 11, 2006)

> Unless you recalibrated the volumes to different levels between taking the measures


Of course, since mains pink noise is used, recalibration of the measure must take place.

The plots are very typical of a room mode at 38Hz.

brucek


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

rogerv said:


> A further piece of info is that I did do a number of sweeps on Thursday (which I didn't post) using different crossover frequencies. All of them show a peak at around this same 40 Hz. point. Some of them are a little narrower than others (I think), but I have no instances out of 12 measurements where this peak is not there.


Sure, raising the crossover frequency isn't going to make it go away in the mains, but it will reduce its level. Even that would be an improvement. I think I'd push the crossover up to 90 Hz.

You might want to take separate readings of the left and right speakers. If only one of them is the culprit, maybe something could be done about that one.

What kind of speakers are you using? I'm going to guess some big ones that have deep extension, as it looks like they go well below 30 Hz even after flattening the room mode. Some smaller speakers with a natural low end roll out considerably above 40 Hz would more or less leave the sub displaying the problem, and it could easily be equalized.

Also, does your sub have its own crossover built-in? If so a "staggered" arrangement might help - say, set the mains for 90 Hz and the sub for 40 or lower.

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

brucek said:


> Of course, since mains pink noise is used, recalibration of the measure must take place.
> 
> The plots are very typical of a room mode at 38Hz.
> 
> brucek


Yes, Bruce, there appears to be a room mode at 38Hz. Agreed. 

But there is something else confusing about the presentation of the graphs. If one does not suspect that the levels have changed, that the measures were taken with different volume or gain settings, then comparing graph 1, green of main+sub, and graph 2, red of main alone, one asks the question, how can the main be putting out so much energy below 40Hz when there is a crossover with its high pass filter in the system? If the levels have changed, then this question doesn't arise, as the apparent levels are an artifact of the measurement process. Were one to imagine graph 2 translated downward about 20db, so that the levels in the 150-200Hz range were comparable to graph 1, the room mode at 38Hz would still be present, but one would see a falloff that would like the effect of the crossover on the mains. I expect, with your experience, this is what you see automatically when looking at them, and you're thinking "Duh!". 

Comparing graphs 2 and 3, one might think the mains and sub should add together to give a nice response. But if the calibration of the measurement process is different between the two and the levels are different, then this may be just appearance, they don't meld together nicely like the curves in the illustration you provided. 

All of which makes me look again at graph 1. I suspect that the sub is set a lot hotter than the mains, 10dB higher, maybe more. It's hard to see for sure, as the displayed range only goes to 200Hz. This is the best hypothesis I have so far that lets me reconcile all the graphs together. 

By the way, Rog, as you can see from your graphs, the phase difference should have no effect when you look at the sub alone. You would expect to see an effect by comparing Main+Sub graphs with different phases. I tried something similar on my system last night. Inverting the phase removed a dip at 60Hz but created a larger one right at my crossover of 80Hz. (I would show you a graph, but I was a klutz and stored my phase 0 file on top of my phase 180 file, so I don't have it anymore.)

Bill


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

I’m beginning to suspect that it’s some kind of extraneous noise in the room. Note that with each set of graphs – the ones in Post #9, and then the ones in Post #18 – the top of the peak stays at the same in each graph. And it virtually disappears once the subs are added. Has anyone ever seen a room mode that was swamped by the sub??? That’s just not right – the peak level of a room mode typically goes up and down with volume level changes. 

I think a 1000 ms waterfall would tell us a lot...

Regards,
Wayne


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## brucek (Apr 11, 2006)

> I expect, with your experience, this is what you see automatically when looking at them, and you're thinking "Duh!".


I simply look at the sub + mains trace and examine the relative levels between the two. It's pretty obvious your sub is set at a far higher level than the mains. That's fine, some people like it that way, but I immediately discount the level of a mains only and examine the response, not its level. This doesn't remove the fact that you have a huge peak below the crossover in the mains. So, do I, so do a lot of people. The answer is to raise the crossover to ameliorate its effect, since the peaks frequency will be further down the crossover slope and won't overwhelm the mix of the mains + sub quite as much.



> Comparing graphs 2 and 3, one might think the mains and sub should add together to give a nice response. But if the calibration of the measurement process is different between the two and the levels are different, then this may be just appearance, they don't meld together nicely like the curves in the illustration you provided.


Yeah, because your sub level is too high.



> All of which makes me look again at graph 1. I suspect that the sub is set a lot hotter than the mains, 10dB higher, maybe more. It's hard to see for sure, as the displayed range only goes to 200Hz. This is the best hypothesis I have so far that lets me reconcile all the graphs together.


Set the measurement out to 500Hz.

brucek


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## rogerv (Nov 8, 2009)

brucek said:


> Not an outstanding question really - it's your room. You have a nasty resonance at 38Hz. It's as simple as that.
> 
> brucek


Bruce,

O.K. Good start then. So to moderate this resonance, I know of three things that I can modify: 

1) Speaker Locations
2) Room Treatment (amount of reflectivity on the walls, speaker locations, seating location etc.), although some of these such as seating location can't be modified very much)
3) Add Equalization [Being a gear guy, this one is my personal favorite] 

Are there other categories of things that could be considered in this context as ways to correct the room response ?


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## rogerv (Nov 8, 2009)

laser188139 said:


> Equally curious, though, is the levels in the graphs. In the range above 150Hz, the response of the mains alone is about 20dB higher than the response when the sub is added. Now how does that make sense? Unless you recalibrated the volumes to different levels between taking the measures, or adjusted the graphs to measure the same value at the 40Hz peak. That might help explain why the graphs seem so confusing, that they are not really apples and apples comparisons changing only one variable.
> 
> Bill


Bill,

I did have to adjust the levels when I ran the tests. This was because the levels for the sub only were o.k, but when I turned the sub off and did the test to see how the levels were, I got a message telling me that the levels were low. So, I had to turn them up for the mains only sweep. I didn't know what else to do. Hopefully it doesn't invalidate anything. :gulp: 

Rog


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## rogerv (Nov 8, 2009)

Wayne A. Pflughaupt said:


> What kind of speakers are you using? I'm going to guess some big ones that have deep extension, as it looks like they go well below 30 Hz even after flattening the room mode.


They're B&W 603's, and they're pretty good sized. I like them a lot. For guitar music they lack a little "sharpness" or "brightness" which I kind of like. Another rationale for adding equalization (can you tell I really want to do that ?)  Having said that I find that the quality of the voices for women singers is very good.

I do have some crossover capability in the sub's amp, but I think it's only for speaker level input, not line level. I'll check.

Rog


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## rogerv (Nov 8, 2009)

Wayne A. Pflughaupt said:


> I think a 1000 ms waterfall would tell us a lot...


Wayne,

Sounds like fun. Any specific sweep(s) that I should post ? Please let me know which one to send, and the settings that I should use for the waterfall. 

Rog


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

A waterfall of any of your previous graphs should be fine. Just set the "window" for 1000 ms.

Regards,
Wayne


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## brucek (Apr 11, 2006)

> So, I had to turn them up for the mains only sweep. I didn't know what else to do. Hopefully it doesn't invalidate anything.


Certainly not, REW isn't about the level, it's about the response. If you want to balance the levels, use your receiver test tones.

brucek


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## rogerv (Nov 8, 2009)

Hi Wayne,

Attached is a waterfall of the sub only sweep with a 60 hz. crossover that I posted. 

Are there any articles that you could point me to that would explain what I'm looking at ? Right now my only response is "Hey that's kind of pretty":huh:

I also grabbed the settings that I used in case I didn't get one of them right.

Regards,

Rog


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## laser188139 (Sep 19, 2009)

Rog, most people prefer that the frequency axis stay logarithmic, where yours is linear. You can press the Freq Axis button at the top right to flip these. 

As I understood Wayne's suggestion, it was to calculate the measures over 1000ms of time, to make sure it shows the full decay of your low end peaks. You changed the window to 1000ms, which is something different dealing with how the signal is analyzed. 

Bill


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## rogerv (Nov 8, 2009)

Bill,

:thankyou: I really appreciate it.

I took Wayne literally and selected the only setting with "window" on it 

Attached is a new one with different settings (also posted). 

Rog


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## brucek (Apr 11, 2006)

> Attached is a new one with different settings


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

brucek


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## rogerv (Nov 8, 2009)

Hopefully third time's a charm


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## brucek (Apr 11, 2006)

Again it shows that your sub level in relation to your mains is too high.

1000msec decay time as the third axis is only used when there is an insane amount of decay and you want to see where it actually enters the noise. Normally 300ms-500msec is used.

brucek


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## laser188139 (Sep 19, 2009)

brucek, for a moment I thought the same thing when I looked at the first waterfall graph with the linear axis, but then I reread that Rog said these graphs were from the sub only.


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## brucek (Apr 11, 2006)

> these graphs were from the sub only.


Then he didn't measure at 75dBSPL, which is required for waterfall to establish the noise floor.

brucek


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

brucek said:


> 1000msec decay time as the third axis is only used when there is an insane amount of decay and you want to see where it actually enters the noise. Normally 300ms-500msec is used.


Yeah, that's what I was expecting to see, an "insane amount of decay," but that doesn't seem to be the case. Not sure what to think at this point...

Regards,
Wayne


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## laser188139 (Sep 19, 2009)

rogerv said:


> Bruce,
> 
> O.K. Good start then. So to moderate this resonance, I know of three things that I can modify:
> 
> ...


Rog, it does seem you are getting close to the fun part, or at least the chance for lots of experiments. 

Looking at the sub curve, with the high levels below 40Hz and the dip above 40Hz, that might be a characteristic of your sub. I see something a little similar, with a Hsu sub, when I turn equalization off, although my dip from 40-60Hz is on the order of 8dB, where yours looks like 20dB. Other hypotheses are possible, of course. It could be that moving the sub from midwall to corner, or vice versa, might make this response more smooth. I'm sure you could use an equalizer to attack just the peak at 38Hz. It could be you could use an equalizer to smooth the overall levels below 40Hz relative to above 40Hz, but I am no expert on controlling filters in an equalizer. 

To understand the apparent room mode around 38Hz, you might try one of the room mode calculators on the web. I'm fond of using this one, as it shows multiple modes, which helped in my room as it has a complex shape. RealTraps offers a nice converter between freq and distance. Besides 38Hz, you seem to have another mode with a long lasting decay near 20Hz. If these match dimensions in your room, they might suggest ways you could move the sub to avoid putting so much energy into the mode. 

I'm sure you will have lots of fun with this,
Bill


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## glaufman (Nov 25, 2007)

Hey Rog, How about a quick sketch and description of your room and setup?


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## rogerv (Nov 8, 2009)

laser188139 said:


> Looking at the sub curve, with the high levels below 40Hz and the dip above 40Hz, that might be a characteristic of your sub. I see something a little similar, with a Hsu sub, when I turn equalization off, although my dip from 40-60Hz is on the order of 8dB, where yours looks like 20dB.
> Bill


Bill,

Nice to meet another Hsu user. What model do you have ? 

I can't figure out how to do multiple quotes in the same message, so I'll just type away. I'm going to attach some additional stuff to this message including a room diagram which Greg asked about later in the thread. The room is 8 feet high. It came out more "squarish" than I hoped for, but sometimes you need to make some concessions 

Thanks a lot for the links that you posted. These look very cool, and I will definitely take a look at these when I get further along with this. I expect that they will be more flexible than what I used originally.

When I was planning this project out, I found a room response calculator by Vavuz Aksan. It's an Excel spreadsheet into which you plug room dimensions and listening positions, and I thought that it was pretty cool. I used this to do multiple iterations of locations to help determine where the seating would be relative to the front of the room, and where to put the subwoofer. I have attached a graph of the predicted frequency response for the room with the subwoofer in it's current location. As you can see, the model didn't predict the rooms actual frequency response very well. Some of the general characteristics are there (such as the steep drop off between 40 and 50 hz.), but it didn't predict the large peak around 38 hz., and it also didn't predict the magnitude of the drop off from 40 - 50 Hz. Even though I recognize that predictive models are never as accurate as actual measurements, I was surprised when I started running measurements using REW and discovered how different the room's actual characteristics were.

I guessed that either the modeling was not accurate, or I didn't enter some of the room characteristics properly. I recalled that there are some values on the spreadsheet that represent "room reflectivity." Not knowing how to estimate these values, I just left them all at their default values. 

Yesterday I started playing around with some of the settings to see if I could make the predictive model more closely align with the actual results. I started modifying the reflectivity settings. Although the room is very quiet and isolated inside (and out), it's mostly just plain sheetrock all around. The window has some thicker coverings on it to keep light out, but that's the only one. What happened, I thought, if I plugged in more reflective values for the walls and ceiling ? Would I get more predictive results ?

I have attached the results of modifying the reflective values, and I think they're pretty interesting. I've put annotation on all of them describing what they're showing. Although the graphs are plotted from 15 - 200, I couldn't figure out how to make the x axis show only that range. 

The second graph from the model shows what happens when I increase the reflectivity values for all of the walls, except for the wall with the window coverings on it. This graph has some differences from the ones produced by REW, But I think that for the most part it looks a lot closer to what REW showed. It seems to have captured the peak and drop from 38 - 50 hz. pretty closely. Other parts after 50 hz. are closer as well I think.

Finally, Graph 3 shows the predicted results from reducing the reflectivity of the front wall by half. It seems to moderate the peak at 38 hz.

This whole process is just a lot of fun for me.  I expect to fiddle around with lots of different things as I move along including looking at equalization solutions. I'll probably plug my room's values into some of the other response tools that you provided to get their view of what's going on. 

Bottom line is that this is a hobby for me, and it's nice to be around like-minded people. I will say that I am very very happy with the performance of the theater both for movies and for listening to music (even though the bass seems to be set too high). I'll re-visit that aspect along the way as well.

Regards,

Rog


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## glaufman (Nov 25, 2007)

Yup, that's a pretty square room indeed. And 38Hz and 15 ft are a match. So you've got a dobule mode operating there. Just for the sake of argument, see what a scan looks like if you placed the mic 9.3 ft from the front wall.


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## laser188139 (Sep 19, 2009)

rogerv said:


> Bill, Nice to meet another Hsu user. What model do you have ? ...


Rog, I have a VTF-3 Mk3. If you are interested I discussed its Max Output and Max Extension performance corner loaded in my living room in the Hsu forum. 



rogerv said:


> ... When I was planning this project out, I found a room response calculator by Vavuz Aksan. It's an Excel spreadsheet into which you plug room dimensions and listening positions, and I thought that it was pretty cool. ...


I may have to play with that to see what it would indicate for my room. With my complex shape and openings to other rooms, the predictions might not be very accurate. But as you are doing, when you have a model and you can tweak it to approximate the measured response, it can tell you something about what is really happening. 

Thanks,
Bill


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## rogerv (Nov 8, 2009)

glaufman said:


> Yup, that's a pretty square room indeed. And 38Hz and 15 ft are a match. So you've got a dobule mode operating there. Just for the sake of argument, see what a scan looks like if you placed the mic 9.3 ft from the front wall.


Greg,

Now that was a remarkable call. How'd you do that ? :rubeyes:

Attached is a scan with everything the same as previous, including the sub being set too high. I like to change only one thing at a time. Putting the listening position at 9.3 feet eliminates the 38 Hz. peak. :T

I think the next thing I want to do is to listen to some of my favorite recordings at this spot in the room. While I like most of my favorites as is, I find that I'm missing the "strike" of some bass drums that I recall being there when the system was positioned in a different room. More stuff to fiddle with.

Thanks !

Rog


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## glaufman (Nov 25, 2007)

Well, 38% is sometimes a magic number in LP placement. 

Also, this hasn't done anything for your 40-70 Hz region (although I don't think it's done any harm either) which due to how wide/deep it is could be more problematic to SQ... You might try moving the mic a little further front or back, or even left-right (38% again?).

How do you feel about moving the sub?

And I'm still wondering about why there was so much energy in the scans of your mains... perhaps your AVR has pre-outs where you can scan just the preamp to make sure the bass management is doing it's job.


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## rogerv (Nov 8, 2009)

Greg,

I'd be open to moving the sub. I'm not sure how much flexibility I have though (given how the room is currently configured). I've got the amp and other equipment under the screen which limits placement there. The windows and doors on the side walls limit placement there. :sad: But, anything is possible. It just takes time and commitment. I could moose the sub to different locations to get an idea of how it might affect the results. What locations were you thinking about for re-positioning ? 

The amp has tons of inputs and outputs. I've been kind of frustrated by the explanation of how some of these are used, though. I've got audio in and audio out which are labeled "tape". I've also got a stereo output labeled "Fixed main" which has the following description:

"Fixed Main is a line-level output, and the volume is not adjustable. This can be used as a record output, or to feed another audio system." 

Whatever happened to the good old-fashioned "tape monitor" switch ?

I also can't figure out where the bass management occurs in relation to all these inputs and outputs. I'll have to resolve this issue before I can consider adding an external equalizer. onder: 

Rog


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## glaufman (Nov 25, 2007)

Well, as for adding the external EQ, if your bass management is operating correctly, you only need to insert it in the line going to the sub. Hopefully. Don't quote me on that. Assuming you're using line levels (RCA) to the sub which has it's own integrated amp.

As for sub placements, I'd only be guessing. There's another old adage about putting the sub in your LP, playing some music, and crawling around till you like the sound of the bass, then putting your sub there. But you might try moving the mic around first, and put the sub where you get the best plot. To be honest, I'm not sure exactly what is your best next step. 

If I were you, I'd take scans in more locations (specifically other spots on the couch) and ovelray them on the same plot before moving anything heavy like the sub. But if you want to listen first, that's ok too.

I also might create an IR and WF from that latest scan just to see where you are with decay times.


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

> There's another old adage about putting the sub in your LP, playing some music, and crawling around till you like the sound of the bass, then putting your sub there. But you might try moving the mic around first, and put the sub where you get the best plot. To be honest, I'm not sure exactly what is your best next step.


 No need to wear out your knee pads – just use REW’s RTA feature, move the mic around to all the different viable sub locations, and see the response on screen change. 



rogerv said:


> The amp has tons of inputs and outputs. I've been kind of frustrated by the explanation of how some of these are used, though. I've got audio in and audio out which are labeled "tape". I've also got a stereo output labeled "Fixed main" which has the following description:
> 
> "Fixed Main is a line-level output, and the volume is not adjustable. This can be used as a record output, or to feed another audio system."
> 
> ...


What kind of receiver are you using? Can you post a link to the manual? Typically bass management is only active on the primary outputs – speaker terminals, and RCA outs for mains, center, surrounds, etc. However, we have seen cases where the bass management was only active for digital signals, which created problems trying to use REW (since it’s using analog signals).

Also, I’ve heard that with a severe room mode like this, moving the sub a few feet down the wall from the corner will nuke it, while retaining the other benefits of corner loading. If you can, try moving it down towards the window, maybe take a reading at 1-ft. intervals.

Regards,
Wayne A. Pflughaupt


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## laser188139 (Sep 19, 2009)

glaufman said:


> ...
> Also, this hasn't done anything for your 40-70 Hz region (although I don't think it's done any harm either) which due to how wide/deep it is could be more problematic to SQ... You might try moving the mic a little further front or back, or even left-right (38% again?).
> ...


Rog, following up on Greg's comment, I decided to look again at your room configuration. Playing with the numbers, it suggests that the drop off in the 40-70Hz region is from the reflections off the side and rear wall. 

Assuming that you took your measurements from the center of the couch, in its initial position 12' back, if one compares the straight line distance to the sub, 12.5', to the distance of a reflection off the opposite wall, 22.8', the difference, 10.3', corresponds to a half wave at 55Hz, in the region of the drop out. 

With the couch moved forward to 9.3 feet, the difference in the reflection off the opposite wall and the direct distance is 11.4', corresponding to a half wave at 49.6Hz. Although this reflection would now be off the doorway, and I expect that it is open, not closed. But you are now far enough from the back wall that the reflection from there drops down in frequency; the reflected distance from the back wall should be 20.6' for a delta of 10.3', which corresponds to a half wave at 55Hz. 

Basically this suggests the wide dip in the response is from reflections here and there in the room. As Wayne suggests, moving the sub down the wall toward the window will change how it energizes room modes, but it will also change how these reflections come together and might give you a more even response before equalization. (I would have tried something like that in my room, but my obstacle in that direction is a fireplace, not a window.) And your measurements should be a little different at the two ends of the couch, compared to the center.

Bill


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## glaufman (Nov 25, 2007)

Wayne A. Pflughaupt said:


> No need to wear out your knee pads –move the mic around to all the different viable sub locations, and see the response on screen change.



Agreed. That's what I meant, even though Wayne said it better...


> just use REW’s RTA feature,


Didn't think of that... nice call


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## rogerv (Nov 8, 2009)

Wayne, Greg, and Bill,

Thanks so much for all of your insights on this :thankyou: I really appreciate it. 


Wayne A. Pflughaupt said:


> No need to wear out your knee pads – just use REW’s RTA feature, move the mic around to all the different viable sub locations, and see the response on screen change.
> 
> What kind of receiver are you using? Can you post a link to the manual?


I like the RTA idea and the approach of moving the mic around to different locations to get some of idea where the best response might be. That should be a lot easier. It's funny that I had seen the letters "RTA" in other posts, but never realized that this was part of REW, or what it was and how it might be used. I think I'll make some small incremental changes in the current location before moving the sub to the listening location for additional RTA measurements. 

In looking at the help files to find a description of RTA, I also found descriptions for other measurements that REW can do and what they might indicate. What a remarkably useful set of tools that is for the audio hobbyist. :wow: I'll be spending some time looking at these help files to gain some additional insight into some of the terms and concepts described there.

The amp is a Sunfire Ultimate Receiver II. Here's a link to the manual. http://www.sunfire.com/manuals/913-108-00 Rev A URII.pdf 
I've pretty much decided that I'm going to incorporate a BFD into the system if it's possible to plug one into that jumble of inputs and outputs. onder:

Thanks again to everyone. I'll be spending some time over the long weekend doing lots of additional fiddling. I hope everyone has a nice holiday.

Regards,

Rog


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## brucek (Apr 11, 2006)

> I'll be spending some time looking at these help files to gain some additional insight into some of the terms and concepts described there.


Rogerv,

Take a look at this thread (about half way down) to understand how to use the RTA.

brucek


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## rogerv (Nov 8, 2009)

Hi Everyone,

I've been spending a lot of time since my last post reading various threads here and on other sites as well as re-reading the help files for REW. I've also been through many many sweep and RTA iterations with speakers in different locations. In doing this I discovered that I had made some mistakes in previous posts which largely invalidate everything up to this point. 

Here's a quick summary of the mistakes that I made that: :doh: 

1) Mis-understanding about calibration files. 

Prior to starting all of this, I read about the need for a microphone calibration file and the need to make it available to REW to adjust the readings for various mics / spl meters. I downloaded the Radio Shack calibration file and had it on the laptop. I also read all of the more recent threads about the need to create a sound card calibration file. So, I created a sound card calibration file, and told REW where it was. But, I didn't put two and two together to realize that REW requires TWO calibration files, and that they are identified under different tabs in the setting window. :yikes:

I get it now, but unfortunately all of my previous sweeps didn't have a Radio Shack calibration file in them. In previous posts, several people pointed out that the mains seemed to be putting out an awful lot of energy below the crossover points. I really didn't understand that until I read some more stuff about crossovers and typical curves. Could the lack of SPL calibration file have produced some of that effect i.e., without calibration bass level measurements are too high ? 

2) Lack of consistent set-up procedures. 

I wasn't very consistent in the steps that I went through in setting up the various levels required for REW. I mostly fiddled with various settings to eliminate "low level" messages that I would get from time to time. Recently, I found the following checklist procedure to use before doing any sweeps: 

http://www.hometheatershack.com/forums/rew-forum/23280-first-measurements.html#post210631

As a novice, I find this type of summary checklists really valuable. The more the better. I now use this checklist every time I use REW, and it seems to help. Would it be worthwhile to have this as a sticky ? 

So, I pretty much started all over again, and I hope I'm making some progress. Here's where I'm at:

My mains have a port at the top which can be plugged with a foam plug. The manual says that they can be plugged to reduce bass response. So, I measured the responses with and without plugs. Here's what I found with mains only 80 hz crossover. The lower values are with the plugs in:









I've still got that pesky room peak at 38 Hz., but the plugs do seem to moderate some of the bass energy. The mains may very well be too big for the room, but they sure don't seem like it when they're sitting there in front of the room. :dontknow:

Over the thanksgiving weekend, I moved the sub from it's previous location in the front left of the room. Right now it lives in the back right (corner / back on the side with the door) and repeated the measurements. I think I've got some candidates that I might be able to equalize with a BFD. Following are the candidates. I ruled out any responses that have sharp dips in them (based on a recommendation by BruceK I believe in another thread about the futility of trying to equalize those types of deficiencies). 

To my untrained eye, these look better than previous ones. I've put them in what seems to me to best first. If I'm on the right track, I'll move the sub around to different locations to see if any of them produce better responses before going out and buying a BFD. 

40 hz crossover - phase 180









60 hz crossover - phase 180









80 hz crosover - phase 0









80 hz crossover - phase 180









Thanks and regards,

Rog


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## glaufman (Nov 25, 2007)

Do us a favor and repost the sub plots after switching the freq scale to "log"
That being said, I think these are more believable, showing the peak at 38 affecting the mains response, but at a far lower level than the sub resposne, indicating that hopefully the crossover is doing it's job.
OTOH, are those sub plots the sub together with the mains? If not, it's the sub alone, then we have another crossover issue...
Also, you went back to the couch position? Didn't like the distance from the front wall?


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## rogerv (Nov 8, 2009)

glaufman said:


> Do us a favor and repost the sub plots after switching the freq scale to "log"


I sure seem to be having a hard time getting things right :blush: 

Here they are with log set. 

40 Hz









60 Hz 









80 Hz zero phase









80 Hz 180 phase











glaufman said:


> OTOH, are those sub plots the sub together with the mains? If not, it's the sub alone, then we have another crossover issue...
> Also, you went back to the couch position? Didn't like the distance from the front wall?


Plots are subs and mains together. 

Unfortunately, moving the couch forward puts us too close to the screen for comfortable movie viewing. More compromises ..... :sad:

Thanks for your patience,

Rog


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## glaufman (Nov 25, 2007)

Any time you're reeling like you're ego's been bruised, just read the line in my signature. 
I hear you on the "too close to screen thing."
You might try putting the sub in that position along each of the side walls (4 points to try/scan), i.e.:
1) on the left wall, 5.7 ft from the front wall
2) on the left wall, 9.3 ft from the front wall
3) on the right wall, 9.3 ft from the front wall
4) on the right wall, 5.7 ft from the front wall (if that's not in the doorway)...


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## rogerv (Nov 8, 2009)

Greg,

Many thanks for the encouragement. 

I did some additional sweeps in as many of those locations as I could. I wanted to make these measurements even though it wouldn't have been practical to leave my current sub in those locations. The sub is an older HSU sub which is a 4 foot long cylinder with a 12 inch driver at one end, and an opening at the other end where the air comes out. The normal position for the sub is upright with the open end pointing down and the driver 4 feet or so from the floor. With this configuration the unit is somewhat top heavy, and could be knocked over. So, leaving it exposed away from the front or rear walls probably would result in it being tipped over at some point in the future. (Visions of my lovely wife bumping into it while vacuuming come to mind) :no:. 

Having said that, I still wanted the measurements. I thought that if something terrific showed up in any of the positions maybe I could consider a more conventional cube-shaped sub for some time in the distant future that might be suitable to locate at one of those spots. 

All of the sweeps in those positions produced some variation of the following. They pretty much all removed the big peak at 38 hz. but typically produced some sharp drop off at some other higher frequency, and other peaks at different locations. Here's a sweep that I think is fairly typical of these locations. Sweep is mains and sub together.










So, time to try something different. A second configuration for the sub is to remove the feet and have the cylinder lying on it's side. This eliminates the top-heavy issue, but takes up 4 feet somewhere. I put the sub behind the seating with the driver end facing the window wall and with the open end facing the door side-wall, and did some more sweeps (using RTA to find the best looking candidates) before actually running the sweeps. This sweep is mains and sub together with a 40 hz. crossover










I'm still looking for a good starting point to equalize, and to my untrained eye, this might be a candidate. Here's my beginner's analysis of this sweep: 

I see two pretty good peaks from 18 - 22 hz. and a sizable drop off around 120. The peaks would need to be lowered, but if I have a house curve (I already read about that subject  ), maybe the target point wouldn't require the full 13 db drop which seems large. I'm hoping that it's feasible to raise the dip around 120, but don't know if that's reasonable or not. Presumably the rest of the smaller peaks and valleys would be filtered out as well.

Am I getting any closer on this ?

Thanks,

Rog


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## glaufman (Nov 25, 2007)

Well, I guess I win some and lose some... I can live with that... 
Keep in mind that in some positions you may have to play with the phase to really see where you are in the crossover region ... (you didn't indicate where the xover was set for these scans)
I'm not the expert that these other guys are when it comes to setting the EQ, but I would agree with your analysis on where to start, IF you can fix that 120Hz without boosting...
If you want to start with this curve, I'd then move on to separate scans again to see where the dip is coming from.


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

rogerv said:


> I'm still looking for a good starting point to equalize...


Based on which graph?

Regards,
Wayne


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## rogerv (Nov 8, 2009)

Greg,

I'll work on separate scans next to see if that provides some more insight. 

:thankyou:

Rog


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## rogerv (Nov 8, 2009)

Wayne A. Pflughaupt said:


> Based on which graph?


Wayne,

I was thinking the very last one might be an acceptable starting point ? 

Rog


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## rogerv (Nov 8, 2009)

Hi Everyone,

Well I've been pretty busy up here in the frozen north since my last post. I don't know if I've progressed or not, but I've done a lot of stuff. Here's a quick update: 

1) The sub has been moved back to its upright position. It now lives in the rear corner of the window wall.
2) I picked up a brand new BFD 1120P which is installed. I've got the infamous hum, but I've worked around that for now with a cheater plug. I'll look into the root cause for the ground loop later. 
3) I've run many many sweeps (again) both mains only / sub only / left main only / right main only, plus some sub and main sweeps with filters engaged. 

I have sweeps for everything from 40 - 90 hz in 10 hz increments. I tried to use Wayne's simplified minimal eq method, and things look a lot better when looking at them with the vertical scale from 20 - 130. I have to say that when I set the vertical scale from 45 - 105 things definitely don't look too good. I don't know if it's o.k. to use 1/3 db smoothing or not, but I did for these. I used Wayne's hard knee house curve verbatim. I thought I'd use that to start then experiment later with different ones after I become more familiar with everything.

Anyway, here are some 50 hz sweeps. I used 50 because it seemed to be about the best looking of all of the ones that I have (using the 20 - 130 vertical). If it would be better to look at a different crossover, just let me know. I've got them all. 

*Here's the sub sweep (no BFD)*








*Here's the sub sweep with my best guess BFD filters engaged.* 

I had to set the gain higher for this one to get past all of the check signal processes, so it's higher overall than the previous one, and I raised the target level curve as well.









*Here are the BFD filters. * 

For these, I just started with the automatic settings, then modified and added additional filters to try and smooth out the response.









*Mains together.* 

The level on these is lower than the previous ones, but I think it's because of the check signal processes again, but can't remember exactly why they ended up this way. One of the things that I've never understood is whether I should use 12 or 24 db / octave when looking at targets for bass limited speakers. I couldn't understand the help file, but I got the sense that I'm supposed to use 12 db / octave for these. Any help on that subject would be appreciated.









*Left Main*









* Right Main*









*Subs and mains together with filters.*









The suck out between 70 - 120 jumps out the most for me. Should I just throw in some boost around there to try and fix this, or is that futile since it looks like it's mostly coming from the mains ?

Anyway, I'm going to spend some time listening with these settings to see what it sounds like. As always, any comments about how I might go about improving this are greatly appreciated. 

Thanks and regards,

Rog


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## glaufman (Nov 25, 2007)

Better to not use any smoothing in bass region scans.


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## brucek (Apr 11, 2006)

> I have to say that when I set the vertical scale from 45 - 105 things definitely don't look too good.


But that's the axis you should use. It's a standard 60dB swing around 75dB target - there's no real reason to use anything else.



> One of the things that I've never understood is whether I should use 12 or 24 db / octave when looking at targets for bass limited speakers.


The first thing you need to do is remove the house curve when you're displaying your mains target trace.
The receivers HPF would be 12dB/octave, plus your speakers will drop off at about that rate, so it's up to you which target you should use depending on the low end response of the speakers.



> I had to set the gain higher for this one to get past all of the check signal processes


Run the Check Levels routine and set the input level appropriately and it won't produce any warnings. Your input level is too low if it does.

You have a peak in your mains around 40Hz, so use a higher crossover (i.e. 80Hz), then the eq can be done in the sub - and the mains will be in the HPF at that frequency.

brucek


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

Sorry to leave you hanging,Roger – for some reason I didn’t get an e-mail notification after your Dec. 5 post.




rogerv said:


> One of the things that I've never understood is whether I should use 12 or 24 db / octave when looking at targets for bass limited speakers. I couldn't understand the help file, but I got the sense that I'm supposed to use 12 db / octave for these. Any help on that subject would be appreciated.


 Use the Target that coincides with slope your AVR uses. If you’re measuring the speakers full range (i.e. no bass management), use the “Full Range” option. Of course, if you’re measuring your speakers full range w/o bass management, it won’t hurt anything to use a “Bass Limited” setting; it just means that the Target is meaningless.

As brucek noted, you have that 40 Hz peak in both your mains and sub. It would be best to shift your crossover point upward so it can be equalized as much as possible with the BFD.

Regards,
Wayne


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## rogerv (Nov 8, 2009)

Wayne A. Pflughaupt said:


> Sorry to leave you hanging,Roger – for some reason I didn’t get an e-mail notification after your Dec. 5 post.


Wayne, 

No problem at all. I'm just glad for input whenever it comes. :T btw, I'm hoping to order a Basia cd from Amazon soon. Thanks for the recommendation. 

So here are the sweeps for 80 hz crossovers. I've turned off all smoothing, and removed the house curve from the mains sweeps. I could never find what the Sunfire's slope was, so I used 12, which looks kind of close. 

*Sub only*









*Sub with Filters*









*Left Main*









*Right Main*









*Mains Together*









*Sub, mains and filters*









*Filters*









Regards,

Rog


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

I'd suggest:

1. Shift the Target up to about 86 dB before you start equalizing.
2. Try to track the Target tighter. Right now your post EQ graphs appear flat from 18 to 40 Hz, then slope down too fast above that point.
3. The 97 Hz filter is above the crossover point and as such is unnecessary.

Aside from that, looks like you've got it on the run. :T

Regards,
Wayne


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## rogerv (Nov 8, 2009)

Hi Wayne,

I've taken another stab at this for 80 hz crossover. I wasn't exactly sure what you meant by shifting the target up to 86 db before starting to equalize. Does that go in the target level checkbox ? I tried that but I think I ended up having to apply an awful lot of boost at almost all points to get it up to that target. (All of these equalizing sessions have pretty much blended together, and I'm having a hard time keeping them straight :scratchhead: )

I think I'm tracking the target better, but this stuff is like pushing on a balloon. Push on one area and another area bulges out.

Anyway, here's the sweep with subs and mains together.









Here are the filters:









I see those wiggles from 20 - 40 hz, but I haven't been able to figure out how to flatten all of them out. I tried to make wider filters wherever possible as you suggested in your papers on minimal equalization. The hump at 38 was troublesome as I recall. I had a hard time fixing that one without messing up the rest of the curve. 

I'm still wondering about valleys above the crossover (around 100 and 130). Do I just live with those because they're above the crossover ? After having worked so hard to get the lower part flatter I'd like to try and do something about those areas. I think that would probably bug me knowing that there are some frequencies where I'm missing some of the sound. Can I have some effect on them by increasing the sub's relatively small output at those frequencies to counteract the nulls ? Or do I have to look at room treatments or something else to try and fix this ?:dontknow:

Thanks and Regards,

Rog


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## glaufman (Nov 25, 2007)

rogerv said:


> I've taken another stab at this for 80 hz crossover. I wasn't exactly sure what you meant by shifting the target up to 86 db before starting to equalize. Does that go in the target level checkbox ? I tried that but I think I ended up having to apply an awful lot of boost at almost all points to get it up to that target. (All of these equalizing sessions have pretty much blended together, and I'm having a hard time keeping them straight :scratchhead: )


It would, but I think he was referring to a specific graph you posted where unlike most of your graphs, the curve was already at 86-88dB ...


> I think I'm tracking the target better, but this stuff is like pushing on a balloon. Push on one area and another area bulges out. Anyway, here's the sweep with subs and mains together. I see those wiggles from 20 - 40 hz, but I haven't been able to figure out how to flatten all of them out. I tried to make wider filters wherever possible as you suggested in your papers on minimal equalization. The hump at 38 was troublesome as I recall. I had a hard time fixing that one without messing up the rest of the curve. I'm still wondering about valleys above the crossover (around 100 and 130). Do I just live with those because they're above the crossover ? After having worked so hard to get the lower part flatter I'd like to try and do something about those areas. I think that would probably bug me knowing that there are some frequencies where I'm missing some of the sound. Can I have some effect on them by increasing the sub's relatively small output at those frequencies to counteract the nulls ? Or do I have to look at room treatments or something else to try and fix this ?:dontknow:Rog


I definitely think you'll get more benefit from attacking those tips in the xover region than the ripples in the bass... trouble is, you may need vastly different techniques... be careful to avoid over-filtering to try and eliminate every little ripple... there's a point of diminishing returns, and then a point of loss... at any rate...
To determine what to do about you xover regions, you'll want to run separate scans of the sub alone, and the mains alone, to see where it's coming from...


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## rogerv (Nov 8, 2009)

Hi Greg,



glaufman said:


> I definitely think you'll get more benefit from attacking those tips in the xover region than the ripples in the bass... trouble is, you may need vastly different techniques... be careful to avoid over-filtering to try and eliminate every little ripple... there's a point of diminishing returns, and then a point of loss... at any rate...
> To determine what to do about you xover regions, you'll want to run separate scans of the sub alone, and the mains alone, to see where it's coming from...


I did post the mains scans in message #44459, but I should probably re-run them. I removed the media storage towers from the room and did a bunch of measurements, then moved the media towers back into the room (left and right front corners). I know that the scans showing sweeps with mains / subs and filters had the towers in place, but I just can't remember if the scans that I did in 44459 had them in the corners or not. So, probably best to re-do them to make sure we're working from a known good baseline.

For the sub should I sweep with and without filters, or only with filters ?

What areas around the crossover are of concern ?

Rog


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## glaufman (Nov 25, 2007)

Sorry, I'll go back and look at that post... Generally, I look at anything within 1 octave of the crossover point, so if you're running at 80Hz, any anomaly from 40-160Hz is in what I consider "the crossover region"... so in your case, we're looking at the anomalies from 90Hz on up... certainly by 200Hz your mains should have pretty much taken over, but there's some big swings up there still...


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## rogerv (Nov 8, 2009)

Thanks for the clarification. 

I didn't realize that the crossover point would cover such a large range (I was looking from 70 - 90, and didn't see anything that looked too bad in there 

Rog


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## glaufman (Nov 25, 2007)

OK. I've looked, and indeed your mains alone had some problems up there before, but not the depth the combined scan is showing now... but I'm not sure how much of what we're seeing is from the sub+mains interaction, vs the interaction of the filters your using... if I assume your filters are only on the sub...
The 130Hz suckout is there on all sub scans (with and without filters), but not nearly as bad on the mains scans... I think you want to spend some time figuring that out.


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## rogerv (Nov 8, 2009)

Filters are only on the sub. (BFD sits between receivers subwoofer output and sub's amp).

I don't have a game plan for what to do next, but I can always do some more fiddling.  

Thanks,

Rog


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## rogerv (Nov 8, 2009)

I figured that since the suckout seems to be in the sub range with and without filters that I'd try to equalize it. I understand that big boosts aren't such a good idea, but I thought it would be worth a try. 

I added a +16 db boost at 130.2 hz, and BW / 60 of 8, and set up in the HT. The screen is retractable, and was in the down position when I ran this first sweep. Here's the result from that sweep. it's starting to look better, but still has a sizable dip in it: 









Subjectively, I've always felt that things sounded different when comparing screen up and screen down configurations. So, I retracted the screen and re-ran the sweep. The screen is 106 inch diagonally, and is 1 foot from the front wall when down. Mains are at the corners of the screen. 

Here's the result with the screen up:









Looks better than with the screen up I think.

I don't know what to make of these two pieces of information. It looks like the screen has some effect on the frequency in question, but I don't have the technical chops to figure out how. 

How big of a deal is it to have a 16 db boost under these conditions ? 

At any rate, this is interesting stuff. I think I'll listen to the new settings and see how it sounds. 

Rog


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## glaufman (Nov 25, 2007)

Very interesting indeed... I guess that's not an acoustically-transparent screen?:whistling:
OK. That explains quite a bit, namely: how come that dip suddenly appeared in both the filter and non-filter modes when it wasn't there when you started... now...
With the screen up, let's double check the dip is gone whether filtered or non-filtered...
As for having a 16dB boost, as you know we are wary of such things... best case scenario is you eat up 16 dB of whatever headroom you have there... that might be worse than it sounds...
My guess is that where your screen is relative to your updated sub placement and your LP, the screen is reflecting 130Hz to the LP with a path length difference of 4'4", introducing a cancellation. You might get some benefit from the boost because the screen is probably not an efficient reflector, and by boosting that frequency that high you increase the ratio of direct sound to reflected sound, limiting the cancellation. You currently have the sub further towards the rear of the room rather than the front left corner where it was originally, yes?


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## rogerv (Nov 8, 2009)

Greg,

Yes - the sub is in the back corner now. It's 65 inches from the listening position. 

I'm a bit frustrated right now because I went back to re-measure as you suggested, and I'm getting some different results than before. I thought I was getting a handle on this stuff, but now I can't seem to get the same results from one day to the next. If something produces different results, then something must have changed. I haven't changed anything (users always say that). But, right now I can't figure out what might have changed :dontknow: 

I guess I'll just stop for now and try again later. 

Thanks for your help.

Rog


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## glaufman (Nov 25, 2007)

rogerv said:


> I haven't changed anything (users always say that).


:rofl:

Yeah, intermittent things is why I've lost my hair... even though I tell my wife it's her fault!

I usually find there's no substitute for stepping away from it for a little while, how long, usually depends... 

I'm actually at a loss for how to help you figure out what changed... but don't forget to think about things like the weather (rain/wind noise), other people in the house, HVAC systems, clanging in the kitchen and the like...

What is it that's changing day-day now?


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## glaufman (Nov 25, 2007)

Also don't forget that depending on the frequency, small changes in mic position can make big differences in FR.


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## rogerv (Nov 8, 2009)

glaufman said:


> :
> 
> I usually find there's no substitute for stepping away from it for a little while, how long, usually depends...


I think that's a good idea. I'm going to let things be for a while. :time-out:

I thought I was getting pretty close to locking this thing down and just enjoying the system. I'll get there, but it will just take a little longer than I thought. I will say that in some of the listening sessions with different equalization settings that things are starting to sound better. I never really understood what people meant by "tight" bass. In some of the set ups I've evaluated I think I'm getting a better understanding of what that term mean (particularly on some of the drums). 

Hopefully I'll get everything dialed in before my new CD's come in. I got a nice Amazon gift card for Christmas and ordered the Basia CD that Wayne recommends. I also ordered a CD that was referenced in a recent Sound and Vision: "Circle of Drums". They described it as having lots of interesting low frequency drum stuff. 

I had two significant differences that I noticed between Sat. and Sun. I went through the individual measurements and although the 130 hz dip was corrected as before, now I've got this monster suckout between 138 and 154 hz (centered at 148 hz). It's deep (35 DB) and sharp. Unfortunately, it was still there with everything on (sub / mains and filters). The other thing that seemed weird was that I didn't seem to track the house curve as tightly as on Sat (big sag in the middle.) :dunno:

I saw your other note about small distance changes possibly having an effect. I'll have to control that variable better. Right now, I sit in the right hand chair, and hold the SPL meter where the head from the center seat should be. That's not a real precise way to do it. I'll also go back and re-check everything (lots of moving parts with this test environment, and I've made lots of iterative changes to equalization settings .... always the possibility of not having the right filters loaded .... ). 

Next step will be to try and find out (and re-create) what might be causing these session to session variations

Regards,

Rog


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## rogerv (Nov 8, 2009)

After taking a break, I figured out why I was getting different results from one day to the next. Turns out "someone" :innocent: flipped the phase switch on the sub's amp between Sat. and Sun.

Anyway, Here are some comparisons between responses with the screen up and down with and without filters. Looks like the screen does have some small effect on the responses from 113 - 180 hz, but maybe not as large as in the previous posts. I'm controlling more carefully for meter locations now and wasn't before. So that might be a reason for the difference. I'm not as critical about movie sound as I am about music sound. So, if I can just listen to music with the screen up.

















After re-creating and verifying the previous measurements, I changed the balance between sub's amp and receiver's amp using my Avia DVD. Previous measurements all had the sub's gain quite high relative to the receiver's amp. I moved the dial on the sub's amp about 1/4 turn less than previously set. I don't know how it ended up where it was, but I've noticed that there's a lot less noise coming from the sub at idle with the lower settings. 

I've re-tested with the re-balanced settings and here what I get (subs, mains and filters):

























Here are the waterfalls for the current iterations (subs mains and filters). I gather for these that better response is indicated by the graph dropping down to the floor after some period of time. I've read some on other forums, but I still don't know much about these graphs. What jumps is the continued presence of signal between 15 - 40 hz. I'm guessing that's not too good. (Looks like it goes on forever). Above 40 hz looks better than that I guess. Any comments, of course are appreciated. 

















I used RTA to get a measure of the room's background noise (in case that matters for the waterfalls). I see some peaks at 29 and 60. I thought maybe the 60 hz might be from something plugged into the house current. But the measurement is with everything unplugged from the outlets in the room (including the laptop). :scratchhead:









Regards,

Rog


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## glaufman (Nov 25, 2007)

Congrats on tracking down that phase switch. Knew it had to be something like that. Consistent results can be fixed (within constraints of time/space/budget/WAF/etc). Intermittent things drive me crazy.:dumbcrazy:

As for the waterfalls, you might try running a sweep, but with the soundcard's output disconnected from the amp. Many people use the RTA function instead, but I find it helpful to see the graphs being taken/calculated via the same manner.


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## rogerv (Nov 8, 2009)

glaufman said:


> Congrats on tracking down that phase switch. Knew it had to be something like that. Consistent results can be fixed (within constraints of time/space/budget/WAF/etc). Intermittent things drive me crazy.:dumbcrazy:


Yup. It's just a matter of time / effort and money. I'm just happy that there's order to things again. :bigsmile:



glaufman said:


> As for the waterfalls, you might try running a sweep, but with the soundcard's output disconnected from the amp. Many people use the RTA function instead, but I find it helpful to see the graphs being taken/calculated via the same manner.


So rather than just generating the waterfall from the existing sweep, I should disconnect the sound cards output side and do the waterfall that way ? 

How do I do that ? Do I put the sweep tones on some external media then play it using only the input side for REW ? 

Regards, 

Rog


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## glaufman (Nov 25, 2007)

rogerv said:


> Yup. It's just a matter of time / effort and money. I'm just happy that there's order to things again. :bigsmile:
> 
> 
> 
> ...


Forgive me, I omitted a vital phrase there... "To see the noise floor"...:doh:


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## rogerv (Nov 8, 2009)

Greg,

Thanks for the clarification. That makes a lot more sense. With as many posts as you moderators have to make it's easy to see how a slip of the fingers can happen.:T

Anyway, here's the waterfall with the output side disconnected. Nothing much there except that room mode that shows up in everything that I do. :sad:









In my previous waterfalls I saw a lot of recurring signal from 15 - 40 hz. Aside from the apparent room noise from 30 - 40 (based on the above) I'm assuming that the rest must be "ringing" , and that there's not much that can be done about this given how low it is (rules out room treatments) ? 

Rog


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## glaufman (Nov 25, 2007)

rogerv said:


> Thanks for the clarification. That makes a lot more sense. With as many posts as you moderators have to make it's easy to see how a slip of the fingers can happen.:T


I'm amazed at how often I have to re-read an entire thread before I can respond to the lastest post


> Anyway, here's the waterfall with the output side disconnected. Nothing much there except that room mode that shows up in everything that I do. :sad:


Technically, that's not a mode (at least, I wouldn't think it was), but it might be interesting to track it down... not the primary concern though. You can take that graph and scroll the vertical axis until the noise floor begins to show up (just so you/we know where it is).


> In my previous waterfalls I saw a lot of recurring signal from 15 - 40 hz. Aside from the apparent room noise from 30 - 40 (based on the above) I'm assuming that the rest must be "ringing" , and that there's not much that can be done about this given how low it is (rules out room treatments) ?


Treatments that low not being practical is usually the conventional wisdom here, but you might go over to Acoustics and see what Bryan and the guys say. There are tuned absorbers that might make better use of space than a trap... I'm going to have to send this and then go back and re-read some old posts to see exactly where you are...:hissyfit:


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## glaufman (Nov 25, 2007)

So, no that I've reviewed the history, are you saying that with everything connected but nothing playing, the sub's making a bunch of noise, but with the cable disconnected, there's much less? And even with things connected, there's less than before you reduced the sub's level control in favor of raising the level conrol in the avr?


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## rogerv (Nov 8, 2009)

glaufman said:


> So, no that I've reviewed the history, are you saying that with everything connected but nothing playing, the sub's making a bunch of noise, but with the cable disconnected, there's much less? And even with things connected, there's less than before you reduced the sub's level control in favor of raising the level conrol in the avr?


Sorry. I've been inundating this thread with so many posts it's no wonder that it's not clear. 

When I had the sub amp turned up I could hear some noise coming from the sub when the system was on but idle. I wouldn't call it excessive, just noticeable (barely above the persistent ringing in my ears :bigsmile. Now that the sub's amp is turned down I don't hear much coming from the sub at idle at all.

Right now I'm mainly trying to understand the waterfalls and find out if they're horrible or not. I saw the long duration signals below 40 hz. and I thought that it it didn't look too good, and maybe it was the result of noise from the room or something. So that was why I I've been chasing the noise measurements using RTA and now the scan with the output disconnected. I probably should have just asked the simple question: "How do these waterfalls look ?"

Hope that helps.

Rog


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## glaufman (Nov 25, 2007)

Well, the truth is, I'm not sure. Obviously, killing that long duration low end stuff would make them better. What I'm not sure of is what that stuff is, and therefore how to kill it. This is where I might not have enough experience reading the waterfalls... if it were modal, I would expect to see higher peaks in the FR. But if it was background noise, we should've seen it even when disconnected. I suppose it's possible that modal influences are being excited by other frequencies around them, but I don't know if that's reality or fantasy. I'm going to take a look for your room dimensions and see if they calculate to modes at these frequencies.

Maybe you could try turning the sub level down again on the sub and up again on the AVR to see if it diminishes further.


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## glaufman (Nov 25, 2007)

Maybe run an IR plot.


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## glaufman (Nov 25, 2007)

I've got to learn to start reading and thinking before posting.
OK, so you "rebalanced" the level controls between your sub and AVR, but we don't have an FR plot without your EQ filters for this new configuration yet. So I suppose it's possible that you've killed the peaks and dips that would show in that FR, and perhaps some of the ringing in the waterfall as well, but we just don't quite know.
If your filters haven't changed much, you've got a high boost just under 30 Hz. Not sure what effect that may be having on the waterfall.


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## rogerv (Nov 8, 2009)

Greg,

:thankyou: to you and everyone else (Wayne, BruceK and Bill come to mind) who helped with this seemingly endless thread. It's not really about level questions any more. 

I think I'm going to spend some time just listening to the system and see how it sounds with the current settings. At least I've got the overall system response better than when I started. It may not be perfect, but hopefully it's better than it was. 

I'll continue monitoring various forums to continue learning. There's lots of interesting and fun stuff here. I suspect that I'll show up in acoustics when I'm ready to consider room treatments, and the music area because I like music.

Regards,

Rog


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