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Discussion Starter #1
I have had to replace four amplifiers in my subwoofer because of audible distortion at the area around speech. Changing the crossover would make the distortion from the subwoofers change slightly but I never measured or got an idea what that did. Since changing out the amps the audible distortion did not sound like a digital mess any longer, and I have been able to enjoy movies most of the time. The problem I seem to be having comes and goes, and I am having a difficult time finding if it is related to my room, maybe a subwoofer box that needs damping, distortion, setup, or even the movie I'm watching. It is a very directional sound from the left side of my room. In my waterfall plots, the decay in the left seat does not show any ringing that would lead me to think it is related to the subwoofer being near the corner. When I stand over the subwoofer in my left corner however I can hear that the subwoofer is making noise that is sounding similar to the problem I hear, and I am unable to hear it standing over the other three subwoofers that are near my front wall. One of my subwoofers has carpet in it in place of the damping material because I used this to cover other to cover areas in subwoofer boxes that had slight gaps. If this is the subwoofer that has some carpet in it I am unsure, but the sound problem seems around the area of the ports. To make things more confussing, this is also an area in my room with bass build up, but I was not aware this might cause sound directly next to a subwoofer to sound boomy. Would that be a possibilty? Then there is the only other thing that I could think that might cause it which is distortion. There seems to be some higher levels of distortion around my crossover area when I measure sine waves on a CD I made. Do these graphs bellow look like it might be something loud enough that is audible? When I measured them my meter began to clip at 80Hz until around 84Hz, and measured as high as 89dB in REW, but I did not have the meter calibrated. I had taken sweeps that were at -1dB FS and reduced the level by around -20 or -33 in Audacity. Sorry that I forget which one but I think it was -33. I measured with my subwoofers and the right speaker.

The problem I hear while watching movies is really strange. For example in the begining of Saving Private Ryan it sounds fine for the first few moments, then when they get closer to explosions, the sounds of them sound very localizable on the left side of the room when they are very long sounding. Then the problem seemingly is gone when they are off the beach throwing granades etc. After the get orders and are off on the mission there is then some more localizable bass there in the scene that is also like the menu of the DVD where they walk against the background of explosions. After that it seems like there are not much more problems there. I was watching a different movie last night and something similar happened. There was a moment when there was very strong localized bass from the left corner that was a very long amount of time. It almost seemed to come from the front wall also. Then later there was the same sounding frequency that was much louder and it was not localizable at all and sounded very undistorted. That sound seemed to be almost as long sounding so I can't tell if it's bass build up. :gah: Could it be that very subtile difference that I hear when I improve the sound of the subwoofers by adding more power? If that were true than why would I hear it only in the corner? I'm not sure how else to address the issue and it does not seem related to other side of the wall. The problem corner is at the left front corner next to my partition wall, and the other walls (including ceiling which also has steel) all have the concrete foundation. There is a good amount of room treatments in the room. If you have questions about the treatments or equipment let me know. I will try experementing with the room treatments around this area and see what difference I can make, but I would like to know if this might be something to do with the crossover again. I do not hear this problem with music. If this is a crossover issue I'm not sure how to deal with it. Sorry for the long post. :sad2::unbelievable::bigsmile::scratch::help:





 

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Discussion Starter #2
I found that with closer examination, this time not using my adapter for my laptop but instead the battery, that there was in fact some distortion around the 79Hz - 81Hz area. I also checked using the output of my player directly into my soundcard. While doing this I decided to run my XA2 DVD player on it's own surge protector. I then moved my left and right subwoofers out of the corners which were causing a 90Hz peak and placed them next to the other subwoofers, which had a 90Hz dip. I then measured each checking they were all similar. I went ahead and then proceeded to measure all the subwoofers.

This is when things got really strange. :thud:

First off, I had to turn up my soundcard to 100 for REW to get the input and output to match. I checked my meter in the HT and it said 83dB, and I checked REW and it said 73dB. I calibrated the mic and told REW it was a 75dB signal. So my settings are 100, -18dB FS sweep, and -1 setting bellow full input for the mic which was .983 or something close. Then I measured and did the check levels and got a 78dB target, and REW suggested one filter, which I added. Then I put my THX optimizer disc in and measured levels. The settings are -11 all channels except the subwoofer at -1. They all measured at 85dB. :unbelievable: That is so strange because it usually measures 75dB. A few other strange things have happened recent such as.. While I was showing some guest my THX Demo the disc kept playing these same two THX intros between every demo scene. Then there was the day before that when my copy of DVE was telling me my channels measured 64dB, and the subwoofer +10dB higher. Is this my player telling me it is time to update the firmware? I am using 2.7. What is going on with REW? This is :coocoo: and I could use some help.

Here is after moving the subwoofers.



This is white noise from my XA2 with and without 1/6 smoothing. This time there is the crossover and the mains added. My right channel was not positioned yet and was kind of pointing off to the right.



 

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Discussion Starter #3 (Edited)
The problems that I were describing are gone. There is now bass that I feel in the center of the room, left of the room, and now the right also. :bigsmile: Those were actually 96dB sine waves btw.
 

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Discussion Starter #6 (Edited)
How did you determine that was the problem? Did you swap out the signal source to verify it?
I also tried a Malata n996 which also has 5.1 analog connections. The signal played much louder +10dB more for the subwoofer output, and the digital type distortion around the level of speech was still present. That was not however the recent problem. I will post a better example of what I think was the issue.
 

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Elite Shackster
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What does this distortion sound like? Does it only happen at loud levels? What are you settings on your receiver?

To me this sounds like one of three problems.
1 - Improper crossover settings in the receiver or subwoofer
2 - Overdriving the sub resulting in distortion signals outside of it's normal passband (leading to the localization)
3 - Room related response bump.

Are you using eq in the system?
 

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Discussion Starter #8
What I think might have happened is that having two of the subwoofers in the corners which caused the peak at around 90Hz, made my left subwoofer very boomy there, as a result to the crossover since I use 80Hz. It was not down -6dB at the crossover point. In my past trials, changing the crossover does nothing to change the response.

Before moving subwoofers out of the corner.



After moving subwoofers out of the corner.



My subwoofer response now does not look flat after the crossover, but at least the left corner is not really loud sometimes. If there are better suggestions to dealing with it I'm still open to ideas.
 

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Discussion Starter #9
What does this distortion sound like? Does it only happen at loud levels? What are you settings on your receiver?

To me this sounds like one of three problems.
1 - Improper crossover settings in the receiver or subwoofer
2 - Overdriving the sub resulting in distortion signals outside of it's normal passband (leading to the localization)
3 - Room related response bump.

Are you using eq in the system?
Sorry I should have been more specific. I don't have a receiver, and my amplifiers do not have gain or trim controls. All my amplifiers are MA-500 mono amps except for surrounds powered by a POA-5200. The settings I am able to control are on the XA2 which are... distance, small/large, gain, crossover 80Hz - 120Hz. There is no crossover on the subwoofer amps therefore. The previous amps had a THX switch, in or out of phase switch, and a gain control, but I'm not using that now. The settings on my XA2 are -11 for all channels but the subwoofer which is -1. There is distance settings and the 80Hz crossover. I have one filter on my BFD that is 7dB at near 50Hz. I redid that filter after the above test, but for the single one above that.
 

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Elite Shackster
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Looking at your plots I think that 90hz bump is your culprit.

A couple of things...
The crossovers in your dvd player aren't necessarily passing along information to the sub that is filtered out of the main channels. Some players do this, some do not. You may be losing a substantial amount of information by not using a receiver. How do you control volume?

The LFE channel of movie sountracks is not bound by any of the crossover settings in your player. If the director decides to put a powerfull 100hz tone in that track, it will be played at the level they recorded it. In your examples above I would not doubt this possibility.

Why are your sub levels 10db higher then everything else?
 

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Discussion Starter #11
I don't really mess with the volume anymore although I used to. -11 is pretty low on my XA2 for the other speakers. It goes from -12 to 0. There are no headroom issues. One problem that I do have with this is that music on a CD, which is recorded more around -20dB FS is always very loud. I try to limit myself to at most 30 minutes of music since this averages 105dB or more. I have also tried making my own CDs and reducing the level in Audacity which works well, but I still need to perfect the settings.

I have been thinking about getting a Blu-Ray player and Receiver around christmas time. I understand it is not normal to play a test noise from the subwoofers and change the crossover and see no change which bothers me. One other option might to be get an external crossover and a dedicated LFE subwoofer. Just an a thought that I have not considered much.

My subwoofers each are at what is shown in the graphs around 65dB each. They equal 75dB. I'm not sure why I have to turn up the level on the XA2 so high there. When I had a receiver the THX setting on one subwoofer (when I used the older amps) would equal near 73dB, then I could turn it up without the switch to 85dB. I recently used REW and a different plate amp in my bedroom and it went to 85dB again with the same settings I use for the other amps and my four subwoofers from around 5 feet away. The dial was around 4 oclock however. I had some strange results with that amp before where my subs were flat to 15Hz. It has it's own phase and crossover on it. Then I also compared the difference of my Malata n996 and the XA2 with my plate amps that came with the subwoofers. I tested one subwoofer and the THX setting was 75dB, where as in the XA2 this was around 63dB. All I know is I have to leave it at the level and I am not running my subwoofers hot. :huh: I asked bruce about getting an external line level control for my amps so that I might turn down the level in the XA2 but he said the level from the XA2 was correct according to specs.

You think my next purchase should be a receiver?
 

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Discussion Starter #12
One thing I could also do is place the left and right center subs in the corners now. Then I would have a 90Hz peak to equalize without causing a dip in them to get worse. I think that might more accuratly address the peak, and might get rid of the boom sound from the left corner to go away. :scratch:
 

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Elite Shackster
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Corner placement may be worth a shot. Should net you a gain in headroom as well.

Should your next purchase be a receiver? That's up to you, but I cannot imagine how you get along without one. Crossover setting, level trimming and volume adjustmet are all going to be much much easier and more accurate. You can always look into a use processor as you already have some nice amps.
 

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Discussion Starter #14
I will try the corner placement. This would give me more an option to treat my front wall also if it works. One thing about these corners that important to mention is that the have been very difficult to treat. I have extra insulation and treatment in the left corner and it is about as treated as I can get it. The right corner however has been near impossible to get good results from treatments since this area is concrete floor, two walls, and a concrete/steel ceiling. I have pretty much given up trying to treat that corner, and there is nothing much up there except the layer of ceiling tile with insulation, then Quiet Batt and insulation in the corners. The other ceiling corner has insulation above the Quiet Batt also which improves the 60Hz null. I could never get as good results in the right corner as that one. I might be able to sit a GIK Pillar trap on the sub in the right corner and see if that helps later on. So the corners are not treated the same right now and thought I should mention that also since you point out that info of the LFE is being sent to the subwoofers. The problem does seem to be with LFE track which does seem to be in line with my description of the problem being with the really loud and long sounding explosions. It is the sound when they get more quiet after being loud that is the problem.

Edit: Might try and cut off some extra Quiet Batt that extends over the length of the front of my room, then stick it in the right corner.
 

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Discussion Starter #15
I ran log sweeps at -12dB FS and could not find the problem, but with the subs in the corners I still hear it over on the left side of the room. Midbass has improved now after moving the subwoofers out of the 90Hz nulls somewhat but it is difficult to tell with the scene I keep watching in Saving Private Ryan. The midbass seems less directional, but the lower sounds still seem to last longer in the left corner. I checked with my RS Meter and the explosions are around 97dB - 99dB loud. It very well could have been something lower in frequency so I checked by moving my mic around the room and also checking by holding Quiet Batt over the mic in different directions. There was some significant changes in the level of higher frequency sounds and also the lower ones. I found it more easy to observe by simply placing the mic on my left speaker or right speaker shown bellow.

This is the right corner. You can see the 60Hz area that is not treated, and other midbass is not very uniform in decay.




This is the left corner that I am having trouble with. Notice that the 35Hz - 40Hz area is higher, but the midbass is less a problem. I think that the problem I am hearing is that there is very low 40Hz range punch, but good sounding midbass in the left, and the right has good sounding very low bass, and poor midbass. That is enough to get kind of confussing, espicially if your subwoofers do not match in the midbass from the center of your room, to the corners. :yes:



I will try adding the Quiet Batt to the upper right corner and smooth out the midbass, then stick a GIK Pillar trap on my left corner subwoofer later on and see if things improve. I really did think this was something only crossover related, and had no idea there was a problem with the 40Hz area in the left corner. I noticed some change to when adding absorption to the left portion of the stage, but thought nothing of it.
 

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Discussion Starter #16
Well I watched the same scene on my computer with my headphones and I hear the same thing. Lots of explosions from the left that are long and sound boomy, and not very many from the right. :blink:
 

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I've read everything in your posts and am still struggling to figure out what your complaint is. All the experimental adjustments you've been making would make logical sense in helping to cure some frequency response null and peak in-room response problems . . . . but you say they don't. And now you say you hear the same problem through head phones when playing the same movie through your computer.
Are you SURE what you thought you heard in your HT system is real? Those last waterfall plots don't show a problem similar to what you've described. I'm completely confused.
Could it be that what you thought you were hearing is actually a part of the sound track of "Saving Private Ryan" ?
 

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Discussion Starter #18
I've read everything in your posts and am still struggling to figure out what your complaint is. All the experimental adjustments you've been making would make logical sense in helping to cure some frequency response null and peak in-room response problems . . . . but you say they don't. And now you say you hear the same problem through head phones when playing the same movie through your computer.
Are you SURE what you thought you heard in your HT system is real? Those last waterfall plots don't show a problem similar to what you've described. I'm completely confused.
Could it be that what you thought you were hearing is actually a part of the sound track of "Saving Private Ryan" ?
Yes that was the problem. I can clearly hear it on my headphones, and they are cheap headphones. I can also feel the left side of my headphones moving when I watched it. It was much more easy to understand what they were saying with the headphones, but very strange they were all yelling. I will check what frequency that is but the headphones sounded much worse, and there was some faint crackle noises like my headphones were bottoming out. This is the DD version on DVD and does not have DTS on it. I think the quality may also be playing a small factor but not sure as I don't have another copy to compare. I thought louder tracks usually were a pretty good indication of something wrong in the room which is why I thought something was wrong.
 

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Discussion Starter #19
I need to check other listening spots in the room. That might have improved things with getting a similar response from all the subwoofers, and that should have cleaned up the crossover area some. The 90Hz area might be more uniform across the front row now. It isn't going to show on that particular listening test, and wasn't the actual problem that I heard however. I'm not sure I will hear any difference.
 
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