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post #91 of 146 Old 04-29-2012, 08:21 PM - Thread Starter
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Here are a couple graphs I took tonight, the only change was the mic position from front center seat to rear center seat, what a difference!! What do you guys do when you are trying to EQ for multiple rows? Since I'm sure that EQ can't make my response flatter for both rows, what are my next options, some other form of bass trapping?

Front Center Seat



Rear Center Seat



Overlayed

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post #92 of 146 Old 04-30-2012, 06:20 AM
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Quote:
Originally Posted by Digital_Chris View Post

Here are a couple graphs I took tonight, the only change was the mic position from front center seat to rear center seat, what a difference!! What do you guys do when you are trying to EQ for multiple rows?

Now you know why people look at their situation carefully and don't put all of their eggs in one basket. Room eq is one basket and room acoustics is another. In general the eq basket is cheapest and fastest, but it has strong limitations and you just found one of them.

When a room has large variations among nearby seating positions in the bass range, the usual cause is some kind of standing wave. It might be possible to do something with multiple subwoofers, but the far more straightforward approach is bass-oriented room treatments.

I had a room where the standing waves were so pronounced that if I played a 100 Hz tone, I could walk from seat to seat and hear it almost totally disappear, and then if I moved a few fee it would reappear. Classic standing waves! Treating the back wall of the room with large custom made sound absorbing panels that were composed of 2" thick 705 spaced about 4 inches from the wall pretty well erased them.

Most people who enter the room and sit there for hours never notice the panels visually. Big sonic difference - the overall sound is significantly more pleasant. There was a big audible slap echo off the back wall that also disappeared, no surprise.
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post #93 of 146 Old 04-30-2012, 06:55 AM
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Originally Posted by arnyk View Post

Just a humble little link that provides tools for designing porous absorbers with perforated fronts via a cookbook technique that many forum participants, perhaps even you, could benefit from:

http://www.iperf.org/pdfdownloads.html

more specifically: http://www.iperf.org/IPRF_DES.pdf

im not sure what your links have to do with the respect to the discussion that flow-resistivity is the key value of porous insulation, not density as apparently is still attempted to be propagated...

and AFMG SoundFlow is more than sufficient for perforated panel design and modeling.

and if the goal is a tuned, resonate (pressure-based) absorber - then chapter 6 of AA&D by Cox/D'Antonio is a good place to start - http://www.amazon.com/Acoustic-Absor.../dp/B001Y35IHW
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post #94 of 146 Old 04-30-2012, 08:18 AM
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Originally Posted by Digital_Chris View Post

Thanks for the link to your graphs. I haven't played around with the BFD yet, I'm going to get myself down there to run a few more graphs for both rows and see how much of a difference there is between the two. I'm afraid that if I EQ for one row, the other row will sound even worse and there will be no compromise

Do you have 1 or 2 rows of seating if your space?

EDIT: Just saw your construction pics, nice color :P Mine is just about the same. How did the wagner sprayer work out? Any streaks? How about overspray, did it cloud up the room while you were painting? I need to re-do my ceiling and was curious is the gun was the way to go

Eqing for the main position is obviously more important. arny has a good point that this is a multi-basket deal. Room modes are dominant and your graph is showing that. I tpyically like to eq to the main position as close as I can get, then go back and see what it does to the other seating areas. The way my friends see it, my room sounds better than any commercial theater, and definitely better than any of theirs systems, even when the response looks like mt everest... they dont care, and moreover, cant notice.

Now before you read into that too far, I still would prefer to have a flat response across all seats, but for me, in my odd shaped room, I havent found that to be quite possible. ive gotten close, but not exact. That leaves me with having to make small sacrifices, therefore I tend to eq to the MLP and then tweak to make the rest of the room sound as good as it can.

This was one reason I shied away from a IB type setup as I was quite nervous about doing all that and then the position I chose not being optimal for the room :/

In regards to the wagner sprayer, it was awesome!! It definitely clouds the room up, and youll want to cover all doors, windows, vents, floor with plastic. The overspray wipes off pretty easily after dry, but it was funny, the dust cloud would still work its way into wherever the air was escaping and I had to scrub off the inside of some door panels in spots. all in all, for a bigger space it is totally worth it. and it is super efficient. I only used 2 gallons of paint for my whole room!!

I actually have 3 rows of seating, but I need to update my gallery something aweful, most of what is in that album is not even there anymore!!! stereo rack has moved, new bigger a-t screen, new subs, new speakers, new surrounds, new AVR, (with another on the way), yea I need to update!!!

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post #95 of 146 Old 04-30-2012, 10:20 AM
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Originally Posted by arnyk View Post

Now you know why people look at their situation carefully and don't put all of their eggs in one basket. Room eq is one basket and room acoustics is another. In general the eq basket is cheapest and fastest, but it has strong limitations and you just found one of them.

Well, acoustic treatment has strong limitations too. Please see below.

Quote:


When a room has large variations among nearby seating positions in the bass range, the usual cause is some kind of standing wave. It might be possible to do something with multiple subwoofers, but the far more straightforward approach is bass-oriented room treatments.

It is not just "might be possible" with multiple subs. It absolutely is possible and the most powerful tool we have to cancel/attentuate out some of the modes. From my article on low frequency room optimization:, here is a single sub response across multiple seating positions:



Now this is what happens when you use four subs:



We have almost completely done away with seat to seat variations. The article then goes on and talks about how electronic correction (and not just EQ) flattens the curve for all the seating positions and the overall response. Nothing is as easy to understand and apply than those techniques.

OP does have four subs but unfortunately they are all on the front wall. If they were put in opposing sides and seats places away from the remaining room modes, then he would be most of the way there.

Quote:


I had a room where the standing waves were so pronounced that if I played a 100 Hz tone, I could walk from seat to seat and hear it almost totally disappear, and then if I moved a few fee it would reappear. Classic standing waves! Treating the back wall of the room with large custom made sound absorbing panels that were composed of 2" thick 705 spaced about 4 inches from the wall pretty well erased them.

100 Hz tone? His problems as typically exists, is below that frequency. In his example, it is down to 30 and 50-60 Hz. Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:


We see that at 100 Hz and below, it has no absorption ability to speak of. So it will do nothing for those resonances. Acoustic products can be helpful in low frequencies but they are challenging to design and use, and can take considerable amount of space. If OP bought just one other sub and put it in the middle of the opposing wall, he would sharply reduce two of the modes length-wise.

Quote:


Most people who enter the room and sit there for hours never notice the panels visually. Big sonic difference - the overall sound is significantly more pleasant. There was a big audible slap echo off the back wall that also disappeared, no surprise.

What you describe is what it does. Reduce room issues at transition frequency and above. Let's take disagreements to this thread: http://www.avsforum.com/avs-vb/showthread.php?t=1407637

My advice to OP is as was given by beastaudio. Go ahead and take out the peak at the main seating position. You are likely more sensitive to it than others sitting in the room. If you can borrow another sub and experiment with, try what I explained above.

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post #96 of 146 Old 04-30-2012, 10:23 AM
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Originally Posted by localhost127 View Post

im not sure what your links have to do with the respect to the discussion that flow-resistivity is the key value of porous insulation, not density as apparently is still attempted to be propagated...

and AFMG SoundFlow is more than sufficient for perforated panel design and modeling.

and if the goal is a tuned, resonate (pressure-based) absorber - then chapter 6 of AA&D by Cox/D'Antonio is a good place to start - http://www.amazon.com/Acoustic-Absor.../dp/B001Y35IHW

You are both right in a way . As Mike and OP have asked to not side-track on topics from what OP has asked about, I created a thread and put the response there: http://www.avsforum.com/avs-vb/showthread.php?t=1407637. Let's take disagreements there.

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post #97 of 146 Old 04-30-2012, 10:50 AM
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holy crap - all of my parroting and i finally got another user to actually USE SoundFlow!
and to think it was only a week or so ago that some were debating that validity of the modeling inherent in such software!


and why do you guys apply smoothing to your modal region frequency responses?
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post #98 of 146 Old 04-30-2012, 11:11 AM
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Originally Posted by localhost127 View Post

holy crap - all of my parroting and i finally got another user to actually USE SoundFlow!

No, I am not a user. If I had the data for real panels in that configuration handy, I would post that. I happen to have found the SoundFlow simulations posted elsewhere and thought that in a discussion with you, you would accept them better since you cut and past them the same way. Again, let's take debates to the other thread.

Quote:


and why do you guys apply smoothing to your modal region frequency responses?

The problems he has at 1/6th will be there unfiltered. So while you don't want to apply that much smoothing in general (e.g. if you want to know the specific frequency to filter), for the purposes of the discussion, it is still fine.

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post #99 of 146 Old 04-30-2012, 11:39 AM
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Originally Posted by amirm View Post

No, I am not a user. If I had the data for real panels in that configuration handy, I would post that. I happen to have found the SoundFlow simulations posted elsewhere and thought that in a discussion with you, you would accept them better since you cut and past them the same way. Again, let's take debates to the other thread.

oh,
so then your above modeling isn't accurate representation as arnyk was using OC705 and you are at the mercy of whatever the user used that you "borrowed" the photos from. heh. you said: "Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:" clearly you did not present simulation based on modeling of OC705...

SoundFlow is free for 30-day trial. why don't you model arnyk's proposed solution instead of arguing against it based on data for a different material?



Quote:
Originally Posted by amirm View Post

The problems he has at 1/6th will be there unfiltered. So while you don't want to apply that much smoothing in general (e.g. if you want to know the specific frequency to filter), for the purposes of the discussion, it is still fine.

only apply smoothing in the modal region if you're attempting to hide something.
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post #100 of 146 Old 04-30-2012, 01:24 PM
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Originally Posted by amirm View Post


In his example, it is down to 30 and 50-60 Hz. Your proposed solution doesn't work there, nor does it even work at 100 Hz. Here are the simulated results for the panel you are proposing:

Amir, you appear to be off in fantasy land, again. I made no specific recommendation. I only provided an anecdote about some work I did involving a 100 Hz standing wave.

Your modeling program or your interpretation of its report seems broken because the audible effect of the absorber I mentioned @ 100 Hz was nothing short of dramatic.

Edit: I can't make out your parameters well, but the material and density may be incorrect. I ran my own choice of models with density of about 25% of what 705 actually is, and obtained results very much like yours.

However, the effect of the anecdote's absorbers at 50 Hz and below leaves a lot to be desired.

Edit: With the proper material and density, my model predicts poor performance below 50 Hz as well.
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post #101 of 146 Old 04-30-2012, 02:29 PM
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Originally Posted by localhost127 View Post

SoundFlow is free for 30-day trial. why don't you model arnyk's proposed solution instead of arguing against it based on data for a different material?

I suspect that Amir tried to model my absorber, but he may have screwed up the data entry.

That might be an err unnh.. Rookie Mistake. ;-)

Careful workers run their models with test cases for which solutions are published and see how they agree.

I found a modeling program that doesn't have a time limit on it and ran my absorber. Its results agree with my real world observations. Also agrees with published specs for common materials.

I ran it with sound absorbing material that has about 25% the absorbency of 705 and got something very similar to what Amir posted.
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post #102 of 146 Old 04-30-2012, 02:54 PM
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Originally Posted by arnyk View Post

I found a modeling program that doesn't have a time limit on it and ran my absorber.

PAC (http://www.whealy.com/acoustics/Porous.html) is available as well - regardless, flow-resistivity NOT density is the key value for porous materials in this context.

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Its results agree with my real world observations. Also agrees with published specs for common materials.

regardless, porous insulation is a velocity-based absorber and needs to be placed into areas of high particle velocity in order to be most effective. for the modal region, the wavelengths get very long and as such the absorber needs to be physically large with respect to wavelength (to be 'seen') as well as sufficiently thick and/or spaced away from rigid boundary into areas of high particle velocity. as the LF absorber becomes thicker and thicker, porous materials with lower flow-resistivity (lighter fibre) are more effective.

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I ran it with sound absorbing material that has about 25% the absorbency of 705 and got something very similar to what Amir posted.

what does "25% the absorbency" mean?
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post #103 of 146 Old 04-30-2012, 04:18 PM
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Originally Posted by localhost127 View Post

PAC (http://www.whealy.com/acoustics/Porous.html) is available as well -

I guess I was able to trick you into admitting that there are other sources of reasonable information than your holy grail with a 30 day expiration.

LOL!

Quote:


flow-resistivity NOT density is the key value for porous materials in this context.

Since it is obviously your false belief that there is no substance known to man in which flow-resisitity has any relationship at all to density, there is simply no discussing anything acoustical with you.
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post #104 of 146 Old 04-30-2012, 05:04 PM
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Originally Posted by arnyk View Post

I guess I was able to trick you into admitting that there are other sources of reasonable information than your holy grail with a 30 day expiration.

LOL!

yep - and the conclusions do not change. thicker porous absorbers become more effective with porous materials of low flow-resistivity than those of higher wrt: LF absorption.

oh, and did you happen to notice this little comment on the PAC webpage?

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Originally Posted by PAC View Post

The transfer matrix calculations in this spreadsheet are reimplementations of the MATLAB scripts printed in Appendix B of the first edition of Trevor Cox and Peter D'Antonio's book Acoustic Absorbers and Diffusors. Theory, Design and Application .





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Since it is obviously your false belief that there is no substance known to man in which flow-resisitity has any relationship at all to density, there is simply no discussing anything acoustical with you.

im starting to question your understanding of just what the term density means vs that of flow-resistivity, porosity, etc.

and you forgot to explain what you meant when you said, "25% the absorbency". how do you define that?
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post #105 of 146 Old 04-30-2012, 06:47 PM
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Originally Posted by localhost127 View Post

regardless, porous insulation is a velocity-based absorber and needs to be placed into areas of high particle velocity in order to be most effective. for the modal region, the wavelengths get very long and as such the absorber needs to be physically large with respect to wavelength (to be 'seen') as well as sufficiently thick and/or spaced away from rigid boundary into areas of high particle velocity. as the LF absorber becomes thicker and thicker, porous materials with lower flow-resistivity (lighter fibre) are more effective.

All very true. The tricky part is at what point does thick lower flow-resistivity overcome thinner high resistivity absorbers? I imagine it depends on specifics of depth and resistivity and frequency. Since you have the software, and experience, I'd like to see you comment in arim's disagreement thread. We'd all love to have 10' thick absorbers in all walls/ceilings. But for most that is not going to happen. Perhaps you can generate a plot that shows maximum efficiency as a function of porosity, depth, target frequency? Perhaps you can also provide porosity for various commonly available materials.

To the OP - more big "bass" absorbers - or more big subs - is the only real solution. When I have guests I give them the best seat.

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #106 of 146 Old 04-30-2012, 07:10 PM
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Originally Posted by dknightd View Post

All very true. The tricky part is at what point does thick lower flow-resistivity overcome thinner high resistivity absorbers? I imagine it depends on specifics of depth and resistivity and frequency. Since you have the software, and experience, I'd like to see you comment in arim's disagreement thread. We'd all love to have 10' thick absorbers in all walls/ceilings. But for most that is not going to happen. Perhaps you can generate a plot that shows maximum efficiency as a function of porosity, depth, target frequency? Perhaps you can also provide porosity for various commonly available materials.

http://www.afmg-support.eu/AFMGRegTr...SoundFlow.aspx
http://www.whealy.com/acoustics/Porous.html
http://www.stanleyhallstudios.co.uk/pacalc/
http://www.rockwool.it/download/software
http://www.gearslutz.com/board/bass-...roperties.html
http://www.gearslutz.com/board/bass-...er-sweden.html
http://www.gearslutz.com/board/bass-...s-germany.html
http://www.gearslutz.com/board/6328646-post88.html
http://www.gearslutz.com/board/6863157-post6.html
http://www.gearslutz.com/board/bass-...sistivity.html
http://www.gearslutz.com/board/studi...y-numbers.html


why not dive in and explore for yourself -
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post #107 of 146 Old 04-30-2012, 07:32 PM
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post #108 of 146 Old 04-30-2012, 07:39 PM
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Originally Posted by dknightd View Post

I was hoping you could summarize for us.

you mean you lack the drive or motivation for the opening of a simple excel spreadsheet and the entering of a few values ??

summary: 34" faced or larger corner chunks, go with the low flow-resistivity (~5000rayls/m) light fibre (loosely filled; uncompressed) w/ horizontal supports every few ft such that the upper layers do not compress the lower layers.
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post #109 of 146 Old 04-30-2012, 08:09 PM
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Originally Posted by localhost127 View Post

you mean you lack the drive or motivation for the opening of a simple excel spreadsheet and the entering of a few values ??

summary: 34" faced or larger corner chunks, go with the low flow-resistivity (~5000rayls/m) light fibre (loosely filled; uncompressed) w/ horizontal supports every few ft such that the upper layers do not compress the lower layers.

I gave my due diligence a few years ago. But I have more to learn, and further to go. I like to visit these sites to see what new might have come along.

You recommend ~5000rayls/m. I don't think I've ever seen a product advertised that way. Do you have a product in mind that meets this spec?
I have to ask, are you a pro, or an interested amateur? Have you treated your room - or are you just crunching numbers?

I've tried "loose" fiberglass. My experience was "compressed" fiberglass worked better. At least up to depths of about 24". A "703" like product seemed to work better than a "705" product. No doubt in my mind we could do better.

Everything I say here is my opinion. It is not my employers opinion, it is not my wife's opinion, it is not my neighbors opinion, it is My Opinion.
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post #110 of 146 Old 05-01-2012, 06:30 AM
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Originally Posted by dknightd View Post

I gave my due diligence a few years ago. But I have more to learn, and further to go. I like to visit these sites to see what new might have come along.

Some people post here to shed light. Some behave like they want to impress by turning what they know (or maybe don't know) into mysteries.

It would appear that Whely's Excel spread sheet is an acceptable tool for what it does. You can download it from http://www.whealy.com/acoustics/Porous.html . I made it work in Excel 2003 by changing tools, macro, security to medium and allowing the macro to run when prompted. I also turned on all of the available add-ins (tools, addins). I haven't gone back to see which ones I can turn off.

Quote:


You recommend ~5000rayls/m. I don't think I've ever seen a product advertised that way. Do you have a product in mind that meets this spec?
I have to ask, are you a pro, or an interested amateur? Have you treated your room - or are you just crunching numbers?

I spent some time searching for values for absorber flow resistivity, and found no consolidated listing with any breadth at all.

I further found inconsistent results for the the few that I found. One of the best guides I've found so far is at: http://www.gearslutz.com/board/7421723-post126.html.

I crunched some numbers for a 10" (256 mm) thick absorber with no air gap (Whealy's calculator doesn't like zeros, so I used 1 mm for the air space). I found that Absorbency @ ca. 60 Hz peaks for materials with flow resistivity of about 8,000 rayls/m which is something like 701, depending on who you believe.

It thus turns out that this particular configuration works more poorly with materials with appreciably higher or lower flow resistivity, so both 705 and ordinary pink thermal insulating batts are suboptimal.

Therefore, I'd suggest that the OP either overstuff his bass absorbers by about 3:1 to get the batts to act more like 701 or get some 701 or something like it.

I'd also suggest that if we can all agree that the numbers generated by Whealys calculator are good enough, that people start using it instead of blowing wind.

Coming up with a reliable table of flow resistivities for common absorbing materials seems to be of the essence.
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post #111 of 146 Old 05-01-2012, 03:26 PM - Thread Starter
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Originally Posted by localhost127 View Post

with respect to the OP --- unfortunately, as stated much earlier, the primary issue is lack of surface area coverage.

Ok, understood. Now, can anyone recommend new ways to tame this bass? I know small rooms are a bitch but theres gotta be something thats not extremely big, difficult or pricey... I'm almost willing to give up my rear surrounds or at least adapt their location to stick out further if filling out the back wall with thick absorption is a feasible attempt at helping to fix my issue.

Any and all recommendations are welcome, another thing I'm willing to do is scrap my whole wall panel design for a new one although throwing away the money "and more importantly the time spent building these" will be hard to swallow :/

And once again, PLEASE STOP cluttering up my thread with any topics not directly related to my issue.

Thank you.
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post #112 of 146 Old 05-01-2012, 07:29 PM
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Read back through for some of my suggestions. You have an excellent piece in the BFD, at least give it a shot. As has been said, placement of the subs could and more than likely would help... But alas that is not an option. Would you be against a filler sub (doesn't need to be up to the performance of your others, just filler) that could be placed in the rear of your theater. Multi sub placement has been proven and WORKS!! Look up the geddes approach for multi sub placement.

I feel your pain, I don't have any placement options myself but I'm starting to reconsider the consequences of having subs in the back (barely any walking room with an 11' width) I love how my setup sounds near the perimeter of the room and the second row. For some reason that I am still figuring out, my MLP has a terrible response without some serious Eq. I have 703 2" panels in the right spots for the non sub freqs and 4" panels lining the back wall ( no room for corner traps once again but im trying my best). My berry DCX has done wonders and I have been able to tame the room almost completely to a +\\- 5 db response from 10hz-100hz and about the same further up not considering the boost in the low end.

This takes some work but you have what it takes. Assuming a flame war, sound deadening/ absorption will only get you so far in a tough room.

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post #113 of 146 Old 05-01-2012, 10:43 PM
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Chris, let me preface this by saying that I'm probably newer at this than you, but I've been doing a lot of reading and internet-searching. So I've got a thing or two to say that hopefully will be helpful. ...I hope it will help, because then I can copy what you do for my own room

First, look again at your waterfall graphs. You'll see that the sound persists the longest at a few of your low bass (and very low bass, but not too much infrasonic, IMO) peaks. This contributes significantly to the "boominess" you experience. Remember, your room, like a bell, will ring. The notes the room plays naturally (it's modes) will sustain for a long time. Even when this ringing is quiet, because you've turned down the gain of the signals at those frequencies, the persistence of the sound remains present in your bell of a room - it's still ringing and still muddying the response. My point here is that you can do a lot with EQ, but you can't remove energy once it's in the room - and that is much of the problem in small rooms. Making the bass energy decay at a rate similar to the midrange is a serious task, but it's important. The effective way to do this is with bass traps.

For that reason, Ethan Winer always recommends more bass traps. I'm with him. You can cover them with reflective whatever and EQ back in some higher frequency later if you need, but that bass energy can't be allowed to persist that long, IMO.

Here's one of your graphs you posted a couple weeks ago:


You've noticed, I'm sure, that most of you graphs show the same peak around 63 Hz (my guess of the peak center frequency) which I think you'll find corresponds to the axial mode for the length of your room - somewhere around 17 to 18 feet. In fact, I put your room dimensions into BobGold's Room Modes Calculator, and the first major peak it predicts is: 62.8 hz 0.7% 17'12", 8'12", 4'6" (2,0,0 Axial) I suppose that makes sense, since your subs are built into the front wall. If you use porous absorption when you tame this problem, then you'll probably have gotten the rest of them too. (There's also a predicted tangential mode at 62.3 Hz, so you've been double-whammied in that small range.)

Now, in terms of specific recommendations for your problem... it seems you don't have the floor space (wall space) to give up for too much porous absorption. Still, it's the best bet, in general. That said, their may be some good alternatives. Ethan Winer's bass trap article shows how to build some traps that are very small compared to what you would imagine recommended for pure porous traps. He does use a lot of them, however.

He makes a few important points in that article which have significant bearing on your room. First, and most significantly, he issues this warning at the head of the article
Quote:


Please understand that the bass traps described in this article are intended mainly for larger rooms. For rooms smaller than 25 by 15 feet you'll do better with broadband bass traps made from thick rigid fiberglass placed in the room corners. Small rooms have peaks and nulls at all frequencies, so broadband absorption straddling corners is better than the tuned traps shown in this article. This is described in my Acoustics FAQ linked above. Once all of the corners are treated, then it makes sense to consider adding bass traps like these flat on the walls.

Second, his note at the end off the article (Added later) further limits the application of this smaller style trap:
Quote:


Although it is not stated in the article, the low-bass trap is effective at frequencies between about 80 Hz. and 160 Hz.

That said, I bet that if you were to cover as much of your rear wall as possible with these (less than four inches thick) traps, you'd be well on your way. Further, figuring out how to tune these a little lower is a much more "researchable" problem.

The other solution, and one I hope to be able to use to some extent, is Helmholtz absorbers. If you read at Gearslutz and elsewhere on the internet, you find mostly failed attempts at tuning them effectively. Also they tend to be very narrow in their effective frequency range, not to mention sensitive to positioning within your room. This might be a last resort.

Hope that helps...

Fred
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post #114 of 146 Old 05-01-2012, 11:14 PM
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Quote:
Originally Posted by HopefulFred View Post

My point here is that you can do a lot with EQ, but you can't remove energy once it's in the room - and that is much of the problem in small rooms.

You made very good points up to here . In this region, frequency domain corrections using EQ will absolutely reduce time domain ringing. The two universes are two sides of the same coin. Here is some measurements to show the same:



We clearly see the ringing is sharply reduced.

Quote:


The effective way to do this is with bass traps.

Unfortunately making acoustic products effective at such a low frequency is non-trivial. OP has already tried some and it showed nary a difference.

Quote:


For that reason, Ethan Winer always recommends more bass traps. I'm with him. You can cover them with reflective whatever and EQ back in some higher frequency later if you need, but that bass energy can't be allowed to persist that long, IMO.

That is because it is the only tool Ethan knows . There are a suite of solutions some far more powerful than acoustic treatment. You need to first reduce the impact of the problem. Then you can resort to acoustic products if your environment allows it.

Quote:


Ethan Winer's bass trap article[/url] shows how to build some traps that are very small compared to what you would imagine recommended for pure porous traps. He does use a lot of them, however.

A lot is the word. Have you seen a picture of his living room? If you took all the walls away the room would still stand the way it is due to all the panels on the wall . This is just the front of his room:



I showed results earlier that used no acoustic products at all! Yet it achieved flat response across multiple seats.

Quote:


That said, I bet that if you were to cover as much of your rear wall as possible with these (less than four inches thick) traps, you'd be well on your way. Further, figuring out how to tune these a little lower is a much more "researchable" problem.

Four inch panels simply won't be effective at modal frequencies. OP's room already appears to have too much absorption at high frequencies. Putting more panels on the walls will continue that theme and not resolve any of the modal issues.

I think you did summarize the conventional wisdom according to forums but sadly, that wisdom is dominated by use of acoustic products which is usually misapplied and overused. Advice is heavily tilted by the industry people who choose to participate on these forums as opposed to all the good advice that exists. Ask Keith Yates how he would design a room. His first task is multiple subwoofers and optimization of the same. You would probably refuse to do the job if you didn't allow him to use multiple subs at the start. Following the forum crowd is just going to lead to disappointment as OP has found out. Please read the first page of this thread and his before and after.

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post #115 of 146 Old 05-01-2012, 11:14 PM - Thread Starter
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Quote:
Originally Posted by beastaudio View Post

You have an excellent piece in the BFD, at least give it a shot. Would you be against a filler sub (doesn't need to be up to the performance of your others, just filler) that could be placed in the rear of your theater. Multi sub placement has been proven and WORKS!! Look up the geddes approach for multi sub placement.

I have 703 2" panels in the right spots for the non sub freqs and 4" panels lining the back wall ( no room for corner traps once again but im trying my best). My berry DCX has done wonders and I have been able to tame the room almost completely to a +\\- 5 db response from 10hz-100hz and about the same further up not considering the boost in the low end.

Thanks a lot for the reply

I do plan on trying out the BFD in a the next couple of days, I just learned how to calculate corrections in REW and apply them to the BFD

I have thought of running subs in the back, briefly I might add, but for a couple reasons I don't want to... One reason being that it's not recommended to run box subs with IB subs, forgot the reason but it's been talked about. Two, If I did that, I would have to run another amp for the extra subs and running wiring won't be an easy task... Also, giving up even more floor space is not on the top of my list. So, idk :/

Did your 4" panels make a big noticeable difference on the back wall? I'm willing to line my back wall with FG if a sound ifference is a given.

Did you have any serious nulls in your room that you were able to treat with absorption or EQ?


Quote:
Originally Posted by HopefulFred View Post

First, look again at your waterfall graphs. You'll see that the sound persists the longest at a few of your low bass (and very low bass, but not too much infrasonic, IMO) peaks. This contributes significantly to the "boominess" you experience. Remember, your room, like a bell, will ring. The notes the room plays naturally (it's modes) will sustain for a long time. Even when this ringing is quiet, because you've turned down the gain of the signals at those frequencies, the persistence of the sound remains present in your bell of a room - it's still ringing and still muddying the response. My point here is that you can do a lot with EQ, but you can't remove energy once it's in the room - and that is much of the problem in small rooms. Making the bass energy decay at a rate similar to the midrange is a serious task, but it's important. The effective way to do this is with bass traps.

For that reason, Ethan Winer always recommends more bass traps. I'm with him. You can cover them with reflective whatever and EQ back in some higher frequency later if you need, but that bass energy can't be allowed to persist that long, IMO.

Here's one of your graphs you posted a couple weeks ago:


You've noticed, I'm sure, that most of you graphs show the same peak around 63 Hz (my guess of the peak center frequency) which I think you'll find corresponds to the axial mode for the length of your room - somewhere around 17 to 18 feet. In fact, I put your room dimensions into BobGold's Room Modes Calculator, and the first major peak it predicts is: 62.8 hz 0.7% 17'12", 8'12", 4'6" (2,0,0 Axial) I suppose that makes sense, since your subs are built into the front wall. If you use porous absorption when you tame this problem, then you'll probably have gotten the rest of them too. (There's also a predicted tangential mode at 62.3 Hz, so you've been double-whammied in that small range.)

Now, in terms of specific recommendations for your problem... it seems you don't have the floor space (wall space) to give up for too much porous absorption. Still, it's the best bet, in general. That said, their may be some good alternatives. Ethan Winer's bass trap article shows how to build some traps that are very small compared to what you would imagine recommended for pure porous traps. He does use a lot of them, however.

He makes a few important points in that article which have significant bearing on your room. First, and most significantly, he issues this warning at the head of the article Second, his note at the end off the article (Added later) further limits the application of this smaller style trap:
That said, I bet that if you were to cover as much of your rear wall as possible with these (less than four inches thick) traps, you'd be well on your way. Further, figuring out how to tune these a little lower is a much more "researchable" problem.

The other solution, and one I hope to be able to use to some extent, is Helmholtz absorbers. If you read at Gearslutz and elsewhere on the internet, you find mostly failed attempts at tuning them effectively. Also they tend to be very narrow in their effective frequency range, not to mention sensitive to positioning within your room. This might be a last resort.

Hope that helps...

Fred

Thanks a lot Fred for taking the time to reply

What's a tangential mode? I don't think I've ever heard of that one.

I'm willing to cover my whole back wall with thick FG if this will help, hoping others that have done this will chime in. I understand that 4" isn't a fix all solution but was hoping it would make a huge difference before I "try it out" and spend all that money on insulation..

I have read quite a bit of Ethans writings but might need to go back. I'm just hoping to hear from others that have done "X" treatments with major success, and then copy their solutions

Thanks again for the reply, I still can't follow waterfall graphs too well yet but thanks for pointing that out
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post #116 of 146 Old 05-01-2012, 11:35 PM - Thread Starter
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One last question for now that seems to have many different outlooks on... Is EQ'ing not recommended for nulls? Some says that EQ'ing nulls is a big no no or even can't be done, others say it's ok if you have the headroom. What are your thoughts?
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post #117 of 146 Old 05-02-2012, 03:38 AM
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Originally Posted by Digital_Chris View Post

Ok, understood. Now, can anyone recommend new ways to tame this bass? I know small rooms are a bitch but theres gotta be something thats not extremely big, difficult or pricey...

Chris: I just skimmed this thread and it reminded me of what I went thru 3 years ago. A word of caution: making the REW plots look "pretty" can drive you bonkers.

My room is 12x22x8 with the projector screen on one of the 12' walls. I started with only ATS 4" panels on the side walls for first reflection absorption. A friend came over one day and suggested bass traps, which I had thought were "smoke and mirrors." Boy, was I wrong!

A little digging into the subject led me to discussions with bpape on hometheatershack.com in the Room Acoustics thread. He is affiliated with GIK and is very knowledgeable on room acoustics. He spent about an hour on the phone with me one night discussion options. Following his suggestion, I added two GIK Monster Traps at the back of the room, ran REW and started noticing differences in the before and after plots. Well, if a little made a difference, what about more...

I ended up with 6 Monster traps in the room. At first, 4 were in the back (in corners and in the center of the back wall) and two up front in the corners. Also at bpape's recommendation, I stuffed R30 insulation above the suspended ceiling tiles. This is a dedicated, wife-hands-off room, so I can do almost whatever I want, as long as she has a recliner

The end result produced a very significant difference in the waterfall plots as well as greatly improved transient response from the subs and sub frequency response flatness.

When I added Height speakers for A-DSX, the front traps were moved to the back of the room behind the two in the center. Did not see much difference in plots or sound.

There is certainly a point of diminishing returns in doing all this. Chasing the perfect waterfall plot can be very time consuming and costly, as well as completely unattainable, especially in small rooms. About halfway thru stuffing the R30 above the suspended ceiling was where I stopped noticing differences.

Also, remember that "ringing" at the lowest frequencies is very difficult to control due to the wavelengths involved. I had room ringing at 26Hz which was only slightly attenuated after I put in all the traps.

Don't get me wrong - I am certainly a bass trap fanboy now. Just remember to try to "stay sane" in making your choices.
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post #118 of 146 Old 05-02-2012, 03:49 AM
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Quote:
Originally Posted by Digital_Chris View Post

One last question for now that seems to have many different outlooks on... Is EQ'ing not recommended for nulls? Some says that EQ'ing nulls is a big no no or even can't be done, others say it's ok if you have the headroom. What are your thoughts?

You won't accomplish much trying to EQ room mode nulls. You will "run out of speaker" before you accomplish much. 3-4 db, yes. But one of these 20-30db suck outs - no way.
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post #119 of 146 Old 05-02-2012, 06:49 AM
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Just to follow up: Amir points out that multiple subwoofers is the better route; I wouldn't disagree with that at all. I plan for two at least myself, eventually four - budget allowing... I was trying to work within what I thought were Chris's stated limitations.

Also, notice that the traps I linked to were not simple porous traps like the one Chris has already tried to employ. I can't personally vouch for their increased effectiveness, but they include a non-porous resonant membrane (thin plywood is what Ethan has recommended).

A tangential mode is one based on one of the diagonal dimensions of a room - one tricorner to another, I believe; such as wall-wall-ceiling by the screen to wall-wall-floor in the rear.

Anyway like I said, I'm totally new at this. I'm just trying to broaden the scope of the conversation a little to include ideas not yet fully considered.

Fred
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post #120 of 146 Old 05-02-2012, 07:01 AM
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Something else that occurred to me: is it possible to adjust the phase of the signals to some of the IB drivers? This may be a total non-starter of an idea for any number of practical or scientific reasons (like it wouldn't be effective even if you could do it), but what do I know?
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