2" vs 4" deep absorbers - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 21 Old 03-29-2013, 12:34 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
I currently have absorbers setup on the side walls in my home theater / listening room. They are 1' wide and 3' long, 2" deep and mounted flush with the wall.

My question is will going with deeper and bigger absorbers improve the bass response in my room overall? I would make some that are 2' x 4' x 4". I made the absorbers in the first place to take care of "flutter echo" and early reflections from my ESLs but now I would like to build something a bit better since I can spare the extra few inches of wall space. I just wanted to know if it is going to be worth the time and effort and if I'll notice an improvement in bass.

Appreciate any advice
BB1111 is offline  
Sponsored Links
Advertisement
 
post #2 of 21 Old 03-29-2013, 12:45 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Yes, absorbers on the side walls should be wider than one foot, unless you're literally three feet away from the loudspeakers or closer. Speakers radiate outward in an arc, so the term "reflection point" is a misnomer. It's really an area.

Early reflections is mainly a problem at mid and high frequencies, though making them thicker can only help. I wouldn't expect a lot of bass trapping from absorbers mounted there because bass tends to collect more in the corners. So I'd do both - larger panels at reflection points, plus bass traps in more suitable places such as the rear wall behind you.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #3 of 21 Old 03-29-2013, 07:21 PM
Advanced Member
 
Nyal Mellor's Avatar
 
Join Date: Aug 2010
Location: SF Bay Area, California, USA
Posts: 926
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 29 Post(s)
Liked: 70
Depending on how far your speakers are from the side walls using thicker products, preferably with a membrane in them somewhere, will help reduce speaker boundary interference related nulls from the sidewalls that often show up in the 100-300Hz region.

Master of Minions, Acoustic Frontiers. We specialize in the design and creation of high performance listening rooms, home theaters and project studios for discerning audio/video enthusiasts.
Nyal Mellor is offline  
post #4 of 21 Old 03-29-2013, 11:41 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
Quote:
Originally Posted by Nyal Mellor View Post

Depending on how far your speakers are from the side walls using thicker products, preferably with a membrane in them somewhere, will help reduce speaker boundary interference related nulls from the sidewalls that often show up in the 100-300Hz region.

Currently bass at my MLP position is pretty good except for the 100-125hz range where I have a huge null. Just moving my head forward a foot brings back a lot of decibels in this range, this is in stereo without my subwoofer on and no Audyssey, it may help correct that when its turned on. Havent tested yet.

Mains are 4 feet from each corner. Overall a thicker absorber will be better? Also what sort of membrane is needed?
BB1111 is offline  
post #5 of 21 Old 03-30-2013, 02:06 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by BB1111 View Post

Currently bass at my MLP position is pretty good except for the 100-125hz range where I have a huge null.

Huge nulls are common, and often due to reflections from the rear wall behind you. But they can also be SBIR as Nyal explained. It's not difficult to tell which is the cause, by moving the speakers sideways versus forward and back while measuring. Or use my Frequency-Distance Calculator to relate the exact frequencies you measure versus the exact distances. Either way you need to measure. This cannot be done by ear.

Yes, thicker absorbers are always better for bass frequencies. Membrane absorbers when implemented properly are better than plain rigid fiberglass.

--Ethan

RealTraps - The acoustic treatment experts
Ethan's Audio Expert book

Ethan Winer is offline  
post #6 of 21 Old 04-02-2013, 11:43 AM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,016
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 30
The easy answer is to test it, with your current absorbers, by pulling them out 2-4".

I've attached a couple charts from Everest's Master Handbook of Acoustics.

The first shows the effect of thickness for surface mounted panels. It supports the approach of using thicker panels to improve bass absorption.


However, when you reallize the data below is for the 1" thick panel, above, and that you're starting with a 2" panel, it seems as if you can simulate 4" panels by simply spacing your current panels away from the wall a few inches.


If this test shows the kind of improvement you're looking for, then you know it's worth the time and effort.

Regarding your 100-125Hz null, any chance your speakers are ~2.5' from the front wall? If so, put an appropriate panel on the front wall behind the speaker, to absorb the front wall reflection that's a likely contributor to the null. I've seen lots of data that sidewall reflections improve sound quality, conventional wisdom not withstanding, but none that say the front wall contributes anything desirable.

HAve fun,
Frank
fbov is offline  
post #7 of 21 Old 04-02-2013, 12:06 PM
AVS Special Member
 
localhost127's Avatar
 
Join Date: May 2009
Posts: 2,277
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 24
regardless of thickness, the absorber still needs to be large with respect to wavelength.
localhost127 is offline  
post #8 of 21 Old 04-02-2013, 01:16 PM
AVS Special Member
 
jim19611961's Avatar
 
Join Date: Mar 2011
Location: Texas
Posts: 1,343
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 89 Post(s)
Liked: 80
Quote:
Originally Posted by localhost127 View Post

regardless of thickness, the absorber still needs to be large with respect to wavelength.

+1

My Room
http://www.gearslutz.com/board/studio-building-acoustics/817205-my-listening-room.html

My Music
http://rateyourmusic.com/~jim1961

My Equipment

Rega - Apollo
Rega - DAC
Goldpoint Passive
(2) Classe CA-100 bridged power amps (350w)
Jenzen Next ( http://www.troelsgravesen.dk/Jenzen-NEXT.htm )
...
jim19611961 is online now  
post #9 of 21 Old 04-02-2013, 02:22 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
Quote:
Originally Posted by fbov View Post


Regarding your 100-125Hz null, any chance your speakers are ~2.5' from the front wall? If so, put an appropriate panel on the front wall behind the speaker, to absorb the front wall reflection that's a likely contributor to the null. I've seen lots of data that sidewall reflections improve sound quality, conventional wisdom not withstanding, but none that say the front wall contributes anything desirable.

HAve fun,
Frank

Heh, the speakers are almost exactly 2.5' from the front wall. The Martin Logans are pulled out as far as I can get them in this room. A thick absorber would be better for the wall behind the panel? I just made some skyline diffusers to help diffuse the rear backwave... the sidewalls have the 2" absorbers currently. I was told that absorbing the backwave will kill the spaciousness that an ESL is known for so I went with diffusers but I'm open to trying something different if it will improve sound quality.

Room is 14" W x 8" H x 20" L with the speakers firing into the length of the room. MLP is 10 feet from the back wall.
BB1111 is offline  
post #10 of 21 Old 04-02-2013, 02:59 PM
AVS Addicted Member
 
sdurani's Avatar
 
Join Date: Oct 2001
Location: Monterey Park, CA
Posts: 19,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 844 Post(s)
Liked: 783
Quote:
Originally Posted by BB1111 View Post

Room is 14" W x 8" H x 20" L with the speakers firing into the length of the room. MLP is 10 feet from the back wall.
You're at the midpoint of room length? (which I'm guessing is 20', not 20")

Sanjay
sdurani is online now  
post #11 of 21 Old 04-02-2013, 03:37 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
Quote:
Originally Posted by sdurani View Post

You're at the midpoint of room length? (which I'm guessing is 20', not 20")

No, it's inches. I have a REALLY tiny room

smile.gif



I'm not sitting in the midpoint, about 3 feet in front of it. I think my original measurements are a little off, room is probably more like 18' deep.
BB1111 is offline  
post #12 of 21 Old 04-02-2013, 04:08 PM
AVS Addicted Member
 
sdurani's Avatar
 
Join Date: Oct 2001
Location: Monterey Park, CA
Posts: 19,159
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 844 Post(s)
Liked: 783
Quote:
Originally Posted by BB1111 View Post

No, it's inches. I have a REALLY tiny room
LOL, gives new meaning to "small room" acoustics.
Quote:
Originally Posted by BB1111 View Post

I'm not sitting in the midpoint, about 3 feet in front of it
That doesn't reconcile with your previous numbers: room is 20' long, MLP is 10' from the back wall (half of 20), which should be the midpoint of room length.

The reason I ask is to find out if there are ways to solve some of your frequency response problems using placement, augmented with treatments (e.g., bass traps) rather than trying to solve them primarily or solely with treatments.

Sanjay
sdurani is online now  
post #13 of 21 Old 04-02-2013, 04:13 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
Quote:
Originally Posted by sdurani View Post

LOL, gives new meaning to "small room" acoustics.
That doesn't reconcile with your previous numbers: room is 20' long, MLP is 10' from the back wall (half of 20), which should be the midpoint of room length.

The reason I ask is to find out if there are ways to solve some of your frequency response problems using placement, augmented with treatments (e.g., bass traps) rather than trying to solve them primarily or solely with treatments.



Re measured the length of the room. Seating position is 11 ft from the back wall and 8 feet from the front wall. If moving the speakers would help that would be great, as long as it doesn't cause problems else where in the frequency.
BB1111 is offline  
post #14 of 21 Old 04-03-2013, 09:48 AM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,016
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 30
Quote:
Originally Posted by BB1111 View Post

Heh, the speakers are almost exactly 2.5' from the front wall. The Martin Logans are ....
Missed that... Any panel speaker has a special relationship with it's room. Many of the conventional tricks don't apply.

HAve fun,
Frank
fbov is offline  
post #15 of 21 Old 04-03-2013, 03:57 PM
AVS Special Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 6,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 145 Post(s)
Liked: 255
A 2" panel with a 2" - 3" airspace is not going to absorb as well as a 4" panel without an airspace.

2.5' is about a quarter wave at 112 Hz.

My Maggies sound much better with the back wave heavily damped.

IMO - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #16 of 21 Old 04-03-2013, 08:02 PM
AVS Addicted Member
 
arnyk's Avatar
 
Join Date: Oct 2002
Location: Grosse Pointe Woods, MI
Posts: 14,301
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 690 Post(s)
Liked: 1144
Quote:
Originally Posted by DonH50 View Post

A 2" panel with a 2" - 3" airspace is not going to absorb as well as a 4" panel without an airspace.

I strongly recommend spending some time with Chris Whealy's porous absorber calculator: http://www.whealy.com/acoustics/Porous.html

In fact a 2" panel with a 2" airspace can be soooo close to a 4" panel in terms of performance.
arnyk is offline  
post #17 of 21 Old 04-03-2013, 08:23 PM
AVS Special Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 6,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 145 Post(s)
Liked: 255
Thanks for the link, I shall do that.

But, even at 125 Hz and below? Yeah, I know, load the %$^%@# program... smile.gif I can type while resting during my practice sessions, but my focus is on my music, not the computer; I'd have to actually think to load and run it. I _will_ do it, however!

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #18 of 21 Old 04-03-2013, 08:54 PM - Thread Starter
Member
 
BB1111's Avatar
 
Join Date: Sep 2010
Posts: 173
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 5 Post(s)
Liked: 14
Quote:
Originally Posted by DonH50 View Post

A 2" panel with a 2" - 3" airspace is not going to absorb as well as a 4" panel without an airspace.

2.5' is about a quarter wave at 112 Hz.

My Maggies sound much better with the back wave heavily damped.

IMO - Don

Have you compared with a diffuser and a thick absorber behind your Maggies?
BB1111 is offline  
post #19 of 21 Old 04-03-2013, 09:15 PM
AVS Special Member
 
DonH50's Avatar
 
Join Date: Feb 2010
Location: Monument CO
Posts: 6,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 145 Post(s)
Liked: 255
Yes, but long ago, mine and others (used to work for a dealer and helped install systems). Diffusors generally cost much more and must be very large to affect low frequencies. My present treatment is all absorption; I hope to gradually add diffusion, probably replacing some of the absorbers.

What do you want to know? Diffusion tends to help keep the more "spacious" sound many like while still breaking up higher-frequency cancellations. I have also heard a system with large (8' tall, roughly 4' wide and 4' deep) corner diffusors behind them, and they helped quite a bit. IME, diffusion does not provide as stable an image but tends to "open up" the sound more, and most people prefer the sound with diffusion rather than absorption. A room as dead as my current setup (the smallest and deadest room I have had them in, I think) provides excellent imaging and virtually no cancellation effects across the listening position, but all ambiance comes from the recording and not the room.

With the exception of the one system with massive diffusors, bass was better with absorbers behind the Maggies. The wavelengths are such that diffusors have to be huge, and even absorption at LF is difficult to achieve in practice. I have 10" corner traps and numerous 6" and 4" panels, all with 2" - 4" air gaps, along the front wall. A large room that allowed the Maggies to sit well out from the back wall is also less sensitive to that durn back wave.

All this applies to ESLs as well, natch.

Ethan can cover this in much greater depth than I, as can others who have posted here. My audio work and those pesky grad acoustics classes were long ago...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
DonH50 is offline  
post #20 of 21 Old 04-04-2013, 09:19 AM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,016
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 30
Quote:
Originally Posted by arnyk View Post

...In fact a 2" panel with a 2" airspace can be soooo close to a 4" panel in terms of performance.
It's a cheap and effective way to test the hypothesis regarding bass response and listen to the result - that's the whole point of suggesting it.
fbov is offline  
post #21 of 21 Old 04-04-2013, 09:57 AM
AVS Special Member
 
jim19611961's Avatar
 
Join Date: Mar 2011
Location: Texas
Posts: 1,343
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 89 Post(s)
Liked: 80
Quote:
Originally Posted by arnyk View Post

I strongly recommend spending some time with Chris Whealy's porous absorber calculator: http://www.whealy.com/acoustics/Porous.html

In fact a 2" panel with a 2" airspace can be soooo close to a 4" panel in terms of performance.





Looks to me that 4" is about 2/3 of an octave deeper.

My Room
http://www.gearslutz.com/board/studio-building-acoustics/817205-my-listening-room.html

My Music
http://rateyourmusic.com/~jim1961

My Equipment

Rega - Apollo
Rega - DAC
Goldpoint Passive
(2) Classe CA-100 bridged power amps (350w)
Jenzen Next ( http://www.troelsgravesen.dk/Jenzen-NEXT.htm )
...
jim19611961 is online now  
Reply Audio theory, Setup and Chat

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off