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Need Room Treatment Advice. Willing to pay!

post #1 of 97
1/6/13 at 7:02pm
Thread Starter 
Hi Guys,

I am looking to treat my home theater. 50/50 music and movies.

Can anyone help me decide on the type of panels to use, the location, and number of panels I would need? I don't need it to be perfect- just general advice. Also, you don't have to be a certified expert.

I would be willing to pay someone willing to consult with me over the phone. I've contacted some acoustic panel companies online but their advice is so generic its tough to figure out what to get.

Anyone?

Images of my room:




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post #2 of 97
1/7/13 at 12:26pm
I'll be glad to help you. Email me through my web site http://www.ethanwiner.com and we'll determine if this is to be done on a purely consulting basis, or as part of the purchase of products from my company in which case the advice is free.

--Ethan
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post #3 of 97
1/7/13 at 1:45pm
Brian,
The first step is always defining the problem, but at a higher level of detail than "I'm looking to treat my home theater." There are two general approaches you can use:
- measure your room acoustics, identify specific acoustic issues, address them, measure the change to assess effectiveness, repeat until happy
- apply some of the common "rule of thumb" approaches and listen for major residual issues, then address the major issues.

Clearly, the former starts with mic, mixer, PC with sound card, software, etc. Not everyone wants to start here; the inital cost isn't prohibitive, but the learning curve is intimidating.

The latter will be incomplete to the extent that some acoustic issues may not be audible to you, but it's where you'll get the most bang for your effort, and I can make some suggestions. If you don't have Toole's book, buy it. Most of this comes from his conclusions regarding what's generally applicable. I also have a link for Everest's Master Handbook of Acoustics which complements Toole by providing construction details.
http://www.amazon.com/Sound-Reproduction-Acoustics-Psychoacoustics-Loudspeakers/dp/0240520092/ref=la_B001JS2MQ2_1_1?ie=UTF8&qid=1357592961&sr=1-1
http://andrealbino.wikispaces.com/file/view/Master+Handbook+of+Acoustics+-+5th+Edition+-+F.+Alton+Everest,+Ken+C.+Pohlmann.pdf

Be aware that acoustic issues (and their remedies) are of two very different types, depending on frequency above or below the "transition frequency."
- Below the transition frequency range, room modes are isolated and audible so we apply wave interference analysis methods and use acoustic devices that are effective at low frequency.
- above the transition frequency range, room modes are very dense and so merge to become inaudible. We use ray tracing methods to analyze the room, and a wide range of acoustic devices as these frequencies are more easily absorbed.

Lookinig at the photos, I assume:
- above grade construction
- stick construction walls
- a basement below and more rooms above

I also observe:
- wall-wall carpeting, hopefully with a thick pad beneath,
- non-porous (acoustically reflective) furniture
- thin, sparsely-pleated curtains on the windows

My assumptions are major drivers of bass issues, my observations major drivers at higher frequencies. All affect the acoustics.

Generically, Toole recommends:
- absorption on the front wall
- absorption on the rear wall.
- diffusion on the side walls
- no treatment at first reflection points when the goal is enjoymnet (you're not looking for a recording studio...)

The former are the panels you've likely seen, 2'x4' based on commercial fiberglass or mineral wool panel insulation. These are most effective at higher frequencies, gaining low-end effect by becoming larger, and being spaced farther from walls than your room supports. You could also increase the density of the curtains, and should consider a matching set for the doorways (symmetry is beneficial). Diffusers are designed to reflect sound in various directions, masking the direction of the initial sound. Both are working above the transition frequency, so they're only one half of the equation.

Bass modes will be determined by room dimensions - any frequency that has a wavelength that matches the room size will resonate like a pipe organ. This is one you'll hear as a variation in bass response with seating position, and with subwoofer location in the room. Just as room furnishings absorb higher frequencies, room constuction may do the same for the bass. Stick walls are more transparent to bass than cinderblocks, and windows have a degree of bass absorption as well. The quesiton becomes whether underdamped resonances still exist that intererfere with your enjoyment, as the most effective bass traps are both large and complex, compared with acoustic panels.

So... what size is the room, how's it built, and how handy are you? I tend to DIY rather than buy, but that's by choice.

Have fun,
Frank

PS Ethan's a bit of a salesman, but so are most entrepreneurs. If you aren't DIY-ish, I'd take him up on his offer. Lots of experience in this area...
Edited by fbov - 1/7/13 at 1:51pm
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post #4 of 97
1/8/13 at 11:46am
Quote:
Originally Posted by fbov View Post

Ethan's a bit of a salesman, but so are most entrepreneurs. If you aren't DIY-ish, I'd take him up on his offer. Lots of experience in this area...

LOL, I try to keep the self-promotion to a minimum. But Brian asked specifically for someone willing to help him for a fee. When people buy from my company the same level of advice is free.

--Ethan
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post #5 of 97
1/8/13 at 4:13pm
Before I started worrying about room treatments, I would try to do something about the placement of your main speakers.

It appears to be a real problem, and if that is the case, no amount of room treatment or software noodling is going to fix the basic problem.

What kind of speakers are they and exactly how are they placed?

The pictures make it hard to tell.
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post #6 of 97
1/8/13 at 8:19pm
Thread Starter 
I'd love to buy your products but they are very expensive. I'll PM you. I'd love to buy an hour or two of your time. Email would probably work just fine.

-Brian
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post #7 of 97
1/8/13 at 8:21pm
Thread Starter 
Quote:
Originally Posted by commsysman View Post

Before I started worrying about room treatments, I would try to do something about the placement of your main speakers.
It appears to be a real problem, and if that is the case, no amount of room treatment or software noodling is going to fix the basic problem.
What kind of speakers are they and exactly how a
re they placed?
The pictures make it hard to tell.

At the moment there is only a TV. Eventually I will be putting Salk Soundscapes on either side of the TV, slightly foward of the same (as shown in the diagram). You can click on the images for a large view.

-Brian
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post #8 of 97
1/8/13 at 8:26pm
Thread Starter 
Thanks Ebov!

You are right on most accounts.

The room sits above a garage on the 2nd floor. The home is two floors (no basement); ground floor and top floor.

Would it behoove me to buy the OmniMic system and takes measurments before buying anything? Due to time constraints I would again, most likely, need to pay someone to work with me and help me takes some measurment.

Perhaps this a better approach?

-Brian
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post #9 of 97
1/8/13 at 8:28pm
Thread Starter 
Quote:
Originally Posted by fbov View Post

Brian,
The first step is always defining the problem, but at a higher level of detail than "I'm looking to treat my home theater." There are two general approaches you can use:
- measure your room acoustics, identify specific acoustic issues, address them, measure the change to assess effectiveness, repeat until happy
- apply some of the common "rule of thumb" approaches and listen for major residual issues, then address the major issues.
Clearly, the former starts with mic, mixer, PC with sound card, software, etc. Not everyone wants to start here; the inital cost isn't prohibitive, but the learning curve is intimidating.
The latter will be incomplete to the extent that some acoustic issues may not be audible to you, but it's where you'll get the most bang for your effort, and I can make some suggestions. If you don't have Toole's book, buy it. Most of this comes from his conclusions regarding what's generally applicable. I also have a link for Everest's Master Handbook of Acoustics which complements Toole by providing construction details.
http://www.amazon.com/Sound-Reproduction-Acoustics-Psychoacoustics-Loudspeakers/dp/0240520092/ref=la_B001JS2MQ2_1_1?ie=UTF8&qid=1357592961&sr=1-1
http://andrealbino.wikispaces.com/file/view/Master+Handbook+of+Acoustics+-+5th+Edition+-+F.+Alton+Everest,+Ken+C.+Pohlmann.pdf
Be aware that acoustic issues (and their remedies) are of two very different types, depending on frequency above or below the "transition frequency."
- Below the transition frequency range, room modes are isolated and audible so we apply wave interference analysis methods and use acoustic devices that are effective at low frequency.
- above the transition frequency range, room modes are very dense and so merge to become inaudible. We use ray tracing methods to analyze the room, and a wide range of acoustic devices as these frequencies are more easily absorbed.
Lookinig at the photos, I assume:
- above grade construction
- stick construction walls
- a basement below and more rooms above
I also observe:
- wall-wall carpeting, hopefully with a thick pad beneath,
- non-porous (acoustically reflective) furniture
- thin, sparsely-pleated curtains on the windows
My assumptions are major drivers of bass issues, my observations major drivers at higher frequencies. All affect the acoustics.
Generically, Toole recommends:
- absorption on the front wall
- absorption on the rear wall.
- diffusion on the side walls
- no treatment at first reflection points when the goal is enjoymnet (you're not looking for a recording studio...)
The former are the panels you've likely seen, 2'x4' based on commercial fiberglass or mineral wool panel insulation. These are most effective at higher frequencies, gaining low-end effect by becoming larger, and being spaced farther from walls than your room supports. You could also increase the density of the curtains, and should consider a matching set for the doorways (symmetry is beneficial). Diffusers are designed to reflect sound in various directions, masking the direction of the initial sound. Both are working above the transition frequency, so they're only one half of the equation.
Bass modes will be determined by room dimensions - any frequency that has a wavelength that matches the room size will resonate like a pipe organ. This is one you'll hear as a variation in bass response with seating position, and with subwoofer location in the room. Just as room furnishings absorb higher frequencies, room constuction may do the same for the bass. Stick walls are more transparent to bass than cinderblocks, and windows have a degree of bass absorption as well. The quesiton becomes whether underdamped resonances still exist that intererfere with your enjoyment, as the most effective bass traps are both large and complex, compared with acoustic panels.
So... what size is the room, how's it built, and how handy are you? I tend to DIY rather than buy, but that's by choice.
Have fun,
Frank
PS Ethan's a bit of a salesman, but so are most entrepreneurs. If you aren't DIY-ish, I'd take him up on his offer. Lots of experience in this area...


Really, no treatment on the 1st reflections points on the side walls? That's anti to most advice I've read and received. GIK Acoustics recommended I put diffursors on the side walls at the reflection points.

-Brian
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post #10 of 97
1/9/13 at 10:46am
Quote:
Originally Posted by Bghead8che View Post

Really, no treatment on the 1st reflections points on the side walls?

The notion of leaving reflection points bare is a "minority position" that is ignored by serious audio professionals. Virtually every professional recording studio control room either absorbs early reflections, or re-directs them away from the listening position. Maybe in a very large living room you could get away without absorption at those specific places. Same for diffusion at reflection points, which just "smears" the reflections. In a normal size room you want to kill all early reflections to better hear the direct sound from the speakers.

--Ethan
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post #11 of 97
1/9/13 at 11:05am
Quote:
Originally Posted by Bghead8che View Post

...The room sits above a garage on the 2nd floor. ...Would it behoove me to buy the OmniMic system ...
Quote:
Originally Posted by Bghead8che View Post

Really, no treatment on the 1st reflections points on the side walls? ...
In order...

Your room's construction leads me to expect bass mode issues will be minor at worst. That's a good thing. It took me years to see all the bass traps in my room, and understand that room construction and architectural features have beneficial acoustic properties.

OmniMic is an excellent, full featured measurement sysytem. At ~$300, it ought to be. I use REW (freeware) a calibrated mic and mixer at roughly 1/3 the cost. Here are REW links; stickies in the second link should cover your quesitons.
http://www.hometheatershack.com/roomeq/
http://www.hometheatershack.com/forums/rew-forum/#axzz2HUyQAmCu

Once you can measure, it's a simple process to create a waterfall plot which will show room resonance issues unambiguously. There's an example here, page 220, Figs.12-38 and 12-39 show a waterfall with a resonance, and after it was treated.
http://andrealbino.wikispaces.com/file/view/Master+Handbook+of+Acoustics+-+5th+Edition+-+F.+Alton+Everest,+Ken+C.+Pohlmann.pdf

Or, you can use your ears, and a sine wave generator to ID resonances. Bad ones stick out like sore thumbs, and those you can't hear don't matter. Forums like these prefer data, but that's us...

Read Toole for a description of the research on first reflection perception (with references), but the data shows:
- when listening for enjoyment, people (even sound engineers) prefer a high level of sidewall reflection
- when listening for business (i.e. sound engineer in a recording studio), sidewall reflections are undesirable.

So, the appropriate room treatment depends on the room usage. Most all HT are intended as entertainment, not work space, so including 1st reflection points will contribute to the room's intended purpose. Personally, I find this very evident in stereo listening, where the room provides the majority of the ambiance. With multichannel program, not so much since there are now speaker channels providing the ambiance. Thus there's a degree of preference, too - some folks like pinpoint imaging, where each instrument is localized. I like a broad apparent source width where instruments have locations, but you can't point to anything more than a region of the room as the location.

I also think there's a bit of human nature involved; Energy Time Curve (ETC) analysis allows you to identify the arrival time of a reflection, and a piece of string allows you to find what surface is the right distance, so you can see the effect of placing absorbers at the 1st reflection points.

We're also talking mostly about absorbers here. A proper room treatment will also include diffusers. That's where someone like Ethan can steer you to a balanced approach.

Have fun,
Frank
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post #12 of 97
1/10/13 at 10:43am
Quote:
Originally Posted by fbov View Post

Read Toole for a description of the research on first reflection perception (with references), but the data shows:
- when listening for enjoyment, people (even sound engineers) prefer a high level of sidewall reflection
- when listening for business (i.e. sound engineer in a recording studio), sidewall reflections are undesirable.

Have fun,
Frank

just an FYI but not all lateral energy is "undesirable" in critically accurate mixing/control rooms - just those indirect signals that are destructive to intelligibility, localization, and imaging.

LEDE (2ch) termination (sharply delineating the effectively anechoic ISD-gap) is via that of a LATERALLY arriving, exponentially decaying diffused sound-field. hence why the 1dimensional reflection phase grating diffusers are oriented w/ vertical wells such that spatial dispersion is in the horizontal plane.

Blackbird Studio C ("Amebechoic" control room primarily for surround sound applications) features arguably the most REFLECTION-RICH sidewalls on the planet. granted, they are densely diffused and the first-order returns are below human detection threshold such that they are not keyed on by the ear-brain for localization, imaging...

the time-arrival, gain, spectral content, and type (sparse/dense/dense-diffused) of the indirect sidewall specular energies are important characteristics. not all sidewalls "reflections" are the "same" or necessarily comparable, as so many here like to dumb things down to (not you in particular; just general/vague consensus). polar response of the driver and complex acoustical impedance of the sidewall/boundary are other factors at play...

the dedicated home theater guys seem to "prefer" binary amplitude diffusers versus that of untreated sidewalls. depends on the design requirements.
Edited by localhost127 - 1/10/13 at 11:07am
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post #13 of 97
1/10/13 at 1:19pm
Quote:
Originally Posted by fbov View Post




Read Toole for a description of the research on first reflection perception (with references), but the data shows:

- when listening for business (i.e. sound engineer in a recording studio), sidewall reflections are undesirable.

If you mean early arriving side wall reflections, I agree. If you mean later arriving (>20ms) then I disagree.
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post #14 of 97
1/10/13 at 3:23pm
Quote:
Originally Posted by Bghead8che View Post

Really, no treatment on the 1st reflections points on the side walls?
Scores high on preference based tests. For recreational listening, people tend to like a broad soundstage; more immersive, like moving closer to your display screen when watching a movie, in order to get a bigger/more involving image. Other benefits include improved intelligibility and ability to detect subtle differences in timbre. All of that is covered (with source citations) in the Toole paper mentioned earlier in this thread, which can be found here. First read section 9.2.1 (22nd page of the PDF), which should take you less than 60 seconds, then go back and start reading from section 2 for explanations.

BTW, understand preference tests for what they are. Just because vanilla is by far the most popular ice cream flavor doesn't guarantee it will be your favourite as well. Statistical preference can tell you what most people prefer but not whether your personal preference falls into that category. But if you're human and have human traits, looking at what most people prefer is a good starting point. You can always adjust to taste from there.
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post #15 of 97
1/10/13 at 4:10pm
Quote:
Originally Posted by Ethan Winer View Post

The notion of leaving reflection points bare is a "minority position" that is ignored by serious audio professionals. Virtually every professional recording studio control room either absorbs early reflections, or re-directs them away from the listening position. Maybe in a very large living room you could get away without absorption at those specific places. Same for diffusion at reflection points, which just "smears" the reflections. In a normal size room you want to kill all early reflections to better hear the direct sound from the speakers.

--Ethan

Really you need to look at the off axis response of the speakers, the reflected path distance and the direction of the reflection to get a proper understanding of what to do with the reflection points.

We do remote consulting work. I'll PM you some more details. There is also some info about our services on our website.
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post #16 of 97
1/11/13 at 12:06pm
Quote:
Originally Posted by Nyal Mellor View Post

Really you need to look at the off axis response of the speakers, the reflected path distance and the direction of the reflection to get a proper understanding of what to do with the reflection points.

I understand that loudspeaker directivity is a factor, but I've never seen a room that didn't benefit from absorbing side-wall reflections. Most speakers beam outward widely horizontally but less so vertically, so the ceiling may or may not benefit from absorption. This is just my experience and preference, which is all I can report.

I will say that I find the notion that early reflections increase width and soundstage to be suspect. Short delays sound like a small space, versus the larger sounding reverb imbedded in most recordings. A good recording of a symphony in a good sounding auditorium sounds huge on headphones. Adding small-room ambience to that in the form of early reflections just drowns out the larger reverb. IMO, YMMV, etc.

--Ethan
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post #17 of 97
1/13/13 at 8:37am
Quote:
Originally Posted by Ethan Winer View Post


I will say that I find the notion that early reflections increase width and soundstage to be suspect.

--Ethan

+1
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post #18 of 97
1/13/13 at 8:46am
Quote:
Originally Posted by jim19611961 View Post

+1

+2. I think we can all agree that every room is different but the vast majority of room's and builds on these forums are just that... Rooms. As such I feel Ethan's advice is spot on and is advice that I have indeed applied using the information he has made available to the general public. If you are willing to read his site you can get a lot of complimentary information; Read: FREE! The improvements I have HEARD thus far have not been small and MOST of the benefits have been much better imaging, a wider and deeper soundstage, and better overall frequency response. All of this from simply treating first reflection points and diffusing the later reflections.
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post #19 of 97
1/13/13 at 4:47pm
Quote:
Originally Posted by dynfan View Post

+2. I think we can all agree that every room is different but the vast majority of room's and builds on these forums are just that... Rooms. As such I feel Ethan's advice is spot on and is advice that I have indeed applied using the information he has made available to the general public. If you are willing to read his site you can get a lot of complimentary information; Read: FREE! The improvements I have HEARD thus far have not been small and MOST of the benefits have been much better imaging, a wider and deeper soundstage, and better overall frequency response. All of this from simply treating first reflection points and diffusing the later reflections.

Like Ethan, I have tried different things at first reflection points. Bare wall, 2" Auralex studiofoam, 2" OC703, 4" OC703 with 4" gaps and 16" pink fluffy. Of all of these, bare walls had the most harmful effect on imaging. Additionally, the cleaner and longer my ISD gap, the better the imaging. Yes, all rooms are different. But early untreated reflections have similar consequences no matter what the room.
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post #20 of 97
1/14/13 at 8:10am
Quote:
Originally Posted by jim19611961 View Post

Additionally, the cleaner and longer my ISD gap, the better the imaging.

and the larger the perceived size of the reproduction space smile.gif
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post #21 of 97
1/14/13 at 10:12am
Quote:
Originally Posted by localhost127 View Post

and the larger the perceived size of the reproduction space smile.gif

In this line of thinking, would a 20ms terminated gap make it sound like your in a room 45 feet wide assuming the termination arrived from a lateral direction? (20ms = 22.5 feet x 2)
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post #22 of 97
1/14/13 at 1:54pm
Quote:
Originally Posted by Ethan Winer View Post

The notion of leaving reflection points bare is a "minority position" that is ignored by serious audio professionals. Virtually every professional recording studio control room either absorbs early reflections, or re-directs them away from the listening position. ...
Quote:
Originally Posted by Ethan Winer View Post

...I will say that I find the notion that early reflections increase width and soundstage to be suspect. ...
When making blanket statements, it would be helpful if one provided something other than one's own opinion, preferably something that's published in well-respected peer review publicaitons. Ethan, statements like these are the reason I call you a salesman, not a scientist.
Quote:
Originally Posted by jim19611961 View Post

+1
Quote:
Originally Posted by dynfan View Post

+2. I think we can all agree that every room is different but...
That others follow only compounds the problem.

Here's the fundamental problem: the data disagrees with your advice. Established data published 35 years ago (Y. Ando, “Subjective Preference in Relation to Objective Parameters of Music Sound Fields with a Single Echo,” J. Acoust. Soc. Am., vol. 62, pp. 1436–1441 (1977)).


(Taken from: http://www.aes.org/tmpFiles/elib/20130114/13686.pdf)

Preference for music improves when our ears hear different sound, and reflections provide that difference. Clearly, very early reflections are effective; you'd need a truly tiny room to have less than 10msec reflection delay (that's 11.3' path length).

Regarding speach intelligibility (Toole, same reference):
"Readers who have been keeping score will have noted a distinct absence of negative effects from reflections on any aspect of speech perception we have looked at. In fact, the effects range from neutral to positive. No single reflection has been shown to be a problem for speech reproduction in small rooms (see Table 1). Multiple early reflections contribute even more to intelligibility."
and (referring to J. S. Bradley, H. Sato, and M. Picard, “On the Importance of Early Reflections for Speech in Rooms,” J. Acoust. Soc. Am., vol. 113, pp. 3233–3244 (2003)):
"The result was that early reflections (<50 ms) had the same desirable effect on speech intelligibility as increasing the level of the direct sound. The authors go on to point out that late reflections (including reverberation) are undesirable, but controlling them should not be the first priority,"

Thus, the rational for including sidewall reflections is based on multiple studies by a number of investigators in various countries over several decades, or what one might call "scientific consensus." If Ando or Bradley were wrong, someone would have refuted his result, or at least published contradictory results. Please provide links to such references if you have them. Note that late reflections are not part of the discussion; we'll all agree that needs management.

Finally, under the heading of "Everything Has Its Place:"
"A long-standing belief, in the area of control-room design,
is that early reflections from monitor loudspeakers
must be attenuated in order to allow those in the recordings
to be audible. Consequently embodied in several standards,
and published designs, are schemes to deflect, diffuse,
or absorb at least the first reflections from a loudspeaker."

In his book Toole goes into this a bit more, as the needs of audio engineers are real, and are not the same as the listening public. When you're adding the reverb and other ambiance that Ethan mentions as some of the things engineers add to a program to increase enjoyment, you need to hear only what you put in. In studies Toole discusses, those same engineers, when listening for enjoyment, preferred the added side reflections.

Work vs Play - not the same. That was my original point; everything has its place...

Finally, I've tried to present data, not opinions. Please feel free to argue with the data... the Scientific Method gets to reality. As Schopenhauer said:
"The discovery of truth is prevented more effectively, not by the false appearance things present and which mislead into error, not directly by weakness of the reasoning powers, but by preconceived opinion, by prejudice."

Have fun,
Frank
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post #23 of 97
1/14/13 at 2:18pm
Quote:
Originally Posted by jim19611961 View Post

Like Ethan, I have tried different things at first reflection points. Bare wall, 2" Auralex studiofoam, 2" OC703, 4" OC703 with 4" gaps and 16" pink fluffy. Of all of these, bare walls had the most harmful effect on imaging. Additionally, the cleaner and longer my ISD gap, the better the imaging. Yes, all rooms are different. But early untreated reflections have similar consequences no matter what the room.
So... what do you mean by "better" imaging? What makes it "better?" Please be specific.

Reading how folks describe sound, I find two camps
- pinpoint imaging
- disappearing speakers

The former I associate with those who advocate high levels of room treatment and seem to prefer controlled directivity speakers. This camp talks a lot about dynamics...

The latter was the defining characteristic of the two "winners" on my sheet at InDIYana 2009, a Jim Salk MTM, and Jeff Bagby's Continuum.

So... what are you calling "better?"

HAve fun,
Frank
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post #24 of 97
1/14/13 at 2:52pm
Quote:
Originally Posted by fbov View Post

So... what do you mean by "better" imaging? What makes it "better?" Please be specific.

Reading how folks describe sound, I find two camps
- pinpoint imaging
- disappearing speakers

The former I associate with those who advocate high levels of room treatment and seem to prefer controlled directivity speakers. This camp talks a lot about dynamics...

The latter was the defining characteristic of the two "winners" on my sheet at InDIYana 2009, a Jim Salk MTM, and Jeff Bagby's Continuum.

So... what are you calling "better?"

HAve fun,
Frank

Fair enough.

I define better in the context of the comparison I outlined as:

1) Better pinpoint detail and clarity in the image
2) more "air" around the image
3) more space between images
4) deeper soundstage

Bare wall 1st reflection points revealed only the left speaker, the right speaker and a moderate middle. Images rarely were discernible outside of the speakers. Images between middle and the speaker were hazy and unclear.
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post #25 of 97
1/14/13 at 3:11pm
Seems we go around and around with this topic!

Personally I think speaker off axis performance is a strong indicator of the best type of acoustic treatment to use on a side wall.

Those listening tests summarized in AES were to my knowledge done in anechoic chambers using a speaker positioned at the angle that the side wall reflection would arrive from. This is NOT the same as putting any old speaker, especially a conventional forward firing cone / dome (which represent 99% of speakers out there) in a room as the side wall reflections do not have the same spectral content as the direct sound. Toole's WHOLE POINT (as far as I can tell from reading the book and talking to him personally) is IF you have well designed speakers, with smooth off axis performance then these listening tests referred to are relevant, as the spectrum reflected from the side wall will be very similar to the direct sound from the loudspeaker. Your ear sums the direct sound and reflections for all reflections arriving before 40ms. All the reflected sounds are added to the direct and that is what you hear. If your speakers have poor off axis performance with large frequency response dips off axis and you are not absorbing the sidewall reflections then what you hear is not going to be as timbrally correct as if you absorb the reflections.

Without referencing the type of speaker people are using and measuring it's off axis performance discussing 'what's best' to use at sidewalls is to me a non starter.

I do admit though that the generalization of 'apply absorbers to sidewalls' makes sense in reality for most people because their speakers have poor off axis response.

IF you have a speaker with nice off axis performance (which can be a conventional cone / dome, a constant directivity type or even a dipole) then you can get more creative with the side walls. To properly select sidewall treatments then becomes a case of evaluating:
a) speaker off axis performance - what is the spectrum at the angle of incidence
b) distance of the reflected path from speaker to listener in comparison with direct sound path - to understand the dB level of the reflection vs the direct sound
c) listener preference for balance of imaging vs envelopment in the soundstage

A cone/dome speaker with poor lateral off axis performance (B&W 802D):

A cone/dome speaker with good lateral off axis performance (YG Anat)
Edited by Nyal Mellor - 1/14/13 at 3:19pm
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post #26 of 97
1/14/13 at 3:27pm
Nyal, Even a speaker that had a perfect off axis (60 degrees) I wouldnt want a 8ms @ -5db reflection from (which is what I was getting in my room). Now put that speaker in a room where that first reflection point is at 18-20ms and -10db down, now were talking!

In a nutshell, my preference for absorbing the first reflection points is not only your point, but when it arrives and at what magnitude.
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post #27 of 97
1/14/13 at 3:36pm
Quote:
Originally Posted by jim19611961 View Post

Nyal, Even a speaker that had a perfect off axis (60 degrees) I wouldnt want a 8ms @ -5db reflection from (which is what I was getting in my room). Now put that speaker in a room where that first reflection point is at 18-20ms and -10db down, now were talking!

In a nutshell, my preference for absorbing the first reflection points is not only your point, but when it arrives and at what magnitude.

Jim, don't disagree with you at all. You know what you are doing. Personally I don't subscribe to ISD but have no problem with people following a 'small room acoustical model' as Dragon puts it smile.gif

However if you have speakers with good off axis performance you can try leaving the side wall reflections as is, and choose for yourself which you prefer. It's quite an easy listening test to undertake!!

If your speakers have poor off axis performance (like most out there), then you have be more careful about what you are doing with the sidewalls in terms of the acoustic treatment strategy you are using.
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post #28 of 97
1/14/13 at 3:37pm
Quote:
Originally Posted by fbov View Post



Preference for music improves when our ears hear different sound, and reflections provide that difference. Clearly, very early reflections are effective; you'd need a truly tiny room to have less than 10msec reflection delay (that's 11.3' path length).

11.3' feet PLUS the speaker to ear distance. Now you need a large room indeed for a 10ms delay. And frankly, that is not long enough in my book to begin with.
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post #29 of 97
1/14/13 at 3:45pm
Quote:
Originally Posted by Nyal Mellor View Post

Personally I don't subscribe to ISD ...

Why not?
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post #30 of 97
1/14/13 at 5:45pm
Quote:
Originally Posted by fbov View Post

So... what do you mean by "better" imaging? What makes it "better?" Please be specific.

HAve fun,
Frank

http://www.audiocheck.net/audiotests_ledr.php
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