The Room Acoustics Master Disagreement Thread - AVS Forum
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post #1 of 55 Old 04-26-2012, 03:51 PM - Thread Starter
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It seems that there is not consensus on how one approaches the topic of room acoustics. As such, threads asking for advice seem to immediately generate deep discussions, full of jargon, that do not appear to converge. This may lead to frustration by the person asking the original question, having had hopes of simple answers.

So I thought it might be useful to have a general thread where these deeper discussions can be redirected to and as such, can be the full archive of the positions taken as opposed to being spread and repeated across many discussion threads.

This has been requested by a number of people so if the thread doesn't get traction, then we know the will of the community is to have them occur as they do now . So vote with your keyboard if you like this central place to hash out the major disagreements in this area.

For this thread to have long term value, it needs to remain open. As such professional conduct is requested. The topics are near and dear to many's heart to be sure. But there is no reason why we can't stay focused on the topic as opposed to the person. The vocal members among us put a ton of work in these posts. Let's not have them go to waste by having the thread locked.
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post #2 of 55 Old 04-26-2012, 03:54 PM
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I must say, I had to do a double take when I saw the title to the thread. Hopefully, will be interesting.
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post #3 of 55 Old 04-26-2012, 04:16 PM - Thread Starter
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OK, without any rhyme or reason , I am going to make this the first post, seeing that it is another deep dive . This discussion started on how to determine the effectiveness of Fiberglass as an absorber. Position was taken that higher density means more effectiveness. Dragon/Localhost are opposing that saying that it it is the gas flow resitivity that determines that. I agree with that but not fully with the following:

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Originally Posted by dragonfyr View Post

Seeing as we do not smoke, a good thing. But I might suggest others lay off smoking stuff until they gain a more complete understanding of the causal relationship between gas flow resistivity and absorption, the behavior of perforated plates for use in noise abatement and control, and jettison the notion of density, which only accounts for how much stuff is available per unit volume but utterly fails to account for the critical factors of how such mass is distributed within said unit volume - unlike gas flow resistivity which via its focus on porosity and tortuosity, and their effects on the acoustical impedance of a material, does.

Do us all a favor, and before trotting out another ill-formed case for density being a determinant causal basis for evaluating the absorptive behavior of porous material, PLEASE read Acoustic Absorbers and Diffusers and learn a bit about the physics of how the material actually works. And then, if one is really brave, they can actually access the various studies and models upon which the prediction and modelling of the materials performance are based.

This topic is done.

Well, the topic is not done . [bolding mine] While it is true that gas flow resistivity may not be proportional to density for all material, it is in the case of fiberglass. Dragon is requesting that we use D'Antonio and Cox's text above as a reference in this matter. So let's do that:

Page 170: "Bies and Hansen showed that fibrous materials have an approximately linear relationship between flow resistitivy and density, but this is not necessarily true for foam."

Bies and Hansen are authors of the book, Engineering Noise Control: Theory and Practice. This is what they have to say: (Page 54)

"For fiberglass and rockwool fibrous porous materials, which may be characterized by a mean fiber diameter, d, the following relation holds (gives forumula). In the above euqation, in addition to the quantitities already defined, the gas density, p, the porous material bulk density, Pm, and the fiber material desntity, Pf, have been introduced... The dependence of flow resistance on bluk density, Pm, and fiber diameter, d of the porous material is to be noted."

And this from Dr. Tool, quoting D'Antonio on this topic:

"For optimal absorption, a porous absorber should offer a surface impedance with a low flow resistivity, which matches that of air to remove reflections, while offering a high internal acoustic attenuation. When attempting to control reflections with a single density material, it is fair to say that thin fiberglass panels should not be used, and in my view lower density is preferred over higher density. In addition, thicker panels and a rear air cavity both contribute to extending the absorption to lower frequencies."

So it seems one way or the other, when it comes to fiberglass, density is a proper term to use to describe effectiveness, albeit, in an inverted way relative to what we might intuit in that more is not better.

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post #4 of 55 Old 04-26-2012, 07:30 PM
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+1 Amir.
I'd like to suggest the people who post here follow the 3 R's that are taught to my elementary school kids.
I just came back from my 4th grade daughter choir concert, they sang a song with these in it:
-Reason
-Respect
-Responsibility

I could have instead said "lets follow the NSPE Code of Ethics for Engineers ", but the 3 R's are simple and straight forward.
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post #5 of 55 Old 04-26-2012, 07:44 PM
 
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amirm, who is or are master/s the title refers to? If not who, then what's master about it?
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post #6 of 55 Old 04-26-2012, 08:28 PM
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Well that didn't take long for someone to try to derail the thread. Honestly - if you don't want to contribute with any actual content then why bother posting?

Here's my contribution - it seems to me if we can't agree on how to "best" treat a room (because there almost certainly is no single "best" solution) then I wonder if it would be instructive to at least itemize the different acoustical parameters of a small room, and try to describe how those parameters affect the sound we hear in that room. (by that I mean try to describe what one extreme or the other of that parameter sounds like)

Or perhaps some text has already presented this information succinctly?
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post #7 of 55 Old 04-27-2012, 10:18 AM - Thread Starter
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Quote:
Originally Posted by kromkamp View Post

Here's my contribution - it seems to me if we can't agree on how to "best" treat a room (because there almost certainly is no single "best" solution) then I wonder if it would be instructive to at least itemize the different acoustical parameters of a small room, and try to describe how those parameters affect the sound we hear in that room. (by that I mean try to describe what one extreme or the other of that parameter sounds like)

Or perhaps some text has already presented this information succinctly?

Nothing wrong with reinventing the wheel . How about listing the areas of disagreement? I think they are mostly the same as what you are asking:

1. What is the priority order? Room response is different below 200-400 Hz than above. So clearly strategies and impact are different.

2. Reflections. What and why to treat.

3. Multi-use rooms. Do they need purpose built acoustic treatment? How can we tell if they need anything at all?

4. Speakers. That is the thing that excites the room. Surely it matters what it does relative to our optimization goal here.

5. Different acoustic material. Why use one vs the other? And performance within types.

6. Pro/recording/mixing studio practices vs home. How applicable are they to home use? Do we hear like they do and have the same needs?

7. Related to above, the "room models" practiced in pro industry. Why were they created and do they have applicability to home use?

8. Measurement systems to figure out what to do. Analysis tools exist that show what happens in "time domain" as you spike the room, and watch what comes back. The counterpart to that is frequency domain where we see the familiar frequency response chart. Which should be the tool of choice and why?

9. Electronic correct; automatic and otherwise. Are they better than we think they are or worse? What problems do they solve? And what problems can they create?

10. Who is right? I say that half seriously. There are lot of industry experts. Yet they don't seem to agree often. I sat through two separate training sessions at CEDIA. One by Dr. Toole and another by one of the most popular theater designers. The latter's advice at times conflicted what Dr. Toole said. When I asked him about it, he simply said they disagree. Clearly few of us are positioned in a way where we can gain the hands on experience that these people have. So ultimately you do need to decide whose teachings are your general guiding principals of what is right. Without it, you are trying to integrate data from multiple sources which may be in conflict.

11. What is the science that guides us here? We need to get to a simplified version of that if this topic is ever going to make sense. I am confident few people want to go and compute "gas flow resistivity" to figure out what needs doing . The one-liner though that density tells us that for fiberglass is what we need.

12. What are the definitive references so that when we are invariably challenged, we can put forward authoritative data that says we are right beyond our opinion? Can we agree on what that is?

I will pause here and see what reaction folks have .

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post #8 of 55 Old 04-27-2012, 11:13 AM
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Thanks for doing this Amir. I agree a calm on-point discussion is always the best approach. One thing I didn't see mentioned in your lists is that the size of the room also affects the treatment strategy. The ideal treatment for a 25 by 35 foot great room is very different than for a 10 by 12 foot bedroom.

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Originally Posted by amirm View Post

1. What is the priority order? Room response is different below 200-400 Hz than above. So clearly strategies and impact are different.

It's all important. The only reason to begin with this versus that is when someone can't afford to treat everything all at once, and so has to start somewhere. I used to say start with bass traps, but these days I suggest starting with reflections since that affects clarity over a larger range of frequencies.

Quote:
2. Reflections. What and why to treat.

You missed and how to treat. Why treat? To avoid echoes and comb filtering that muddy the sound.

Quote:
3. Multi-use rooms. Do they need purpose built acoustic treatment? How can we tell if they need anything at all?

All rooms benefit from some amount of treatment. I've never seen a room that would not benefit. If it's very small the bass range is a big problem. If it's very large there's too much reverb.

Quote:
4. Speakers. That is the thing that excites the room. Surely it matters what it does relative to our optimization goal here.

All speakers are different, and flawed in some way, and people's preferences are a factor. So I mostly stay out of that.

Quote:
5. Different acoustic material. Why use one vs the other? And performance within types.

Cost baby, cost.

Quote:
6. Pro/recording/mixing studio practices vs home. How applicable are they to home use? Do we hear like they do and have the same needs?

Yes, same goals and needs. I see no functional difference between a recording studio control room and a home listening room.

Quote:
8. Measurement systems to figure out what to do. Analysis tools exist that show what happens in "time domain" as you spike the room, and watch what comes back. The counterpart to that is frequency domain where we see the familiar frequency response chart. Which should be the tool of choice and why?

A waterfall plot shows both. I use that for bass frequencies, and 1/3 or 1/6 octave averaged plain response for mids and highs. Those two graph types, plus RT60 by third-octaves, tell all that's needed, though an ETC can help identify where problem reflections might be coming from.

Quote:
9. Electronic correct; automatic and otherwise. Are they better than we think they are or worse? What problems do they solve? And what problems can they create?

I'm okay with using EQ to reduce the one or two worst peaks at very low frequencies. Any other application of room EQ is misguided IMO.

Quote:
10. Who is right?

Well I am of course!

Quote:
I sat through two separate training sessions at CEDIA. One by Dr. Toole and another by one of the most popular theater designers. The latter's advice at times conflicted what Dr. Toole said. When I asked him about it, he simply said they disagree.

There is an art to room "setup" (all things related to the room's acoustics), but in the end the goal is always the same: A flat response with minimal ringing and echoes.

Quote:
11. What is the science that guides us here?

Programs like Room EQ Wizard reveal all of the problems.

Quote:
12. What are the definitive references so that when we are invariably challenged, we can put forward authoritative data that says we are right beyond our opinion? Can we agree on what that is?

Toole's latest book, and my latest book.

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post #9 of 55 Old 04-30-2012, 11:54 AM - Thread Starter
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I am answering this here.
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Originally Posted by localhost127 View Post

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.

Correct on some level. Real products for example could be reflective at higher frequencies that the simulations using perfect material construction does not pun intended, reflect . Fortunately in this case Arny was saying that modal resonances at 30/60 Hz could be solved with a 2 inch panel with 4 inch air gap and simulations show the ineffectiveness just the same.

Quote:


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...

That's right. They are based on rockwool material. More below.

Quote:


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?

Since you are a user of said software, would you be kind enough to post it with OC705?

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post #10 of 55 Old 04-30-2012, 12:03 PM
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I would like to see a discussion around can there be too much treatment? If you primarily use if for multi-channel movies and music does that differ as to whether you want a more lively room or a more dead room? How much does the profit motive affect expert's opnions? In other words, should we be leery when someone suggest that you need to "treat your room" and they have just the right product to do that?
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post #11 of 55 Old 04-30-2012, 06:13 PM
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Quote:
Originally Posted by Randy Bessinger View Post

I would like to see a discussion around can there be too much treatment? If you primarily use if for multi-channel movies and music does that differ as to whether you want a more lively room or a more dead room? How much does the profit motive affect expert's opnions? In other words, should we be leery when someone suggest that you need to "treat your room" and they have just the right product to do that?

No doubt in my mind you can over damp a room in the upper frequencies. But that is just because it is so hard to damp the lower frequencies. I'm assuming home sized room. I cover my big bass traps with a thin layer of plastic so the room is not too dead at high frequencies. But that is just my opinion. I have no basis in fact. I have no theory or science to explain why an overdamped room might sound bad - I just know that it did to me.

I recommend using first reflection point absorbers as thick as your room can handle (at least 4-6"). Then as many big blocks of "porous" absorber as you can fit (if the room sounds too dead, cover the surface of them with thin plastic - I use 50 gal garbage bags).

At least that has been my experience using a "703" like product.

I suspect we are trying to replicate outdoors (or a large concert hall), but we live in small boxes. Perhaps what I'm trying to do is get approximately the same decay time for all frequencies. But since it is so much easier to absorb high frequencies, more attention has to be paid to not over absorb it.

One thing I see people do, which I think is a mistake, is enclosing their first reflection point absorbers in a wood frame. By leaving the sides and top open you are providing a longer path to absorb bass frequencies that for reasons, not entirely clear to me, seem to propagate along room boundaries. With a typical 2'x4'x6" panel it is shame not to have that 2' and 4' depths available to absorb the more difficult bass regions.

I think the room/speaker issue is a matter of personal taste. You can't tell me scientifically why you like the music you like - or why certain instruments sound good to you. In part in might be what you are accustomed to. And might evolve with time. To me the speaker/room thing is about the same - it is almost like a musical instrument, one you can change to suit your preference.

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 #12 of 55 Old 04-30-2014, 09:41 PM
 
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Good thread. its a shame it died out.

In weight of options, I noted that diffusion was given little if any consideration.

A sonic experience is based on a position of observation (or sample), therefore one should focus their efforts on regulation of energy in such areas. Diffusion permits a 'scattering' of sonic energy, which greatly mitigates many types of nulls and troughs. Combining absorption techniques, with that of diffusion techniques always brings about superior outcomes, for prescribed positions of observation/audition.

Smartly done, home furnishings and décor products and be aligned to deliver audible improvements, without making the living space look like an acoustic lab (studio environment).

I understand that many appreciate the cosmetics and sonic benefits of studio like environments, I happen to be one of them; but having a lot of natures sunlight, a decent view and a space that many can appreciate and enjoy with me, is becoming more important...
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post #13 of 55 Old 04-30-2014, 09:44 PM - Thread Starter
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It was quite puzzling to see people not want to participate. Perhaps asking to be cordial was the thing that was hard to comply with. Who knows.

Thanks for refreshing the thread smile.gif.

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post #14 of 55 Old 04-30-2014, 09:54 PM
 
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You might be right. I noted a fair sum of aggression around these parts. But so fair, more decent apples then rotten ones. A little game, can be fun - a little...
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post #15 of 55 Old 05-01-2014, 06:59 AM
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I posted a link to this thread in the Kung fu dojo thread.....mc2ed is that how you got here?
Anyway let's see what discussion ensues.


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post #16 of 55 Old 05-01-2014, 11:35 AM
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Quote:
Originally Posted by dknightd View Post

No doubt in my mind you can over damp a room in the upper frequencies.
Quote:
I suspect we are trying to replicate outdoors (or a large concert hall), but we live in small boxes. Perhaps what I'm trying to do is get approximately the same decay time for all frequencies.
Two somewhat conflicting statements there. You can't get more "overdamped" than outdoors, which is basically anechoic. An "outdoors" acoustic is quite different from a large concert hall.

Personally, the best-sounding concerts I have experienced were outdoors. I do have emotional attachments to some indoor "concert hall" events, though. To my mind, the best solution in the home is to make a go at an anechoic (outdoors, "lab") listening space, and then supplement that with DSP-generated effects radiators that can be managed to emulate the desired acoustic for the material or mood. In the end, as pointed out, it's a matter of taste....
Quote:
I think the room/speaker issue is a matter of personal taste. You can't tell me scientifically why you like the music you like - or why certain instruments sound good to you. In part in might be what you are accustomed to. And might evolve with time. To me the speaker/room thing is about the same - it is almost like a musical instrument, one you can change to suit your preference.
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post #17 of 55 Old 05-01-2014, 01:36 PM
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Quote:
Originally Posted by amirm View Post

Perhaps asking to be cordial was the thing that was hard to comply with.

LOL, so true! And not just here. biggrin.gif

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post #18 of 55 Old 05-01-2014, 01:45 PM
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I've never believed the thermal absorption concept. If that was true then steel wool would be FAR more effective than any organic material or fiberglass. I agree with those suggesting its impedance of gas movement not dissimilar to aperiodic vents.
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post #19 of 55 Old 05-02-2014, 10:38 AM
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The great thing about science is that it's true whether people believe it or not. biggrin.gif

For all I know steel wool is a good absorber. I never tested that. But there's no question that acoustic energy is converted to heat energy by the absorption.

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post #20 of 55 Old 05-02-2014, 12:16 PM
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Quote:
Originally Posted by Ethan Winer View Post

The great thing about science is that it's true whether people believe it or not. biggrin.gif

For all I know steel wool is a good absorber. I never tested that. But there's no question that acoustic energy is converted to heat energy by the absorption.

--Ethan

Anyone tested this theory? If not then why not?
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post #21 of 55 Old 05-02-2014, 03:07 PM
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Quote:
Originally Posted by Ethan Winer View Post

The great thing about science is that it's true whether people believe it or not. biggrin.gif...

--Ethan

Fantastic objectively correct statement.

Belief is an extremely powerful force. If someone believes it then it is true to them no mater what the (science) facts say and science is independent of subjective beliefs. Beliefs do not make facts.
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post #22 of 55 Old 05-02-2014, 03:25 PM
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Room treatment should align with pre-described goals. While we could debate how to treat a room, I think the more useful narrative might be what the design goals should be. And of those, the most controversial is in the area of reflection control.

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post #23 of 55 Old 05-02-2014, 03:39 PM
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Quote:
Originally Posted by Ethan Winer View Post

The great thing about science is that it's true whether people believe it or not. biggrin.gif


--Ethan

I agree. But is psycho-acoustics real science given its dependance on subjective accounts for much of its research? If its not or in theory cant be, then are we back in the stone age?

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post #24 of 55 Old 05-02-2014, 03:41 PM
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Quote:
Originally Posted by jim19611961 View Post

Room treatment should align with pre-described goals. While we could debate how to treat a room, I think the more useful narrative might be what the design goals should be. And of those, the most controversial is in the area of reflection control.
The reason it's controversial is that acoustical tastes vary so widely as to be, at times, irreconcilable. This is why, for all of the measurement science thrown at it, professional acousticians have to be psychologists and politicians in addition to architects/audiologists: they are often trying to appeal to diametrically opposed clients and situations.

Disney Hall in LA is a prime example. The Japanese acoustician hired to design/treat/tune the place created an extremely live space. It's great if you're a string player, or a diva, or a front-row-center season ticket holder: you revel in the tastefully demure reverberations that embellish these delicate acoustical instruments with a heavenly aura.

But if you're someone with a livelier instrument who is looking for precise articulation of notes -- Keith Jarrett, say -- you're confounded by the hopeless muddle of sound that everyone who is not FRC experiences. (An exasperated Jarrett described Disney Hall as a "giant toilet bowl, where the sound just whooshes and swirls around and around....")
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post #25 of 55 Old 05-02-2014, 03:56 PM
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The reason it's controversial is that acoustical tastes vary so widely as to be, at times, irreconcilable. This is why, for all of the measurement science thrown at it, professional acousticians have to be psychologists and politicians in addition to architects/audiologists: they are often trying to appeal to diametrically opposed clients and situations.

Disney Hall in LA is a prime example. The Japanese acoustician hired to design/treat/tune the place created an extremely live space. It's great if you're a string player, or a diva, or a front-row-center season ticket holder: you revel in the tastefully demure reverberations that embellish these delicate acoustical instruments with a heavenly aura.

But if you're someone with a livelier instrument who is looking for precise articulation of notes -- Keith Jarrett, say -- you're confounded by the hopeless muddle of sound that everyone who is not FRC experiences. (An exasperated Jarrett described Disney Hall as a "giant toilet bowl, where the sound just whooshes and swirls around and around....")

Its the subjective human element that makes the statement "Here is how to treat your room and how to go about it" an impossible one to make. Perhaps the most we can accomplish is to steer folks to a fairly flat FR (or house curve), avoid the worst of what modes do to small spaces, and good decay characteristics in the bass region.

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post #26 of 55 Old 05-02-2014, 04:10 PM
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Fair enough...

But for me, personally, I take the absolutist position here. Which is to say, "good decay characteristics in the bass region" are "good" to the extent that they approach the ideal: The Great Outdoors.
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post #27 of 55 Old 05-02-2014, 04:28 PM
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Quote:
Originally Posted by PrimeTime View Post

Fair enough...

But for me, personally, I take the absolutist position here. Which is to say, "good decay characteristics in the bass region" are "good" to the extent that they approach the ideal: The Great Outdoors.

On that note, it might be interesting to establish what the Good, the Bad and the Ugly are in terms of measured decays in typical rooms. That is to say, point to targets. For example, ive read that getting down to 40hz to decay to -20db at 300ms is a "good" decay rate. Compared to outdoors, that might be downright Ugly though wink.gif

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post #28 of 55 Old 05-02-2014, 04:33 PM
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As a practical matter, I think that "good" bass performance in a room is defined as the point at which the person attempting to improve it has (1) done everything conceivable to absorb bass, (2) decides to draw the line at knocking out the walls, because (3) he wants to stay married.
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post #29 of 55 Old 05-03-2014, 11:18 AM
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is psycho-acoustics real science given its dependance on subjective accounts for much of its research?

It's probably real science if you use large enough group of listeners to obtain a statistically significant "opinion" of what sounds good. But in this case the issue is how much one material absorbs versus another. And that of course is purely objective.

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post #30 of 55 Old 05-03-2014, 11:27 AM
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Quote:
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It's probably real science if you use large enough group of listeners to obtain a statistically significant "opinion" of what sounds good. But in this case the issue is how much one material absorbs versus another. And that of course is purely objective.

--Ethan

I suppose it depends on what we define as real science. Dr. Lawrence Krauss, a theoretical physicist, has said that if one time in a hundred you get a contradictory result, then its not science. That criteria would rule out much we assume to be scientific in regards to this topic.

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