[PhilNYC]

Where can I find this Carl Saunders recording?  I looked at his website, and it's not in his discography...

[8thnerve]

Ok, I'm still not getting something here.  Check out these tiles:

http://www.truesoundcontrol.com/products/VERST24.html

They don't list much data about them, other than representative NRC.  Why would I buy your system over these tiles, especially since these tiles will cover 48 lineal feet?  (And I ask this question because I have a beam that is parallel to my speakers and needs to be treated; I'm just trying to figure out what to buy to treat it.)

As for whether to treat first reflection points or the corners, I do believe that corners would be better to treat.

Those products will do nothing to treat corner distortion.  There is no reflective surface, it is simply a fancy shaped foam product.

I'm not asking anyone to take me word for it.  There is a 30-day money back performance guarantee, and no one that has installed the product has ever returned it.

[Eric D]

Certainly questionable. I keep thinking of the proof that a bumblebee can't fly. With 3.8 hours, is sounds like an error in the equation.

I can't say that I disagree with that - hence my laughter.  But then again - have you ever listened to thunder roll through the mountains?  Hmmmmm.

I am admittedly writing this as an audio noob, certainly NOT as an expert in the field.  And in no way to I mean to question the effectiveness of treatements in general or anything specific, or Nathan's audio engineering abilities for that matter.

My core problem with the model suggested was that was/is deriving an "ideal rooms" maximum RT60.  Nathan's chain of logic showed that RT60 for "any given space cannot exceed 6/100ths of a second."  He didn't buy that amount himself.  I was offereing another way to get there that gave answers that exceed his derived max.  I think both he and I would agree that the real world values can only be less than the ideal.

I don't believe RT60 only exceeds 0.06 sec. for resonant frequencies.   Yes, my values are somewhat larger (), but remember they are *ideal*.  The inverse square law *does* apply to reduce the intensity of the sound from the moment it is generated at the speaker until it fills the room.  Interactions at the room boundries (walls, carpet, furniture, people, etc) absorb a lot of energy.  And then there's what "leaks" out of whatever openings there are, or even possible Helmhotz resonator effects.  All of these will quickly bring my "not to exceed" values down to what you should experience in a real-world situation.

Still hoping refine this model to explain that bumblebee.  

enjoy,

[John Casler]

It looks like we will have to agree to disagree on most of these points. I am not saying that you do not have a grasp of the current understanding of room acoustics, I am saying that the current understanding of room acoustics is wrong.    

That is interesting!!  

But let me be clear on what I think we disagree on, and I would love to know "how" it is wrong.

You state:

Exposed absorption ALWAYS overattenuates high frequencies leaving you with a bottom heavy frequency response. By overattenuating high frequencies, you reduce much of the areas of the frequency bands where distortion is most apparent, which is percieved as the reduction of echo, and the increase of detail.

To be more clear, I agree that absoption attenuates "reflected" HF.  Additionally I am not saying to treat HF only, but suggest a "broad band or full spectrum" approach.

I also suggest that attenuating "reflected" frequencies, makes the perception of "direct" frequencies, more correct in FR, Amplitude, Detail, and Dynamics.

Are you saying that "mixing" reflected room sonics "adds" accuracy?

The point is, it's not a matter of "using" the reflected wave. Reflection is part of the system, whether it fits in with our ideals of how sound should be reproduced or not, and it is even a bigger part than the direct wave itself. And since most of the sound we hear is reflected sound, exposed absorption rolls off the high frequencies for the sounds we hear. What we hear is the sound we are concerned about, isn't it?

The actual point is "how much damage/distortion", reflected sound produces, and how much more you can hear of the original without it.

I have done "thousands" of hours of highly critical listening over tha last 40 years and I know what differences I can hear.

I can walk into any room and "hear" it behind the recording.  It's like trying to view the Mona Lisa, through a dirty window with light reflecting off it.

"What we hear", is certainly what we are concerned about, but most like to think they "lean" towards accuracy, not re-mastering or adding to the original.  Every other component in the system is generally selected for accuracy to the signal.  The room should be no different.

The "most of the sound we hear is reflected" argument, is not valid, and went out with Bose 901's.  It is only valid at the original venue, not in reproduction.

The bridge film is worth seeing, it is a standard physics example of resonance. A large suspension bridge starts swaying then twisting a full 90 degrees over the course of a minute or so and eventually breaking and toppling down, all because the wind blowing across the bridge excited its resonant frequency amplifying the effect of the wind. Amplification is the key here.
   

I have seen the video many times and agree it shows how wind energy can create specific resonance, and it more accuratly depicts how the reed works on a sax or clarinet, but it doesn't explain why we have dips and peaks in the listening room.

But nodes and modes are dips and peaks of sonic energy, based on energies summing with, or opposing each other.

It is true that the creation of such is based on the room geometry, but it isn't magical, it is simple energy affecting energy, to the plus or minus.

Maybe I have a unique explanation, but I am unaware of any more simple that demonstrates it.

 My entire reponse to this of course can be seen above. It is a nice ideal, and it sounds good on paper, but anyone who has listened in an anechoic chamber will tell you that it does not in fact sound natural, and does not sound like "you are there." This leaves us with only one conclusion, that we do not yet understand what is necessary to recreate the original event, and until we start looking at things differently, we won't make any progress.  

Again I must respectfully disagree.  This "rumor" about an anechoic chambers and "listening" is false, and generally perpetuated by those who have not critically listened under anechoic conditions or near anechoic conditions in any "serious' way.

I have spent hundreds if not thousands of hours performing critical listening this way, and can assure you that if you under stand that when there is "no sound" there is supposed to be "no sound" then you will be OK.

That is, many might find it "foreign" to NOT HEAR their room.

My chambers have been self constructed, and supplemented with hours of "outdoor" (no walls or ceiling) listening, which is also anechoic.

 I can assure you, that the purity on good recordings, is beyond description.  The detail, tone, soundstage, depth, imaging and most every other desired performance parameter is by magnitudes more accurate than more reflective and interactive environments.

While many of these qualities can be enjoyed (maybe to a lesser degree) in a well treated room, the goal would see to be to strive to "approach" elimination of room created sonics.

And while I have had some contend that they had "experienced" an anechoic environment, they all have admitted that they have not performed any "serious" audiophile listening with reasonable gear under such conditions.

An Anechoic Environment to original recording is like a "Totally Darkened" theater to a motion picture.

[John Casler]

Where can I find this Carl Saunders recording?  I looked at his website, and it's not in his discography...

Hi Phil,

Look here:

http://www.audiohigh.com/lines/blueport/blueport.html

The picture below is during practice, and the actual show was recorded a bit to the right and als engineered that way.

The trumpet will be center stage, with drums far right.  The sax will be midway between the drums and trumpet. The trombone will be to the left of the trumpet, and the Piano will be on the left with the Bass behind it.

On a well set up system in a good room, it is a magic carpet.

[8thnerve]

In a "a fully reinforced environment where sound can travel in only one direction without expanding," the wave quickly becomes a plane wave, and ideally does not dissapate at all (think waveguide). And by a quirk, (I love physics and it's quirks, or was that quarks?), that is the same condition for an enclosed box, as long as all reflections are ideal.

I'm not sure which of your links supports this.  From the NDT Resource center you linked to:

When sound travels through a medium, its intensity diminishes with distance. In idealized materials, sound pressure (signal amplitude) is only reduced by the spreading of the wave.

Air is by no means an idealized material, and as is mentioned in the first sentence, sound diminishes with distance.  The second sentence is additive information, not alternative.  For instance, sound travels much faster in water, and therefore decays much slower over distance.

I *believe* your -3dB/meter refers to the intensity of a cylindrical sound wave rather than the propagation in a cylinder. This is how a wave behaves when it is captured between two plates (think sonar in a *shallow* ocean). There is definitely application for this in rooms, but I don't think in how you used it.

Sound traveling in a cylinder is a cylindrical sound wave by defenition.  And your example is absolutely accurate and applicable to what I am saying.  The transfer of motion from one air molecule to the next requires energy.  The more molecules that are transfered to, the less energy each of these target molecules have.  A cylinder is an environment for sound travel where the wave front has roughly an equal amount of particles to transfer energy from and to. (A given slice of the cylinder contains roughly the same amount of air molecules as the next slice, and so on)  It is essentially a 1 to 1 transfer of energy, and during that transfer energy is lost at the rate of 3db per meter in air.  (this is a widely known and accepted figure)  The application for this in rooms is that the decay rate of sound in air given a 1:1 ratio in total source air molecules to total target molecules is 3db per meter.  Once all of the air molecules of the room are excited, you essentially have a 1:1 transfer ratio for continued sound propagation, or -3db per meter.

The calulator you are using is giving you funny values because it is a calculator for absorption of sound by the atmosphere, and is under the environmental modeling section of that site.  These numbers are not applicable.  If it really took 3.8 hours to dissapate a 20 Hz wave, we'd never be able to listen to anything!

My core problem with the model suggested was that was/is deriving an "ideal rooms" maximum RT60. Nathan's chain of logic showed that RT60 for "any given space cannot exceed 6/100ths of a second." He didn't buy that amount himself. I was offereing another way to get there that gave answers that exceed his derived max. I think both he and I would agree that the real world values can only be less than the ideal.

I don't believe RT60 only exceeds 0.06 sec. for resonant frequencies. Yes, my values are somewhat larger, but remember they are *ideal*. The inverse square law *does* apply to reduce the intensity of the sound from the moment it is generated at the speaker until it fills the room. Interactions at the room boundries (walls, carpet, furniture, people, etc) absorb a lot of energy. And then there's what "leaks" out of whatever openings there are, or even possible Helmhotz resonator effects. All of these will quickly bring my "not to exceed" values down to what you should experience in a real-world situation.

Since those numbers you were using are not applicable here, we need a way to decrease the rate of decay rather than increase it.  Many things in the room will in fact increase the rate of decay as they absorb sound energy.  As I said before, in order to decrease the amount of decay, we need to add energy to the sytem.  The only way to add energy to the system is by means of amplification.  Resonant frequencies are ONE of the forms of amplification, and the corners, which are horns, are another form of amplification.  And these corners amplify the sound hundreds of times before a half second has passed, hence the RT-60 time of the same.

[PhilNYC]

An Anechoic Environment to a Stereo Listening room is like a "Totally Darkened" theater to a motion picture.
 [ ...

Is this a good thing?  Just as most filmmakers are going to light their sets and expose their film in a way that is going to look the best in "normal" movie-viewing circumstances (which is not a "totally darkened" theater), I would guess that most recording engineers don't record things to sound best in an anechoic listening environment...

Oh..thanks for the CD info!

[8thnerve]

The "most of the sound we hear is reflected" argument, is not valid, and went out with Bose 901's. It is only valid at the original venue, not in reproduction.

Saying that most of the sound we hear is not reflected based on the sonic qualities of the Bose 901 speakers is a little naive, don't you think?  The math is simple and the physics are clear.  An RT-60 time of 0.5 seconds means that the overall rate of decay is -0.35db per meter.  This means that every 0.003 seconds we are bombarded by another reflection that is only -0.35db quieter than the previous.  A perceptible difference in sound level is defined at 3db.  That means that until the sound seems just a tiny bit quieter to us, -3db, we hear 10 reflections of the sound at perceptibly the same level, and all these occur within 0.03 seconds.  At 0.3 seconds, we have heard over 100 reflections, the quietest of which is -30db, still very audible.  How is this not listening primarily to reflected sound?

Your assertations that you have listened to a hi-fi system in a truly anechoic chamber have not been clear.  Your listening room is far from an anechoic chamber, and most anechoic chambers are not truly completely without reflection, they decay at a significant enough rate that they are considered anechoic. It is engineering after all.  And besides, even if there were a perfect anechoic chamber where you would only hear the "direct sound wave", your very presence in it would cause reflections, as would the speakers, etc.

Also, listening outside is not an anechoic chamber.  Outside measurements from a high enough point can be accurate enough for certain types of readings, but by no means is it anechoic, as even the ground is reflective.

I understand that you enjoy listening to music in a LEDE environment, and good for you.  I find it hard to believe however that you can stand on your soapbox and flat out proclaim that it is the only way to accurately listen to music based on your knowledge of some acoustic engineering principles and "40 years of experience."  40 years of breathing wouldn't make me an expert on the molecular makeup of air.

I am sorry if I seem harsh, but I must admit that I am a little curious as to why you inject your theories into a thread where people are asking me how my products work.  This isn't the first time, and I'm not the only acoustics manufacturer you have done this to.  You certainly have a right to your opinions, and to share them.  But to push them over and over, when they are not solicited is frankly a little strange.  I do not refute every post that you put up which are many and that I obviously disagree with.  I answer direct questions as frankly and honestly as I can.  You know, I do design acoustic products for a living, and some people really seem to like them.  I must not be entirely wrong, ya know?

[Hantra]

JCC:

Nice review.  I am looking forward to getting my own Adapt setup to replace my current 8th Nerve treatements.  

I tend to trust my ears versus my calculator and the very limited amount of knowledge available on acoustic theory.  I am positive that what all of us combined know about acoustics and the phyiscs of sound pales in comparison to what we do not yet know.

L8r,

B

[John Casler]

An Anechoic Environment to a Stereo Listening room is like a "Totally Darkened" theater to a motion picture.
 [ ...

Is this a good thing?  Just as most filmmakers are going to light their sets and expose their film in a way that is going to look the best in "normal" movie-viewing circumstances (which is not a "totally darkened" theater), I would guess that most recording engineers don't record things to sound best in an anechoic listening environment...

Oh..thanks for the CD info!

Hi Phil,

That is an excellent question and might illustrate how this can sometimes get confusing.


The "making of a film" is like the "making of a recording".  

Lighting ambience to that film, might be likened to the acoustic ambience of the recording venue.

The perfect reproduction of video is accepted to be in as dark a room as possible, since the most difficult color to produce is black.  Black is a light dynamic representing the smallest amount of light.

It would seem to me that damping a room as much as possible would be the counterpart to sonics, since the most difficult dynamic to produce in a room would be "no sound".  

To me, sound reproduction is most accurate in a "sonically damped" room.

As far as the actual "mixing and engineering" of music, as I said earlier some might find it a lofty goal to "treat" their room to the same degree as a sound engineer, but they are extremely varied.

I would seriously doubt that "anyone" in even a "dedicated room" will reach even close to anechoic conditions, BUT...Each step of acoustic treatment is designed to "or it would seem" to reduce room interaction.

[Eric D]

Nathan,

Thanks for your considered response.  I will be doing some more reading - I'm still working my way through the Everest book.

This source discussed the same mathematical models for sound wave propagation for a slightly different example, but I hope that the analogous situation is clear:
http://www.squ1.com/index.php?http://www.squ1.com/sound/propagation.html

From there:

A point source in free space exhibits the inverse square law, and a 6dB reduction in intensity per doubling in distance.  

A line source exhibits the inverse law, and a 3 dB reduction in intensity per doubling of distance.  

And a plane source exhibits no reduction in intensity.

Back to my writing:
When a wave exhibits no reflections or interference, the inverse square  law prevails.   When a wave spreads in a cylindrical fashion, either because of reflections or interference, the inverse law prevails.  And when a wave moves as a plane, either because it comes from a plane source or because it is moving through a tube (cylindrical, rectangular, or otherwise), this is the mathematical model.  Note that each of those models might be appropriate for calculating the intensity of the sound over some part of it's domain.

Hopefully the following is a better explanation of two-dimensional cylindrical spreading in a "shallow" ocean.  I hope it's analogy to a large room (where the ceiling height is no where near as large as the height or width) is apparent
http://www.dosits.org/science/adv/cvss1.htm

All the above is just modelling ideal waves.  We're in complete agreement about the mechanics of attenuation.  My sticking point (and I consider it mine) is that I just can't find that -3dB/meter absorption coefficient for air anywhere yet.  It's just too perfect a fit to the inverse law that I somehow wonder if it isn't a common misconception.  

The other part of my questioning that value is that if it were that high, I wonder how we would hear anything over any kind of range.  One resource I could find puts talking at 55-65 dB at 3 feet - say one meter.  If the attenuation coefficient is -3dB/meter, then I wouldn't be able to hear normal talking levels from beyond 20 meters - 65 feet.  And that doesn't include any reduction due to spreading, inverse square, inverse, or otherwise.    

I don't think that's correct.  So I question the number....  Not saying it isn't right - I just can't get it to process in my brain.

I do definitely agree that in trying to reduce RT60 for low frequencies that we may make the room dead for HF.  But I would say that we're trying not to overattenuate the HF rather than to amplify it.  

respectfully,

P.S.  Corners are still an effective place to treat!

[John Casler]

Hi Natham.

I have read ahead and wanted to clear something up.  I am not posting into this thread to post negatives and sincerely do not wish in any way to feel that my opinions on acoustics will affect the perception of you or your (or anyone elses) products.

I find the subject beyond interesting and fully support you, and Eighth Nerve, as well as your interest in helping all of us here at AC, choose the best and most effective products and methods to make our "rooms" sound the best.

Your happy customers speak volumes about the quality of products and services you can provide.

To that end, I would certainly hope that just because I question or suggest something that you not take it offensively.

My questions are with the best intentions of offering opinion, and experience.  They are also opportunities for you or anyone else to further provide details of philosophy or product design goals.

I would hope that just because I might (repsectfully) disagree (or hope to seem to) that "anyone" would doubt the quality of your products, your expertise, and the effectiveness of your system.

I do not.  

You are infinitly more educated in this field, where mine opinion is a practical and logical awarness developed from experience and exploration.

Now that said, I would hope that we can exchange thoughts, as you have time and inclination.

As Acoustics is a "very" small science, I will continue to question and offer opinion.  Very few of my suggestions come with less than significant thought and trial "in the real world".  

However, since my goal is to acheive my sonic preferences within the framework of what I now know, (awareness)  and have, (system)  I am very "open" to any, and every, change that makes sense to me.

Point being, if it makes sense and works then I assimiliate it.  If it doesn't I will continue to ask questions until the answer is clear. (or becomes clearer, since there may be no clear cut answer)

So on that note, let me explain the BOSE 901 comment.

Saying that most of the sound we hear is not reflected based on the sonic qualities of the Bose 901 speakers is a little naive, don't you think? The math is simple and the physics are clear.  .

This might be the crux of where we lose each other.

The Bose 901 was based on the "clear physics" you (I think) are referring to.  It is how much reflected sound we might hear in our everyday natural environment, in the real world.

I don't feel this applies to the way we look to "reproduce" sound in "critical listening" audio system.

I feel the ultimate goal when we are using a "reproduction" system is "not" to overlay the "reflected ambiance" of the original room, with another set of "reflected ambiance" sonics from a substantially differing reproduction room.

Your assertations that you have listened to a hi-fi system in a truly anechoic chamber have not been clear. Your listening room is far from an anechoic chamber, and most anechoic chambers are not truly completely without reflection, they decay at a significant enough rate that they are considered anechoic. It is engineering after all. And besides, even if there were a perfect anechoic chamber where you would only hear the "direct sound wave", your very presence in it would cause reflections, as would the speakers, etc .

Years ago, I constructed several chambers using multiple thicknesses of used cotton matresses (don't laugh   ) for the floor/walls/ceiling of a very small room, and supplemented that with various acoustic treatments.

The point however, is not how closely I came to "completly anechoic" conditions.  The point was that all of the important sound qualities that became so much more available as room interaction is reduced.

But I did spend "years" visiting that room and others I built like it when I wanted the most accurate and captivating sound.  Its biggest limitation was size and the amount of equipment I could get in it.

Basically all I had was the CDP and the speakers, inside, with a wireless remote to the preamp which was outside.  I have to say it was magical sonically.

I now personally use very limited dispersion speakers, in a highly damped room and listen within a "listening tent", open only to the front with top sides and rear enclosed.

Not close to anechoic but very well damped, and a continuing, evolving, experiment.  Additionally, I even use driver and baffle treatment to further restrict as much as possible defraction and dispersion.  Even my ceiling is well treated.

I might add that I would not expect any but the most serious and experimental (or is that just mental   ) would ever attempt to travel my route.

It could only be done in a totally dedicated room and to do it right would be rather pricey $$.

I understand that you enjoy listening to music in a LEDE environment, and good for you. I find it hard to believe however that you can stand on your soapbox and flat out proclaim that it is the only way to accurately listen to music based on your knowledge of some acoustic engineering principles and "40 years of experience." 40 years of breathing wouldn't make me an expert on the molecular makeup of air.  .

Whew!  I didn't intend to be on a soapbox.  (but we could enter into a discussion of pulmonary gas composition and exchange too )

I think my very first post to this thread was that I "was not" preaching.

And my only proclamation was that I didn't beleive that reflected sound could add "accuracy" to a recorded event.

I would still say that has to be true.

I am sorry if I seem harsh, but I must admit that I am a little curious as to why you inject your theories into a thread where people are asking me how my products work. This isn't the first time, and I'm not the only acoustics manufacturer you have done this to. You certainly have a right to your opinions, and to share them. But to push them over and over, when they are not solicited is frankly a little strange. I do not refute every post that you put up which are many and that I obviously disagree with. I answer direct questions as frankly and honestly as I can. You know, I do design acoustic products for a living, and some people really seem to like them. I must not be entirely wrong, ya know? .

As with my opening statements, I find Acoustic Treatment of rooms very interesting, and "I" was one of those people asking how your products worked.

I am sorry my opinions might differ from yours.  I stated earlier that I think your products and services offer excellent value and performance.

I am on many (22) internet forums, the majority of which are based on SportsScience, Fitness, BIOMECHANICS, and Physical Therapy.

When posting to these lists, it is not unusual to encounter those with differing opinions.  Many times contentious exchange as long as it is done in a gentlemanly fashion yeilds greater understanding.  In fact, the greatest acheivements and growth come from diveristy of opinion rather than validation.

While much of science has a basis in fact, the cutting edges have much speculation.  Many times these exchanges from those with dissimilar views "do" add information that can yeild "stepping stones" to greater enlightenment for all parties involved.

I would like to think the same can happen in most any area.


And in closing (for the third time), I feel your products are excellent, have seemingly great performance (all I can say for not having used them personally) and would suggest them (along with Ethans bass traps) as the first line of defense agains room "uglies".

[JCC]

John Casler wrote

“The "only" frequencies and sound that is accurate and important to accurate reproduction, is the "direct" sound. (unless as I said earlier you are trying to "mimic" a specific recording engineers environment -- which is futile)”

When I read this statement, I immediately thought about an anechoic chamber which is great for measuring frequency response. That aside, most feel that the sound in an anechoic environment is unrealistic and unpleasant. Every time you go to a concert, sound reflection is part of the equation. Hang a bunch of foam on the walls, and you will start to create a dead room, without a lot of high frequency. John, if that is your preference so be it. Regardless, it is the opposite of my preference.

Several questions from multiple individuals were asked about high frequency degradation and sound absorbing material? We all know that sound waves are long at low frequencies. Conversely, at high frequencies the wave lengths are very small, and are easily absorbed by foam. You can create a physical analogy by dropping or throwing a BB onto a sponge. The BB will fall into a crevice and stay there. Throw a baseball onto a sponge and it will bounce off.

There also several statements that room modes were only the results of the additive waves bouncing. Room modes are obviously much more than the additive. The horn effect is real, and while I never equated corners with a horn, the concept makes a great deal of sense. To prove it out, I went into the corner and spoke. The sound was definitely distorted and amplified, both to me and the person to whom I was speaking. If you don’t believe me, try it yourself.

I have posted in this thread about the improvement in music in my new 8th Nerve treated room. But that’s not all. Surprisingly even conversation is now much clearer in this room compared to the rest of the house. When I have used my cell phone in the room, other parties have commented about the clearness of the voice. I experimented in a conversation, which I started in the room. We were talking and I walked out into the hall and the other party asked what happened because things suddenly were not as clear.

Reiterating my previous post, the acoustics in this room were dramatically improved by the 8th Nerve installation. I could hardly believe the difference. Any of you who wish, can come and visit me in Houston. You can listen in this room, and I think that you will be impressed. This is a serious offer. Just send me a PM.  I would love to have you over.

[ctviggen]

Do you have a program to test the frequency response of your room?  That would help to quantify what's happening.  I have ETF, but haven't had time to do a "before" (no Realtraps) and "after" (with Realtraps), but I will one of these days.

[ctviggen]

As for the Handbook of Acoustics, it's a good book, but it's not detailed enough for me.  There's not enough physics in it for me.  For instance, he talks about a resonant chamber (I forget what they're called right now) that's basically a large tube with a smaller tube at one end.  He says that he used ETF to design it with a Q=1.  Well, I've tried to use ETF to design such a resonant chamber, and getting Q near one is very hard.  Also, you have to just guess at what factors (outer tube diameter, inner tube diameter, inner tube length, etc.) affect the result.  Additionally, he says that the nodes of a room are determined by solving the wave equations; I'd like to see the wave equations.  

I haven't been following this whole thread, but from what I understand, the reflective outer surface provides a benefit in that high frequencies reflect off the surface, thereby not reducing absorption of these frequencies.  But then you said that the reflective outer surface acts to reflect sound from the walls back through the material.  Ah, I see.  What you're saying is that the reflection/diffusion off the front surface acts to  limit the amount of sound getting to the corner, which therefore limits the "amplification" by the corner.  Moreover, any sound (in certain frequencies, of course) that does get behind the material will get reflected back through the material (and perhaps this could go on several times, from the corner surfaces to the reflective surface and vice versa), thereby further reducing the "amplification" by the corner.  Is my theory correct?

[8thnerve]

This source discussed the same mathematical models for sound wave propagation for a slightly different example, but I hope that the analogous situation is clear:
http://www.squ1.com/index.php?http://www.squ1.com/sound/propagation.html

From there:

A point source in free space exhibits the inverse square law, and a 6dB reduction in intensity per doubling in distance.

A line source exhibits the inverse law, and a 3 dB reduction in intensity per doubling of distance.

And a plane source exhibits no reduction in intensity.

This is another formula based on the propogation of sound in the atmosphere.  I have seen these figures many times, and although it seems like these figures should be directly applicable to our purposes, the data shows us that it is not.  By this formula, a line source would reach -60db in 524 KILOMETERS!!  Thank goodness that is not the case or noise pollution would be a SERIOUS problem.  That and it would take 30 minutes to reach that level of decay.

An important point to remember is that most formulas used to calculate room acoustics are based on measurements and the theories applied to those measurements.  The problem is that any measurements taken in any room without consideration of the effects of the corner amplification are subject to error.  That is why I mentioned before that I disagree with the currently held acoustic beliefs.

We have to take it back to physics and really, thermodynamics.  There is very little difference between heat and sound transfer.  Haven't you noticed that good insulators of heat are also good insulators of sound and vice versa?  To transfer energy from one molecule to another requires some energy be spent.  This spent energy amasses to the rate of decay of sound energy.  The "science" of acoustics is often simply the engineering application of formulas that have been defined for hundreds of years.  Many have said that acoustics is a very early science and it is.  True breakthroughs do not come from accepting the current understanding and building off of that.  Innovation requires us to remove assumptions and rebuild the theories from the ground up.  At this point in acoustics, that is what we must do to achieve the next level.

The other part of my questioning that value is that if it were that high, I wonder how we would hear anything over any kind of range. One resource I could find puts talking at 55-65 dB at 3 feet - say one meter. If the attenuation coefficient is -3dB/meter, then I wouldn't be able to hear normal talking levels from beyond 20 meters - 65 feet. And that doesn't include any reduction due to spreading, inverse square, inverse, or otherwise.

Well, let's think about that.  In what situation would you be 65 feet from two people having a normal conversation (that figure is pretty low, they would be talking in quiet, normal voices, my speech is usually around 70db, but I just may be a loudmouth) and be able to hear them?  If you were in a large space like an auditorium or sanctuary you would have plenty of corners amplifying the sound.  If you were in an open field, you would have to use -6db, but add back for the ground to about -4.5db, that would put us at around 40 feet.  At 40 feet in an open field, you have to raise your voice considerably to speak to someone.  That and outside, sound does travel differently. (as we can see from the wacky figures we get with atmospheric sound propogation calculators)

I do definitely agree that in trying to reduce RT60 for low frequencies that we may make the room dead for HF. But I would say that we're trying not to overattenuate the HF rather than to amplify it.

It seems as though you are stuck on the assumption that lower frequencies take a significantly longer time to decay, but that is only applicable for room modes which are amplified.  What I am saying is that exposed absorption used to treat any frequencies is a trade off that I don't believe is worth it for the most part.  That is not an absolute, I think that carpet helps tame a room as we are unable to reasonably treat EVERY corner surface within a room, and even if we could, while our treatments are effective at reducing the corner distortion, they are by no means perfect.  But I think that the benefit gained by absorbing a small portion of the "first" reflection is simply inconsequential.  I do not disagree that many people have had improvements by doing this, but I believe that it is due to other factors which include the masking of parts of the spectrum where these errors still exist, and these factors become less relevant when you use proper corner treatment.  Many of our customers have taken down their treatments at the first reflection points after installing our products.  There is no question that treating a room without absorption in much more challenging, but when it is realized, there is no comparison.

Thanks for your questions, and enjoy that Everest book.  It is a good snapshot of acoustical engineering for the last part of the 20th century, although nothing of consequence has happened in architectural acoustics in hundreds of years so I wouldn't say it is out of date.  And I am aware that I am challenging the theories of echo and reverberation, and perhaps even sound propogation as a whole, but there is no reason that my products would have any effect otherwise.

[8thnerve]

I haven't been following this whole thread, but from what I understand, the reflective outer surface provides a benefit in that high frequencies reflect off the surface, thereby not reducing absorption of these frequencies. But then you said that the reflective outer surface acts to reflect sound from the walls back through the material. Ah, I see. What you're saying is that the reflection/diffusion off the front surface acts to limit the amount of sound getting to the corner, which therefore limits the "amplification" by the corner. Moreover, any sound (in certain frequencies, of course) that does get behind the material will get reflected back through the material (and perhaps this could go on several times, from the corner surfaces to the reflective surface and vice versa), thereby further reducing the "amplification" by the corner. Is my theory correct?

That's the idea, yes.  Not a perfect elimination of course, but a good start.

[csero]

There is very little difference between heat and sound transfer. Haven't you noticed that good insulators of heat are also good insulators of sound and vice versa? ...

NO. How about styrofoam, just to begin with  

the assumption that lower frequencies take a significantly longer time to decay, but that is only applicable for room modes which are amplified...

I'have yet to see a measurement which can show that the decay at the room mode is disproportionately higher and not caused by physical resonance of the wall surface.

[8thnerve]

John ,

I appreciate your response, but your style of "conversation" is not entirely innocent.  For instance:

Are you saying that "mixing" reflected room sonics "adds" accuracy?

This is not something I ever said, nor implied.  Saying things in this way is a rhetorical device used to accuse someone of making a statement which is obviously incorrect, and therefore results in challenging the questioned speaker's credibilility.  Whether you do this coinsciously or not is not of much interest to me, but it isn't appropriate in the course of actual productive conversation.  If you don't understand what I am saying, then simply ask for clarification.  Other people read this than just us, and it can be confusing and overwhelming.  Let's not try and undermine the clarity of this discussion by speaker for each other.  Speaking for ourselves will get us in plenty of trouble by itself.

Now, in response to the points I think we are still unclear on...

The Bose 901 was based on the "clear physics" you (I think) are referring to. It is how much reflected sound we might hear in our everyday natural environment, in the real world.

No, it is not.  The Bose 901 is a poorly designed dipolar speaker.  That is it.  It is in no way relevant to what I am talking about, and frankly, I am flabbergasted that we continue to discuss this.  We are listening to the reflections of the original sound wave created by the speakers whether it comes out of one driver, 8 drivers, 3 drivers pointing front and 3 pointing back, or any other combination.  The differences caused by these designs simply produces a different set of reflections.  I am not saying that this is what we want to listen to or what god wants us to listen to or anything else regarding theory or recording versus playback, etc.  I am saying that we cannot discern the difference between the first wave that hits us and the subsequent hundreds of reflections that reach our ears at almost the same level within a few hundredths of a second, period.

I'm not saying that you don't hear what you consider to be an improvement when you put up a lot of absorbtive material, I am saying that it is not for the reasons that you believe it is.

I continue to express that your goal to hear only the "direct" sound is an interesting and idealized fascination.  There has never been a person who has ever heard only the "direct wave" of any sound.  Even when sound travels through our ear canal it causes reflections.  Every surface causes reflections to a certain extent, these refelctions happen incredibly fast, and our brain integrates them all into a whole.  The ratio of direct to reflected sound that we hear is for all practical purposes 0:1.  Your experimentations that tell you that when you put up absorptive material to absorb reflections that you hear more of the direct sound than before are simplified and inaccurate conclusions to a complex set of results.

Let me make my point very clear: putting absorptive surfaces in a room does not improve your ability to hear the direct sound wave by any statistically significant amount.  We hear the summation of the direct wave and the multitude of reflections.  Reducing the level of these reflections simply results in a percieved wave that measures lower in the areas that were reduced, not some grand uncovering of the original wave.

The reason you think that it does from your listening, is that the reduction of the high frequency energy eliminates the lowest level harmonics, which increases the perceived ratio of fundamentals to the noise floor.  This allows you to pick out more of the individual sounds because the spurious ambient information (that otherwise would be distorted due to the corners) has been reduced.  Please don't respond back to this with all the attributes you get with your setup.  You have made that very clear.  This is my explanation for why you percieve the benefits you claim.  You are more than welcome to disagree, but there is no point in reiterating why you believe otherwise.  I am acknowledging that for you.

I think my very first post to this thread was that I "was not" preaching.

This statement is almost always proceeded by the very thing you proclaim you are not doing.  The rhetorical argument is that if you are not preaching, you would have no reason to deny it beforehand.

I am happy to answer questions about our products, no matter who asks them.  At some point, some people are going to disagree with our beliefs, and that is to be expected.  But in the end, the proof is in the products.

[8thnerve]

There is very little difference between heat and sound transfer. Haven't you noticed that good insulators of heat are also good insulators of sound and vice versa? ...

NO. How about styrofoam, just to begin with  

Styrofoam may make a poor absorber of sound, but it makes a good isolator of sound, similar to it's properties regarding heat.

I'have yet to see a measurement which can show that the decay at the room mode is disproportionately higher and not caused by physical resonance of the wall surface.

Whatever it is caused by, the decay is proportionately higher, and I believe that Ethan has some measurements on his website that confirm this as well.  Resonances are easy to see on a waterfall plot.