[PhilNYC]

Interestingly enough, a friend told me that room treatment would deaden the room. While this is true for some products, this is not the case with 8th Nerve approach, because it is reflective in the front and absorptive in the back. In fact natural ambience and room liveliness is improv ...

If you look at the full product offering from most room treatment companies, it's rare that you'd find one that only offers products to absorb/deaden sound.  I don't claim to be anywhere even close to an expert in acoustics, but most (not all) professionals I've spoken to in the industry talk about proper room treatments being some combination of absoption, diffusion, and reflection.

One thing I like about 8th Nerve's approach is their focus on eliminating corner distortion.  I also believe in treating first reflection point.  Am not too keen on worrying so much about balancing frequency response using room treatments, because it seems like an unsolveable task (except for a very specific sweetspot), and with the variations in recording equalization/quality, it also seems somewhat pointless.

[Eric D]

Room treatment is also controversial for me (used alone without ambience recreation) because it will make the ambient sound of the listening room even more unnatural, compared to any live event.

An overly treated room would definitely sound unnatural - an anechoic room being the extreme example.  But a small, hard-surfaced room is the other extreme.  Maybe you're lucky and have a room that already has natural-sounding characteristics.  But I certainly know that mine doesn't.  RT60 is too high, I get some severe Bass reinforcement issues.  While I certainly don't think you should throw more treatments at a room willy-nilly, appropriate treatments can help take a room towards a more "natural" sound.

I personally want to measure the untreated room, and then settle on treatments,  But I also suspect that since most of us are nearer that small/hard room end of the spectrum, the 8th Nerve setup (or several other company's offerings) are good approximate solutions for those who don't want to get into details.  It may be undertreating some rooms and overtreating others, but I'd hazard a guess that it would help get a lot of people closer to a "natural ambience" than their untreated room.

enjoy,

[John Casler]

CSERO wrote:

Room treatment is also controversial for me (used alone without ambience recreation) because it will make the ambient sound of the listening room even more unnatural, compared to any live event.

Interestingly enough, a friend told me that room treatment would deaden the room. While this is true for some products, this is not the case with 8th Nerve approach, because it is reflective in the front and absorptive in the back. In fact natural ambience and room liveliness is improv ...

Now this is interesting stuff

I always find the too live and too dead, natural and un-natural thoughts intersting and useful to discuss and examine.

First we need to understand that many of us listen to our systems differently.

Some sit down and seriously listen in a method that is designed to come as close as possible to the information on the recording, and others simply want sound "spread" throughout the room so that they get a semblance of a full frequency response as the walk around vacumning, having breafast, or whatever.

The second thing we have to remember is that "all recordings" are not created the same way.  The two primary groups are "live" as opposed to "studio".

And even within those groups various miking techniques, mixing and engineering can greatly affect what you hear.

If you are in the first group and the only sonic that is important to you, is the truest reproduction of the recording when you are in the sweet spot, then "any" additional sound created by the room will be a "distortion".

There is no way a room reflection of a speaker produced soundwave can add "any" accuracy to a recording

If you are of the second group, then you sacrifice much "accuracy" for the ability to enjoy your system in less serious listening activities in positions other than the sweet spot.

Now there is the argument that the "recording engineer" does not engineer a recording in an "anechoic" chamber, and this is "partially" true.

Each engineer does his task differently.  Some "do" use a room that is almost anechoic, others use LEDE, others use minimal treatment, still others even listen to the mix on a "car" system or even a boom box to get it right.  And there are some who use the anechoic environment of headphones, somewhere in the mix.

It could be said that you should attempt to "copy" the engineer's studio to get it right.  And that would be a reasonable goal, "if" you knew what the engineers room was like, but very few are exactly the same.

Additionally, the engineer, doesn't "add" his room sonics to the mix, he just uses them to create the mix by listening through them that he likes.  In essense he is looking for frequency ranges, dynamic ranges, and balances.

So what does the group who uses room treatment to minimize interaction give up?  Basically it is the sparkle and reflected energy that bounces around the room.  This means that the sound will be subdued anywhere but the sweet spot.  For backround music, it will be fine, but if anyone is doing serious listening around the room (which I can't imagine) the quality would suffer slightly, depending on the dispersive qualites of their speakers.

So what does the group who "uses" reflected sound "give up"?

They give up the accuracy of not distorting the original signal with room created distortion.  While there are many acoustics experts who will argue that this is not the case, I would argue just as much that it is.

In the science of psychoacoustics, we "cannot" circumvent the laws of physics.  However, various laws can be used in the treatments of various applications.

I have mentioned this before, but there are "HUGE" differences in treating a performance venue, like a club or concert hall, and treating a 2 channel reproduction room.

In the hall we are looking for acoustics to make "every seat in the house" accpetable.  We do this by using treatment that will evenly spread the sound of the performers and the sound of the hall.  In fact the performers "and" the hall "are" the SOUND.  This is acceptable because it is "supposed" to sound like this.

In a reproduction room, if we want to hear the original "sound of the hall and performers" we need to minimize all the sound created by our own rooms because it "distorts and covers" the delicate ambience cues by overlaying them with reflected ambience from a room/space with totally different dimensions and interaction.

So it depends on which "camp" you are in, and your personal preferences.

I don't intend this to "preach" what should or should not be "important", and also acknowledge that the "quality" and engineering of recordings will still have a major effect on what you hear.

I also know that the stereo recording process is, "in itself", flawed from the get go.  However, there are some incredible adventures in listening, that can be had for those with an interest in "going pure" (or as pure as possible within your situation).

So within the contest of this thread, I would certainly from a serious listener standpoint maximize the treatment of room interaction to "minimize" the amount of digital equalization.

Further more, the Room packs offered by 8th Nerve seem to be the logical place to begin since it seems that the greatest sonic distortions from room interaction emenate from the corners and tri-corners and the points of 1st reflections.

While I may not agree with their "reflective properties" (hey guys why not offer both reflective and non-reflective??)  I certainly agree that corners and points of first reflection are the begining.

Sorry for the length of this   I know thats why Frank says not to get him started

[8thnerve]

While I may not agree with their "reflective properties" (hey guys why not offer both reflective and non-reflective??) I certainly agree that corners and points of first reflection are the begining...

The products have to be reflective to reflect the sound coming from the corners back into the corners.  Otherwise the distorted energy would still come into the room, but the higher frequencies would be attenuated... not what we want.

Our research has shown that 80% or more of "echo" and any reflected sound we perceive in a room is from the corners; not from parallel wall surfaces, not from first reflection points, not from anything but the distorted and amplified wave from a corner.  The laws of physics dictate that in a cylinder, a fully reinforced environment where sound can travel in only one direction without expanding, sound decays at a rate of 3db per meter.  In free space sound decays at a rate of 6db per meter.  A room is a semi reinforced environment, and it's decay rate should fall between these two numbers.  Even at the maximum sustain rate of -3db per meter, sound travels at 340 meters per second through air at sea level.  This means that the RT-60 (time it takes for sound to decay by 60db) of any given space cannot exceed 6/100ths of a second.  Since we have never seen an RT-60 time that low in any environment, and a good RT-60 time is considered to be around 50/100ths of a second, with many rooms measured at over 1 and a half seconds, something else must be happening.

Most acoustic physicists will of course question the rate of decay, saying that the sound waves bouncing off the walls somehow reinforce themselves decreasing the decay rate.  But even at a -1db per meter decay, the RT-60 should still measure 17/100ths of a second, far less than can explain this behaviour.  Sound bouncing off a wall and interfering with another wave only affects the make up of the spectrum of that wave of sound in that particular point in space.  Constructive interference simply sums the waves at a given point, it does not increase the overall energy of the pressure of the air molecules, and therefore cannot decrease the decay rate.

In a cylinder, the total amount of air molecules that are excited by the sound pressure wave does not change with distance.  This gives a true sound decay rate of 3db per meter as energy is exhanged with a fixed number of air molecules.  In free space, the amount of molecules that can be excited increase exponentially as the sound radiates outward spherically 360 degrees, which excites more molecules per time unit, therefore reducing the overall amount of time required to burn up all the energy.  6db is an exponential increase over 3db; QED.

In a room, sound starts to decay at 6db per meter until the boundaries are reached, and then the decay rate declines to 3db as all the air in the room is excited.  As the overall same amount of air molecules are exchanging pressure information, and we are not introducing more air molecules to use energy, the rate remains more or less consistent.

Hold on!  Then how is it possible to have RT-60 times that are longer than 6/100ths of a second?  Well, the only way to increase the total amount of energy in a system is to amplify it.  Room modes are a good example.  The geometry of a room causes resonant frequencies which amplify the sound at a given frequency.  Most of us have seen the film of the bridge that starts twisting and swaying as the wind excites its resonant frequency.  This explains room modes, but what about everything else?

Again, in order to increase the energy in a system, you need an amplifier.  Think about the tweeters of most of the pro audio speakers you have seen, and then look around your room and see if you see a similar shape.  Yes, the corners are horns, the original acoustic amplifier.  Haven't you noticed that when you clap your hands in a live room and hear that zing that it always seem to be coming from above your head?  It is.  Corner to corner, cycling through a distortion, then amplification, then right back into another corner.  This is what causes echo and almost all of the non-geometry based anomolies in a given room.

The reason I say that I don't treat the first reflection points is that the sound is arriving about 4/1000ths of a second later and at a level of about -4db (normal sized listening room).  The sound from the front tri-corners is arriving at about 10/1000ths of a second later at a level of -0.12db.  This is an order of magnitude more significant, and is only from one of the many corner surfaces of your room, all more important and harmful than the first reflection by a large margin.

I hope this helps to explain the importance of treating your corners in a way that traps the energy from returning from it.  This new research is why these products are patent pending, and marks a large step forward in our understanding of architectural acoustics.


Nathan Loyer
Eighth Nerve

[ctviggen]

That's a good analysis, Nathan.

[brj]

Very informative analysis and explanation, Nathan - thank you!

The products have to be reflective to reflect the sound coming from the corners back into the corners.  Otherwise the distorted energy would still come into the room, but the higher frequencies would be attenuated... not what we want.

This make sense, but the difficult part would be finding the acoustic equivalent of a one way mirror with which to cover the room-facing surface of the corner trap.  You want the facing material to be perfectly transparent to sound of all frequencies coming from the room, but perfectly reflective to all sound bouncing back out of the corner.  (As the reflections bounce back and forth with in the trap, the energy gets dissipated in the damping material.)

Fiberglass makes for great damping material, but does such a "one way" facing material currently exist?  (Of course, I realize that this may be the proprietary part...)

[JoshK]

I have yet to evaluate the new Adapt line of products but I recently acquired 3 of the new Seam-like products.  I use to have a number of the other ones as well.  I can certainly say I really like the looks of the new ones much better.  Much easier to get WAF.

[John Casler]

The products have to be reflective to reflect the sound coming from the corners back into the corners.  Otherwise the distorted energy would still come into the room, but the higher frequencies would be attenuated... not what we want.
..

Hi Nathan,

Sorry if I misunderstood the "reflective" surfaces of your product.

I thought that the "front" (facing the listener) was reflective.  Is that not true?

From your clarification, I get that the "backside" (facing the corner) is reflective???

[8thnerve]

Hi Nathan,

Sorry if I misunderstood the "reflective" surfaces of your product.

I thought that the "front" (facing the listener) was reflective.  Is that not true?

From your clarification, I get that the "backside" (facing the corner) is reflective???

The side of the product facing into the room is reflective, so you were right in your understand.  But it is reflective in both directions.  The reflective front is really for the sound coming from the corner, which travels through the fiberglass, hits the reflective surface, then reflects back towards the corner through the fiberglass again and repeats the cycle.  This allows us to burn off the sound coming from the corner.  The only benefit from the front also being reflective is that we are not presenting any exposed absorption.  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.  It is essentially the same as Dolby Noise Reduction.  Unfortunately you also lose all the delicate upper harmonics that encode the characteristics of instrumental timbre, space, and environment.

brj, a one way acoustic reflector sounds like it would be very cool, but as far as I know, it does not yet exist.  As it is, the sound that is reflected back into the room from the front of the product does not suffer from the distortion or severe amplification as the sound from the actual corner does, it acts the same as sound reflecting off a flat wall surface.  And the half inch gap from the product edge to the wall surface is plenty of space for the sound to collect behind it.

[ctviggen]

Why does exposed absorption reduce high frequencies?  Is your reflective material band-specific?

[8thnerve]

Why does exposed absorption reduce high frequencies?  Is your reflective material band-specific?

Because all absorptive material to date absorbs more high frequencies than low frequencies.  All materials have varying degrees of performance at different frequencies, we look for those that are as linear as possible across the audible band.

[JCC]

Intuitively it seems like the absorption would relate to wave length. Low frequency waves are much longer than high frequency waves. Miniscule high frequency wavelengths easily fit within the fibers of the absorbing materials, and are could then dissipate. It's a different story with the much longer low frequency waves.

[John Casler]

The side of the product facing into the room is reflective, so you were right in your understand.  But it is reflective in both directions.  The reflective front is really for the sound coming from the corner, which travels through the fiberglass, hits the reflective surface, then reflects back towards the corner through the fiberglass again and repeats the cycle.  This allows us to burn off the sound coming from the corner.   .

Very interesting      And cool idea  

The only benefit from the front also being reflective is that we are not presenting any exposed absorption. 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. It is essentially the same as Dolby Noise Reduction. Unfortunately you also lose all the delicate upper harmonics that encode the characteristics of instrumental timbre, space, and environment.

I might tend to disagree with that.

While I agree that it is best to attenuate room generated sound "broadband", I cannot agree that the energy from reflected sound should be "used" as you're suggesting.

Aren't you saying that these "reflected" HF's bolster a measured HF response?  If not, how do they attenuate?

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)

Exposed absorption only attenuates "reflected" HF sound.

In the sweet spot, these reflected HF's "reduce" the accuracy of the direct HF information by competing with that direct sonic energy.

And I might also question the area of "primary reflections".

The reason I say that I don't treat the first reflection points is that the sound is arriving about 4/1000ths of a second later and at a level of about -4db (normal sized listening room). The sound from the front tri-corners is arriving at about 10/1000ths of a second later at a level of -0.12db. This is an order of magnitude more significant, and is only from one of the many corner surfaces of your room, all more important and harmful than the first reflection by a large margin.

While I don't question your numbers, I would never say don't treat first reflection points.  The sonic affects of first reflections are very damaging, and can destroy balance/symetry as well as soundstage, imaging and detail.

I feel both areas (as well as many others) need treatment to attain the best sound.

I should reaffirm that my comments are directed "specifically" to 2 channel audio, and not HT.

Hold on! Then how is it possible to have RT-60 times that are longer than 6/100ths of a second? Well, the only way to increase the total amount of energy in a system is to amplify it. Room modes are a good example. The geometry of a room causes resonant frequencies which amplify the sound at a given frequency. Most of us have seen the film of the bridge that starts twisting and swaying as the wind excites its resonant frequency. This explains room modes, but what about everything else?

You lost me on the bridge  

Room Nodes/Modes are caused by sonic energies "opposing" each other "DIPS" or "summing" with each other "PEAKS/SPIKES".

While this is a rather complex physics problem, the concept is rather simple.

Let's just try a "simple" path just for explanation purposes,

As a Soundwave leaves the speaker and "hurtles" toward you, it has energy.  Once you hear it, it doesn't stop, it continues on to the back wall (remember simple path).  

It loses a bit of energy and bounces back forward again toward the speakers.  At some point it will enounter its "matching" frequncy/energy, and reduces its energy, by opposing it.  If this collision happens (due to room dimensions in front of you, then that energy reduction will be heard by you as a "dip" in response.

Alternatively sound is also reflected (bass is the best example since low bass is spherical in its radiation) off the front wall.

So this energy leaves the speaker travels behind it to the front wall and again bounces off and is now traveling forward in the same direction as the "direct" waves.  If it passes the speaker and "syncs" with a like frequency they "sum" their energies and this creates a higher SPL or a "SPIKE/PEAK".

Now that is the "ultra simple" version and in fact the reflections and angular incindence of all the room boundaries severly complicates the processes, but in essense, that is what we are dealing with.

Hope that makes sense.

[John Casler]

Why does exposed absorption reduce high frequencies?  Is your reflective material band-specific?

Because all absorptive material to date absorbs more high frequencies than low frequencies.  All materials have varying degrees of performance at different frequencies, we look for those that are as linear as possible across the audible band.

But the goal, is not to preserve the "sum" of all the HF (or any frequency) in the room, direct and reflected.

The goal to accurate reproduction is to subtract/absorb/block all "room" generated interaction and sonic artifacts.

The goal is to make the room boundaries "acoustically transparent", so that the sonics heard by the listener will reproduce the "acoustic boundaries" (sonically) of the original venue (assuming there were some) contained in the recording.

Having two sets of "sonic space" acoustics destroys the original.

[csero]

The goal to accurate reproduction is to subtract/absorb/block all "room" generated interaction and sonic artifacts.

The need for "accurate" would assume that what is on the record is faitful and complete representation of the sonic event.

The goal is to make the room boundaries "acoustically transparent"...

You can not reach that. You ocan only hope, that after heavy treatment the sound of your room is no more deterimental than the chairs, audience etc around you in a real  concert hall, and blend in the same benign way. But the more you treat, if you don't do anything else, the farther you move acoustically from any venue where music played.

... so that the sonics heard by the listener will reproduce the "acoustic boundaries" (sonically) of the original venue (assuming there were some) contained in the recording.

It is simply not possible, especially not with a stereo speaker pair. A "live" record played back in a dead room sounds like a "live record played back in a dead room", not like the original acoustic environment. The "acoustic boundaries (sonically) of the original venue" are around you, so the reflected sound comes from every direction. The ear is quite sensitive to the directionality of this. That's why a front speaker pair will never reproduce a realistic ambience. Also IMHO that is the reason that the lack of bass impact of hi-fi, compared to any live event.

Having two sets of "sonic space" acoustics destroys the original.

Agree. That's the single biggest reason why the audiophile demo music is (closemiked) small jazz combo or LGWG music.

[8thnerve]

I might tend to disagree with that.

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.

I cannot agree that the energy from reflected sound should be "used" as you're suggesting.

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)

Exposed absorption only attenuates "reflected" HF sound.

What is futile is trying to turn a listening room into an anechoic chamber.  This will probably come as a surprise to most, but we are listening to reflected sound almost exclusively.  In a room with an excellent RT-60 time of half a second and dimensions of say 15' x 13', we hear one "direct wave", and over 200 reflected waves of sound. (taking into account both horizontal reflections, and vertical reflections, but ignoring the multitude of  incidence reflections that would increase the number to well over 1000, but since these are reducing in amplitude with time, 200 is about all we need to concern ourselves with -  remember, sound travels at 340 meters per second; very, very fast.)  Trying to reduce the energy of one pair of these reflected waves is about as effective as putting a band-aid on a crack in the Hoover Dam.

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?

You lost me on the bridge.

Room Nodes/Modes are caused by sonic energies "opposing" each other "DIPS" or "summing" with each other "PEAKS/SPIKES".

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.

Room nodes and modes are not caused by constructive or destructive interference.  All sounds at all frequencies exhibit constructive or destructive interference at a certain points in space along their path of travel.  Room modes and nodes are constructive and destructive interference (respectively) that are amplified due to a standing wave forming based on the geometry of the room.  It is a resonance just like the bridge example above.  This is an important distinction because it is the amplification of this behavior that is of relevance to us.  And as Ethan also often notes, the reduction of the amplitude of these frequencies does not solve the ringing problems as not only is the amplitude of the frequency amplified, but the time of its duration as well.

Alternatively sound is also reflected (bass is the best example since low bass is spherical in its radiation) off the front wall.

All sound radiates spherically, at all frequencies.

But the goal, is not to preserve the "sum" of all the HF (or any frequency) in the room, direct and reflected.

The goal to accurate reproduction is to subtract/absorb/block all "room" generated interaction and sonic artifacts.

The goal is to make the room boundaries "acoustically transparent", so that the sonics heard by the listener will reproduce the "acoustic boundaries" (sonically) of the original venue (assuming there were some) contained in the recording.

Having two sets of "sonic space" acoustics destroys the original.

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.

[ctviggen]

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.

[Eric D]

[edited to remove a sentence accidentally left in the wrong place]

The laws of physics dictate that in a cylinder, a fully reinforced environment where sound can travel in only one direction without expanding, sound decays at a rate of 3db per meter. In free space sound decays at a rate of 6db per meter. A room is a semi reinforced environment, and it's decay rate should fall between these two numbers. Even at the maximum sustain rate of -3db per meter, sound travels at 340 meters per second through air at sea level. This means that the RT-60 (time it takes for sound to decay by 60db) of any given space cannot exceed 6/100ths of a second. Since we have never seen an RT-60 time that low in any environment, and a good RT-60 time is considered to be around 50/100ths of a second, with many rooms measured at over 1 and a half seconds, something else must be happening.

I most respectfully disagree.  But please let me add, caveat lector - I have publishing without review.  I'm hoping someone either backs me up or points out errors in my research and statements.  I respect the authorities who are holding this discussion and it is with trepidation that I step it.  Anyway, here it goes:

I believe what you refer to above to is the decay of sound intensity, not attenuation; and that it's inappropriate to use that to calculate RT60.

In free space, sound waves are spherical and the intensity obeys the inverse square law.  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.  

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.

*All* those were for ideal conditions (like an EM wave in a vacuum).   If nothing attenuates the sound, either by scattering or absorption, an enclosed room would ring forever.  I don't disagree with the discussion of the boundries - I think we're well represented there - indeed it's the purpose of the sound treatements.  I'm only talking about the attenuation by the air - the natural decay rate of sound in an ideal room, with air.  Hmmm, guess there's no purpose to having this room without air...

Here are two websites I googled-up in researching this.  The first is the calculation for the attenuation of sound:
http://www.ndt-ed.org/EducationResources/CommunityCollege/Ultrasonics/Physics/attenuation.htm

The second is a calculator for the attenuation coefficient of air:
http://www.npl.co.uk/acoustics/techguides/absorption/

Anyway, from what I can find, the natural attenuation rate is greatly dependent on the frequency of the sound.  I used the second and plugged in 20 deg C, 100 kPa, and 50% relative humidity.  

Code: [Select]

20 Hz         0.000013 dB/m
100 Hz        0.00029 dB/m
1,000 Hz      0.0047 dB/m
10,000 Hz     0.16 dB/m
20,000 Hz     0.52 dB/m


Multiplying the 1,000 hz attenuation coefficient by 340 m/sec and dividing into 60 dB, I come up with an RT60 (1,000 Hz) in a completely reflective room of 38 seconds.  

So sorry, but I don't think "something else is happening" that raises the sound energy level of the room (2nd law of thermodynamics, and all that).  I think there's plenty of "overhead" in the natural decay rate in the room that is used up by boundry interactions or openings to arrive at the values of RT60 we find when we actually take the measurements.

None of this says your treatments don't work.  And I repeat my request to be corrected - it's been a while since I've done any of this seriously, and I'm just re-learning all of it because I want to start measuring my room.  Hey do you really want to listen to a guy who can't get ETF running on his home computer yet?  

take care,

P.S.  Did anyone calculate out RT60 for 20Hz?  I got 3.8 hours!  I need me some bass treatments!  

[JCC]

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.

[John Casler]

 The need for "accurate" would assume that what is on the record is faitful and complete representation of the sonic event.
   

Hi Frank,  Yes, I mentioned that earlier.  We have to assume that the goal during the whole process from production to reproduction is accuracy, but we know we can only work to "approach" accuracy and never acheive it 100%.

 John Casler wrote:
The goal is to make the room boundaries "acoustically transparent"...

You can not reach that. You ocan only hope, that after heavy treatment the sound of your room is no more deterimental than the chairs, audience etc around you in a real concert hall, and blend in the same benign way. But the more you treat, if you don't do anything else, the farther you move acoustically from any venue where music played  

I agree, but I don't think we can use people and chairs as a reason to not try and subtract reproduction room interaction.  The best we can do is subtract the reproduction room as much as possible to let us "hear" the original space as recorded.

I disagree that treating moves you farther away.

I would suppose that "in the future" looking into the "Sonic Ball" we could have Digital Processing that would produce a phasing matrix similar to Q-Sound or any of the more recent processes, that would be able to take our room measurments (during set up) and then create a sonic matrix to provide a more accurate representation on a recording by recording basis.

Now that would be cool

 John Casler wrote:
... so that the sonics heard by the listener will reproduce the "acoustic boundaries" (sonically) of the original venue (assuming there were some) contained in the recording.

It is simply not possible, especially not with a stereo speaker pair. A "live" record played back in a dead room sounds like a "live record played back in a dead room", not like the original acoustic environment. The "acoustic boundaries (sonically) of the original venue" are around you, so the reflected sound comes from every direction. The ear is quite sensitive to the directionality of this. That's why a front speaker pair will never reproduce a realistic ambience. Also IMHO that is the reason that the lack of bass impact of hi-fi, compared to any live event  

It depends on what you mean by possible.  

First what is a "dead room" a dead room is a room that has no sound or reduced sound interaction.

My room is approaching more dead than not.  I am not trying to make my room sound like the "original environment".  I am "subtracting my room", so I can "hear" the origninal environment as much as is possible, when available.

I agree that a two speaker set up will not produce side and rear directionality, but once you have subtracted the listening room, the frontal information will help the brain "fill in" some of that.

It is still much better than not being able to hear the recording environment details at all.

I certainly agree with you that there is no "perfect" recording system, that allows for a more accurate experience, but what I suggest is a "step" toward accuracy "within" what is available.

John Casler wrote:

Having two sets of "sonic space" acoustics destroys the original.  

Agree. That's the single biggest reason why the audiophile demo music is (closemiked) small jazz combo or LGWG music    

Yes, and I have a Jim Merod recording "Carl Saunders Quartet "LIVE in San Francisco" that is absolutley incredible.

One of the reasons it sounds exceptionally real in a highly treated room, is that it is recorded "outside" so there is "no hall" sound or reverb, but there is an open "sonic" and sounds, like a street car bell, that are truly remakable.  In a reflective room is sounds like a recording being listened to in a reflective room

If you like Jazz Combos, I highly suggest it.  

And Frank, as always I appreciate your comments and views.  I know you have specific "critiques" of the current recording to reproduction process that are relevant and valuable.