Room treatment for mid & high frequencies

[damonrpayne]

Having nearly digested a brazillion pages of sound treatment ideas and science, it seems that much of what I've found deals with taking care of low freq issues. I really like Ethan Winer's homade bass traps etc.

There seems to be an accepted idea that a room that's too 'dead' probably will not sound very good, eerie maybe and having some liveliness in a listening room is preferred. If one's room is TOO lively in the mid- and high-frequencies I must assume there are alternate treatment methods available. I assume depending on actual room measurements a combination of absorpion and diffusion could be used. I'm not really interested in spending a shedload of money on foam products and would be looking for a homemade solution at least initially.

Just looking for some pointers to websites that talk about treating a room that's very bright or some chapters in Master Handbook of Acoustics that I should reread.

[picky]

Damon: My room is fairly "dead" but the sound I get is superb, or so I have been told. Colter can relate to you what I am talking about. So could Michael Hurd, if he still had a computer, as he has spent many hours in our theater. His only detrimental comment was that our tiny room could use more echo time. The room is quiet. Yet, all of the proper elements are there when the media is running. The surround channels tend to filter in the proper ambience. The room can seem quite large at times. It all depends on the mix on the media. I like it because the room tends not to add anything that isn't already on the disc. You hear what the producers or engineers wanted you to hear; even the bad ones, unfortunately. []

Not to confuse you, as you sound a bit frustrated by all the reading you've done (me too!); to sum up, it is my opionion that I would prefer a room that was a bit too dead over a room that was a bit to lively.

I used that heavy rubber roofing membrane in the walls and the melamine foam tile in the ceiling. What can I say? It works! -Glenn

[wuzzzer]

My plan is to get some 2" for the walls and 1" for the ceiling acoustic wedge foam from www.foambymail.com. Some corner bass absorbers are also in the works. Total cost should be just over $50 and I think my game plan of installation should make my lively basement sound much, much better.

[picky]

wuzzer: Wow, Mark. Those are some pretty low prices on that site. I hope it performs to your liking. Nice find! Thanks for sharing with us. Please let us know how that foam works out in your room! -Glenn

[mas]

A suggestion...<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

The treatment of rooms is well understood. And there are different criterion used for different goals, be it intelligibility, gain, etc. So first the desired use must be determined.

Additionally, the characteristics of the acoustical space are different dependent upon whether it is a "small" acoustical space or a "large" acoustical space. These are very specific definitions with a primary distinction being that a "small" acoustical space lacks a diffuse reverberant field. Typical home listening rooms and studios fall into the small acoustical space categories.

Many of the works cited, and I will risk kicking a sacred dog here in mentioning that Everest's Master Handbook of Acoustics is an adequate overview of many of the basic ideas and research developed by others. But in order to understand and benefit from the research and the myriad advancements of those who are actually doing the research and whose materials and diagrams he uses, you need to move to the sources themselves. His book provides a good introduction to acoustics, but you are not prepared to begin operating as a surgeon by simply looking at a copy of Gray's Anatomy.. It does not provide sufficient depth to understand exactly how each of the principles and technologies mentioned are actively employed - nor what has been learned during the advancing implementation of these technologies and concepts.

To learn more and to advance past this, you need to learn more about the basis for, and the application of the technologies to which he refers.

And the place to start is:

Sound System Engineering, Don and Carolyn Davis, ISBN: 0240803051, Focal Press (800.545.2522). This classic deals with sound system design and theory for both large and small rooms, and provides an excellent overview of test and measurement, impedance, acoustics, and more. ***Note the 3rd Edition is about to be released for widespread availability authored by Don Davis & Dr. <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Eugene Patronis. These are absolute must haves.

Also, several titles that may have not been mentioned in other threads that you will find useful:

The Audio System Designer, Peter Mapp. Small enough to fit in your briefcase, this is an excellent resource of the charts, data, and coefficients sound system designers need.

An Introduction to Mathematics and Engineering Science, Dr. Sidney Bertram.

Sound Reinforcement Engineering, Wolfgang Ahnert . Wolfgang Ahnert is best known for his development of the EASE modeling program for sound designers. His textbook covers all aspects of system design.

And for instruction into the latest advances in theory and the latest applications and test & measurement in acoustics: Synergetic Audio Concepts (Syn-Aud-Con). This has been the historical clearing house of almost all of the significant innovators since the 1970's. Pat Brown assumed leadership when Don & Carolyn Davis decided to 'retire' (almost a misuse of the term) in 1996.

Additionally, while many web sites try to provide simplified cookie cutter approaches, you need to not only become familiar with, but understand the value of the time domain based test and measurement gear. To advance to the next level about guesswork and simple emotional reaction, you have no alternative.

It can be as basic as RPlusD, the replacement for ETF, or it can be as advanced as TEF, Easera, SMAART, or MLSSA, etc. (each having various strengths and weaknesses such as ambient noise immunity, etc. as well as varying degrees of completeness and scope.). But these are the tools required to allow you to examine the acoustical characteristics in their component aspects.

Now I know many are not intimate with these tools. And many also believe that while they are nice, they are not necessary.

Regarding the specific issue of the treatment of mid and high frequencies, these are well understood, and the various approaches determined by the specific application and the specific goal are well understood. this area of acoustics has experienced a quantum leap in the past 25 years. And much of what you read is based upon only the very basic introductory ideas as first proposed 25-30 years ago. And these models have been significantly refined! A great example is LEDE & RFZ configurations. The irony is that much of what you read in many of the books (including Everest) is obsolete and based upon the very initial proposals that further testing ad research has modified significantly. And the test gear is what has made the further investigation and refinement of this possible.

In a nutshell, LF modes below ~300Hz are determined by room topology and are treated with various diaphragmatic traps. You have several considerations with the mids and highs. But in general, after the arrival of the direct signal there is a natural ITD (initial time delay - or more properly - and initial signal delay gap) between the arrival of the direct signal and before the arrival of the initial first order reflection. Knowing the rooms natural ITD, you are then able to establish a desired ITD greater than the rooms natural response. This period will typically range anywhere from 5ms up to 25ms in a small room (and this is not arbitrary; there are factors that enter into this), where you absorb the first order reflections that fall into this time range sufficient to trigger the Haas Effect. This period is going to be terminated by what is referred to as a Haas Kicker - the first reflection within 6dB of the highest magnitude reflection.

Absorption is useful to absorb the first order reflections within the ITD gap. Beyond this, it is desirable for the reflected energy to exhibit a well behaved decay following an exponential rate. Reflections that exceed that slope are audible and to be addressed. Likewise, in a small room that by definition lacks a diffuse reverberant field, the specular reflections are to be diffused, thus scattering the acoustical energy further, eliminating distinct focused speculate reflections. Thus, except in unusual special conditions, except for the definition of the ITD, absorption is not beneficial. Diffusion is to be used on the preponderance of the side walls, back wall and ceilings. Absorption is not desirable! Absorption reduces an already sparse diffuse sound field into distinct specular reflections rather than increasing the diffuse field.

And new techniques such as that developed by Russ Berger allow additional unused attic or closet or adjoining rooms to add a pseudo-reverberant component to the diffuse field decay.

This is a 15 cent tour. There is MUCH more specific information available. And I wish I could say that by going to a website and simply giving them a drawing or the dimensions of your room that someone could reliably give you a turnkey package that was worth more than what you could do yourself with a ruler and a pencil.

It is actually not that difficult. But it is important that you specifically address certain signals and diffuse the rest. And if you desire a simple summary, you only absorb the critical first order reflections defining the ITD. There after (unless there is an exceptional anomalous circumstance), you will diffuse the remaining sound field.

As always, if anyone wants to deal with this in greater depth or with additional tools, PM me. I am available to chat via phone. And for all the toes I have stepped on and for any sacred cows I have tipped, I apologize, but please give me a holler and I think I can help to clarify any points anyone may want to discuss. MANY resources and much info is available, but it is simply not practical to cover it all here.

ConcatSmallRoomResponseCharacterisitcs.pdf

[picky]

mas: What do you do for a living? Outstanding post, man!

[colterphoto1]

I got the 4" foam, remember it's in wedges, so the thickness varies from 0" to the greatest thickness. For WIDE-band absorbtion, get the thickest you can. Otherwise you're not taming many frequencies.

Here's how I attached mine. My basement walls are cinder block for now, so I wanted some moveable panels that I would attach to a finished wall later. Purchased some black foam-core board 1/4 thick (wish I'd gotten heavier though). Cut sheet into several different sizes, all based on the foot-square theme. Some 2x4, some 4x4, etc. Laid out square grid pattern on the foamcore.

Then using caulking gun, put dollop sized globs of paneling adhesive near each of the corners where each foam square would be attached. This smaller amount also meant that I could remove the foam later should I choose to do so. Then apply squares in criss-cross or other patterns- PUSHING DOWN at each corner so that the foam would attach securely to the glue globs. Then laid panel on the floor with some weighted boxes on top to dry over night. The panels are very lightweight, I just poked some holes through them and hung on hoods with framing wire.

Michael

[colterphoto1]

Yes, I just reread Mas's excellent post. I actually understood that. Quoted here for those who didn't finish is his summation -

"It is actually not that difficult. But it is important that you

specifically address certain signals and diffuse the rest. And if you

desire a simple summary, you only absorb the critical first order

reflections defining the ITD. There after (unless there is an

exceptional anomalous circumstance), you will diffuse the remaining sound field."

Now go back and read that paragraph again.

I would ask the question- for rooms that display exceptionally harsh reverberant fields (like my basement room, is more absorbtion called for?

M

[wuzzzer]

Thanks for your post, colter. My basement is probably one of the most unsymmetrical, weirdest basements you'd see. Very low ceiling, parts of the ceiling jutting out around ductwork, odd part of the wall sticking out a few feet in the room to fit around the fuse box behind it. The more I think about it the more I'm tempted to move my system to our main floor living room.

But, my plan is to buy some double-sided tape as a temporary placement for the acoustic foam. Once its in place as I like it I'll probably just leave that on and see how well it holds. If not I'll get something like a spray adhesive.

[mas]

If I may, let me ask a couple of questions and then reply to Mike's question...and I will hopefully use it to illustrate a few fundamental issues that we commonly encounter in talking about this subject. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

You (Mike) mention a "particularly harsh reverberant field"...

While I certainly do not dismiss your point, I do have an issue with its real meaning. I suspect the reason for this problem is in terminology, and the tendency for us not to use standard terms that have real meaning in acoustics. So I will use it as a focal point to try to point out a few problems we commonly make and propose what I think may be going on, and hopefully a solution.

First, we must come to an understanding of the very real distinction between small and large acoustical spaces. Fundamental to the understanding of small acoustical spaces is the fact that they (as distinct from large acoustical spaces) do not have a reverberant field. Rather than debate this, please refer to Sound System Engineering, by <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />Davis (pp. 151-234)

Very quickly, the word reverberant is used in a myriad number of ways, and although the word may be used, its meaning varies substantially depending upon the context and the acoustical environment. And a proper understanding the use of this word is critical. A good example is our example here. Even I will take issue with someone's use of the word reverberant in the context of a small acoustical space and then turnaround and use it myself. But inherent in my use is the knowledge of the fundamental limitations and the fact that I am actually referring to a semi-reverberant field.

As it is FAR beyond the scope of this post, let me mention a few general definitions. And please be aware that these generalities have much detail beneath them!!

{Please be aware that several other concepts that are critical to the proper understudying of reverberation (as well as to large acoustical space acoustics) is the critical distance, Dc and RT60. But these are beyond the scope of this topic; I will not delve into them here. Again, while they are simple terms, the contributing factors are anything but! And while it is very important to understand them, it is their absence in a small acoustic space that is most significant here! }

There are five general classes of sound fields: free fields, diffuse (reverberant) fields, semi-reverberant fields, pressure fields and ambient noise fields.

In reverberant field "the time average of the mean square sound pressure is everywhere the same. The flow of energy is all directions is equally probable, which requires an enclosed space with essentially no acoustic absorption. The reverberant sound level is labeled Lr".

"In a semi-reverberant sound field, sound energy is both reflected and absorbed. Energy flows in more than one direction. Much of the energy is truly from a diffused field; however, there are components of the field that have a definable direction of propagation from the noise source. The semi-reverberant field is the one encountered in most of the architectural acoustic environments. The early reflections (i.e., under 50 msec after Ld) are labeled Lre.

But, now lets look at another very important qualification.

To quote a section for Sound System Engineering (p.211):

To quote Ted Shultz (formerly of Bolt, Beranek, and Newman):

In a large room, if one has a sound source, one can determine the total amount of absorption in a room by measuring the average pressure throughout the room. This total absorption can them be used to calculate the reverberation time from the Sabine formula. This method fails badly in a small room, however, where a large part of the spectrum of interest lies in a frequency range where the resonant modes of the room do not overlap but may be isolatedIn this case the microphone, instead of responding to a random sound field (as required by the validity of the theory on which these methods depend), will delineate a transfer function of the roomIt does not provide a valid measurement of the reverberation of the room.

What is often overlooked in the attempted measurement of RT60 in small rooms is that the definition of RT60 has two parts. The first part is unfortunately commonly overlooked.

1.) RT60 is the measurement of the decay time of a well-mixed reverberant sound field well beyond Dc.

2.) 2.) RT60 is the time in seconds for the reverberant sound field to decay 60 dB after the sound source is shut off.

In small rooms there is no Dc, no well-mixed sound field, and, hence, no reverberation. There is merely a series of early reflected energy. Consequently the measurement of RT60 becomes meaningless in such environments

The control of the early reflections becomes most meaningful because there is no reverberation to mask them.

So, fundamental to our discussion are two issues:

1.) What is the level of the reverberant field?

2.) How uniform is the reverberant sound levels distribution in the space?

(And I hope you see the multiple use of the word reverberant here! Essentially we are asking when is a reverberant field reverberant, and when is it not reverberant!)

This is precisely the issue I want to address regarding Mikes point, as he has zeroed in on precisely the issue we need to address!

In small rooms, we experience a preponderance of distinct room modes as well as a preponderance of distinct specular (non-diffused) low order reflections rather than a truly diffuse reverberant sound field.

Thus the room topology dependent LF modes must be dealt with by the use of LF traps.

First order early arrival time reflections that arrive within the ITD gap are absorbed. And please note, while this addresses Haas (Henry precedence Effect) issues, it also reduces the intensity of the specular reflections that contribute to a diffuse sound field!

And while some focus on this as a positive, there is also the other half of the situation to consider! It is difficult to increase the diffusion if you increasingly decrease the sources that may be diffused! The result, instead, is an increase in the number of specular reflections relative to, and at the expense of, the diffuse sound field!

Thus, the desire is to surgically control the early arrival first order reflections. But you do not want to remove all of these! You desire the reflection that is referred to as a Haas kicker. This point is often ignored in the race to remove all of the reflections! And the corollary problem for most is WHICH first order reflections should be removed and which should remain! Without a measurement to indicate the intensity and arrival time of each component reflection, just how does one determine which reflection to keep????

Beyond the ITD and the Haas kicker, it is desirable to have a well behaved diffuse sound field. But a small room lacks a truly diffuse sound field with equally distributed sound energy, the specular reflections tend to be focused and of relatively high intensity. The diffuse sound field should decay at an exponential rate, without the presence of reflections that exceed this level. Energy that exceeds this level is audible and detrimental.

Herein lies Mikes issue. How uniform is the reverberant sound levels distribution in the space? And does it exceed the exponential decay rate It is a very valid issue!

But simply knowing that there is a problem is not enough to correct it. The reason is that this diffuse sound field is already sparse in a small room. And the presence of a well-behaved diffuse field is a very desirable element! So, is the answer to simply absorb and indiscriminately diminish this diffuse sound field, all the while making the specular reflections even more apparent? The answer is an emphatic no!

But still, we are left without a way to know just which offensive reflections need to be addressed.

So we have two options.

The first for those who still run from the thought of moving beyond RTA and SPL meters, is to simply increase diffusive treatments in the attempt to increase the diffuse sound field while simultaneously diffusing the offensive reflections further.

Here I need to interject another observation before stating the second option.

Thus far we are treating the room based upon abstractions and suppositions. It is rather like Christopher Columbus in his initial voyages, setting out with the goal to land precisely at the Myrtle Beach pier without a map! I think you will agree that the odds of that are rather precarious, and any chance of success reduced to pure luck and coincidence.

The reason for this is that the ordinary tools can tell you the intensity of the total sound field, but little else. They cannot identify the component reflections that comprise the sound fields. Nor can they identify the arrival times of each of the component reflections. Nor can they identify the orientation and reflective path of the component reflections. Thus, you are wandering in the dark, persisting on faith based on abstract theory.

Here is why the time based tools are critical and also why it was their development that has allowed acoustics to move forward in such a dramatic fashion. They are pre-requisites to a greater understanding, and yet it is fascinating that so few are really aware of them, and how so many who are aware of them still dismiss them!

As these tools allow you to see not only the sound field, but also each component part, along with detailed information regarding the intensity, arrival time, and (in the case of TEF-PEQ) the ability to resolve each reflection into its 3-Space coordinates showing exactly where the effective reflection on each surface occurs, we are able to see the big picture as well as all of the atomistic component parts. This detail allows us to very surgically address each anomaly and to see the effect of any step we take. It becomes an easy process at this point.

Thus, the second option is to measure the room and to view the overall trend and then to focus on the individual component parts to surgically address the specific problem without adversely effecting other elements. This has the benefit of saving allot of time, and potentially saving allot of money in materials, as you only address the specific sources of problems rather than indiscriminately treating surfaces which unfortunately usually only move the problems around without actually resolving the problems.

So, in Mikes problem, we have specular reflections that are insufficiently diffused. We do not have too great a reverberant field, but instead we have a semi-reverberant field with specular components of excessive intensity. It is these specific reflections that need to be diffused so that they will contribute to the overall diffuse field while being eliminated as hard harsh reflections that are audible and detrimental to the listening environment. Often these offending signals are not single reflections, but are instead summed lower intensity specular reflections. And without measuring tools these would be impossible to resolve into their component parts for treatment. Only in rare instances would they need to be absorbed. And measurements would quickly identify the nature of the source of these reflections and tell us if this was indeed the case. But in either event, we would be proceeding based upon a solid understanding of the problem rather then an emotional guess.

I am reposting the graphic from the last post. Please look at the 2^nd and the 4^th diagram. The signals that Mike is referring to are those that exceed the exponential decay level of the diffusive field.

I apologize if I have both dealt with this subject too deeply for many, while at the same time without sufficient depth and explanation of so many prerequisite and co-requisite principles and considerations.

Again, if anyone has specific questions regarding problems, or would like to discuss or explore any other related issues, it is easier to speak to them by voice. Also, if you have pictures and or drawings, that always makes things easier! So, if you have questions, please PM me and we can talk by phone if you like. I am glad to refer you to more detailed references depending on the issue or to talk about more specific solutions.

ConcatSmallRoomResponseCharacterisitcs.pdf

[colterphoto1]

"But simply knowing that there is a problem is not enough to

correct it. The reason is that this diffuse sound field is already

sparse in a small room. And the presence of a well-behaved diffuse

field is a very desirable element! So, is the answer to simply absorb

and indiscriminately diminish this diffuse sound field, all the while making the specular reflections even more apparent? The answer is an emphatic no!"

Let me detail the problem. This basement room has concrete floors with only hard vinyl tile on it, cinder block walls, and 1/2" plaster board (not drywall) ceiling. Currently it is a workout room with a small Ht setup. I am hoping to make it my HT room eventually, but the walls will be be finished with traditional construction methods at that time.

I understand what you mean about well-behaved diffuse fields, and that some of the reflections make the room more 'interesting' for fine listening. I have exactly this in my Hearth room where I'm set up currently. The mix of carpet over double thick pad, plaster ceiling, and 3/4 real knotty pine walls gives a very nice 'warm' sound to the room that is not overly 'pingy' (the sound of hand claps in an empty drywalled space), nor entirely dead. This particular room works well for HT, but particularly sounds nice when 2ch listening. The room is more critical during 2ch listening imho.

If the basement room (or those of other Forum members) is to be a room constructed mostly for HT use, can it be assumed that the artificial acoustical space created by the mix engineer is considerably more important than any room effects I could invent, create, leave undisturbed, etc.? So that almost the ideal would be to totally remove the room from the equation so as to hear ONLY the mixed signals as coming from the 5.1, 7.1 9.2 speakers?

M

[mas]

If the basement room (or those of other Forum members) is to be a room constructed mostly for HT use, can it be assumed that the artificial acoustical space created by the mix engineer is considerably more important than any room effects I could invent, create, leave undisturbed, etc.? So that almost the ideal would be to totally remove the room from the equation so as to hear ONLY the mixed signals as coming from the 5.1, 7.1 9.2 speakers?

The listening environment is an integral part of the playback environment. While headphones come closest to eliminating this, even they cannot avoid this. And to this end a room exhibits both an ambient noise level as well as a relationship of the direct signal to the reverberant sound level (be it true reverberation or a semi-reverberant field). Thus the goal is to establish an optimal balance in order to create an optimal listening environment.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

The well designed room properly adds a diffuse field that adds a sense of space while preserving the primary focus which is the direct signal. The goal then becomes that of establishing a well behaved balance wherein the room does not become a source of deleterious effects.

Personally, I think the best room imparts a 'reasonable' ambience. Just as in a live performance. In a live performance (an acoustical performance sans sound reinforcement) the direct signal is presented, and a well designed room adds a subtle ambience. (...as distinct from some of the horrendous halls that seem to inhabit a Twilight Zone somewhere between a House of Mirrors and a Fun House.)

If one seeks to hear only the direct signal source without the effects of the room, they desire a configuration known as a reflection free zone (RFZ). This geometry was utilized pre-TEF to minimize the effects of reflections from the floor, walls and ceiling. Assuming the absence of speaker diffraction (as diffractive surfaces act as secondary acoustical points of origin), absorption was used to minimize reflections from control surfaces (boards, consoles, etc.). With the development of TEF, the natural progression of RFZ became the LEDE, and its practical progression of that design. But one must be aware, that with the removal of the room acoustics, the next order of magnitude concern becomes the design of the speaker itself with its multipoint sources of signals, diffraction, etc.!

The most significant advancement in the LEDE room was the movement away from the over use of absorption. And unfortunately, the topology of the early incarnations of the LEDE room seems to be the models represented in Everest and other sources. The result being a strange mix of negative reviews (due to the excessive use of absorption) and plans which still feature the over use of absorption! Few sources speak to the optimized design that has replaced these initial iterations of the concept! So, for many, this new acoustical science is stuck in 1977 where some of the new models are mentioned, but the more important associated advances in understanding that evolved as a result of these early models has not!

Be aware, the role of an engineer in a studio is to focus solely upon the direct sound. As they have no control over the playback environment, the focus should be only on the direct signal. To attempt to do otherwise would only serve to introduce even greater anomalies.

But, more to your question, the studio environment can indeed have a profound effect on the direct signal source, both positive and negative. And this brings us back to the other recent thread regarding soundstage. The source can range from a coherent source to a Frankenstein like artificial creation that represents a completely artificial and fabricated sonic environment. In my opinion, we have control only over the environment in which we listen. Beyond that we are free to evaluate and comment on the job of the engineer - and hence Mix Magazines TEC Awards! But we are not at liberty to change or rectify that job.

So I think it only reasonable that with regrads to recorded material we assume the best of the engineer and their efforts, as we are stuck with whatever they have 'created'. It serves as a baseline with which we much deal. Thus we need to focus on the elements over which we have control.

;-)

[WMcD]

Thank you very much, mas, for taking so much time and effort to describe all this. Excellent information.

The following is a bit of looking for cookie cutter approaches or cook book recipes. For good or bad.

I wonder if you could comment a bit on the Live End - Dead End room a bit more. It seems to me this is probably a fundamental. You have just about said as much, if I read correctly. Yes, we all can see that an optimization can't be accomplished without time domain measurements. That is becoming possible these days, and with the insights you've provided, that seems to be within reach of home tinkerers.

People are looking for guidance toward a goal using available materials. Some gurus talk about non parallel walls, proper room ratios, or building all the walls with some special foam. But most of us just can't move walls or cover all of them with foam material.

OTOH, the LEDE is "buildable". More importantly, existing rooms can be modified with panels which abosorb and panels which diffuse. These can be built in the garage. (Of course, I always write about polycyliners to diffuse.)

It looks to me that the average guy decides his room needs improvement. Then he hunts around and finds that there are sellers of absorbers and diffusers, and traps, and doesn't know whether he should add one or the others. All three, where, how?

One of my sophmoric thoughts was that the average listening room is so bad that anything will help. But of course that is a gross generalization. It might be better to say absorption at the front third, diffusers at the back two-thirds (I'm picking those fractions out of thin air), LEDE, is, very generally, the configuration to use.

I can appreciate that there are optimum targets to hit as a goal. These can only be hit with accuracy with energy time measurements and adjustments and lots of tinkering after the graphs are interpreted.

None the less, it seems to me that folks can make vast improvements by LEDE concepts. So they should not be discouraged by lack of perfection or problems arising from lack of measurements.

It is kinda the opposite of the stunt shows which say, "Do not attempt this at home, these are trained professionals." We can and should attempt it at home.

I wonder just how many home made panels we need. There is the "put up a mirror to see where the first reflection is caused." So some placement is critical.

It could be that only 20 percent or less of the walls need treatment to get an improvement. I dunno. That makes for a lot of work in the garage to make panels. Yet the final result could look like artistic wall hangings.

Best,

Gil

[colterphoto1]

On Gil's concept of LEDE, one technique that I think is effective for the average listener with no test equipment is the mirror test.

Sit in your fave seating position, with speakers splayed for best soundstage. Then have an some assist you by holding a mirror against the wall near the speakers. when you can see the horn's throat in the mirror, mark that spot as an area to place absorbtive panels. This is the point of first early reflection.

By taming these, I think it helps tighten up the image by eliminating the 'blurring' sound from this first early reflection, whilst leaving the all important 'room cues' or other reflections intact for a somewhat live sound. This is a bit more tame approach to creating an entire Dead End at the speaker end of the room and requires considerably less material.

[Rudy81]

I needed to tame a rather live room and am using some DIY 2" sound absorbers. The results are perfect for what I needed. Both sides of the room are treated symetrically.

[wuzzzer]

Looks great Rudy! I'll take some pics of my setup when I get it installed.

[damonrpayne]

What are those made of Rudy? Owens Corning 704?

[Rudy81]

I found the OC 704 panels, and for the price vs. performance, I chose 2" rock wool as explained in the Master Handbook of Acoustics. After looking at the absorption coefficients of both materials, the rock wool is virtually identical and half the price. The only caveat, is that rock wool is not rigid and needs to be contained by some sort of enclosure. In my case, a 1"x2"x8' frame and black material on the front did the trick.