Klipschorns and ASC tube traps

[mas]

Here is another view of the typical diffusive behavior versus reflection and absorption.

[mas]

As far as building diffusors....

Sure, they can be built, but calculating the units and the optimal effective bandwidths is a little bit tricky.

While you needn't study allot of math to do this, the work of Manfred Schroeder is definitely the place to begin.

The biggest problem is that they tend to be extremely labor intensive, and there is a problem with many of the diffusors being too absorptive.

When I get back I will try to address this subject a little more. (But may I suggest giving me a PM and talking 1 on 1 via the phone about this. Hint...)

[Arkytype]

Here's a great site for the acoustic treatment DIYer.

http://www.mhsoft.nl/Helmholtzabsorber.asp

After plugging in appropriate room or frequency values, you can build several absorber or diffusor treatments. Be sure to click on the the links inside the Quadratic Residue Diffusor link. Good info there for the newbie or old timers as well.

[Arkytype]

Almost forgot Ethan Winer's contributions. He makes the RealTraps bass traps and has written extensively about room treatments. He's even posted plans for some DIY diaphragmatic bass traps.

http://www.ethanwiner.com/acoustics.html

http://www.ethanwiner.com/basstrap.html

http://www.realtraps.com/art_etf.htm

[mas]

Here's a great site for the acoustic treatment DIYer.

http://www.mhsoft.nl/Helmholtzabsorber.asp

After plugging in appropriate room or frequency values, you can build several absorber or diffusor treatments. Be sure to click on the the links inside the Quadratic Residue Diffusor link. Good info there for the newbie or old timers as well.

Be aware of the error on the slot absorber calculations (equations).

Also, be aware that effective frequencies for diaphragmatic traps (as posted on Ethan's site) are rather narrow and hence limited. Tuning is advantageous and room measurements to determine just what those frequencies are are even more advantageous (it helps to know where you are and where you need to go). You would do well to consider this before simply using a generic diaphragmatic trap.

Also, the problem with using lots of large panel traps is that this is essentially the same as absorbing 'everything' and creating a very dead room (as low frequency traps trap all of the mids and highs that are incident), not all all the approach that diffusion offers in creating the appearance of a larger room.

[gaspr]

There certainly seems to be two main schools of thought on how a
room should sound after treatment. On one side is Ethan Winer and
his followers who are always preaching that "you cannot have too much
broadband absorbtion". His remedy for almost any acoustic
problems is to add more bass traps. Ethan seems to really
believe what he is preaching and seems to have the musical and
acoustical knowledge to back it up. However, he does sell
the very products that he continually is recommending.

On the
other side, mas and many others are saying that you should only
use as much absorbtion as necessary to treat the measured
problem. This side also preaches that "you cannot use too much
diffusion" in the treatment of a room.

These two approaches must result in very different sounding rooms. Your thoughts on this??

[PrestonTom]

To cut to to the chase ...

Re: "never too much broadband absorption". The awful truth is that the absorption will not be broadband. It is rather difficult to absorb low & lower frequencies because the wavelengths are relatively long (exceeding 10 feet below 100Hz). At very high frequencies it is a piece of cake, So you end up with a very uneven degree of absorption across the frequency range. This is hardly "lots of broadband absorption".

The issue is: what is the goal. Here are where the two camps differ. Do you want to absorb as much sound as possible and maybe create a very dead room. Or can reverberation sometimes not be the "enemy"? In a nutshell, the other camp feels that reverberation is "bad" if it arrives to close in time to the direct sound.

I will not speak for MAS, but it is sometimes easier to understand the other "camp" by understanding the forerunner of this approach. This antecedent was referred to the Live End Dead End (LEDE) approach from about 20-30 years ago. There is plenty of info about it on the WEB and in a sense it would serve as an introduction to the more contemporary approaches. I mention it since it seems more intuitive for many folks, especially if they are shy about the physics and math. Actually LEDE is not a bad way for one to think about their own situation.

You should be aware, and I am painting with a broad brush, that some of the folks you are citing in the "lots of broad band absorption" camp, make money by selling absorbers etc. The measures they advocate are also simpler to measure and "interpret". In some cases, these guys do not even bother emphasizing the importance of measurement (IMO)

IMO, failing to have any sort of acoustic goal (whether it is LEDE, or speech intelligibility, attenuation of sound from the next room, or what ever), and failing to measure before hand to guide the path is a recipe for failure. Some of these goals are quite different and require different solutions.

But I don't sell absorbers,

-Tom

[mas]

They DO result in two different results!

(Thanks Tom! I goofed around while writing this and did not see your post in the meantime!)

One groups is using what they have access to and also what they sell. And I am not trying to denigrate them! They have had an interest and have been trying to accomplish results although using a much more basic approach - much of it based upon what they could glean from the 'other' groups research.

Ethan, with all due respect, as he has been very active in making many aware of room problems, has only begun using measuring equipment, and he recommends the ETF unit as it is very accessible to users (and I agree). But to put things into perspective, he only recently figured out that EQ does not correct room problems (in 2005!). So one may say that their approach is much more home brew and not based upon much of the current state of the art tools and research.

And before I run on further, let me clarify something. My position is not to simply use as much diffusion as possible. My position is to use what is necessary. I advocate employing current measuring gear to know exactly what is going on and to treat what is real in an effective verifiable manner.

The irony is after doing this for so long and after encountering the "use lots of absorption" mantra from those who have just discovered that the room effects the intelligibility of the sound is that diffusion is the more general purpose treatment with absorption being used surgically for bass modes and to establish the ITD gap.

Now, as far as what I propose, I am not the originator. I am but a messenger. I will defer to the folks at SynAudCon and to Don Davis, Dick Heyser, Don Keele, Peter D'Antonio (RPG), Russ Berger, Bob Todrank, Manfred Schroeder, Dave Andrews, Dr. Ahnert and many others who have done much of the preliminary work and who continue to push the current envelope. This is the same group that brought you the TEF and time based analysis with Dick Heyser. I have been lucky enough to be associates of theirs for the past 23 or so years and to have participated in many of the functions in which we all contributed and listened and exchanged ideas.

To really confuse things, and as much of what you read on the web is incredibly dated and published by folks who had little clue what was originally postulated, let alone where it has evolved, I advocate what has become known as the LEDE concept. But again, this concept has evolved into a much more elaborate model that is definitely not 'Dead End' (although the comparison is fine - although far too many take this literally). And you will not read of the current model on the web. What you will find (and which I love reading in a very perverse way) is the complete nonsense, pro and con, published regarding it from folks who have only heard about it and interpret it based upon other 3rd party interpretations. If you want to experience it, find Russ Berger designed room.

But as Tom mentioned, the basic concept is valid, but the implementation has evolved greatly into a much more surgical application. In other words, the MAJOR change is that the "dead" end of the room was very quickly upon its first use (at Wally Heider's) determined to be far too dead! And the limitation of absorption, as well as the advanced in diffusive materials, have greatly advanced leading to a very surgical application of absorption and much greater use of advanced diffusion.

And for a really amazing evolution of the model, we are now moving into a new paradigm that builds upon what we have discovered. But I will defer mentioning this model (see what a tease I am! PM me if you are really anal and need to know) as this will only confuse things and it is not reasonable to reproduce without state of the art diffusion materials with wells >12 feet deep and elements numbering >~15,000. Not exactly what anyone is going to do in their garage or basement! Especially when a 2D 100 element skyline (RPG) style diffusor freaks most out.

So, is there a difference, aside from name dropping? You bet!

One is done on a feeling. A sincere attempt by many to do it yourself or to sell you their attempts to do it. But done with little analysis and knowledge of where you are and where you are going. And folks, a hand clap is not the basis to do anything, except perhaps to return to perform an encore performance. ...But certainly not acoustical treatment. But they are trying and I applaud them.

The latter approach is based upon allot of very advanced acoustical analysis and MUCH advanced experimentation and subsequent scrutiny. The latter group is the group which has 'written the book' so to speak on modern acoustics, and others have subsequently and to various degrees based their approaches on this work.

The alternative is a well behaved optimized room that goes far beyond what Ethan tries to do. And this approach also allows you to vary the response for your personal bias as well. And you see exactly what is happening and you can objectively correlate exactly what the response is with the response characteristic of the room. And you can also surgically address specific anomalies that less sophisticated approaches cannot begin to ascertain.

So the various panels and treatments are simply tools to affect the room response. They are not used indiscriminately and they are definitely not 'one size fits all', but rather as pieces and parts to achieve a greater more reasoned response model. We use the tools as they are needed. It is like a cabinet, where nails and screws are employed strategically to hold it together; but it is ill advised to use as many nails or screws everywhere as you can!

And where this is pointing is the need to post more details on the specific approaches to tuning a small acoustical space! As, if you do not know why you are doing something, putting up the most expensive panels, be they absorption OR diffusion, without knowing exactly why, or what they change, is not going to fix the problem! There is a method to the madness. And I suspect what folks would benefit from most is a greater understanding of the method.

[Guest " "]

"""Re: "never too much broadband absorption". The awful truth is that the absorption will not be broadband. It is rather difficult to absorb low & lower frequencies because the wavelengths are relatively long (exceeding 10 feet below 100Hz). At very high frequencies it is a piece of cake, So you end up with a very uneven degree of absorption across the frequency range. This is hardly "lots of broadband absorption"."""

Excellent point.....you might have to fill the whole room with cotton balls to get down to 100hz...but then...how would we get in the room with out all the cotton balls leaking into adjacent rooms.

Should I use tube traps...felt on various parts of my horn ( closer to the source), ...a napkin over the exit path of the horn, ...or should use an electrical method of lowering db's at on the HF end (see Mcintosh Autoformer guide)....maybe audiophile earplugs (something I would wear and the wife would not have to look at),...or a plain and simple fuel saver magent over the tweeter wires...or maybe retractable walls (they would go up when the music starts)

All answers may be correct.

McIntosh%20Autoformer%20Training%20Page.pdf

[mas]

They all may be correct for radically different applications. They are not interchangeable, and that is the common error.

All of the tools in a craftsman's shop are 'correct', but it would be an error to think that a saw and a screwdriver may be effectively interchanged to serve the same purpose!

You can change the character of the direct signal to your heart's content. But with the exception of signal alignment, none will have an appreciable impact with regards to improving the room-speaker interaction.

Also, for those who are caught up with the frequency aspect of absorption, the acoustical impedance of the absorptive material will indeed result in the absorption and reflection of various frequencies in a non-linear manner. But to focus on the frequency aspect is to completely miss the point. Our focus is NOT EQing the room! We are aligning signal arrivals and their relative gain within the time domain! This will resolve the majority of the problematic frequency domain anomalies! An EQ won't!

Standing waves are dealt with in a different manner only because of their wavelengths being large relative to the room, whereas all other frequencies are small relative to the room. Thus different techniques are required. Thus we focus on their frequencies for the purpose of identification and tuning the load impedance of the traps necessary to terminate them, but we are most concerned with their persistence in time - their resonance - which makes them a problem.

The largest impediment to understanding this topic is that one must re-frame their frame of reference. If you still thinking solely in terms of frequency response, you won't get it, and the same debates will continue unresolved ad nauseum. What we have learned in the past 30+ years is that we must fundamentally approach the topic in the time domain, and once this is optimized, the vast majority of frequency domain issues shake themselves out. Again, this shift in perspective is critical to understand this topic.

[Groomlakearea51]

"One must re-frame their frame of reference. Nobody gets in to see the Wizard. Not Nobody. Not No How."

Love it!!!![H]