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Diffusive Panels In Stereophile Question


Strabo
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On page 17 of the July, 2007 issue of Stereophile there is a picture (top right of the page) of some equipment but I noticed one of the walls in the room has what looks like diffusive panels assembled together into a pattern.

Does anyone recognize the diffusive panel and know who makes it? They look like they are used in a listening room in the "Industry Update" section of the magazine and I did not see any discription of the room, just the equipment from the picture.

I'd like to look into them and maybe discuss them here if we could figure out where they came from.

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There is an irony here.

The post is about "diffusive" panels, and all those two sites offer are OC 703/705 absorptive panels... And these can all be easily made instead of bought.

We continue to confuse absorption with diffusion, much like we confuse sound transmission with in-room reflections. This is like a surgeon saying: "Heart...lungs...hey, they're all pretty close...What's the big deal all about?"

There is a HUGE difference.

One might better look at the RPG site to discover what examples of real diffusion are.

http://www.rpginc.com/

Read Manfred Schroeder to understand why.

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I finally had a chance to scan the image. I doubt they would be effective very low because of their lack of depth.

I doubt they are random, but are they effective? Wondering if I could live with them on a wall or more.

Anyone recognize them?

post-10480-13819334999276_thumb.jpg

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Bumping this back up with another question.

I was playing with the quadratic diffuser tool on this site, http://www.mhsoft.nl/diffusor.asp#calcul

Was experimenting with different depths to get to a lower effective frequency when I decided to transpose the measurements. How effective would a QRD diffuser be if it was built to be 12 feet long and 1 1/2 inches deep using only seven wells?

The calculations show a frequency range of 402hz - 3Khz. Would that be more or less efficient at 400hz than a 3' X 1' 13 well diffusor that has a range of 400hz - 2.9Khz?

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Bumping this back up with another question.

I was playing with the quadratic diffuser tool on this site, http://www.mhsoft.nl/diffusor.asp#calcul

Was experimenting with different depths to get to a lower effective frequency when I decided to transpose the measurements. How effective would a QRD diffuser be if it was built to be 12 feet long and 1 1/2 inches deep using only seven wells?

The calculations show a frequency range of 402hz - 3Khz. Would that be more or less efficient at 400hz than a 3' X 1' 13 well diffusor that has a range of 400hz - 2.9Khz?

Diffusor width:

365 cm

theoretical depth:

3.8 cm

Prime seed:

7

11

13

17

19

23

Speed of sound:

345 m/s

Show sn


Calculations for the Quadratic Residue Diffusor

Width of wells: 52.14 cm
Depth of wells:
Well 1: 0.5 cm sn = 1
Well 2: 2.2 cm sn = 4
Well 3: 1.1 cm sn = 2
Well 4: 1.1 cm sn = 2
Well 5: 2.2 cm sn = 4
Well 6: 0.5 cm sn = 1
Well 7: 0 cm sn = 0

Bandwidth:

flow 3210 Hz
fhigh 402 Hz

Just a suggestion. Before you assume results that sound almost too good to be true, double check.

A LOW frequency limit of 3210 Hz and high frequency range of 402 Hz should give you reason to stop and think.

In most circles, 3KHz is greater than 402 Hz! (Well, unless you are dealing in the negative frequency realm!) There is no free lunch...

Try increasing the depth of the wells.

And as far as comparing the effectiveness of a 3' x1' panels versus a 12 ' x1' panel. which would be more effective?

Let's see. How large is your wall? If it is 12 foot long, what do you think would be more effective?: The entire length being diffusive for a particular bandwidth (albeit for a 1 foot height!!!), versus a wall that has, for a particular length, a 1/3 diffusive surface and a 2/3 reflective surface?

And enlarging our frame of reference slightly and considering that most walls in a room are slightly higher than 1 foot, this leaves the total effective reflective surface at a slightly higher total percentage, I'll let you think about that. ;-)

More total surface area coverage with diffuse rather than reflective surfaces is going to of course be more effective at diffusion!

Above their effective bandwidth they are going to be rather effective reflectors!

Again, there is no free lunch.

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Thanks for the response.

The web tool seems to be set up so that the depth of the well affects the low frequencies and the width of the well sets the high frequencies. It assumes that the depth is the longer distance which in turn affects the longer (lower) frequencies.

Using the web tool, if I want this to work down to 400hz it would need to be 12 inches (30.5 cm) deep. That's probably not going to happen in my room.

That's where I thought, what if I transposed the dimensions (which mixed up the FR readings on the web tool)? What if I have a 12 foot wall and covered it with one big shallow diffuser that was only 1.5 inches (3.8 cm) deep for the 3khz dimension and 12 feet (365.5 cm) long with seven wells that are 20 1/2 inches (52.14 cm) wide? Would it still be effective at diffusing a 400hz wave?

Logic tells me it should (the dimensions match), instinct (years of being wrong married) tells me it wouldn't. [*-)]

Btw, did you happen to recognize the panels used in the photo above?

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There is a fundamental relationship between frequencies and absorption and reflection (using traditional methods) relating quarter wavelengths with effective interaction. Thus a 400 Hz waveform which is ~2.8 feet long can be more easily addressed than a 100 Hz wavelength which is ~ 11.25 feet long or a 70 Hz wavelength which is ~16 feet long.

And generally speaking, wavelengths do not 'see' objects smaller than this, thus rendering low frequencies and long wavelengths more difficult to control than high frequency short wavelengths ( for example, 3 kHz, is ~4.5 inches long and 10 kHz is ~ 1.3 inches long). Thus a 70 Hz wavelength will not even 'see' most chairs or couches.

Accordingly, reducing the wells to extremely shallow depth while increasing the total size of the unit will not be more effective. In fact, to take this to more absurd lengths, we could keep doing this and eventually reach an infinitely large, flat wall that would, by this logic, be an excellent diffusor down to 0 Hz.

And, except for the infinitely large part, this would be a very practical tool!

Unfortunately this is a bit of illogic run amuck. ;-)) But hey, that would seem to mean that this really does belong smack dab in the middle of a home audio forum! (For all of you who can't discern my dry humor, that is a joke...)

Yes, the limit with most diffusion. like most absorption, is that the lower in frequency you go, the larger they will be, until you quite quickly enter a rather sci-fi/modern art' looking landscape.

And without going into any detail, simply because the techniques are NOT available to the home market, the latest diffusors representing the latest incarnation of the acoustic treatment model employ depths of 3 and 7 feet, and ~138, 646 and 24,336 block heights EACH, and require forklifts to move them (each one!). Definitely not a home brew unit in terms of execution or cost.

BTW, a big problem that is still being encountered is that most diffusors are too absorbent, despite being made of solid reflective materials.

And as far as the wall treatments you posted, I looked around to the various reputable sources of which I am most familiar (and a few I am not) and I was unable to identify them. But I can say that I would have a few concerns that would have to objectively be proven false. Basically, what you have are elegantly sculpted absorbers, despite their looking as if they would be diffusive.

And that room is going to be dead! They have done exactly what Chips Davis did in implementing the first iteration of Don Davis' (no relation) LEDE concept at Wally Heider's almost 30 years ago*...which, by the way, had them all running for the doors to modify the concept resulting in a much more judicious application of absorption!

*and which the folks at Auralex seem to have failed to understand...

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Cuz that's how the fysiks work out [;)][:P]

But if the color of a cable's insulation correlates to its
effectiveness and price, why doesn't the appearance of room treatment
stuff?

And to answer my own question with a smart aleck answer, there actually does seem to be a correlation between appearance, effectiveness and price! Unfortunately, the more
abstract and sci-fi it appears, the more it costs and seemingly the
more effective it is! Maybe we need Martha Stewart to become involved
in acoustics...or maybe not.

But a bit more familiarity with fundamentals and allot less concern with gimmicks would be a very welcome development!
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Wow! I again accomplished the reputedly 'impossible', but far too common!, double Triple post!

No wonder it takes so damned long for the process to complete! It's busy doing extra work!

Fisiks according to Microsoft! Now there is a strange landscape!

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Cuz that's how the fysiks work out [;)][:P]

But if the color of a cable's insulation correlates to its effectiveness and price, why doesn't the appearance of room treatment stuff?

And to answer my own question with a smart aleck answer, there actually does seem to be a correlation between appearance, effectiveness and price! Unfortunately, the more abstract and sci-fi it appears, the more it costs and seemingly the more effective it is! Maybe we need Martha Stewart to become involved in acoustics...or maybe not.

But a bit more familiarity with fundamentals and allot less concern with gimmicks would be a very welcome development!

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I think you've got a reflection in your cable...might wanna give that ISP a call!

I think I have a similar impedance mismatch issue with my skull as well. ...Seems some ideas have difficulty coming out in a coherent form, and still more have trouble coming in!

[;)]

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If I understand this, the depth of the well is the only thing that affects the low frequencies?

By widening the wells we see a decrease in the affected high frequencies. This makes me think that theoretically you can build these to be narrow bandwidth and according to that web tool, you can. We are just pretending here. I have no desire to build a single frequency diffuser. Using 60 cm by 4.99 cm deep gives us a well of 8.57 cm by 4.99 cm and a calculated frequency response of 2.445khz - 2.447khz. Is this not true either?

If it is, I don't understand why you couldn't continue to widen the wells to 25 cm each well times seven wells (175 cm total) and have a frequency response of 2.4khx - 840hz, or 840hz - 2.4khz. [:^)]

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You are taking a calculator and trying to derive the laws of the universe from a limited tool![:|]

Exactly the opposite of what it was intended to be used for!

This is a simplified tool to calculate a few of the acceptable combinations based upon number-theoretic principles (primitive polynomials over finite fields, quadratic residues, and discrete logarithms) that contribute to making reflection phase gratings that have the property of scattering nearly equal acoustic intensities in all directions.

If you want to understand how to massage the numbers, please read up on quadratic residue sequences. A good place to start is Schroeder's Number Theory in Science and Communication as well as his Fractals, Chaos, and Power Laws.

It is a multi-variant calculus, and you cannot simply reduce this system to a single variable where "the depth of the well is the only thing that affects the low frequencies". The answer to that is: No. This is true only after you have chosen and specified all of the other variables! Then, if you have defined a system with only one changeable variable, then of course it is the only variable that changes! But the other factors are not fixed, nor must they remain static. That is not a necessary precondition.

Hint, if you propose a QRD that is extremely shallow, it will not be effective at the lower frequencies! This is not some magic tool that somehow overcomes the basic laws of physics. And if you use the calculator that you are playing with and you end up with a lower frequency that is greater than the upper frequency, you have garbage. The calculator can act as an aid, but it does not preclude you from putting nonsense in and getting garbage out. It is a very simple calculator that simply crunches some numbers for you. It is not a comprehensive 'everything there is to know about quadratic residue' tool !

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It is a multi-variant calculus, and you cannot simply reduce this system to a single variable where "the depth of the well is the only thing that affects the low frequencies". The answer to that is: No.

That is the answer I expected. It only took 12 posts to get it. [Y]

I think I get it. If you widen the wells enough to deal with the longer waves, it still will have little to no effect if the depth of the well is too shallow to be hit by the wave. The diffusor needs to protrude into the room to be hit by the wave.

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