Can you have too much diffusion

microstrip

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May 30, 2010
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Vince
Marcs panels are not a conventional method of treatment . They would be better described as reflector/absorbers as they are located to prevent first reflections from front wall, side walls and ceiling.

Can you point a link to some place describing these panels or give us some information on how they behave versus frequency?
 
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spiritofmusic

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Jun 13, 2013
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Since fancy = pricy, I'll take non-fancy.
 

spiritofmusic

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Jun 13, 2013
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Can you point a link to some place describing these panels or give us some information on how they behave versus frequency?
I'll rely on Phil to post some info and pics, the UK website is pretty useless.
 

pjwd

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Jun 23, 2015
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Can you point a link to some place describing these panels or give us some information on how they behave versus frequency?
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Micro
This is for a 12mm panel , Marcs are 25 mm so probably go deeper
It is recycled drinks bottles and is probably not consistent around the world but it would be similar I would think.
You can improve it by doubling up with a insulation filled cavity in the centre , sculpt the edge to reduce diffraction etc so very versatile

I first used it many years ago in recording studios
Cheers
Phil
 

MTB Vince

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May 11, 2019
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[/URL]
Micro
This is for a 12mm panel , Marcs are 25 mm so probably go deeper
It is recycled drinks bottles and is probably not consistent around the world but it would be similar I would think.
You can improve it by doubling up with a insulation filled cavity in the centre , sculpt the edge to reduce diffraction etc so very versatile

I first used it many years ago in recording studios
Cheers
Phil
Hey guys, a semi-rigid bonded fibrous wool insulation product of the same density and material depth will offer similar absorption characteristics whether made from glass fiber, mineral fiber, PET fiber, or recycled denim fiber.

Even more relevant is the fact that all these materials operate under the same physical laws. A 1" deep panel of 3-5lbs/sq ft density made from any of these materials mounted in free air will only absorb sound frequencies passing through it at and above a 4" wavelength or 3.375kHz. That's the way the physics work. The lowest efficient absorption frequency corresponds with a panel depth of 1/4 of that wavelength.

Mounted flat to a wall though, sound is reflected off the boundary behind the panel and back through the fiber a second time. So for 1" deep flush mounted panels where the sound is entering at near a 90 degree angle, we now have a 2" apparent depth able to absorb frequencies with an 8" or shorter wavelength. So panels mounted flat against the front and rear wall boundaries would absorb frequencies above 1.68Khz. Not great, we have left the three very important octaves comprising the entire lower midrange (250-500Hz) and almost all of the midrange (500Hz-2kHz) untreated.

But wait! We get a further performance boost when mounting a panel along sidewalls, floor, or ceiling in order to absorb primary reflections. In this case the sound converges with the panel at an oblique angle. Lets use 45 degrees for this example where the sound wave travels 1.4x the distance through the fiber before bouncing off the boundary and traveling 1.4x the distance again. Now the soundwaves passed through 2.8" of fiber in total which is the quarter wavelength of 1.2kHz. Hmmmm... Best case scenario with our 25mm panels mounted flush along our sidewalls, we still fail to absorb the lower midrange and more than half of the two octaves of the midrange.

The moral of this story is that even when you make use of best practice insulation materials in the optimal density for your absorptive reflection treatments, if they are not deep enough they will not be sufficiently broadband. If the room treatments employed fail to absorb the entirety of the lower-midrange through to the highest audible frequencies, you stand an excellent chance of tipping your room's overall spectral balance towards dull or dead sounding. When you go back and run the math for absorptive panels effective down to 250Hz or lower, you discover why absorptive panels 4" deep or greater are current acoustic best practice.
 

pjwd

Well-Known Member
Jun 23, 2015
299
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Brisbane
Vince
There are complexities in all this beyond my paygrade but you have to add flow resistivity, fibre densiry and I am sure other stuff to the thickness. Engineers at Sydney Uni were able to combine a range of layers of varying flow resistivity and density and achieve the same absorbtion in a 250mm depth as the normal single layer 600 depth used in anechoic chambers.
Marc is not using the panel flat on the wall .. that would be a disaster... they are 300 wide and stick out at angles like a half open louvre so sound will pass through many panels with air gaps in between and create absorbtion but the important point is that residual reflections are away from listener so non correlated early reflections are not smearing direct sound. Both partial absorbtion and diffusion ( apart from some clever geometry) do not do this

I can see from your amazing room you are all in on broadbased absorbtion for a large area of the room ... this makes sense... for your surround sound particularly
In Marcs case we are trying to keep the room live as possible and only treat first reflections for clarity then bass absorbtion for reverb and then , if needed, you would add broadband absorbtion out of the crtical first reflection points. Marc is happy with this and the latter has not been necessary. Other folks may enjoy a more damped space .. good for them.
Cheers
Phil
 

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