goskers,
Proper damping throughout the frequency range is necessary. I once experienced a situation where a friend though his room was too dead. When I looked at his speaker, it was evident that the type of drivers used was less revealing in detail, and thus it was desireable to have a more live room. I demonstrated the case using a different pair of speakers. The reason why LF damping is important is because even without the room, the LF will decay a a slower rate. But the proper damping if the other parts of the spectrum is equally important.
Proper damping throughout the frequency range is necessary. I once experienced a situation where a friend though his room was too dead. When I looked at his speaker, it was evident that the type of drivers used was less revealing in detail, and thus it was desireable to have a more live room. I demonstrated the case using a different pair of speakers. The reason why LF damping is important is because even without the room, the LF will decay a a slower rate. But the proper damping if the other parts of the spectrum is equally important.
Panel absorbers can be effective, but in comparison to what I get with a flexible wall they are not nearly as effective. It all comes down to area. If you covered the walls with panel absorbers then they would be as effective as what I do, half as much, half as effective, a single panel, not much at all - its not a complex calculation. And if you cannot change the structure then panels are the only choice. Let's just not pretend that they can be anywhere near as effective in terms of appearance, cost or effectiveness as doing it in the rooms structure itself. Panels just become the only option that's all.
Markus
Panel absorbers predate Fraunhofer by decades, going back to the 60's and Ted Shultz at BBN. He was really the founding researcher and I still find his work the best on the subject. Next would be a very rare book by Uno Ingard on "Sound Absorption" - a monumental, comprehensive study of what can and cannot be done, alas all but extinct (I have a copy!).
Markus
Panel absorbers predate Fraunhofer by decades, going back to the 60's and Ted Shultz at BBN. He was really the founding researcher and I still find his work the best on the subject. Next would be a very rare book by Uno Ingard on "Sound Absorption" - a monumental, comprehensive study of what can and cannot be done, alas all but extinct (I have a copy!).
gedlee said:
Hi Earl,
don't know the work of Ted Shultz so I'm not sure if it's the same principle. The Fraunhofer "invention" is basically a front plate (with very low internal friction) glued over its entire surface to a material with high internal friction. This does not only form a damped mass-spring system but also allows for flexural vibrations of the front plate.
This is different from all plate absorbers I've seen so far. I guess that's the reason why Fraunhofer got that primitive thingy patented.
Best, Markus
The only difference would be gluing the material on the inside to the plate, thats not usually done, nor necessary IMO. Otherwise a resonate plate backed by absorbing material is decades old. The front plate "having very low internal friction" also seems like a pointless technique when something of high damping is then glued on. More like a "patent" technique than a real one.
At any rate, if you want to know all about how to design those things read Shultz or Ingard.
At any rate, if you want to know all about how to design those things read Shultz or Ingard.
Using a plate that is allowed to vibrate at ALL of its resonances IS different to plates that are mounted in other ways, no? It's all described in the book "Schallabsorber und Schalldaempfer" by Prof. Fuchs–still available but German only.
Anyway, I just posted the example to show that there are add-ons that work. So nobody needs to build a new house in order to get decent absorbtion at low frequencies.
Best, Markus
Anyway, I just posted the example to show that there are add-ons that work. So nobody needs to build a new house in order to get decent absorbtion at low frequencies.
Best, Markus
By the way, this is the schematic of a CBA:
8) open-pore melamine resin foam (e.g. Basotect)
9) metal plate
10) permanently elastic, close bond (e.g. double-faced adhesive tape)
Best, Markus
An externally hosted image should be here but it was not working when we last tested it.
8) open-pore melamine resin foam (e.g. Basotect)
9) metal plate
10) permanently elastic, close bond (e.g. double-faced adhesive tape)
Best, Markus
Ah I see your links you posted now, which explained more... very interesting product.
Unfortunately it is also quite expensive, compared to the drywall approach. - I found a single 16 sq ft RPG version panel is $900.
http://www.silentsource.com/diffusors-modex-plate.html
-Tony
Unfortunately it is also quite expensive, compared to the drywall approach. - I found a single 16 sq ft RPG version panel is $900.
http://www.silentsource.com/diffusors-modex-plate.html
-Tony
Yeah DIY would be an option.
Looking closer, something looks fishy...
Can you have more than 1.0 coefficient of absorption? I thought 1.0 was the max.
They show it going higher than one:
http://www.rpginc.com/products/modexplate/modplate_troom.htm
I see they also used special test chambers and don't follow the industry standards, so comparisons aren't apples to apples with these numbers...
http://www.rpginc.com/products/modexplate/
Looking closer, something looks fishy...
Can you have more than 1.0 coefficient of absorption? I thought 1.0 was the max.
They show it going higher than one:
http://www.rpginc.com/products/modexplate/modplate_troom.htm
I see they also used special test chambers and don't follow the industry standards, so comparisons aren't apples to apples with these numbers...
http://www.rpginc.com/products/modexplate/
markus76 said:
Hi,
the total effect will in essence be proportional to the covered surface area. Having panels lets say about 4 sqm area would be as many as many people wouldn't accept for their homes.
A living room has a surface area all walls included of about 100..200+ sqm. And the absorpion of any panel will not be 100%.
In simulations and very special studios the damping might be an option. A living room would benefit more from even more drivers to densify the (non) modes. At least cost wise. An appropiate driver wouldn't cost much more than 30bucks/pc.
by
TRADERXFAN said:
The idea is to use the mass of a material to substitute for the mass of an air column in a Helmholz resonator system. The material density is not so important its the mass / area that matters.
The earlier panel absorbers just used air as the spring, the Fraunhofer ones use a damped material as the spring.
markus76 said:
Markus, this just doesn't make much sense either from the theoretical standpoint or the measured data. It's a single resonance that is well damped, just like all other panel absorbers. Only the fundamental mode will be at all effective at absorption in a small panel like this. Higher modes will all be 1/2 the area in counter phase with the other half and won't be very effective. Only the lowest mode has all points in phase. Since the wavelength is much longer in air than it is in the plate, the plate will react to the average of the pressure across it. This is zero for all modes but the first.
markus76 said:
My book has a tutorial. Steel is certainly not required, as I said above. Its mass/area and a good plywood or MDF also works well.
There is no standard for measuring absorption at these frequencies so there isn't a lot of good data.
Tony
There are always assumptions made in absorption coefficients and those assumptions are violated for large absorption. Hence it is not uncommon to get numbers slightly greater than 1.0, but they should not be too much greater.
Thanks for the info...
I was just discovering some of this, for myself, here...
http://www.ethanwiner.com/acoustics.html
its a good read for the layman like myself
I was just discovering some of this, for myself, here...
http://www.ethanwiner.com/acoustics.html
its a good read for the layman like myself
gedlee said:
Obviously it doesn't make sense to you but there IS a difference to normal plate absorbers (see Fuchs). I can cite a couple of papers but they are all in German so it would not help. Faist builds anechoic test chambers (http://www.faist.de/typo3/en/faistprodukte/faistakustik0/faistfreifeldraum0.html) with CBAs so I have to assume those panels work. If you need or want to know more about the physics, why not get in contact with Peter D'Antonio directly.
Best, Markus
TRADERXFAN said:
Yes, Ethan's corner traps will work fine (He's a very nice guy and always open for questions). But CBAs should be more effective. In any case the fact where you mount absorbers is critical.
For an explanation of absorption coefficients greater 1 see:
http://zone.ni.com/devzone/cda/tut/p/id/1556
Best, Markus