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Old 6th May 2009, 01:23 PM   #1121
soongsc is offline soongsc  Taiwan
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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.
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Old 6th May 2009, 01:44 PM   #1122
gedlee is offline gedlee  United States
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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!).
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Old 6th May 2009, 02:37 PM   #1123
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Quote:
Originally posted by gedlee
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!).
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
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Old 6th May 2009, 02:51 PM   #1124
gedlee is offline gedlee  United States
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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.
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Old 6th May 2009, 03:03 PM   #1125
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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
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Old 6th May 2009, 03:09 PM   #1126
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By the way, this is the schematic of a CBA:

Click the image to open in full size.

8) open-pore melamine resin foam (e.g. Basotect)
9) metal plate
10) permanently elastic, close bond (e.g. double-faced adhesive tape)

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Old 6th May 2009, 03:28 PM   #1127
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Isn't mass of the panel the primary factor in determining the damping, and then the foam/air/glue behind it determine the bandwidth? So that a thin light metal would affect a different range, higher range, of frequency than the heavy dense drywall -would this be correct?

Tony
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Old 6th May 2009, 03:57 PM   #1128
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No, because a CBA resonates not only at one frequency like a normal plate absorber does.

Best, Markus
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Old 6th May 2009, 04:39 PM   #1129
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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
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Old 6th May 2009, 04:56 PM   #1130
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DIY! Get steel plates (2mm), glue, foam (10cm) and mount it near room corners. I've never seen a tutorial or any data for the drywall approach although I'm sure it works.

Best, Markus
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