# Acoustic absorbtion with a hard surface?



## designosaur (Mar 2, 2013)

I have a large reflective space, and prefer a modernist aesthetic. I don't really like the idea of fabric covered panels. 

Is it possible to achieve worthwhile absorption with a layer of thin wood veneer or similar materials over a 1 or 2in thick rock wool type insulation panel? I realize this will tend to reflect the higher frequencies.

I have seen some perforated wood panel systems for large scale architecture projects out there that might improve on that concept. 

Is there Any data available on perforated open area vs freq response out there?

Your thoughts?


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## bpape (Sep 14, 2006)

Perf panels will be much narrower in scope and more tuned in nature. Slotted can act as a combo absorber/phase grate for scattering. Regardless, you'll need a ton more surface area with treatments like these than with typical broadband and something like these are not really suitable for reflection duties.


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## RBTO (Jan 27, 2010)

Perforated metal absorbers have been used for years in industry. If you remember stand-up pay phones, they employed a perforated metal enclosure whose purpose was to absorb ambient sound within the range of voice frequencies. I know these are available as architectural panels, though I don't know a source, and I would venture to say they are expensive. The problem with this approach is to get a smooth response across the range of audible frequencies because a perforated metal sheet is actually a frequency selective filter which depends on the size of the holes and their spacing. The same principle applies to perforated motion picture screens, and they achieve a pretty flat response over the audio spectrum.

The following is a good write-up on the goal and approaches used in perf-metal sheeting and might lend itself to your application. The perforated material doesn't have to be metal, and could be plywood, though it won't have exactly the same characteristics (hole depth and absorption within the hole - i.e., plywood versus metal - also comes into the equation).

http://www.iperf.org/IPRF_ACUSES.pdf

Ultimately, you might be served just as well by selecting a visually appealing absorptive material unless you specifically want the perforated metal look.

Here's another link you might find useful: http://www.kineticsnoise.com/interiors/knp.html


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## designosaur (Mar 2, 2013)

Perfect. Thanks. Exactly what I was looking for.


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