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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Diffusor w/ Fiberglass for absorbtion? - Will this work? posted by scvbrent on November 19, 2007 at 19:39:43:
Check out Everest's "Master Handbook of Acoustics". The device in your link is what he describes as a polycylindrical diffusor and there are full instructions in the book though they happen to be hidden in the chapter on absorption rather than diffusion and they are called "polycylindrical absorbers" and "polycylindrical diffusors" at different points of the discussion.
bogatg suggests that the wood will be reflective and that you need uncovered insulation material for absorption. That's the stock 'gut reaction' but it isn't the whole of the story.
You can use a panel of plywood as an absorber, a 'panel absorber' to use Everest's term, and you 'tune' their effective bandwidth with the thickness of the panel and the depth of the enclosed air space behind it. Placing some insulation material in the space behind the panel improves the effectiveness of the device as an absorber.
The curved ply surface of the polycylindrical device in your link is stiffer and less effective as a panel absorber but it still provides some absorption at lower frequencies and, as with the panel absorbers, placing insulation material in the enclosed space behind the plywood surface improves effectiveness. The absorption curves shown in Everest for panel absorbers and polycylindrical absorbers/diffusors show similar curves for empty devices and higher absorption coefficients coupled with narrower bandwidths for the panel absorbers compared to the polycylindrical devices. They probably won't be as effective at bass absorption as a proper bass trap but they will certainly assist in bass absorption. From what Everest says, they're most effective at absorption if the cavity is actually filled with absorption material so putting more fibreglass in the cavity than displayed in the photos in your link would be beneficial.
At higher frequencies they are reflective and the curved surface reflects sound over a wider angle of dispersion than you obtain with a flat surface. That will provide useful diffusion at mid to high frequencies.
So the devices really act provide a combination of absorption at frequencies below, say, 500Hz and diffusion at mid to high frequencies. They're not the most effective devices at either function but they are certainly effective at both and it's a useful combination if you can use them in your room.
David Aiken
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- RE: Diffusor w/ Fiberglass for absorbtion? - Will this work? - David Aiken 22:03:39 11/19/07 (0)
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