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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: RE: Aye, cynical I am posted by Jon Risch on October 22, 2009 at 18:41:46:
possibly out of place but also possibly of relevance to panels.
When I was first starting to read up on acoustics and get interested in DIY stuff in my room, I was working in the health and safety area and being asked for info about noise and hearing related stuff. I was sent a test report for a workstation panel system, vertical panels mounted on a frame that supported a desk surface on either side of the panel with the panel acting as a workstation divider. The absorption coefficients measured for the panel were well in excess of 1.0.
I couldn't figure this out but then, rereading the report again, I noticed that the panel had been placed somewhere in the middle of the test room and the penny started to drop. I forget the panel size but I had calculated the area by multiplying height by width. In the location in which the panel was measured, the panel had 2 sides exposed to sound, not one. The actual surface area "collecting" sound was twice the area I had calculated. Using that total area the absorption coefficients came back into line with what I had expected. I phoned the company producing the panels and spoke to one of their people who said that was what was going on.
So, while a tube trap will have surface area as Jon has calculated because the other side of the fibreglass is sealed inside the trap, a panel spaced away from the wall is actually going to have a larger surface area than indicated by height and width alone because both sides are effectively exposed if the panel is spaced away from the wall by spacers that don't block sound access to the space behind the panel.
So I just think it's worth commenting that the issue of what constitutes surface area is going to be a little different for a sealed tube trap than it is for a panel with both sides exposed, even if the exposure to the rear side is only a relatively narrow gap. I would expect a panel with a one sided surface area equivalent to the exterior surface area of a tube trap, both using the same thickness of the same material, to measure slightly better than the tube trap *IGNORING BENEFITS FROM THE PRESSURE TRAP MECHANISM OF THE TUBE TRAP* (ie considering only absorption from the material used) due to the fact that both sides are exposed.
The amount of extra benefit gained by the panel as a result of absorption of sound impinging on the second side is going to depend on placement and I have no idea how much it adds but I definitely think it will add something. Of course it isn't going to extend the lower frequency of the panel's operating range but I expect a panel with both sides exposed is going to be more effective than expected and absorption coefficients significantly above 1.0 are going to be possible. If I remember correctly, the coefficients I was concerned about with the workstation panel I mentioned were around 1.6 in the vocal frequency range which was, of course, the frequency range of concern in an office setting.
David Aiken
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- A comment on measurement… - David Aiken 23:16:11 10/22/09 (0)
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