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Acoustic damping by cutout wood
Acoustic damping by cutout wood
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Old 30th March 2004, 11:23 PM   #1
Kjetil is offline Kjetil  Norway
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Question Acoustic damping by cutout wood

Apardon the stupid title of this thread, I really didn't know what to call it. I am onto a project designing speakers using Accuton drivers, and these drivers have an extremely thin membrane, thus very vulnerable to back-waves from inside the cabinet.

The perhaps very best speakers utilizing these drivers may be Kharma, so I did some research on their approach to acoustic damping of the box. I found that Kharma used the method pictured below, but I wonder.. Will this "hardware" damping be enough in itself, or should i dress it in bitumen/acustilux as an addition?

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Old 30th March 2004, 11:56 PM   #2
markp is offline markp  United States
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No direct reflected waves but also no absorbtion. I would add some absorbing material.
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Old 31st March 2004, 02:26 AM   #3
CeramicMan is offline CeramicMan  Australia
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The effects of having irregular surfaces are different depending on the frequency of sounds reflecting from those surfaces. That is what most people seem to forget. A 1kHz tone has a wavelength of around 340mm, so relatively small 30mm irregularities won't be much different from a completely smooth wall at that frequency.

I think what makes Accuton speakers more susceptible to reflected sounds is because they're unmasked by a conspicuous lack of cone resonances. Furthermore, because the cone moves as a solid piston through a wider range of frequencies, box resonances move the *whole* cone to produce identical directivity characteristics as the sound that the speaker is supposed to be making.

I don't think that the thinness of the cone has that much to do with reflected sounds passing through it, rather it depends on the T/S parameters, specifically: Qes (electrical damping). A high Qes means that the amplifier can't control the cone very effectively. Having a passive crossover may make it significantly worse, because the speakers are decoupled from the amplifier with reactive components.

CM
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Old 31st March 2004, 03:04 AM   #4
Kjetil is offline Kjetil  Norway
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Quote:
Originally posted by CeramicMan
The effects of having irregular surfaces are different depending on the frequency of sounds reflecting from those surfaces. That is what most people seem to forget. A 1kHz tone has a wavelength of around 340mm, so relatively small 30mm irregularities won't be much different from a completely smooth wall at that frequency.
CM

So you are saying I probably will have just as good results by a conventional box and lead&bitumen damping? Area of operation for the Accuton driver will be between 30Hz and 3000Hz.. You know these drivers; what damping would you recommend?
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Old 31st March 2004, 03:06 AM   #5
Kjetil is offline Kjetil  Norway
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I should add that we are talking ported enclosure...
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