Acoustic damping by cutout wood

[Kjetil]

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?

[markp]

No direct reflected waves but also no absorbtion. I would add some absorbing material.

[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.

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

[Kjetil]

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?

[Kjetil]

I should add that we are talking ported enclosure...