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Jhovis 28th September 2003 04:37 AM

Damping Material
Anyone ever use this damping material sold at Parts Express?

I built the L/C/R Audax Home Theater Speakers last year and used foam eggcrate foam mattress covers from Wal-Mart to damp the cabinets. I glued it in with 3M Super 77 spray adhesive. This year, I'm going to build a set of Ellis 1801B speaks and want to be sure I'm using good quality damping material. Black Hole 5 seems to get good reviews but it is expensive.

wintermute 28th September 2003 05:20 AM

Hmmm I've been wondering about something similar.

Would make for some pretty heavy cabinets, but should solve a lot of resonance/standing wave problems???? Would it be likely to provide too much damping?



Jhovis 28th September 2003 05:55 PM

That stuff from Jaycar looks pretty promising.

Ap 29th September 2003 01:26 AM

Sorry but it wont reduce standing waves as they are purely a function of the air resonating in the box volume.
The maximum pressure occurs at the minimum motion which is right in the middle of the box. Conversley the minimum pressure occurs at the maximum velocity which is the box wall.
Same as in your room, adding foam/anything to the wall does not reduce room modes.
This stuff will help damp wall/panel vibration (resonances) providing the walls arent too thick - if you are using 25mm MDF then this won't do much at all.
-In my current project I used the Jaycar stuff without the cloth backing, bonded & sandwiched between a layer of 12mm ply & MDF.
The bass box is outer 18mm MDF/damping material bonded with liquid nails/plaster/bitumous paint - the walls are very dead with the usual knuckle test - this method of damping does 2 things it pushes the resonance to a higher freq & Q (out of the drivers operating range) thereby reducing it's audibility.

In order to reduce the standing waves I will be using a large 3" thick block of foam placed like a shelf centrally in the box.
I probably will also use some egg crate foam to absorb any mid/hf bouncing around which might 'break through' the cone.
Also though about using a large sponge-foam ball instead (haven't been able to source any yet)

Martin Colloms has some great info/test results on this subject in his book "High End Loudspeaker Design" - well worth a read.

I will post some results once the project is finished.

David B 29th September 2003 06:19 AM

PE damping material
I've used the low-cost PE asphalt damping material. It seems to help; it's certainly easy to work with and in informal before and after testing it seems to make a difference. I've never done a strict AB comparison with and without it, or comparing it to black hole or one of the better materials. I have been using it conjunction with egg crate foam also from PE: egg crate to kill mid-high reflections, and this to kill low frequency resonances.

wintermute 29th September 2003 08:35 AM

Thanks AP, Seems I have some more reading to do with regards to standing waves :)



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