[moray james]

interesting damping material  Post #1 
Just finished spending a day experimenting with box cavity damping. The speakers in question are ATC SCM10's which are factory damped with long fiber wool. This ia a small cavity sealed box with an impressive 5.5 inch bass/mid driver that has a very long linear excursion.
A friend of mine attended the Hi Fi Show in Germany this spring and had an invite to spend the nite at a private showing of the new KEF Reference loudspeaker. One of the cool things about the KEF is that it is internally damped with activated charcoal. This is a neat idea as activated charcoal is very porous. Kef claim to have reached a virtually theoretical cavity volume increase of 28 out of 30 % using the charcoal. This got me thinking. Charcoal is messy and expensive. Pearlite is a heat expanded form of rock used in the gardening business usually white but comes in various colours. Pearlite is basically rock heated up like popcoarn or Rice Crispy's and ends up like small kernals of porous soft rock which is soft enough that you can crush it to powder with your fingers. Pearlite is more porus than activated charcoal and is clean and cheap to buy. I replaced all the internal wool damping with the pearlite in the ATC SCM10's. This resulted in a significant improvement across the band with especially improved midrange and more extended bass. You do need to take some precautions however. Pearlite must be sifted first to extract all the fine powder as you only want pieces the size of rice crispy's and larger. Further you need to insure that the pearlite is kept out of the driver/s. This done I would have to say that this is by far the best damping material that I have ever used. This is I think as a result of the fact that pearlite is so very porus and has high resistivity to passage of air and also in that it has tremendous frictional dissapation due to the partical vibrating against one another. Bug screen and fiber batting like polyester or acrylic will keep the pearlite where you want it and permit free air flow about the back side of the driver. For ported boxes you would want to keep a fair size area (should think a minimum of a 1/2 cu. ft.) around the reflex vent free of any damping material to insure correct vent resonance. There you have it cheap and SOTA damping material that works like a charm. For those who cannot readilly get thier hands on pearlite or who disbelieve a good second choice would be rice crispy's (dont laugh) but they will cost more than pearlite however if you are not fussy you can at least eat the rice crispy's after. You can expect the pearlite to be more effective than the rice crispy's as it is far more porous in structure. BE FOREWARNED you must properly prepare for using pearlite to insure that it only goes where you want it to. This is a real gem of a damping material especially for ultra small cabinet speakers and I should think the absolute bomb for TL's. I am sure that some will laugh till they hurt but do give it a try and for those to busy laughing well that's your loss. Very best regards Moray James.

[tianguis]

Moray:

       Nice going! Right from the start of your description, it sounded like it would work a treat in TL's. Have you tried styrofoam peanuts?

Regards,
Larry Welsh

[moray james]

Simple solution to particle contamination of driver with the perlite is to place the perlite into sealed plastic bags and then place the filled bags into the boc cavity.
   While styrofoam peanuts do work they are not porus and so reduce volume significantly. Perlite is very porus and so takes up less volume and provides excellent damping and a maximum of driver precieved volume increase. Regards Moray James.

[Russell Dawkins]

don't think plastic bag will do - needs to be porous. A plastic bag around a volume of porous but rigid solids would behave like one large non-porous solid, rigid except for the small amount of flex in the areas between support of the individual pieces of pearlite. This would radically reduce the effective interior volume.

[avahifi]

Actually, water - - - lots of water, will work as a great damping material.   

Frank

[Builder Brad]

Moray,

I hope you dont work in a garden center, or the EU - Ive heard about their PERLITE mountains, otherwise this post might get moved...or deleted.

Only joking, good idea, and worth a try, unless you have Dipole speakera

[Gordy]

Reemay, a nonwoven polyester or polypropylene, should work nicely to contain the perlite.  Don't know if it's available as a bag, but it's commonly used as a water permeable weed blocker.  The home construction wrap Typar is basically the same thing I think...

[moray james]

there are also bio filter materials used in filters for ponds and such that are in the form of porous beads which would probably work just as well and not suffer the dust problems and be large enough not to get into a drivers gut. Problem is that they probably cost a lot more money. Plastic bags are cheap and easy to get as is perlite. Regards Moray James.

[NagysAudio]

Here's a funny one for you guys and this is based on real measuring tests. The best damping material for ported speakers is BUBBLEWRAP, small bubble type not large. Best midrange and bass I heard. Try it, it's simple and cheap.

[tianguis]

Nagy:

      I used it years ago, combined with styrofoam peanuts, in Hammer Super 12's. It does work a treat.

Regards,
Larry Welsh

[TF1216]

Did you take any pictures of your speaker with the new damping material?