Aerogel cones?

[Javachip]

Is anyone aware of any attempts to use silica aerogel as a diaphragm material for a speaker cone? I am referring to the stuff NASA uses for thermal insulation and for collecting cosmic dust particles.

This material is the lightest known solid, with a density of about 2 mg/cc. (Air=1.2, Water=1000, Magnesium=1738.) It is very strong and rigid up to a certain load, at which point it deforms reversibly. With progressively higher loads it deforms irreversibly, then shatters. Additionally, it is an excellent acoustic insulator.

Of course, one major drawback is its very high cost.

NOTE: Audax makes some drivers that it calls "Aerogel." But this material appears to be an acrylic foam impregnated with carbon and Kevlar fibers, and is not much lighter in weight than other cone materials. It does not appear to be similar to silica aerogel.

Here is more info on silica aerogel:

http://stardust.jpl.nasa.gov/aerogel_factsheet.pdf

Any comments?

[Mr. Wizard]

I am not aware of any or uses of or attemps to use the material in this application, but I think it is a great idea.

[SY]

I don't know present state of the art, but the aerogels I worked with a few years back were much too delicate to be used in speaker cones.

Do you know if Audax's cones used a syntactic foam, i.e., bubbles added as hollow microspheres?

[pinkmouse]

You've got a pair, SY, why don't you chop them up and stick them under the microscope?

[SY]

Not as silly as you think. I've got a cat-damaged quad of HM170Z0 (sob! those were fabulous drivers) stuck away, just in case I could think of something to do with the perfectly good frames, magnets, and coils...

[FullThrottleRic]

I've got a cat-damaged quad of HM170Z0's

I'm using a pair of those in my main speakers with SS 9500's, it's such a shame Audax doesn't make them anymore, wonderful driver. They have some of the clearest, open and most detailed mid-range I've ever heard

[Ian J]

Hi Ric,
what x-o are you using between the Audax and SS? I bought a pair of SS tweeters on ebay to go with my HM170Z18s (currrently paired with SEAS tweeters in an IPL A3) but realised too late that I had bought 38mm 8513 mid-tweeters rather than standard tweeters (can't complain, price was good). I thought series x-o would be promising with this combination but haven't got around to trying it yet.
Ian

[FullThrottleRic]

Hi Ian

I've used the lowpass from Vance Dickason's A651 design...
http://www.rjadcenko.com/hi-fi/Audax/a651.htm
I've tried various configurations but I always end up going back to this design.

The highpass is 3rd order with an RC impedance compensation network I came up with using speaker workshop + measurements

Both filters give a 4th order LR curve meeting at 3kHz.

[454Casull]

I think for a diaphragm of suitable stiffness, you'd have to have a pretty thick "slab" of it.

[Javachip]

SY: Silica aerogel is fragile, but there is a cool photo of a brick sitting on a faily thin slab of it, so it can't be all that delicate. It can be further strengthened by doping with carbon, discussed in the factsheet link.

I could only find a brief description of Audax's "Aerogel" material on Green Mountain Audio's website:

http://www.greenmountainaudio.com/Sp...ifications.htm

It is described under "Midrange" for their Continuum speaker.

Audax's own website does not offer any details about its "Aerogel," at least none that I could decipher with my knowledge of the French language, which is currently limited to "oui" and "bordeaux."

454Casull: Yes, it would look funny compared to other cones. Just as a wild guess, it might be a centimeter thick, but it might still be lighter than a paper, plastic, or metal cone. After I drink some more wine, maybe I will calculate the volume and weight of a 4, 6, 8, 10, and 12 inch diameter cone of 1 cm thick aerogel at 2 mg/cc density. Unless someone else wants to do it for me.

Actually, 2 mg/cc is the lowest density achieved so far. More typical silica aerogels are up to 80 mg/cc.