Aerogel as a loudspeaker stuffing material

[Oborous]

Hi All,

Came across this stuff...

Cheap Aerogel bits

Was wondering about this as a stuffing material for loudpspeakers (specifically subwoofers).

(I only went through six pages of aerogel search on the forums, so if there is a really old thread on this, please forgive me).

I'm thinking the whole purpose of stuffing is to slow down the speed of sound. Was thinking this could work well.

[ScottG]

Originally posted by Oborous
Hi All,

Came across this stuff...

Cheap Aerogel bits

Was wondering about this as a stuffing material for loudpspeakers (specifically subwoofers).

(I only went through six pages of aerogel search on the forums, so if there is a really old thread on this, please forgive me).

I'm thinking the whole purpose of stuffing is to slow down the speed of sound. Was thinking this could work well.

..it has nothing to do with slowing down the speed of sound - just converting spl into heat and dissipating the heat quickly..

the biggest thing that areogel in this form has going for it is increasing volume - substantially.

another nice thing it can do is virtually eliminate interior reflections depending on how its used.

it could also provide a fair bit of isolation from cabinet resonances depending on how it was used.

anyway - good catch! I'd known about Cabot's nanogel version for a while now, but had not seen it being sold to the "public" before.

[Dick West]

Reducing internal reflections generally is not important for a sub cabinet as the wavelengths are mostly too long to "reflect."

Now, if one wants to increase the apparent volume then stuffing will help. A gallon of the Aerogel insulation costs $37 (with shipping). A gallon occupies .13367 of a cubic foot. If a 3 cubic foot volume sub cabinet were loosely stuffed with aerogel bits poured in as many as 22 gallons would be required to fill the box. Twenty two times $37 is $814 for one sub cabinet.

Your mileage may vary but the use of this product seems too expensive and generally not needed. Did I do the math correctly?

[Oborous]

Originally posted by ScottG


..it has nothing to do with slowing down the speed of sound - just converting spl into heat and dissipating the heat quickly..

the biggest thing that areogel in this form has going for it is increasing volume - substantially.

another nice thing it can do is virtually eliminate interior reflections depending on how its used.

it could also provide a fair bit of isolation from cabinet resonances depending on how it was used.

anyway - good catch! I'd known about Cabot's nanogel version for a while now, but had not seen it being sold to the "public" before.

I just assumed that the 'virtual' increase in volume was due to slowing the speed of sound down due to differing media, thus making the sound wave travel for longer. (i.e. 1 metre at 343 m/s for an unstuffed cabinet takes 1/343rd of a second... but 1 meter at 170 m/s due to stuffing the cabinet takes nearly double the time... which would mean an unstuffed cabinet would have to be nearly double the size for the soundwve to take the same amount of time to travel)

Can you please elaborate on how to eliminate interior reflections and cabinet resonances with the stuffing material.

Originally posted by Dick West
Now, if one wants to increase the apparent volume then stuffing will help. A gallon of the Aerogel insulation costs $37 (with shipping). A gallon occupies .13367 of a cubic foot. If a 3 cubic foot volume sub cabinet were loosely stuffed with aerogel bits poured in as many as 22 gallons would be required to fill the box. Twenty two times $37 is $814 for one sub cabinet.

Your mileage may vary but the use of this product seems too expensive and generally not needed. Did I do the math correctly?

It very well could be expensive, but there are some places working on making solid bricks of aerogel for high transparency, high insulation windows... I figure they'll have waste product, and could maybe talk to them... they just don't list prices online; and the $37/gallon is much cheaper than any other posted website.


Is there some better materials for causing a 'apparent' increase in cabinet volume due to stuffing?

[psych&sound]

Cabot is literally selling SiO2 crumbs. And yet it is still ridiculously expensive. Actually the speed of sound is indeed slower in an aerogel medium. I can’t think of any rigid solid with higher internal damping.

But for a subwoofer, I don’t think this is a good idea. Fibreglass insulation is actually a better sound absorber than bulk aerogel crumbs at most frequencies – particularly above 1 kHz. Thick aerogel binder panels can be better between 300-800 Hz at the expense of poorer high frequency absorption. The exact behaviour will depend on the particular formulation and morphology of the aerogel in question. The cost-benefit for a sub is not in your favour. I am assuming you are thinking of a sealed box – a vented box would soon have aerogel all over your room. Further to this, this material is very friable – you will have some of it become dust – and you must be careful not to inhale or get it in your eyes.

Increasing stuffing may give you a slight increase in apparent volume, but you will be reducing the Qtc of the box and the F3 would be higher (i.e. a more gentle roll-off given the same box.)

Reflections are a non-issue in a properly crossovered sub.

[ScottG]

..I shouldn't have said "nothing" to do with actually slowing down sound, but practically speaking this is an inconsequential side effect. Look to Martin King's work on damping material.

..the reduction in reflections was a generalized statement (..and I thought that was obvious, oh well).

..aerogel is a good *insulator*, as such it has the potential to insulate sound from the cabinet by utilizing it between the cabinet walls and the internal volume of the cabinet. Unfortunetly it is not monolithic to the cabinet (i.e. a box of aerogel within a box/cabinet) - so the sound insulation is much less effective because of the physical structure of the Cabbot aerogel - i.e. beads. You could have a filled lining (like a blanket) on the interior walls.

Much more effective though would be to basically nullify sound transmission in the cabinet walls themselves by using it as a sort of aggregate in an epoxy mixture that will be formed into walls for the cabinet. This doesn't mean that the walls themselves would generate sound in the listening room - THAT would depend on the structure of the cabinet and its rigidity. It should however greatly reduce vibrational modes that could well end-up back at the driver's frame.

[el`Ol]

Somebody here had good experiences with perlites. Even cheaper (20€ for 10kg).

[moray james]

pearlite (heat expanded rock) this is cleaner and cheaper than activated charcoal. You will want to sift it to remove all the dust and small bits. You want to go for bits the size of rice crispy's. Make sure that you keep it from going where you dont want it to. This stuff works great. You can find it at garden supply stores. Regards Moray James. PS B&W published a tech paper on activated charcoal use dont know where.

[Curmudgeon]

An article quite a while ago (Audio?) compared various stuffings. Wool was the most effective at creating an apparent volume increase. The photographs showed an overlapping scale structure. A slightly opened pine cone is the best analogy I can think of. As a result, the air friction is higher than any other material. Acusta-Stuf crinkles poly?? which helps, but good ol' wool is still the champ for conventional materials. But the number of aerogel strands in a given volume should be very high, and compensate for the slickness.

The aerogel is very intriguing; I guess the packing density would determine the cost. Is the shipped gallon used as is, or opened up to a lower density? The perlite is a nifty thought... guess I better go make "search" my friend.

Edit: I did find the perlite thread; very nice indeed. The ultimate solution to the moth problem...

Corrected spelling from pearlite a steel microstructure.

[sreten]

Originally posted by moray james
PS B&W published a tech paper on activated charcoal use dont know where.

Hi, KEF, not B&W, /sreten.