Polyfill is out. Sulfur Hexafloride is in!

[Looneybomber]

No more stuffing boxes to gain an extra 20-25% effective volume. What if I told you there is another option, one that could increase your effective volume 2700%!

Quote »Only the woofer/subwoofer were not bipolar. These relied in the use of SF6 (sulfur hexafluoride) gas (which is inert), to increase the virtual volume of the enclosure. As SF6 is an 'ideal gas', it operates as an 'isothermal' spring, thus avoiding the problems with 'acoustic-suspension' loudspeakers that operated partially as an isothermal and partially as an adiabatic system. Some designers seemed to lave little knowledge of Boyles Law or the Laws of Thermodynamics.

In effect, the use of SF6, increases the virtual volume of the enclosure by a factor of 27! As can be appreciated, this both lowers the distortion as well as permitting a lower resonant frequency of the woofer. [/quote]http://www.dayton-wright.com/WATSONLABS_.html

Here's the trick. It's a very powerful greenhouse gas (24,900 times more powerful than CO2), so it can't leak, and the price of it has increased 600% in the last year.*

Obviously you can't use this in a speaker box without some sort of way to keep it, say some type of impermiable soft bladder. But, if you can find a way, you could have 18's installed in 1ft^3 boxes, but actually have them sound good!

*http://www.sf6.net/

[the converted]

Whoever figured this out had way to much free time.

[Looneybomber]

Whoever figured this out had way to much free time.

It was actually patented by Watsonlabs back in '77? The patent is now expired so we can all benefit from it...that is if you can get a hold of the stuff. I may call my local power plant (since it's a dielectric gas) to see if they have any and/or if they know where I could get some. Being that the price has jumped up 600% in the last year alone, it may end up being too expenisive, but we'll see. It would be nice to use that stuff here at home, so instead of building giant 20ft^3 enclosure for a single driver, I could build an enclosure just big enough to fit the drivers and then put in the bags of SF6

[the converted]

I'm just wondering if you are bagging the gas, would there be noise from the membrane? I guess that ideally you would use the driver to seal this into the enclosure but I'm assuming that it would eventually leach out regardless.

[Looneybomber]

Yeah, I don't know about the bladder making noise. It's always a possibility, so to avoid that, a soft rubber bag would have to be used. And I say a bag will have to be used, because, like you said, it will leech out if not. You could easily seal the box with fiberglass resin or something the like, but speakers are still minutely permiable.

Since SF6 is heavier than air, you could always fill an enclosure with it and have an up firing driver, but in an automotive application, the "sloshing" back and forth from turns, inclines ect.. could cause the SF6 to leak out over time? In a home environment, where speakers/subs rarely get moved, it wouldn't be as much of a problem...

...I never did call our power plant. I did homework instead.

[the converted]

I did some looking, aparently it has some uses as a shield gas in welding (not sure what materials) so your local Airgas should be able to get you some.