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Old 30th October 2010, 05:35 PM   #1
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Default Instantly deepen your sub?

Anyone entertained the notion of building a sub in a sulfur hexafluoride SF6 gas chamber to lower its frequency and aid the cone's gas interaction? Its six times denser than air.

http://www.youtube.com/watch?v=d-XbjFn3aqE
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Old 30th October 2010, 08:06 PM   #2
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Shouldn't that video say, "Kids, don't try this at home"? That gas is heavier than the familiar mix of nitrogen and oxygen we love to breathe.

Funny thing, my Dayton-Wright ESLs are sealed in that gas. It is used by some kind of specialty welders and not cheap.

Don't gasp in disbelief, but my one-meter-square ESLs play strong down to 70 Hz and below. And vastly cleaner than you can ever get shaking large hunks of cardboard around using the right hand rule. Join two, and not sure you need any sub except for movies.

I am not sure if the designer, a person of rare hifi genius, had diaphragm resonance in mind. For sure he did know that these ESLs greatly benefit in linearity and efficiency from super-high bias voltage and these speakers can be run at 15 KV. No kidding... at least in dry weather.

My speakers have held their gas without needing a top-up, as far as I can tell, since 1984. Whazzat... 26 years?

.... but then, I don't have any cats.
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Last edited by bentoronto; 30th October 2010 at 08:09 PM.
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Old 30th October 2010, 08:16 PM   #3
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To design a sub, I think you'd treat it like a transformer (AKA megaphone). You'd build an ordinary cabinet and the output would feed a chamber filled with the heavy gas with an "output surface" many times larger than the cone surface.

Like a horn, the heavy clunky cone is not longer working into "thin" air but into heavy gas. And the gas is driving a large surface.

Does that make sense?

I think that logic is inherent in the Dayton-Wright cabinets... not that films of mylar need a lot of impedance matching to air. Not like heavy cardboard cones, eh.
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Old 31st October 2010, 10:33 AM   #4
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LOUD SPEAKER - Google Patent Search

Device for increasing the compliance ... - Google Patent Search
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Old 31st October 2010, 08:07 PM   #5
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djk - Thanks a lot for those patent references.

The heavy gas, SH6, works in a few different ways.

Tucked behind the driver, it adds to the room in the box.

Tucked into the horn, it makes for a big horn. Similar but nutty variations of front-face gas loading are possible as in the patent pictures.

The third way is by magnifying the cone surface area. Instead of shaking a heavy chuck of cardboard to move air directly, you are using that cone (with force transfered by the heavy gas) to shake a far larger membrane surface.

These gas-filled boxes breathe a bit. About once a year or two, I have to set my speakers so that the gas falls to the bottom and the valve (a Schrader tire valve!) is at the top. After settling a few hours, I add or relieve some air.

I'm no authority to trust, but I think SH6 is pretty inert and innocuous. It can still leak out, like any gas. The danger is that it is an invisible gas that collects in low spots and might get in the way of normal human breathing - and be dangerous.

Given the dramatic lowering of bass resonance(s), sure seems like a good idea for DIYers to try. No leading-edge technology needed. But what do I know?
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Old 1st November 2010, 09:28 AM   #6
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Old 1st November 2010, 03:13 PM   #7
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I was thinking a pair of full range drivers could have their 'flat' frequency ranges maximized by using helium for one and SH6 for the other in a 2way. This likely requires a very complex crossover. It would be an interesting experiment.
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Old 1st November 2010, 05:08 PM   #8
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Quote:
Originally Posted by Seyeklopz View Post
I was thinking a pair of full range drivers could have their 'flat' frequency ranges maximized by using helium for one and SH6 for the other in a 2way. This likely requires a very complex crossover. It would be an interesting experiment.
Clever thoughts. But shouldn't SH6 help the impedance match for both drivers?

SH6 seems to have various nice features. But is there a cheaper, inert, friendly, accessible heavy gas instead of SH6?
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Last edited by bentoronto; 1st November 2010 at 05:11 PM.
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Old 1st November 2010, 11:49 PM   #9
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I was thinking more about getting flat response up to tweeter ranges using the helium for the higher frequency.

You would need a circuit that can raise frequencies delivered to the sh6 driver and lower frequencies to the helium driver to compensate for how the gasses alter the sound produced from the signal.

Seems backwards at first

Maybe someone can explain that better and throw in some ideas how that circuit would work with crossovers?
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Old 2nd November 2010, 07:46 PM   #10
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I remembered getting a heart ultrasound using a contrast medium. They injected me with trillions of micro-bubbles of SF6. Pretty safe I'd say.
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