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
http://www.youtube.com/watch?v=d-XbjFn3aqE
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.
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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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.
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.
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?
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?
The minimum quantity a welding shop will sell you is about $100~$200, depends on if you have your own tank.
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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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?
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?
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. 
Might be safer in your bloodstream than clogging your lungs and depriving them of air.
No, helium doesn't seem backwards: it seems the "natural way" what you are proposing. But I don't think it is right.
No trouble getting tweeters go supersonic and far, far higher than most ears go.
But getting lower distortion, linearity, and damping from proper impedance match will always be a problem except for gas-speakers. That's my take on the physics.
Of course, I'm the ESL guy who is always ridiculing cone speakers which shake big hunks of heavy cardboard to make sound in thin air.
No, helium doesn't seem backwards: it seems the "natural way" what you are proposing. But I don't think it is right.
No trouble getting tweeters go supersonic and far, far higher than most ears go.
But getting lower distortion, linearity, and damping from proper impedance match will always be a problem except for gas-speakers. That's my take on the physics.
Of course, I'm the ESL guy who is always ridiculing cone speakers which shake big hunks of heavy cardboard to make sound in thin air.
Hi,
Heavy gas is not what you want inside a subwoofer, the lighter the gas
the better as I recall. I seem to remember some speakers allegedly
loaded with helium filled plastic bags to increase effective box volume.
rgds, sreten.
Heavy gas is not what you want inside a subwoofer, the lighter the gas
the better as I recall. I seem to remember some speakers allegedly
loaded with helium filled plastic bags to increase effective box volume.
rgds, sreten.
I wonder what would happen if you placed and sealed a large helium filled balloon over the front of a driver and pointed it upwards? would you get a huge low mass omni directional driver? you could even have a tweeter mounted coaxially inside on a rod pointing forward as presumably higher frequencies would just past straight through? If you filled all but one mounting holes you could use the last and mount a valve in it??
Or am I just bonkers?
Or am I just bonkers?
"the lighter the gas
the better as I recall. "
That's backwards. The gas must be denser than air. The air load presented to a driver is a poor impedance match because the air is so light compared to the speaker cone.
the better as I recall. "
That's backwards. The gas must be denser than air. The air load presented to a driver is a poor impedance match because the air is so light compared to the speaker cone.
Hi,
Nope. It has nothing to do with impedance matching. Lighter than air
gases make the effective box volume appear larger and heavier than
air gases make the effective box volume appear smaller. In the accounts
I've come across only hydrogen or helium is "apparently" suitable. Some
accounts talk about using heavy gas to restrict movement, but that
is pointless, just use a smaller box or restraining volume if needed.
I cannot remember where I read about the helium bags.
rgds, sreten.
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As I poorly understand these things, you are right that the result is like the box is smaller if a heavier-than-air gas is used. But I think that is no different than saying the impedance match is better or that smaller boxes make the interior compression a bigger part of the compliance. I'm not sure if there is a benefit that couldn't be achieved by adjusting box size... dunno.
The real benefit of the heavier gas is at the front side of the cone. If the room were full of SH6, the cones would work better due to better impedance match. But that can't be done unless you wear a SCUBA mask and tank while listening to music.
But if you use the "megaphone" design, you get some of the advantages in proportion.
Heavier gas, slower speed of sound, longer transit time through box, 'bigger box'. Doesn't that make sense?
Lack Of SF6
I don't know about sulfur hex "deepening" the sound of subwoofers, but lack of SF6 made a hell of a noise in this "switch"!
You Tube-500kv Arc
YouTube - A 500KV three-phase switch failing to interrupt a 2,000 Amp arc Boulder City, NV (Lugo)
Impressive-sounding on a good system, especially the echo slap-back when that 50ft tall arc breaks!😱
I don't know about sulfur hex "deepening" the sound of subwoofers, but lack of SF6 made a hell of a noise in this "switch"!
You Tube-500kv Arc
YouTube - A 500KV three-phase switch failing to interrupt a 2,000 Amp arc Boulder City, NV (Lugo)
Impressive-sounding on a good system, especially the echo slap-back when that 50ft tall arc breaks!😱
Yea, removing the insulator generally has that effect on high voltage equipment. SF6 is a dielectric. Had a similar experience fixing a power outlet that had been improperly wired from 3 circuits. 90% of my screwdriver vaporized. Well, it seemed as scary at the time.
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Agree!
I agree! The linemen saw the 50ft arc from a safe distance. Having a screwdriver explode into vapor while in your hand is actually more dangerous! The linemen weren't endangered by flying bits of molten steel!😱
I agree! The linemen saw the 50ft arc from a safe distance. Having a screwdriver explode into vapor while in your hand is actually more dangerous! The linemen weren't endangered by flying bits of molten steel!😱
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