Wonder if it is the speed of sound that is giving the major benefit or the change in mass loading on the rear of the cone?
Although someone posted that they filled a mylar bag with it... So why just a gas if a mylar bag works? A jell anyone?
_-_-bear
Although someone posted that they filled a mylar bag with it... So why just a gas if a mylar bag works? A jell anyone?
_-_-bear
A gel is incompressible. For the same reason we don't just fill the chamber with water. You need a gas because it is compressible. That is why speed of sound in gas phase vs liquid and solid phases are completely different.
The mass loading is minor compared to sound as the speed of sound gives the apparent increase in time of flight of the sound wave which is equivalent to a larger volume.
The mass loading is minor compared to sound as the speed of sound gives the apparent increase in time of flight of the sound wave which is equivalent to a larger volume.
Reason for mylar is do to the low gas permeability of the material. Ever notice how a regular balloon will deflate, be it air from your lungs or helium filled? Now the same with mylar doesn't leak or rather very low leakage.
Not completely filling the bag allows room for expansion, but also has issue with creating it's own sound from the bag itself. Enclosure interior should have been prepared better, smoother reducing chance of puncture and from frictional wear. Spray adhesive was used on the sidewalls to reduce wear factor, but apparently missed something, somewhere (on a half a dozen occasions). Now a driver made with these characteristics would be best. Non gas permeable surround, cone and dust cap. Bummer it can't be done (added) after the fact.
If gel compressed like a gas I would have used it! 😉
Could be said an open cell viscoelastic foam has very similar properties to a compressible gel.
Also had the thought of subdividing the enclosure internally with a bag for a BR. Driver and port are coupled via air, but internally all pressure waves would be forced to travel through the confined gas bag. Musings of a 20 something, repeating a few thoughts on the subject 30 years later 🙄
Not completely filling the bag allows room for expansion, but also has issue with creating it's own sound from the bag itself. Enclosure interior should have been prepared better, smoother reducing chance of puncture and from frictional wear. Spray adhesive was used on the sidewalls to reduce wear factor, but apparently missed something, somewhere (on a half a dozen occasions). Now a driver made with these characteristics would be best. Non gas permeable surround, cone and dust cap. Bummer it can't be done (added) after the fact.
If gel compressed like a gas I would have used it! 😉
Could be said an open cell viscoelastic foam has very similar properties to a compressible gel.
Also had the thought of subdividing the enclosure internally with a bag for a BR. Driver and port are coupled via air, but internally all pressure waves would be forced to travel through the confined gas bag. Musings of a 20 something, repeating a few thoughts on the subject 30 years later 🙄
Haven't kef done something similar without using noxious gas KEF Innovation - ACE - KEF International
SF6 is not noxious - non toxic because it is inert biologically. It is a greenhouse gas though. Interesting how pores in charcoal improves bass? Maybe we should all go get some fish aquarium charcoal and give it a try?
Perhaps Kynar or Tedlar gas sampling bags are the way to go - gas tight and have valves and fittings. A bit pricey but they won't leak out and are pretty flexible. 1 Liter to 100 L sizes.
Tedlar gas sampling bags
Sampling Bags from Cole-Parmer
Tedlar gas sampling bags
Sampling Bags from Cole-Parmer
Perlite works well also, easier to get locally from any garden supply. I have some that is stuffed into a length of tubular medical bandage. The stuff they wrap legs/arms with before casting and or braces to prevent chaffing. Available in various diameters, stretches well and holds all that loose mess together and reduces dust at the same time.
Mike Wright attributed many advantages to sealing his ESLs in a box and adding SF6, mentioned in various posts above.
Although I was skeptical about the transparency of playing sound through the enclosing films, seems to work fine.
As an ESL fan, I note how crude it is wave cardboard cones to make sound: essential problem is the difference in weight between air and the cone. There's little negative (degenerate) feedback. That's no way to make clean sound!
Going to SF6 changes that a lot. For ESLs, moving towards good match in radiation resistance between the large-surface (a square meter for DW speakers) enclosing mylar bag and the air. But still pretty large mis-match for shaking-cardboard drivers and thin air.
"Sealed" cone-woofer boxes often include pin-hole leaks to adjust for barometric pressure and air expansion with temperature. The DW ESLs certainly breathe quite a bit and if the enclosing diaphragms are in danger of excessive blowup or suck-in, they might have to be turned upsidedown and opened every year or two (upsidedown to allow the heavy SF6 to be remote from the open valve).
Ben
Although I was skeptical about the transparency of playing sound through the enclosing films, seems to work fine.
As an ESL fan, I note how crude it is wave cardboard cones to make sound: essential problem is the difference in weight between air and the cone. There's little negative (degenerate) feedback. That's no way to make clean sound!
Going to SF6 changes that a lot. For ESLs, moving towards good match in radiation resistance between the large-surface (a square meter for DW speakers) enclosing mylar bag and the air. But still pretty large mis-match for shaking-cardboard drivers and thin air.
"Sealed" cone-woofer boxes often include pin-hole leaks to adjust for barometric pressure and air expansion with temperature. The DW ESLs certainly breathe quite a bit and if the enclosing diaphragms are in danger of excessive blowup or suck-in, they might have to be turned upsidedown and opened every year or two (upsidedown to allow the heavy SF6 to be remote from the open valve).
Ben
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Minor aside.
The highly regarded Quad ESL 53 has a "dust cover" inside the metal outer cover...
...I often have thought that the effect of the dust cover was to integrate the output of the tweeter panel and the mid & bass panels, perhaps forming a sort of "balanced mode radiator" (is that what they call it, like the Manger, and others?)??
The highly regarded Quad ESL 53 has a "dust cover" inside the metal outer cover...
...I often have thought that the effect of the dust cover was to integrate the output of the tweeter panel and the mid & bass panels, perhaps forming a sort of "balanced mode radiator" (is that what they call it, like the Manger, and others?)??
Rubbers and plastics have relatively high gas permeability. This includes Mylar (or other PETs) and Kynar (or other PVDF). That's why drinks in plastic bottles go flat faster than they do in glass or in cans, and why Mylar balloons have to be metallized. The lowest permeability polymer materials tend to be crystalline (e.g., PVDC, PVOH), and thus unsuitable for surrounds. Even then, they are not even close to hermetic, compared to metal or glass. Metallization might help, but continued flexing will pretty much reduce the efficacy.
If there's asymmetry in rear versus front, would one expect to increase distortion?
If there's asymmetry in rear versus front, would one expect to increase distortion?
My Dayton Wright LCM 1 s still have their gas bags inflated after all these years.Similar drive units to the Spica TC50 in a different design.
It depends on molecular weight and size of gas molecule. Helium will diffuse through glass tubing and in fact that is how He is harvested from other bulk gasses. They use glass capillary bundle as diffusion filter. sF6 is so big and heavy it won't go through bag easily, but if you put bag in He filled box, the He will actually preferentially go in. Similar effects are used with plastic tubing to separate oxygen from nitrogen out of compressed air.
My 2-cents:
I don't know what plastic Mike Wright chose... but likely chosen with the greatest care.
Even if gas is "theoretically" diffusing in both directions, my "bag" inflates and deflates over the seasons of the year.
While the moving diaphragm bisects the sealed box, I wouldn't be surprised if they are not quite total seals; hence no more inflation on one side than the other. (BTW, I'm sure those textbook pictures of open-baffle losses are not meaningful... so a little cross-flow wouldn't be harmful.)
I can't say exactly what my ESL bias voltage is, but possibly in the 10kv range or more; likely high enough to suggest the SF6 isn't materially reduced.
Got these DW ESLs around 1983 after playing DW panels open-air and direct-drive for years before. Open air sound better, I'd say. But a bit apples-and-oranges.
2014 minus 1983 (and including both start and terminal years) is 32.
Ben
I don't know what plastic Mike Wright chose... but likely chosen with the greatest care.
Even if gas is "theoretically" diffusing in both directions, my "bag" inflates and deflates over the seasons of the year.
While the moving diaphragm bisects the sealed box, I wouldn't be surprised if they are not quite total seals; hence no more inflation on one side than the other. (BTW, I'm sure those textbook pictures of open-baffle losses are not meaningful... so a little cross-flow wouldn't be harmful.)
I can't say exactly what my ESL bias voltage is, but possibly in the 10kv range or more; likely high enough to suggest the SF6 isn't materially reduced.
Got these DW ESLs around 1983 after playing DW panels open-air and direct-drive for years before. Open air sound better, I'd say. But a bit apples-and-oranges.
2014 minus 1983 (and including both start and terminal years) is 32.
Ben
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The idea of using perlite intrigues me too. Any idea how effective that is at increasing effective box size?
Not in the case of differential diffusion of say hydrogen or helium on one side to the other. It can actually unequalize pressure between the membrane.
Surprisingly, no. The driving force is the concentration gradient. When I was doing plastic foam development, this was critical in choosing the blowing agent so that the cells wouldn't rupture or collapse, basically matching the diffusion coefficients of the blowing gas to air for the particular plastic being used.
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