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Discussion Starter #1
Hi.

Is it possble to build a freestanding IB sub using my ht-room as "enclosure", or does it have to go into the attic or another room?
 

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You need to isolate the sound waves radiating from each side of the driver in separate spaces. You could do a really big box in your room. If you just put the drivers in free air, you've got a dipole sub. The sound quality is about the only thing I've heard that might be that tiny bit cleaner and more effortless than a true IB (really, infinite volume sealed) but it has tons of loss due to phase issues. Sub-bass dipole is a really tough task.


Things start to clean up at ~4x VAS. I've seen a number of folks install a seat riser as sub.


C
 

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Discussion Starter #3
Hi

Ok. Then I'll have to think of something else.


Best regards

Bent
 

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There is an old expired patent now by Dayton Wright / Watson Labs where they used Sulfur Hexaflouride (SF6) gas to increase the volume of the enclosure.

http://www.dayton-wright.com/WATSONLABS_.html

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.



I had been contacted by someone a few years back who was doing some research on this again. He stated the only reason the original design didn't work so well was the leaking of the gas over time. Fortunately the bag technology of today is much better than it was in the past.


John
 

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I'd like to inhale SF6 and have a deep voice for a few moments.
 

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The SF6 gas is actually pretty cheap I believe and quite easy to find. Just need some kind of soft flexible bag to put it in and then stick that bag inside the box just like polyfill.


john
 

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If I am not mistaken, this is the same gas they fill windows with to make them more energy efficient.
 

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Quote:
Originally Posted by zordac /forum/post/12982283


If I am not mistaken, this is the same gas they fill windows with to make them more energy efficient.

Windows are filled with Argon. Not sure how the two compare in density or thermal properties.


John
 

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Quote:
Originally Posted by John_E_Janowitz /forum/post/12982370


Windows are filled with Argon. Not sure how the two compare in density or thermal properties.


John

My first degree is in Chemistry. SF6 is good for this application because of two properties, its density and its non-polar molecular structure which causes it to act an as an Ideal Gas. You can Goggle it but the short and skinny is that Ideal gases act like perfect billiard balls, bouncing off each other without intermolecular dipole forces attracting or repelling them. This just means that gases that act in this way more closely follow the Ideal Gas Laws.


The density is the real reason why it’s good for this application. You get lots of intermolecular bouncing that occurs with a characteristic impedance of a larger air space. You could probably spray the enclosure with something that would make it less permeable but you would still have the problem of the driver, which isn't exactly airtight. Probably the only long-term solution would include regular recharging your SF6. Mount the driver firing upward because the density of the SF6 would induce it to settle in the enclosure.


One other issue... at high temps it decomposes into Fluorine which is extremely reactive. You would have to make sure your VC temps where low or somehow isolate the SF6 from the driver.
 

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Quote:
Originally Posted by Kevin Haskins /forum/post/12982614


Mount the driver firing upward because the density of the SF6 would induce it to settle in the enclosure.


One other issue... at high temps it decomposes into Fluorine which is extremely reactive. You would have to make sure your VC temps where low or somehow isolate the SF6 from the driver.

One could effectively install a Tempest-X in a 1ft enclosure of 50/50 air/SF6 mix then. Also, wouldn't a "bladder" work, as John J mentions?
 

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Quote:
Originally Posted by armystud0911 /forum/post/12982885


Kevin, at what temp does this occur?


I'd imagine up around 300-600 deg C. I'd have to research it more as I'm not an expert in SF6 reactions. ;-)


The thing is Fluorine is nothing to mess around with. Its very reactive and poisonous to boot. Its really nasty ****.
 

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Quote:
Originally Posted by Kevin Haskins /forum/post/12983076


I'd imagine up around 300-600 deg C. I'd have to research it more as I'm not an expert in SF6 reactions. ;-)


The thing is Fluorine is nothing to mess around with. Its very reactive and poisonous to boot. Its really nasty ****.

Hmm... 300C would be about 572F. If you get a VC up to that point your driver doesn't have a chance to withstand much more. You would essentially need to have a bladder of a soft material that allows for the transfer of energy from air to the SF6 gas. As long as you keep that bladder away from the driver by even a very short distance it should never have those heat issues.


You can look up the patent if you wish to know more on how it was originally done.


John
 

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Just wondering since we are on the subject of exotic tech to apply to subwoofers..

Would a colder driver or enclosure ambient temperature make any changes to performance?
 

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Quote:
Originally Posted by armystud0911 /forum/post/12984175


yes, you can even model for this in winisd, but the differences aren't as dramatic as what's being discussed here.

Ah, ok.

When I used to be a 'hardcore' computer freak I made a freezer style case that I loaded with peltiers. I'm thinking it could be possible to do something similar to a subwoofer. I had the hot side on the outside of the case and the cold side on the inside. A 120mm fan on each heatsink, ambient temperature inside the case was something like 20 degrees F.


I'm thinking a module that would blow the cold air into the sub somehow. Just a thought.
 

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Quote:
Originally Posted by John_E_Janowitz /forum/post/12983697


Hmm... 300C would be about 572F. If you get a VC up to that point your driver doesn't have a chance to withstand much more. You would essentially need to have a bladder of a soft material that allows for the transfer of energy from air to the SF6 gas. As long as you keep that bladder away from the driver by even a very short distance it should never have those heat issues.


You can look up the patent if you wish to know more on how it was originally done.


John

Yea.... but chemical reactions are not typically all or nothing. Sometimes you have an activation energy that has to be reached but usually the reactions occur at lower temp at lower rates. SF6 is fairly unreactive, its a stable gas due to its structure. I wouldn't want it in contact with the VC even at lower temps though without doing a careful analysis of how quickly it breaks down under temp.


The bladder would be the method to use. That prevents it from leaking and keeps it out of contact with the driver which is really the only source of high temp surface area.
 

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Quote:
Originally Posted by Spezzy /forum/post/12984097


Just wondering since we are on the subject of exotic tech to apply to subwoofers..

Would a colder driver or enclosure ambient temperature make any changes to performance?

I saw something on a car forum where they took a component set and subjected it to temperature changes that may be experienced in a car, then took measurements. The woofers TSPs changed for the worst outside the 50-100ºF range. 0º had the Q and fs rediculously high if memory serves me.
 

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Quote:
Originally Posted by Looneybomber /forum/post/12985336


I saw something on a car forum where they took a component set and subjected it to temperature changes that may be experienced in a car, then took measurements. The woofers TSPs changed for the worst outside the 50-100ºF range. 0º had the Q and fs rediculously high if memory serves me.

The colder the coil gets, the more the DCR drops. That is why the car audio SPL guys "freeze" motors. It simply allows them to draw slightly more power from the amp..... for a fraction of a second until that power has warmed up the coil.


The FS and Q going up would be due to suspension getting stiffer with lower temperatures. This all depends greatly on the material of the surround used. They all get stiffer, but how much stiffer varies greatly. We picked santoprene on our AV series because it has the least amount of variance over a wide range of temperatures.


John
 

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Quote:
Originally Posted by Spezzy /forum/post/12984468


Ah, ok.

When I used to be a 'hardcore' computer freak I made a freezer style case that I loaded with peltiers. I'm thinking it could be possible to do something similar to a subwoofer. I had the hot side on the outside of the case and the cold side on the inside. A 120mm fan on each heatsink, ambient temperature inside the case was something like 20 degrees F.


I'm thinking a module that would blow the cold air into the sub somehow. Just a thought.

lol, I'm running a watercooled, pelted rig as we speak, I still am into the performance PC thing quite a bit, but I don't game as much as I used to so there isn't as much of a point to it.
 
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