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Speaker cab desighns

#21
The closest anyone has come to changing the effect of a given sized enclosure is using helium gas instead of air in the cabinet. Helium is monoatomic (Helium atoms that aren't bonded to any other atoms), while air is primarily diatomic (2 atoms per molecule) nitrogen molecules. The "spring constant" of a box filled with helium is different than one filled with nitrogen (air), which gives you a small benefit. However, porting the box (and using a driver tuned for that purpose) gives a bigger benefit than helium does in an enclosed box - a ported box filled with helium isn't filled with helium for very long; even a closed box leaks helium pretty quickly, unless it's made from very specialized materials.
 
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#25
DukeLeJeune said:
You'd actually want to reduce the pressure on the back of the cone when it moves inwards, and then increase the pressure on the back of the cone when it moves outwards. This would make the cone behave as if it was in a bigger box.
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a bipap is a medical device that pretty much does all the heavy lifting when you breath . Its like a bionic lung it gives more pressure in or out on inhale and exhale it's not a constant pressure it changes from push to pull According to what the input pressure or lack of pressure.
 
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#26
JimChjones said:
I suppose you'd need a driver with no resonant frequency to match the cab with no resonant frequency.
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That would be the plasma speaker. They're not practical. Filling cabs with helium, where the speed of sound is nearly three times that of in air, would have the opposite of the intended effect, as it would make wavelengths three times longer, so cabs would have to be larger. There was experimentation with filling transmission line cabs with materials like wool, in an attempt to reduce the speed of sound and make wavelengths shorter, so cabs could be smaller, but it didn't work.
 
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#27
Rick James said:
Filling cabs with helium, where the speed of sound is nearly three times that of in air, would have the opposite of the intended effect, as it would make wavelengths three times longer, so cabs would have to be larger.
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It's not the velocity of sound within a woofer enclosure that limits performance, it's the gas's comprehensibility, which works the other way - helium is a little more compressible than nitrogen. Nitrogen is diatomic - every atom is already bonded to a neighbor, so it can't compress easily in that direction, where helium is monoatomic - all single atoms - every atom has space around it in all directions, so it's more easily compressed. Hence the cabinet has a smaller spring constant, which allows better performance (it looks bigger) at low frequencies. Of course, there are practical aspects to this - if you seal the cabinet so that helium never escapes, then it'll only really work well at one altitude, as the internal pressure can't adapt to match that on the outside.
 
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#28
Honkey tonk said:
What I'm thinking that with a small sealed speaker box and adding air pressure with a fan or cpap like device could that back pressure make an enviroment that makes the back of the speaker respond like it was in a bigger enviroment.
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You might be interested in rotary woofers. Instead of piston-driven cones, they're fans that rotate at constant speeds and vibrate the air pressure by altering the pitch of the fan blades.

The main downsides are that they're only good for frequencies from 0 to 20 Hz and they need a relatively immense volume of air behind the driver; household installations usually involve sealing off an attic or basement that adjoins the listening room and using it as a speaker cabinet.

So I guess they're not all that portable either. :D
 
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#29
redwingxix said:
Use of different gasses inside the cab was the first thing I was thinking of when reading the OP and what he was trying to do.
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Back in the 70's or early 80's, there was a Hi-Fi manufacturer that filled a bag with a different gas with the intention of making the cabinet appear larger than it really was. A little looking and it was the Cerwin Vega S-1 (thank goodness my mind hasn't completely left me for an alternate, alternate reality ;) )
 
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#30
micguy said:
- helium is a little more compressible than nitrogen. Nitrogen is diatomic - every atom is already bonded to a neighbor, so it can't compress easily in that direction, where helium is monoatomic - all single atoms - every atom has space around it in all directions, so it's more easily compressed.
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Actually at atmospheric pressure and temperature this variation would be negligible. All the gases are very close to the Ideal gas law - Wikipedia

You can make a sealed box appear larger by stuffing it with filling though. though. Link Removed
 
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#34
Nothing new.
The acoustical impedance of air equals ~400 N·s/m³

For different acoustical medium properties the acoustical impedance would change accordingly.
If the acoustical impedance was changed while sound intensity was of steady number means that particle velocity and sound pressure were also changed accordingly
 
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#35
crazyBassClown said:
You can make a sealed box appear larger by stuffing it with filling though. though. Link Removed
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That was proven incorrect before it was written, but since the formulas that show what stuffing really does, which is to lower the system Qtc, were still very much unknown even in the loudspeaker design community it was years before it was totally discounted. To see what really happens model a sealed cab in WinISD 0.7, or any program with the ability to adjust Qa. A Qa value of 100 is a bare enclosure. In the case of WinISD that's the default. Changing Qa to 50 shows the effect of lining the cab with damping, Qa of 10 filling the cab with damping, Qa of 5 filling and compressing the damping material. It's not at all difficult to lower Qtc by a full point, say from 0.8 to 0.7. To some extent that emulates the effect of a larger box, but by no means does it duplicate it, as the lowered Qtc from stuffing also results in a loss of sensitivity, whereas the lower Qtc from a larger box is accompanied by increased sensitivity. More information on what stuffing does, and how it affects ported cabs, can be found at Data-Bass

And it has absolutely nothing to do with how acoustic suspension works.
 
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#36
Makes me think of either isobaric or passive speakers.
Nothing new or amazing though :(

And yes overstuffing a box does not make it bigger. Produces more friction so you loose pressure to heat as per design. Eventually there is a loss of bass from overstuffing or seemingly loss in transients or overall stale sound. It's hard to describe it literally sounds stuffed lol
 
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#37
BogeyBass said:
Makes me think of either isobaric or passive speakers.
Nothing new or amazing though :(

And yes overstuffing a box does not make it bigger. Produces more friction so you loose pressure to heat as per design. Eventually there is a loss of bass from overstuffing or seemingly loss in transients or overall stale sound. It's hard to describe it literally sounds stuffed lol
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So if a speaker sounds muffled from being over stuffed by means of friction between the fiber and sound waves ,
Does that suggest that a speaker needs the volume of space behind it for acustic reasons ? Or is it the actual systematic compression of air that make a speaker box efficient ?
 

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