I was trying to think of some way to get rid of some nasty light bulbs used in another thread as an inductor substitute for a SE amplifier when this scandalous idea occured to me. The inductor problem for SE is quite similar to the speaker cabinet issue for speakers. Could they be combined in such a way as to null out both problems. Yes!
Now imagine a speaker driver that is truly sealed. An airtight driver in a small hermetically sealed backing. This backing would be quite small so as to act as a sealed air spring. To operate this speaker in Class A mode, we would apply a DC current to it of 1/2 the maximum current for the loudest output. This driver would be set up in such a way that the 1/2 max current pushes the speaker coil and diaphragm backwards to the center of its linear range within the magnet, while also pressurising the speaker backing to 1/2 the max pressure exerted by the loadest sound. (conversely, one would simply pre-pressurize the backing until the 1/2 Max DC current centered the speaker coil, probably less than a PSI, in any case it is no more pressure than 1/2 what a normal speaker encounters at its loudest output. )
Then AC would be applied (summed with the DC) to the driver to move the driver back and forth for normal operation. Now since the AC varies from -1/2 Max DC to +1/2 Max DC, the net effect is of 0 to +1 x DC Max current input, or simply, single ended (SE) speaker operation.
Now, how to combine this with a SE amplifier lacking its inductor or OT inductance. We start out with a non-gapped OT (output xfmr) powered by a SE circuit. This would normally saturate the non-gapped xfmr due to 1/2 Max Class A primary bias current. But we will apply 1/2 Max DC current thru the secondary (transformed magnitude) to balance out the primary side DC. So no air gap is needed. This 1/2 Max DC current bias is just what the SE speaker wants too, so we run the 1/2 Max DC current thru both the OT secondary and the SE speaker coil. Both are happy. AC signal just rides right thru the OT and sums with the DC 1/2 Max bias to drive the SE speaker.
This does not require a CCS by the way. No voltage compliance is wanted, we want a low Z DC source in series, which would just be a fractional volt power supply. Adjusted so that the secondary winding resistance and the SE speaker coil resistance produced, or limited, the 1/2 Max DC current. The sealed air speaker backing is providing the energy storage/inductance for the SE system. Hardly any power would be used by the DC bias supply, maybe say 1/2 Volt at 2 amps.
Essentially no backing volume is needed for the speaker (ie, a cabinetless speaker) here since it must be small enough to pressurize to 1/2 Max sound pressure with just 1/2 the Max motion of the speaker diaphragm. The SE amplifier gets to use the much cheaper and better performing P-P OT. Win-Win! Revolutionary.
Now imagine a speaker driver that is truly sealed. An airtight driver in a small hermetically sealed backing. This backing would be quite small so as to act as a sealed air spring. To operate this speaker in Class A mode, we would apply a DC current to it of 1/2 the maximum current for the loudest output. This driver would be set up in such a way that the 1/2 max current pushes the speaker coil and diaphragm backwards to the center of its linear range within the magnet, while also pressurising the speaker backing to 1/2 the max pressure exerted by the loadest sound. (conversely, one would simply pre-pressurize the backing until the 1/2 Max DC current centered the speaker coil, probably less than a PSI, in any case it is no more pressure than 1/2 what a normal speaker encounters at its loudest output. )
Then AC would be applied (summed with the DC) to the driver to move the driver back and forth for normal operation. Now since the AC varies from -1/2 Max DC to +1/2 Max DC, the net effect is of 0 to +1 x DC Max current input, or simply, single ended (SE) speaker operation.
Now, how to combine this with a SE amplifier lacking its inductor or OT inductance. We start out with a non-gapped OT (output xfmr) powered by a SE circuit. This would normally saturate the non-gapped xfmr due to 1/2 Max Class A primary bias current. But we will apply 1/2 Max DC current thru the secondary (transformed magnitude) to balance out the primary side DC. So no air gap is needed. This 1/2 Max DC current bias is just what the SE speaker wants too, so we run the 1/2 Max DC current thru both the OT secondary and the SE speaker coil. Both are happy. AC signal just rides right thru the OT and sums with the DC 1/2 Max bias to drive the SE speaker.
This does not require a CCS by the way. No voltage compliance is wanted, we want a low Z DC source in series, which would just be a fractional volt power supply. Adjusted so that the secondary winding resistance and the SE speaker coil resistance produced, or limited, the 1/2 Max DC current. The sealed air speaker backing is providing the energy storage/inductance for the SE system. Hardly any power would be used by the DC bias supply, maybe say 1/2 Volt at 2 amps.
Essentially no backing volume is needed for the speaker (ie, a cabinetless speaker) here since it must be small enough to pressurize to 1/2 Max sound pressure with just 1/2 the Max motion of the speaker diaphragm. The SE amplifier gets to use the much cheaper and better performing P-P OT. Win-Win! Revolutionary.
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Do you mean to connect the speaker in diagonal of a bridge formed by an amp with DC offset and a compensating voltage source?
Or to inflate a speaker box by an air displacing such a way it's diaphragm?
Please clarify.
Or to inflate a speaker box by an air displacing such a way it's diaphragm?
Please clarify.
By the diaphragm air displacement pressurizing the box (or the "backing" since the box size has shrunk to almost nothing here) 1/2 Max motion of the diaphragm would increase the backing pressure from 1/2 Max to full Max. or in the forward direction from 1/2 Max pressure to 0 (relative) pressure. This could also be made to work for SE SS amplifiers as well (just no intermediate OT involved then). When the SE speaker is disconnected from its amplifier, it would move (diaphragm) to its forward Max position, thus neatralizing backing pressure with atmospheric.
This could be a minor manufacturing variation from current speaker drivers. Normally the speaker diaphragm compliance is centered in the center of the magnet. For an SE speaker, the compliance would center at the forward Max position. (assuming it has little or no springiness of its own)
The backing could be built right into the speaker assembly, no need for any cabinet. A pressure relief valve push button could allow neutralizing the backing pressure when disconnected or un-powered so that the compliance would move to the forward position and entrap the correct amount of air. (this is really just a calibration feature to allow for and compensate slow leakage problems)
This could be a minor manufacturing variation from current speaker drivers. Normally the speaker diaphragm compliance is centered in the center of the magnet. For an SE speaker, the compliance would center at the forward Max position. (assuming it has little or no springiness of its own)
The backing could be built right into the speaker assembly, no need for any cabinet. A pressure relief valve push button could allow neutralizing the backing pressure when disconnected or un-powered so that the compliance would move to the forward position and entrap the correct amount of air. (this is really just a calibration feature to allow for and compensate slow leakage problems)
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Do you mean something like electrostatic inflated concentric bubble?
I like the idea. Can be made of a metal mesh ball (anode) and a made of conductive rubber ball around (grounded cathode)
I like the idea. Can be made of a metal mesh ball (anode) and a made of conductive rubber ball around (grounded cathode)
Hi,
Where does one start to explain why this will not fly ?
Its not complicated, its never been commercially done
AFAIK, there are very good reasons for that, find them.
😎 /Sreten.
Where does one start to explain why this will not fly ?
Its not complicated, its never been commercially done
AFAIK, there are very good reasons for that, find them.
😎 /Sreten.
"Do you mean something like electrostatic inflated concentric bubble?"
No. This is very much a conventional speaker driver setup. Although there is no reason it could not be extended to an electrostatic design, planar or spherical if that's do-able.
No. This is very much a conventional speaker driver setup. Although there is no reason it could not be extended to an electrostatic design, planar or spherical if that's do-able.
I guess vented pole pieces are out.....
Dialing in the speaker cabinet would require dialing in both pressure and volume, since you'll want a certain bias "pressure" for 1/2 the excursion but you'll also need the correct air spring rate for proper max excursion based on the applied voltage. A water manometer connected to the cabinet would probably provide enough pressure while keeping everything dry. It would be easy enough to vary the pressure by changing the height of the water. 30" of H2O is roughly 1 psi. I would imagine that you would need way less than 1 psi, especially for larger drivers.
Of course, keeping the pressure in the cabinet for any length of time will be one challenge. (wait, don't turn the amp on yet-I need to pump up the speakers...)
Using a old 13" car tire for an enclosure may fit the bill here....and it would be non-resonant with non parallel walls. Or maybe a 15" woofer in a 15" car tire. Some sheet metal screws and RTV right into the bead. Pretty low WAF, though. 😀
Dialing in the speaker cabinet would require dialing in both pressure and volume, since you'll want a certain bias "pressure" for 1/2 the excursion but you'll also need the correct air spring rate for proper max excursion based on the applied voltage. A water manometer connected to the cabinet would probably provide enough pressure while keeping everything dry. It would be easy enough to vary the pressure by changing the height of the water. 30" of H2O is roughly 1 psi. I would imagine that you would need way less than 1 psi, especially for larger drivers.
Of course, keeping the pressure in the cabinet for any length of time will be one challenge. (wait, don't turn the amp on yet-I need to pump up the speakers...)
Using a old 13" car tire for an enclosure may fit the bill here....and it would be non-resonant with non parallel walls. Or maybe a 15" woofer in a 15" car tire. Some sheet metal screws and RTV right into the bead. Pretty low WAF, though. 😀
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I think a DIYer could even modify an existing speaker to do this. Just start with a poly... coned speaker or something that is reasonably air tight with a non-permeable surround. Mount a solid metalic cone of the same dimensions as the speaker diaphragm to the front of the speaker with just enough space to the diaphragm to accomodate the backing volume required (essentially it just goes at twice the max forward speaker extension). Sound would then radiate from the rear of the speaker driver. Enough DC current to move the diaphragm to the max backward extension would then be applied, and the metal cone sealed tight to entrap the correct volume of air inside the front space.
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"Of course, keeping the pressure in the cabinet for any length of time will be one challenge. (wait, don't turn the amp on yet-I need to pump up the speakers...)"
Well, that would be the advantage of having the speaker surround centered at the forward position rather than the center travel position. When un-powered, the speaker would move naturally to the zero pressure differential position. A tiny leak could be configured so that the speaker would always tend to entrap the correct volume of air during inactive periods. The leak would have to be small enough to prevent any significant air loss during operation, since the diaphragm would sit on average at 1/2 Max pressure position during operation.
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"Of course, keeping the pressure in the cabinet for any length of time will be one challenge. (wait, don't turn the amp on yet-I need to pump up the speakers...)"
Well, that would be the advantage of having the speaker surround centered at the forward position rather than the center travel position. When un-powered, the speaker would move naturally to the zero pressure differential position. A tiny leak could be configured so that the speaker would always tend to entrap the correct volume of air during inactive periods. The leak would have to be small enough to prevent any significant air loss during operation, since the diaphragm would sit on average at 1/2 Max pressure position during operation.
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Pressurize the speaker cabinet? Why not just evacuate it.
Put some old vacuum tubes inside, and shake it till they break.
Put some old vacuum tubes inside, and shake it till they break.
Just glue a needed amount of magnetic material in the center of the cone: a magnetic field would not deflate. 😀
"Pressurize the speaker cabinet? Why not just evacuate it.
Put some old vacuum tubes inside, and shake it till they break. "
How about dropping the pressure in your house by 1/2 a PSI by just turning on the kitchen exhaust fan? (10,000 RPM) That would effectively pressurize the speaker cabinet. 😀
"Just glue a needed amount of magnetic material in the center of the cone: a magnetic field would not deflate. "
Yea, that could work if it doesn't kill the diaphragm mass allowance. Or just push a spring up against the speaker center. But these approaches don't get rid of the speaker cabinet.
Put some old vacuum tubes inside, and shake it till they break. "
How about dropping the pressure in your house by 1/2 a PSI by just turning on the kitchen exhaust fan? (10,000 RPM) That would effectively pressurize the speaker cabinet. 😀
"Just glue a needed amount of magnetic material in the center of the cone: a magnetic field would not deflate. "
Yea, that could work if it doesn't kill the diaphragm mass allowance. Or just push a spring up against the speaker center. But these approaches don't get rid of the speaker cabinet.
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Good point. Also, you may use your speaker as a barometer to predict weather changes. (I use my legs to predict winds) 😀
"you may use your speaker as a barometer to predict weather changes."
Interesting point. Any sudden big change in barometer would cause some distortion. Not really a long term problem though with the slow leak and biased compliance compensator idea. But could be interesting to hear singers beginning to get a little "off" or squeeky sounding just before the lightning strikes. Probably not much effect though from usual millibar weather changes.
By the way, the speaker "backing" does not want (or need) to be far enough away from the diaphragm to cause resonance effects at the highest audio frequencies. At least for reasonably sized speaker cones. Maybe not so good for some 1 inch diameter acoustic suspension speaker. The larger the speaker diaphragm, the less travel it uses for some sound pressure, so the closer the backing is at 2x cone travel. There may be some issue with pressure linearity with cone displacement though, seeing as how it eventually heads toward infinity as the cone approaches the backing. OK, I'll fix that. The speaker backing space has to be filled with some mix of condensing gas vapor to compensate. Or, the magnetic air gap spacing in the magnet assembly would be slightly tapered in such a way as to compensate the backing pressure non-linearity.
Interesting point. Any sudden big change in barometer would cause some distortion. Not really a long term problem though with the slow leak and biased compliance compensator idea. But could be interesting to hear singers beginning to get a little "off" or squeeky sounding just before the lightning strikes. Probably not much effect though from usual millibar weather changes.
By the way, the speaker "backing" does not want (or need) to be far enough away from the diaphragm to cause resonance effects at the highest audio frequencies. At least for reasonably sized speaker cones. Maybe not so good for some 1 inch diameter acoustic suspension speaker. The larger the speaker diaphragm, the less travel it uses for some sound pressure, so the closer the backing is at 2x cone travel. There may be some issue with pressure linearity with cone displacement though, seeing as how it eventually heads toward infinity as the cone approaches the backing. OK, I'll fix that. The speaker backing space has to be filled with some mix of condensing gas vapor to compensate. Or, the magnetic air gap spacing in the magnet assembly would be slightly tapered in such a way as to compensate the backing pressure non-linearity.
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I rather like the idea of turning myself into the Michelin Man by enclosing myself in toroidal "inners", probably a more direct way to dampen the out of order harmonics of SE amps - might get a bit dark inside though - maybe have to turn on one of those nasty lamps.
😱
What you want would be a spiral rubber tube that could be wrapped around like some giant Boa-constrictor. Then the speaker could be interfaced at the end of the tube, so sound would travel around the spiral. Great for really feeling the music or for surround sound for action movies. Boom.. Boom ...... KaBoom
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Being " mono- blubbed would be alright for a while - But eventually I would want to share the experience with others 😛
Well, after a little cogitating and kicking the tire rims, a few issues are of concern with the idea:
1) air pressurization and leakage
2) linearity of air pressure versus cone translation
3) mismatch of DC bias required between speaker and amplifier
4) resonance in the backing chamber
1) SE operation requires a bias air pressure in the backing chamber. This could leak out during use or during storage. Having the cone compliance and surround set at one limit of the cone travel fixes the issue for storage since the cone would be sitting at the zero pressure differential position. But extended play operates at an average pressure which could leak out during extended play (but would auto restore again when turned off for a while)
2) The air pressure in the back pressure chamber does not vary linearly with cone movement, so introduces distortion. This I think can be cured by a tapered magnet gap to compensate, but this requires a long magnet and short coil (more expensive). Ah-ha, for a short magnet and long coil structure (usual cheap designs) the coil winding pitch could be varied slightly to compensate the pressure non-linearity.
3) A specific speaker will want a specific DC bias to return the cone to the centered travel position. Whereas different amplifiers will want different DC bias depending on design, tubes used, and wattage output. Other than using the Ot xfmr taps to compensate or varying the speaker back pressure, I'm not seeing a good solution here yet. Another fix would be to have the magnet assembly threaded into the speaker frame, so that its position could be moved about to adjust the DC bias required for cone centering. Not the most convenient solution.
4) The back pressure chamber can produce resonance effects for the highest frequencies if the air column length is a significant fraction of a quarter wavelength. Since 20 KHz has a wavelength of 1.6 Cm, this is getting a bit close. Since low frequency bass speakers tend to have a long cone travel (requiring a longer backing space), they will not work well at high frequencies. But then this issue already existed for normal speakers anyway. The solution being to split up the frequency ranges. This then becomes a problem #3 issue with different DC biases required for the different speakers. HF tweeters and mid-ranges can just be operated thru a cap without any DC bias (ie, normal speaker drivers). Just one of the attached speakers needs to have the DC bias to compensate the amplifier anyway. So this technique is best for just the LF woofer/sub.
In any case, the possibility of getting rid of the speaker cabinet effectively is still very attractive. The pressurization leakage issue goes away if the DC bias SE operation feature is dropped. A pressurization back chamber of 2X cone travel length (or longer, longer reducing the non-linearity and magnitude of the pressure variation, as long as its not resonating at the top bass frequency) is still used, but the cone sits at the zero pressure position both during storage and operation. So leakage is not an issue. The back pressure does still change like a spring, so this will appear as an inductance in parallel with the speaker, but is now an AC issue. (a longer chamber appearing as a higher inductance)
Seems to me this could be very attractive commercially. Just hang the speakers on the wall, no cabinet required.
1) air pressurization and leakage
2) linearity of air pressure versus cone translation
3) mismatch of DC bias required between speaker and amplifier
4) resonance in the backing chamber
1) SE operation requires a bias air pressure in the backing chamber. This could leak out during use or during storage. Having the cone compliance and surround set at one limit of the cone travel fixes the issue for storage since the cone would be sitting at the zero pressure differential position. But extended play operates at an average pressure which could leak out during extended play (but would auto restore again when turned off for a while)
2) The air pressure in the back pressure chamber does not vary linearly with cone movement, so introduces distortion. This I think can be cured by a tapered magnet gap to compensate, but this requires a long magnet and short coil (more expensive). Ah-ha, for a short magnet and long coil structure (usual cheap designs) the coil winding pitch could be varied slightly to compensate the pressure non-linearity.
3) A specific speaker will want a specific DC bias to return the cone to the centered travel position. Whereas different amplifiers will want different DC bias depending on design, tubes used, and wattage output. Other than using the Ot xfmr taps to compensate or varying the speaker back pressure, I'm not seeing a good solution here yet. Another fix would be to have the magnet assembly threaded into the speaker frame, so that its position could be moved about to adjust the DC bias required for cone centering. Not the most convenient solution.
4) The back pressure chamber can produce resonance effects for the highest frequencies if the air column length is a significant fraction of a quarter wavelength. Since 20 KHz has a wavelength of 1.6 Cm, this is getting a bit close. Since low frequency bass speakers tend to have a long cone travel (requiring a longer backing space), they will not work well at high frequencies. But then this issue already existed for normal speakers anyway. The solution being to split up the frequency ranges. This then becomes a problem #3 issue with different DC biases required for the different speakers. HF tweeters and mid-ranges can just be operated thru a cap without any DC bias (ie, normal speaker drivers). Just one of the attached speakers needs to have the DC bias to compensate the amplifier anyway. So this technique is best for just the LF woofer/sub.
In any case, the possibility of getting rid of the speaker cabinet effectively is still very attractive. The pressurization leakage issue goes away if the DC bias SE operation feature is dropped. A pressurization back chamber of 2X cone travel length (or longer, longer reducing the non-linearity and magnitude of the pressure variation, as long as its not resonating at the top bass frequency) is still used, but the cone sits at the zero pressure position both during storage and operation. So leakage is not an issue. The back pressure does still change like a spring, so this will appear as an inductance in parallel with the speaker, but is now an AC issue. (a longer chamber appearing as a higher inductance)
Seems to me this could be very attractive commercially. Just hang the speakers on the wall, no cabinet required.
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"mono- blubbed " ?
Put the stereo speakers at each end of the spiral Boa tube. Spatial soundstage resolution could take on a whole new meaning.
Put the stereo speakers at each end of the spiral Boa tube. Spatial soundstage resolution could take on a whole new meaning.
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