I never said I thought it would always be better to have more flux, but I'd think it would be in most cases. I wouldnt really be concerned with making super high amounts of flux, just moderately high amounts in extremely long gaps. Flux consistantcy is also a very important factor. Ruler flat BL is achieveable, and someone is going to figure out how to make it. I dont mean that ripply flat BL either I'm talking smooth.
To achieve a long gap that has consistant high flux we need a strong magnet. Its all a matter of economics from there. You can either use a permanant magnet, or an electromagnet. You can either use ferrite magnets, or neo magnets. Copper wound, or HTS. Buisness makes things hard there.
I guess a project is in order. Make a speaker motor using a HTS feild coil. This could get interesting
To achieve a long gap that has consistant high flux we need a strong magnet. Its all a matter of economics from there. You can either use a permanant magnet, or an electromagnet. You can either use ferrite magnets, or neo magnets. Copper wound, or HTS. Buisness makes things hard there.
I guess a project is in order. Make a speaker motor using a HTS feild coil. This could get interesting
If a driver motor were pumped with liquid nitrogen, I'd rather have a superconducting field coil than a superconducting voice coil. That way you could pump up the current for ultra-high flux and not worry about heat problems and inductance (which isn't really a big deal, though). Then again, if you pumped liquid nitrogen through the motor, you wouldn't worry about heat anyway.
You could make a cone with a big permanent neo magnet, only need a suspension to hold it, then you put a very very huge fixed electro magnet behind the cone to drive the neo magnet. Since the electro magnet is fixed and not attached physically with the cone, you could put it in a small nitrogen tank.
How am I going to keep the voice coil at -160? Im not. I havent yet figured out a way to use a superconductive voice coil, but potentially the silver lamenate 1G wires might work. I think the feild coil would be the best idea anyhow. The magnetic flux could be adjusted easily by increasing and decreasing power, and cooling shouldnt be a problem with a liquid nitrogen system. If the motor is at <-100C then I dont think the voice coil will ever suffer much from thermal compression. I'm not really one for using finite element analysis, so I guess I'll have to learn it if theres any chance at a sucessful result
I haven't read the entire thread, so at the risk of repetition: A driver with zero ohm voice coil resistance would have a rediculously low Qts. In fact, the response would be tilted by + 6 dB/octave from way below the resonance up until the voice coil inductance starts to dominate the impedance. This could be fixed with an amplifier that has negative current feedback, so that it appears to have an output resistance of 4-8 ohms or something, and then the speaker would behave as a usual speaker does, except for the efficiency. I am wondering though, if the indirect heating of the voice coil from eddy currents in the magnetic system wouldn't be a problem. One could cool the magnetic system too, but I wouldn't know what happens in the magnetic circuit then. Somebody else maybe?
You're right about the Qts. When Bl goes up Qts goes down. Yes, efficiency rises, but so does the bandwidth floor. That can be compensated for with EQ shaping, but that demands longer excursion from the driver and more power from the amp. Extremely high Bl products are already available thanks to neo magnets, but there is a limit to how high you can go without bringing too many other problems into play.
After emailing American superconductor corp, I have recieved a reply. Minimum order of HTS wire is 200meters. I am checking on price now. Whether or not I shall do this project depends mostly on the price of the superconductor and compressor(cooling system). If the price is acceptable I think a few superconductive feild coil prototypes would be easily made from 200meters of wire, and possibly a motor with a superconductive voice coil!
Once I recieve details on price, how large the wire is (thickness and width as it is flat wire), and how flexible it is(to determine how small the coil's diameter can be) it will be obvious if this project is practical or not. I'll keep you all updated...
I'm not very learned in the area of magnetics either(mainly the use of Finite element analysis). So I might be asking for help modeling a magnet system from those of you out there who are knowledgeable.
Thanks
Once I recieve details on price, how large the wire is (thickness and width as it is flat wire), and how flexible it is(to determine how small the coil's diameter can be) it will be obvious if this project is practical or not. I'll keep you all updated...
I'm not very learned in the area of magnetics either(mainly the use of Finite element analysis). So I might be asking for help modeling a magnet system from those of you out there who are knowledgeable.
Thanks
in Physics Today,in the late 80's,early90s', Oxford Instruments
often advertised then record flux densitys,(2 billion gauss) their product
resembling compression drivers
in the event bassawdyO" vision is achieved the noise floor of up line
componets will blast off along with the greater resolution of detail.
once the noise is removed detail retrieved should be Truly Shocking
Field Coil Hero Finn Hammer -- http://home5.inet.tele.dk/f-hammer/
Big Field Coil-- http://www.navsource.org/archives/01/01441s.jpg
often advertised then record flux densitys,(2 billion gauss) their product
resembling compression drivers
in the event bassawdyO" vision is achieved the noise floor of up line
componets will blast off along with the greater resolution of detail.
once the noise is removed detail retrieved should be Truly Shocking
Field Coil Hero Finn Hammer -- http://home5.inet.tele.dk/f-hammer/
Big Field Coil-- http://www.navsource.org/archives/01/01441s.jpg
I'm still thinking about superconducting speakers and I really want to make one... I have some ideas, I just need a bit more knowledge of the magnetics and electrophysics to make a solid design. That and I need the materials!!! mostly just HTS wire
If a speaker could have a superconducting voice coil and magnet then how sensitive could things get? I think only db @ w ratings are not the best way of judging efficency. It should really be looked at as the pure percentage of power output versus power imput of the voice coil/motor. We do need some indication of electrical to acoustical however so db @ w can stay to do that.
the problem with having the perfect motor is matching it to the perfect cone! massless and infinitely stiff hmmm well we already threw out massless with the coil, so if you cant have both, at least have one!
And what truely is the perfect cone? what is its shape?
If a speaker could have a superconducting voice coil and magnet then how sensitive could things get? I think only db @ w ratings are not the best way of judging efficency. It should really be looked at as the pure percentage of power output versus power imput of the voice coil/motor. We do need some indication of electrical to acoustical however so db @ w can stay to do that.
the problem with having the perfect motor is matching it to the perfect cone! massless and infinitely stiff hmmm well we already threw out massless with the coil, so if you cant have both, at least have one!
And what truely is the perfect cone? what is its shape?
Actually, dB vs Watts is a perfectly good way of judging efficiency:
This is the way dB is defined for speaker output levels (though technically, when we write 96dB at 1W it is wrong since dB is only a comparison between two levels):
dB = 10log(I/Iref)
Where Iref is the reference intensity, 10^-12 W/m^2, the softest noise we can hear (approximately - it depends on frequency).
I is the actual intensity. Now, (falsely) assuming that the speaker radiates sound uniformly over a sherical surface around it, the power will be divided evenly over this surface. Now, the surface area of a sphere is 4*pi*r^2. Thus, at 1m away, the intensity is P/(4*pi*1^2) = P/(4pi), where P is the output power from the speaker.
Now we see that our equation becomes:
dB = 10log(Pout/(4*pi*10^-12))
So the output dB is a figure related to output power and given this dB reading we could recover the output power, relate it to the input power and hence find the efficiency. This means that for a 100%, uniformly emitting speaker will have a maximum output dB at 1m for 1W input of:
10log(1/(4*pi*10^-12) = 109dB
If we assume that the speaker only radiates forwards (because of a box, or whatever) then we consider the surface area of half a sphere, or half the original area, so the output is doubled, i.e. add 3dB. This gives 112dB.
Obviously no speaker is 100% efficient and no speaker will radiate uniformally like this, so there is potential for higher dB in the listening position if the speakers concentrate their radiation in that direction.
Chris.
This is the way dB is defined for speaker output levels (though technically, when we write 96dB at 1W it is wrong since dB is only a comparison between two levels):
dB = 10log(I/Iref)
Where Iref is the reference intensity, 10^-12 W/m^2, the softest noise we can hear (approximately - it depends on frequency).
I is the actual intensity. Now, (falsely) assuming that the speaker radiates sound uniformly over a sherical surface around it, the power will be divided evenly over this surface. Now, the surface area of a sphere is 4*pi*r^2. Thus, at 1m away, the intensity is P/(4*pi*1^2) = P/(4pi), where P is the output power from the speaker.
Now we see that our equation becomes:
dB = 10log(Pout/(4*pi*10^-12))
So the output dB is a figure related to output power and given this dB reading we could recover the output power, relate it to the input power and hence find the efficiency. This means that for a 100%, uniformly emitting speaker will have a maximum output dB at 1m for 1W input of:
10log(1/(4*pi*10^-12) = 109dB
If we assume that the speaker only radiates forwards (because of a box, or whatever) then we consider the surface area of half a sphere, or half the original area, so the output is doubled, i.e. add 3dB. This gives 112dB.
Obviously no speaker is 100% efficient and no speaker will radiate uniformally like this, so there is potential for higher dB in the listening position if the speakers concentrate their radiation in that direction.
Chris.
A perfect cone can only be a coneBassAwdyO said:
You might be using the word 'perfect' too liberally here
as i'm sure you're aware there is no such thing in transducer design.One of the reasons a cone/dome diaphragm is used is for its inherent structural strength. If your diaphragm no longer needs to be light and stiff, but only stiff, then a flat diaphragm might be worth researching.
On a side note I remember reading about some issues with ESL's when the panel mass becomes the same as the air its loading or something. So not so sure that massless diaphragm would be the ideal in any case.
If you're aiming for the highest efficiency then I suppose you want the highest rigidity, which will come from a straight cone. A very rigid cone material will be desirable too. Diamond springs immediately to mind, but I don't know if it's possible to synthesize large enough peices yet. Otherwise, titanium of aluminium look good, both being rigid and light.BassAwdyO said:
Fun topic..
HTS...coupla pointers..
1. The minimum bend diameter for the high strength American superconductor stainless tape is 50 mm. This allow retention of at least 95% of the critical current capability. Note that this tape is made with stainless on both sides of the super, this puts the super in the zero strain location..the other tape they make has the super on one side of the stainless, so it is strained more, making the minimum diameter 100 mm..
2..They sell it in 4 minimum amperage grades..115 A, 125, 135, and 145. Average width is 4mm, average thickness is .3mm.
3. If you examine the performance charts, it is easy to see some interesting things...At 1 tesla, parallel field direction, the tape capacity is about 1/3rd of the spec. So, at one tesla, the current you'll be able to use is roughly 40 amperes. That is at 77 K, nitrogen boiling temperature at room pressure. If you want higher fields, you'll have to drop the pressure of the nitrogen.
4. If you could get the pressure sufficiently low to allow 50K operation, you could get up to 6 or 7 tesla with only 60 or 70 amps. Unfortunately, the iron magnetic structure will saturate big time as you go over 2 tesla or so. Meaning, the iron contributes less and less to the return structure, and the field begins to expand outside the structure..This drops your transfer function (tesla per ampere), and starts to become dangerous..magnetic objects start becoming projectiles, nearby tv's start to change colors or have the image pulled to one side, and even non magnetic metals become dangerous, as they heat up from eddy currents if they are forced to move in the field gradients. This is why jewelry and makeup are not allowed in an mri. (makeup uses carbon black, so eyeblinks could burn the lashes..)
5. Provision would have to be made to sense the onset of normal conductor operation, this being when the wire starts turning back into normal high resistivity material. Typically, a center tap is used to compare both halves of the coil, for DC application, a simple low pass to ignore the bass could be used.
6. Provisions for the warm to cold transitions will be required, including gas cooled leads.. Or, you could use a persistance switch, charge the coil with energy, then turn off the switch heater, and allow the coil to run in the persistent mode..
7. The voice coil would have to be 50mm minimum diameter..say, 75mm. The problems encountered would be: Not too many engineered plastic materials retain their shear strength capability at 77K. Keeping the voice coil together poses it's own problem. Although, it could be made using Kapton pre-imidized liquid, and bakes at 300C. Yould have to consider how many turns you'd require..If you are replacing a normal coil, say 50 turns, and a kilowatt, your talking say 15 amperes and 750 ampere-turns..that would be 10 turns and 75 amps.. Vc inductance would be 1/25th of a normal copper coil, but the amplifier would need 75 ampere capability..
8. Hoop stresses on the voice coil will attempt to expand the diameter of the coil. This requires a pre-loaded epoxy-glass layer over the HTS, epoxy glass has the same tempco as most coppers and steels, but not aluminum. Winding the coil on the inner surface of a epoxy-glass or epoxy graphite matrix composite former would probably survive, and give the least motional mass. But, you'd have to be very careful not to exceed .35% tensile strain, as this affects the critical current capability of the wire..
9. The best bet is to think outside the box...design the entire structure along the same lines as the servo-subs. Use a directionally strand oriented graphite/kevlar tube to bring the forces out of a cryogenic structure, this tube will also serve as the warm to cold transition piece, bringing nitrogen consumption down without a large mass penalty.
Now, speaker cables, that'd be a different story..
Cheers, John
HTS...coupla pointers..
1. The minimum bend diameter for the high strength American superconductor stainless tape is 50 mm. This allow retention of at least 95% of the critical current capability. Note that this tape is made with stainless on both sides of the super, this puts the super in the zero strain location..the other tape they make has the super on one side of the stainless, so it is strained more, making the minimum diameter 100 mm..
2..They sell it in 4 minimum amperage grades..115 A, 125, 135, and 145. Average width is 4mm, average thickness is .3mm.
3. If you examine the performance charts, it is easy to see some interesting things...At 1 tesla, parallel field direction, the tape capacity is about 1/3rd of the spec. So, at one tesla, the current you'll be able to use is roughly 40 amperes. That is at 77 K, nitrogen boiling temperature at room pressure. If you want higher fields, you'll have to drop the pressure of the nitrogen.
4. If you could get the pressure sufficiently low to allow 50K operation, you could get up to 6 or 7 tesla with only 60 or 70 amps. Unfortunately, the iron magnetic structure will saturate big time as you go over 2 tesla or so. Meaning, the iron contributes less and less to the return structure, and the field begins to expand outside the structure..This drops your transfer function (tesla per ampere), and starts to become dangerous..magnetic objects start becoming projectiles, nearby tv's start to change colors or have the image pulled to one side, and even non magnetic metals become dangerous, as they heat up from eddy currents if they are forced to move in the field gradients. This is why jewelry and makeup are not allowed in an mri. (makeup uses carbon black, so eyeblinks could burn the lashes..)
5. Provision would have to be made to sense the onset of normal conductor operation, this being when the wire starts turning back into normal high resistivity material. Typically, a center tap is used to compare both halves of the coil, for DC application, a simple low pass to ignore the bass could be used.
6. Provisions for the warm to cold transitions will be required, including gas cooled leads.. Or, you could use a persistance switch, charge the coil with energy, then turn off the switch heater, and allow the coil to run in the persistent mode..
7. The voice coil would have to be 50mm minimum diameter..say, 75mm. The problems encountered would be: Not too many engineered plastic materials retain their shear strength capability at 77K. Keeping the voice coil together poses it's own problem. Although, it could be made using Kapton pre-imidized liquid, and bakes at 300C. Yould have to consider how many turns you'd require..If you are replacing a normal coil, say 50 turns, and a kilowatt, your talking say 15 amperes and 750 ampere-turns..that would be 10 turns and 75 amps.. Vc inductance would be 1/25th of a normal copper coil, but the amplifier would need 75 ampere capability..
8. Hoop stresses on the voice coil will attempt to expand the diameter of the coil. This requires a pre-loaded epoxy-glass layer over the HTS, epoxy glass has the same tempco as most coppers and steels, but not aluminum. Winding the coil on the inner surface of a epoxy-glass or epoxy graphite matrix composite former would probably survive, and give the least motional mass. But, you'd have to be very careful not to exceed .35% tensile strain, as this affects the critical current capability of the wire..
9. The best bet is to think outside the box...design the entire structure along the same lines as the servo-subs. Use a directionally strand oriented graphite/kevlar tube to bring the forces out of a cryogenic structure, this tube will also serve as the warm to cold transition piece, bringing nitrogen consumption down without a large mass penalty.
Now, speaker cables, that'd be a different story..
Cheers, John
John,
Thanks for all the info... A bit of it is beyond my knowledge of superconductors. Maybe you should be designing the world's first Superconductive loudspeaker instead of me!
Where did you find that stuff? I've had a hard time finding any technical information about HTS wire anywhere. I would like to research it thoroughly myself.
Thanks for all the info... A bit of it is beyond my knowledge of superconductors. Maybe you should be designing the world's first Superconductive loudspeaker instead of me!
Where did you find that stuff? I've had a hard time finding any technical information about HTS wire anywhere. I would like to research it thoroughly myself.
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