If I understand you correctly, I think you are referring to what is called a field coil driver. Instead of a permanant magnet, they have a large electro magnet. And that's the problem- in order to get decent efficiency out of a speaker the field magnet has to be very powerful.
A coil the size of the existing voicecoil isn't enough. The only way that speakers work well is having that wimpy voice coil reacting to a muy macho field magnet or field coil.
So, since the field coil needs to be powerful, it is made of a LOT of wire and weighs pounds.Generally it is bigger than an equivalent magnet. For this reason Field coil drivers tend to cost at least $600 AFAIK.
A coil the size of the existing voicecoil isn't enough. The only way that speakers work well is having that wimpy voice coil reacting to a muy macho field magnet or field coil.
So, since the field coil needs to be powerful, it is made of a LOT of wire and weighs pounds.Generally it is bigger than an equivalent magnet. For this reason Field coil drivers tend to cost at least $600 AFAIK.
would this be more useful for car spl comps I mean 12VDC and at low resistance could be a strong magnet and they only have to go for a few seconds anyhow? I guess wouldnt transfer to the "showroom" as easy but they can spend mucho $$ on there equipment anyhow. I was always curious about the same thing.
Interesting point. I suppose the reason it is as it is, is because a voice coil can be lighter than a permanent magnet. This reason is obviated by using a coil for both purposes. Since it is possible to achieve the same effect either from a large voice coil and small field coil, or small voice coil and large field coil, I can see no reason to favour one way around over the other. But expanding on this, wouldn't it also be possible to use a very small, light fixed magnet on the cone and a huge, fixed voice coil? It would be a difficult load for an amp though.BassAwdyO said:
Of course, you could probably make them both-the little movable one and the big, stationary one-voice coils if you want to, as Mr. Evil pointed out. 
However, my original reading is that killerfishes meant feed the signal to the big stationary magnet.
An interesting point an engineer can help us out with here:
How much magnetic force per gram, (or ounce), does
A) a copper or aluminum voice coil winding produce, whether on a metallic or nonmetallic voice coil former, (or bobbin),
B) How much magnetic force per gram, (or ounce), does ferrite, neo, alnico, or any other usable magnetic material produce?
Perhaps the answer lies there.
However, my original reading is that killerfishes meant feed the signal to the big stationary magnet.
An interesting point an engineer can help us out with here:
How much magnetic force per gram, (or ounce), does
A) a copper or aluminum voice coil winding produce, whether on a metallic or nonmetallic voice coil former, (or bobbin),
B) How much magnetic force per gram, (or ounce), does ferrite, neo, alnico, or any other usable magnetic material produce?
Perhaps the answer lies there.
Maybe not, but let's assume for a moment that you could make an arbitrarily large voice coil; then the magnet attached to the cone really could be as light as a normal voice coil. How would such a speaker behave? It would have the advantage of not having any wires attached to the cone, which would improve reliability, but even small external magnetic fields might overpower the magnet.SY said:
Mr Evil said:
Okay, let's try this.
We make a permanent magnet of X strength, and an alternating current magnet of X maximum strength..
Now we make the little movable magnet attached to the cone.
Per gram of material, do we get more out of an AC coil operating against the permanent magnet, or more out of a small permanent magnet operating against the large AC magnet?
SY,
HTS (high temperature superconductors) can operate above the temperature of liquid nitrogen. The impractical part is the fact that you need a noisy compressor to keep it liquid and cold, and well I know people complain about amp fans, but even the loudest ones probably dont come close to one of those compressors as far as noise goes.
You really cant give a rating of how much flux per gram of copper used. It depends on so many things such as: the wire used, how tight the windings are, how well the former dissapates heat(how much current you can run safely).
The biggest problem in electrodynamic speakers(the motor at least) if you ask me is efficiency and unused flux. In an overhung design the coil has much of it's magnetic force unused as most of it isnt in the gap. In an undehung design the part of the gap which isnt occupied by the coil is wasted flux.
The only way to really fix this is to use a commutated voice coil where the coil has many segements and the only one that is powered is the one in the gap. The problems there lie in switching between coils. Obviously brushes and contacts would not perform well enough. I'm suprised that it hasnt been on the market yet somewhere though. Tom danley holds the patent... I guess he never thought it was that great of an idea.
HTS (high temperature superconductors) can operate above the temperature of liquid nitrogen. The impractical part is the fact that you need a noisy compressor to keep it liquid and cold, and well I know people complain about amp fans, but even the loudest ones probably dont come close to one of those compressors as far as noise goes.
You really cant give a rating of how much flux per gram of copper used. It depends on so many things such as: the wire used, how tight the windings are, how well the former dissapates heat(how much current you can run safely).
The biggest problem in electrodynamic speakers(the motor at least) if you ask me is efficiency and unused flux. In an overhung design the coil has much of it's magnetic force unused as most of it isnt in the gap. In an undehung design the part of the gap which isnt occupied by the coil is wasted flux.
The only way to really fix this is to use a commutated voice coil where the coil has many segements and the only one that is powered is the one in the gap. The problems there lie in switching between coils. Obviously brushes and contacts would not perform well enough. I'm suprised that it hasnt been on the market yet somewhere though. Tom danley holds the patent... I guess he never thought it was that great of an idea.
BassAwdy:
Well, I would think the high end hi fi people would be the ones who would use such a design, and they don't even like the distortion in class AB designs.
I can just imagine what they would do with switching distortion in a field coil magnet as the voice coil goes back and forth.
On the other hand, I guess it would open up the possibility of some super long excursions at very high sensitivity.
Well, I would think the high end hi fi people would be the ones who would use such a design, and they don't even like the distortion in class AB designs.
I can just imagine what they would do with switching distortion in a field coil magnet as the voice coil goes back and forth.
On the other hand, I guess it would open up the possibility of some super long excursions at very high sensitivity.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.