Hello whgeiger
Have you looked at Magnesium at all?? I have a pair of JBL 476Mg's and they measure very well. Much lower cost than the Be.
What is the advantage aside from higher flux densities in the gap?? If we do get a change of say an additional 10% is it really going to make an audible difference aside from possibly higher output and a skewed frequency response in comparison??
Rob
It Remains All About the Money
If flux density is increased, then the mass of the voice coil can be reduced while still delivering the same [BL] and [RE]. For a tweeter design this is a no-brainer. The only impediment here is cost. This is illustrative of the point I am trying to make. Design here is a trade between motor strength and moving mass.
Regards,
WHG
If flux density is increased, then the mass of the voice coil can be reduced while still delivering the same [BL] and [RE]. For a tweeter design this is a no-brainer. The only impediment here is cost. This is illustrative of the point I am trying to make. Design here is a trade between motor strength and moving mass.
Regards,
WHG
whgeiger,
You can't simply look at the mass, you would have to look at the minimum impedance, the wire turns ratio, the heat dissipation in the wire and such. Typically in compression drivers you are already using edge wound copper clad aluminum so not sure how much mass reduction as part of the total moving mass you would see. I would think it would be insignificant but the loss of current carrying ability may be compromised. All the compression drivers I have looked at use a focused gap, the energy in the gap is at saturation levels because of this. I don't know that his would really change with the use of the high dollar metals in a focused gap design.
Robh,
Magnesium in its pure form is a pain to work with, it has a funny way of going up in flames! Not saying it can't be done, obviously you have some but I know many machinist who hate working with that material.
You can't simply look at the mass, you would have to look at the minimum impedance, the wire turns ratio, the heat dissipation in the wire and such. Typically in compression drivers you are already using edge wound copper clad aluminum so not sure how much mass reduction as part of the total moving mass you would see. I would think it would be insignificant but the loss of current carrying ability may be compromised. All the compression drivers I have looked at use a focused gap, the energy in the gap is at saturation levels because of this. I don't know that his would really change with the use of the high dollar metals in a focused gap design.
Robh,
Magnesium in its pure form is a pain to work with, it has a funny way of going up in flames! Not saying it can't be done, obviously you have some but I know many machinist who hate working with that material.
Yes!
The attached chart should answer you questions(s).
Magnesium has a slightly lower density; but it is weaker, so more of it is needed to make a stiff diaphragm.
It is not "say 10%", it is say 100%+. Typical designs using Swedish Iron deliver about 10,000 Gauss into the gap. For Permendur, 24,000 Gauss is typical.
Regards,
WHG
The attached chart should answer you questions(s).
Magnesium has a slightly lower density; but it is weaker, so more of it is needed to make a stiff diaphragm.
What is the advantage aside from higher flux densities in the gap?? If we do get a change of say an additional 10% is it really going to make an audible difference aside from possibly higher output and a skewed frequency response in comparison??
Rob
It is not "say 10%", it is say 100%+. Typical designs using Swedish Iron deliver about 10,000 Gauss into the gap. For Permendur, 24,000 Gauss is typical.
Regards,
WHG
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There are less turns in the coil as well and that means less inductance in addition to less mass. As [Re] remains unchanged, heat generated by a given current flow will be less, not more, as the motor has less work to do as it moves a smaller mass back and forth. For the same SPL output, less current will be required.
>snip<
Regards,
WHG
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I really think you need to look at the total moving mass and see how little you would change that, less than 2% I bet. As for your Swedish? steel vs electrical steel gauss numbers not sure where that is coming from. You need to look at the flux density in the gap, nothing else really matters, you could have a giant ceramic magnet and get high flux density, not saying there aren't other factors besides flux density, as there are other distortion factors related to magnetic materials. I think that the whole high dollar compression driver thing is marketing more than engineering myself. Just using high dollar materials does not a great product make, that is not how it works unless you are working on the margins of materials properties. There have been compression drivers using Alnico for years that have as high a flux density in the gap as newer Neo magnet designs with much higher MgOe values, they may just be smaller and lighter in weight, not necessarily superior in audio output.
Correct. There are so many different shipping terms that double checking is always a good idea.
I have read a lot about these material, but it seem necessary to get one's hand dirty to really find out how to further improve the designs.
Soongsc,
That is what I do, I actually make things, get my hands dirty and use many different materials. As a product developer that is how you learn what is truly important and what is all smoke and mirrors. You don't use a high dollar material just to use it, you use it because it is the only thing that will reach your goals. Ultimate properties are not always necessary but can be an advantage when you are working on the cutting edge. I do plan on using some of the Carpenter electric steel in one of my designs but the only place it is necessary is for the pole piece. For the rest of the magnetic circuit it had no real advantage and would drive the cost up significantly for no benefit.
That is what I do, I actually make things, get my hands dirty and use many different materials. As a product developer that is how you learn what is truly important and what is all smoke and mirrors. You don't use a high dollar material just to use it, you use it because it is the only thing that will reach your goals. Ultimate properties are not always necessary but can be an advantage when you are working on the cutting edge. I do plan on using some of the Carpenter electric steel in one of my designs but the only place it is necessary is for the pole piece. For the rest of the magnetic circuit it had no real advantage and would drive the cost up significantly for no benefit.
More!
If that thesis was true, you would find copper voice coils in tweeters instead of aluminum or copper clad aluminum.
When the pole pieces become saturated, flux density in the magnetic gap can no longer be increased by increasing magnet size. The low carbon steel used to make the pole pieces is called Swedish Iron. The reason ALNICO is not used any more, is due the increase of the cost of Cobalt (CO) that occurred awhile back. This is the same alloying element that distinguishes Permendur and determines its high cost as well. The point again, it is the high cost of these materials that discourages their use, nothing more. Other considerations are important to good driver design, but they are not relevant to this thesis.
If that thesis was true, you would find copper voice coils in tweeters instead of aluminum or copper clad aluminum.
When the pole pieces become saturated, flux density in the magnetic gap can no longer be increased by increasing magnet size. The low carbon steel used to make the pole pieces is called Swedish Iron. The reason ALNICO is not used any more, is due the increase of the cost of Cobalt (CO) that occurred awhile back. This is the same alloying element that distinguishes Permendur and determines its high cost as well. The point again, it is the high cost of these materials that discourages their use, nothing more. Other considerations are important to good driver design, but they are not relevant to this thesis.
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WhGeiger,
I see on this point we are in agreement. I am planning on using the electric steel for my pole piece, it has a definite advantage in this area of my design. I am not sure that you don't have enough mass and thickness in the pole piece of a compression driver without doing the modeling and checking this in a magnetics analysis program. I my instance it was obvious while doing the modeling and analysis that it was the way to increase the flux density and also because of saturation in that area of the motor. I wouldn't however use the material for the rest of the motor as it showed no improvement in the gap energy to use the higher dollar material.
I see on this point we are in agreement. I am planning on using the electric steel for my pole piece, it has a definite advantage in this area of my design. I am not sure that you don't have enough mass and thickness in the pole piece of a compression driver without doing the modeling and checking this in a magnetics analysis program. I my instance it was obvious while doing the modeling and analysis that it was the way to increase the flux density and also because of saturation in that area of the motor. I wouldn't however use the material for the rest of the motor as it showed no improvement in the gap energy to use the higher dollar material.
Transducer Design
Here is a book that might interest you (if you have not already read it), even though it is Crica 1950's, there are few like it in print:
Title: "Electroacoustics - The Analysis of Transduction and Its Historical Background"
Author: Frederick V. Hunt
Publication: Acoustical Society of America, 1954, Second Printing, 1982
ISBN: 0-88318-401-X
Electroacoustics: The Analysis of Transduction, and Its Historical Background by Frederick V. Hunt: Acoustical Society of Amer 9780883184011 Paperback - ExtremelyReliable
Here is a book that might interest you (if you have not already read it), even though it is Crica 1950's, there are few like it in print:
Title: "Electroacoustics - The Analysis of Transduction and Its Historical Background"
Author: Frederick V. Hunt
Publication: Acoustical Society of America, 1954, Second Printing, 1982
ISBN: 0-88318-401-X
Electroacoustics: The Analysis of Transduction, and Its Historical Background by Frederick V. Hunt: Acoustical Society of Amer 9780883184011 Paperback - ExtremelyReliable
I love Magnesium and consume >10mg every day in my vitamins and vegetables. Beryllium.... not so much.
With modern equalization technology, high frequency diaphragm break-up seems like the main materials challenge. From materials data, Mg appears superior to Al and Ti for small domes/diaphragms.
Any other measurements of Mg compression drivers on-line?
Attachments
That is great! I was working with a local driver technician, trying to find a solution to increase the efficiency of his driver. Too bad he had experience but no technical background. Did not seem to understand what I was telling him, and just made me faint when I gave him a new motor to assemble, and used a cone with a different depth totally presenting a different centre location.
I guess I also need to do something with the pole piece as well. Possibly just using different material.
True, but we have been trying to suppress it with different cone designs. First one was successful to some degree, and what we use now, more costly to produce either by hand or large investment in specially designed machines. The second one designed to reduce production cost is also being patented, soon we will try to adapt it to different materials. Have not tried any on compression drivers, but I think it should not be a problem.
Patent CN101494812B - 消减振膜振波的喇叭 - Google Patents
Chinese Patent for your easy reading. English translation I would not trust.
The new design is in review. I do not wish to discuss details at this time.
Chinese Patent for your easy reading. English translation I would not trust.
The new design is in review. I do not wish to discuss details at this time.