Is one of these clearly better then the other for suppressing distortion when used in the motor structure of the driver (as plates above and below the magnet)? Or does this make no difference at all? I am thinking Seas Excel vs SS Revelator woofers -OR- Seas Excel vs Focal multi-magnet woofers
I think copper is better for reducing back EMF distortion due to its better conductive properties. I believe faraday rings are usually made out of copper. Former material can also have an effect on distortion, as can non-symmetric fringe fields etc. etc.
For what it's worth, I've think the SE line have the lowest distortion. Have a look at the distortion graphs and find out. I think Linkwitz did some distortion tests which included the SE drivers.
This thread might give you some answers, and this one was informative too.
For what it's worth, I've think the SE line have the lowest distortion. Have a look at the distortion graphs and find out. I think Linkwitz did some distortion tests which included the SE drivers.
This thread might give you some answers, and this one was informative too.
More old threads of interest:
http://www.diyaudio.com/forums/showthread.php?postid=58124#post58124
http://www.diyaudio.com/forums/showthread.php?postid=66491#post66491
regards, jonathan carr
http://www.diyaudio.com/forums/showthread.php?postid=58124#post58124
http://www.diyaudio.com/forums/showthread.php?postid=66491#post66491
regards, jonathan carr
Vikash said:
Thanks.
As far as I remember, SL did not test the Revelator woofers. I am curious about these. But I guess if distortion was less of a problem the on the Seas Excell stuff, then they would publish the data...
amo said:
I will readily admit I have no clue as to the techincal factors here, and think that the voice coil materila is really only of interest to the actual designer.
There are so many factors and details that influence how a driver sounds that are far, far more important in terms of sound. I think this probably has more to do with ability to handle power than with distortion.
One thing that comes to mind is TAD 4001's that sell for $3300.00 a pair - they use aluminum voice coils - They're using Beryllium diaphragms so you can figure they're not using the aluminum instead of copper because it's cheaper.
for what it's worth - Lowther offers silver voice coils as an option on most of their better drivers (all?) for a relatively small fee.
Yet I see very few knowledgeable Lowther users that have drivers with the silver voice coils and see almost nothing said about it in posts. If this was a big deal I would think many people would be doing it.
Bottom line - I don't really think you want this to be a factor in a purchasing decision.
regards
Ken L
There is a very interesting property of metals that is in play here.
When you pass a magnet near a metal object, you cause electrical current to flow through it.
Everyone should know that copper and aluminum both are non-ferrous materials(not magnetic and not iron). A piece of copper water pipe will, however, slow down a magnet that is passed through it. This is because the magnet causes a current in the metal which in turn produces a magnetic field of an opposite polarity to that of the moving magnet. This is what slows the movement of the magnet.
Copper and aluminum should react differently in this situation both because of their ability to conduct electricity(affecting the magnetic properties), and their other normal magnetic properties.
When you pass a magnet near a metal object, you cause electrical current to flow through it.
Everyone should know that copper and aluminum both are non-ferrous materials(not magnetic and not iron). A piece of copper water pipe will, however, slow down a magnet that is passed through it. This is because the magnet causes a current in the metal which in turn produces a magnetic field of an opposite polarity to that of the moving magnet. This is what slows the movement of the magnet.
Copper and aluminum should react differently in this situation both because of their ability to conduct electricity(affecting the magnetic properties), and their other normal magnetic properties.
Re: Re: copper vs aluminum
The beryllium diaphragms make their reasoning obvious. It's about moving mass. Be is element #4 on the periodic table. It is not only light, but also solid. Unlike H or He which are gases at room temp and Li which is chalky, this metal is strong. Choosing the aluminum over copper in this instance is only logical.
🙂ensen.
Ken L said:
The beryllium diaphragms make their reasoning obvious. It's about moving mass. Be is element #4 on the periodic table. It is not only light, but also solid. Unlike H or He which are gases at room temp and Li which is chalky, this metal is strong. Choosing the aluminum over copper in this instance is only logical.
🙂ensen.
But that's to do with former material and not copper vs aluminium on the motor structure. Copper would not be used as a former material due to its weight most likely. Using a conductive former material introduces its own eddy current problem which results in distortion. If distortion is the only concern, then a non-conductive former material is preferred. e.g. kapton.
However, both copper and aluminium are used to implement a faraday ring/shorted loop, and as in the SE line, the motor assembly is covered in copper which I'm sure attributes to its lower distortion figures. I also believe that the material choice is sometimes dependent on the specific implemenation of the faraday ring/shorted loop (as well as economics off course).
Since copper is more conductive, then it would be intuitive to reason its advantage over aluminium - to make better use of the phenomenon outlined by Duo.
I've experimented with various types of eddy-control structures - plating, sheets, different types of metals and thicknesses - and I've used some of these techniques in production.
Theoretically, it appears that the conductivity of the eddy-control part should be determined according to the conductivity of the pole-piece structure (and what the designer is trying to achieve).
For most practical applications, however, the higher the conductivity of the eddy-control metal, the lower the distortion - particularly inside the gap or in the immediate proximity, where space is at a premium and it is far easier to fit in thinner layers of a more conductive metal than thicker layers of a less conductive metal.
Copper works well at first, but due to the issue of oxidation and its effect on long-term stability, personally I prefer to use more noble metals like silver and gold.
As I have previously stated elsewhere, most of this stuff is straight from Faraday's Law and Lenz's Law.
More links below. Some of these relate to the subject matter at hand, others will cover the background concepts and theory. But I think that all are good reading.
http://www.amasci.com/neodemo.html
http://www.gp.uwo.ca/es320/lect17.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcon.html#c1
http://web.mit.edu/jbelcher/www/inout.html
http://www.darylscience.com/Lentz.html
Test your knowledge of magnetics and induction here:
http://hydro4.sci.fau.edu/~rjordan/busters_30/push-ups_6.htm
hth, jonathan carr
Theoretically, it appears that the conductivity of the eddy-control part should be determined according to the conductivity of the pole-piece structure (and what the designer is trying to achieve).
For most practical applications, however, the higher the conductivity of the eddy-control metal, the lower the distortion - particularly inside the gap or in the immediate proximity, where space is at a premium and it is far easier to fit in thinner layers of a more conductive metal than thicker layers of a less conductive metal.
Copper works well at first, but due to the issue of oxidation and its effect on long-term stability, personally I prefer to use more noble metals like silver and gold.
As I have previously stated elsewhere, most of this stuff is straight from Faraday's Law and Lenz's Law.
More links below. Some of these relate to the subject matter at hand, others will cover the background concepts and theory. But I think that all are good reading.
http://www.amasci.com/neodemo.html
http://www.gp.uwo.ca/es320/lect17.html
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcon.html#c1
http://web.mit.edu/jbelcher/www/inout.html
http://www.darylscience.com/Lentz.html
Test your knowledge of magnetics and induction here:
http://hydro4.sci.fau.edu/~rjordan/busters_30/push-ups_6.htm
hth, jonathan carr
Re: Re: copper vs aluminum
I would love for this not to be a factor, but distortion data for drivers is not easy to come by (except Excell of cource), unless I am willing to buy each driver and test it. This makes it very tempting to find some shortcuts in understanding distortion.
Ken L said:
I would love for this not to be a factor, but distortion data for drivers is not easy to come by (except Excell of cource), unless I am willing to buy each driver and test it. This makes it very tempting to find some shortcuts in understanding distortion.
From description of the TAD 4001:
MAGNETIC CIRCUIT. Total magnetic flux is 228,000Mx, with flux density of 20,000G, thanks to the use of a very heavy (6 lbs. 10 oz./3kg) alnico 5DG magnet. An oxygen-free copper shorting ring prevents impedance rise, resulting in low distortion.
MAGNETIC CIRCUIT. Total magnetic flux is 228,000Mx, with flux density of 20,000G, thanks to the use of a very heavy (6 lbs. 10 oz./3kg) alnico 5DG magnet. An oxygen-free copper shorting ring prevents impedance rise, resulting in low distortion.
The following might be of interest:
US Patent 5,070,530 Grodinsky, et al.
Electroacoustic transducers with increased magnetic stability for distortion reduction
BACKGROUND OF THE INVENTION AND PRIOR ART
The above-referenced copending application discusses observed differences between loudspeaker constructions utilizing non-conductive ceramic magnets and loudspeaker constructions utilizing alnico-type magnets and points out the general inferiority of the ceramic magnet structures. In particular, the effects of distortion due to eddy currents, in the top and bottom plates, which generate local magnetic fields that are coupled back to the voice coil are noted. These eddy currents produce harmonic distortion effects due to the non-linear iron characteristics as well as frequency selective, i.e., frequency dependent, distortion effects because the amplitudes of the eddy currents are proportional to frequency.
In the prior art, the effects of energy loss due to eddy currents in the conductive parts of an electroacoustic magnetic transducer motor structure have been misunderstood. For example, extra conductive material, generally in the form of copper, has been added to the motor structure to flatten the loudspeaker impedance characteristic, i.e., make the characteristic more uniform with frequency. The fact that the energy transferred into the conductive material reduces the energy that is transformed into useful loudspeaker diaphragm motion, and that this effect, which is non-uniform with frequency, results in a reduction in the accuracy of reproduction of transients, has either not previously been recognized or has been ignored. This frequency selective loss in prior art transducer constructions results in transducers with reduced ability to track the rapid changes in audio signals. Indeed, a flat impedance characteristic in a loudspeaker driver has been found to be of secondary importance and is even undesirable when it is produced by non-linear or frequency selective losses in any of the parts of the magnet structure.
It has been discovered that in addition to eddy current effects in ferromagnetic structure parts, ceramic magnets in contrast to alnico magnets, introduce another distortion component. Magnetic fields are introduced into the magnet material by the motion of the signal-carrying coil, whether in a loudspeaker or a microphone embodiment. This energy, which is effectively subtracted from the available useful energy, is proportional to coil travel and is thus inversely proportional to frequency. There are undesirable consequences associated with the phenomenon. For example, the signal-related AC magnetic energy that is induced into the magnet causes distortion. While the exact mechanism has not yet been proven, it is believed that the induced AC magnetic field modulates the DC field in the magnet.
James
US Patent 5,070,530 Grodinsky, et al.
Electroacoustic transducers with increased magnetic stability for distortion reduction
BACKGROUND OF THE INVENTION AND PRIOR ART
The above-referenced copending application discusses observed differences between loudspeaker constructions utilizing non-conductive ceramic magnets and loudspeaker constructions utilizing alnico-type magnets and points out the general inferiority of the ceramic magnet structures. In particular, the effects of distortion due to eddy currents, in the top and bottom plates, which generate local magnetic fields that are coupled back to the voice coil are noted. These eddy currents produce harmonic distortion effects due to the non-linear iron characteristics as well as frequency selective, i.e., frequency dependent, distortion effects because the amplitudes of the eddy currents are proportional to frequency.
In the prior art, the effects of energy loss due to eddy currents in the conductive parts of an electroacoustic magnetic transducer motor structure have been misunderstood. For example, extra conductive material, generally in the form of copper, has been added to the motor structure to flatten the loudspeaker impedance characteristic, i.e., make the characteristic more uniform with frequency. The fact that the energy transferred into the conductive material reduces the energy that is transformed into useful loudspeaker diaphragm motion, and that this effect, which is non-uniform with frequency, results in a reduction in the accuracy of reproduction of transients, has either not previously been recognized or has been ignored. This frequency selective loss in prior art transducer constructions results in transducers with reduced ability to track the rapid changes in audio signals. Indeed, a flat impedance characteristic in a loudspeaker driver has been found to be of secondary importance and is even undesirable when it is produced by non-linear or frequency selective losses in any of the parts of the magnet structure.
It has been discovered that in addition to eddy current effects in ferromagnetic structure parts, ceramic magnets in contrast to alnico magnets, introduce another distortion component. Magnetic fields are introduced into the magnet material by the motion of the signal-carrying coil, whether in a loudspeaker or a microphone embodiment. This energy, which is effectively subtracted from the available useful energy, is proportional to coil travel and is thus inversely proportional to frequency. There are undesirable consequences associated with the phenomenon. For example, the signal-related AC magnetic energy that is induced into the magnet causes distortion. While the exact mechanism has not yet been proven, it is believed that the induced AC magnetic field modulates the DC field in the magnet.
James
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