People argue that, magnets sound different?
Is this just the force factor of each magnet there talking about or does each type of magnet have a different sound quality?
Lets say we have 2 woofers and everything is equal,
We have one with a Samarium-Cobalt magnet and one with a
strontium-ferrite, lets also say each one has the same field strength, do you think there is a sound quality difference?
Is this just the force factor of each magnet there talking about or does each type of magnet have a different sound quality?
Lets say we have 2 woofers and everything is equal,
We have one with a Samarium-Cobalt magnet and one with a
strontium-ferrite, lets also say each one has the same field strength, do you think there is a sound quality difference?
I second that motion. The magnet merely supplies the driving force for the system. A gauss is a gauss irrespective of the source material. There can be some differences at very high power levels where the magnet's heat sinking abilities can affect the power compression factor, but that's seldom a concern for non-pro usage.
Ideally speaking, a magnet would not have a sound of its own. Here in the real world, it has been my experience that equal-strength magnets of different composition may indeed sound different when used in transducers. Ditto for the polepiece material.
OTOH, I don't think that it is possible to perfectly match different magnets for strict comparison purposes, because the B-H curves will be different (even when comparing magnets all within the rare-earth family - SmCo, Presedymium, Neodymium).
hth, jonathan carr
OTOH, I don't think that it is possible to perfectly match different magnets for strict comparison purposes, because the B-H curves will be different (even when comparing magnets all within the rare-earth family - SmCo, Presedymium, Neodymium).
hth, jonathan carr
I read an article in Electronics World by John Watkinson about loudspeaker magnets, as part of a series on loudspeakers. He replied to a letter criticising his comments on magnetic materials, saying;- "ceramic magnets are good.. for picking up swarfe when I'm machining the pole peices for my neodymium magnets".
He argues that ceramic is an insulator, while neodymium is a conductor, and so it prevents - if I remember the spelling - Barkhaussen noise. It's the movement of the magnetic domains apparently, and is also found in tape heads.
He argues that ceramic is an insulator, while neodymium is a conductor, and so it prevents - if I remember the spelling - Barkhaussen noise. It's the movement of the magnetic domains apparently, and is also found in tape heads.
NdFeB or Field Coil
The current in the voice coil generates a magnetic field that can "appear" to reduce the pole piece magnetic field and create distortion. Ceramic magnets are more susceptible to this reverse field modulation than NdFeB or Alnico. And this BL modulation distortion is much greater in high power woofers than low wattage tweeters/mids. Electric Field coils are theoretically the lowest distortion magnets, but are very large, expensive, and require a well regulated high current power supply. NdFeB is the best permanent magnet material. NdFeB has a 5x to 10x higher magnetic field than ferrite or Alnico magnets, and hence can create high fields, or dramatically reduce weight. Since iron saturates at 1.7 Tesla, this stronger magnet can best be used to create a dual field motor, or a long underhung motor.
For woofers and high excursion mids where a long voice coil is attractive for power dissipation, the JBL Differential drive is very attractive as it lowers coil inductance without requiring a field reducing Faraday ring. This uses NdFeB's strength to create dual fields.
For high detail mids and tweeters where a short coil is attractive for low mass, an underhung radial motor and heavy copper Faraday ring is very attractive. Seas has the Hexadym NdFeB motor to approximate a radial motor, and Aura uses several thin cylinder segments to create a radial magnet since NdFeB cannot be cast to precise tolerances and is too brittle to machine.
The current in the voice coil generates a magnetic field that can "appear" to reduce the pole piece magnetic field and create distortion. Ceramic magnets are more susceptible to this reverse field modulation than NdFeB or Alnico. And this BL modulation distortion is much greater in high power woofers than low wattage tweeters/mids. Electric Field coils are theoretically the lowest distortion magnets, but are very large, expensive, and require a well regulated high current power supply. NdFeB is the best permanent magnet material. NdFeB has a 5x to 10x higher magnetic field than ferrite or Alnico magnets, and hence can create high fields, or dramatically reduce weight. Since iron saturates at 1.7 Tesla, this stronger magnet can best be used to create a dual field motor, or a long underhung motor.
For woofers and high excursion mids where a long voice coil is attractive for power dissipation, the JBL Differential drive is very attractive as it lowers coil inductance without requiring a field reducing Faraday ring. This uses NdFeB's strength to create dual fields.
For high detail mids and tweeters where a short coil is attractive for low mass, an underhung radial motor and heavy copper Faraday ring is very attractive. Seas has the Hexadym NdFeB motor to approximate a radial motor, and Aura uses several thin cylinder segments to create a radial magnet since NdFeB cannot be cast to precise tolerances and is too brittle to machine.
Re: NdFeB or Field Coil
The distortion ripples can be seen on a TV screen, this gives a visual trace of the reverse field modulation, the magnet and coil in battle, my friend swear by NdFeB for tweeters but I think they can sound rather harsh which is subjective, but in woofers I feel they offer a lower distortion at large linear travel, some manufacturers use a combination of magnets which I think is a gimmick or do they know something I don’t?
ATC claim to have Super Linear magnet system, I personally agree with most of the work.
Here is a link to the to download an attachment of there theory.
Super Linear Technical White Paper (.zip)
I still believe that magnets have some way to go!
Super Linear Technical White Paper (.zip)
LineSource said:
The distortion ripples can be seen on a TV screen, this gives a visual trace of the reverse field modulation, the magnet and coil in battle, my friend swear by NdFeB for tweeters but I think they can sound rather harsh which is subjective, but in woofers I feel they offer a lower distortion at large linear travel, some manufacturers use a combination of magnets which I think is a gimmick or do they know something I don’t?
ATC claim to have Super Linear magnet system, I personally agree with most of the work.
Here is a link to the to download an attachment of there theory.
Super Linear Technical White Paper (.zip)
I still believe that magnets have some way to go!
Super Linear Technical White Paper (.zip)
too many people focus on the Strength and ignore the physical properties
Frequently, people focus on gauss- or relative strength.
However, the different physical aspects at times plays into different areas of concern in a major way
Excellent post, Line Source _big grin_
Regards
Ken L
Frequently, people focus on gauss- or relative strength.
However, the different physical aspects at times plays into different areas of concern in a major way
LineSource said:
Excellent post, Line Source _big grin_
Regards
Ken L
If I was any good at dismantling and re-assembling a loudspeaker, an experiment I would love to try is - count the number of turns of wire on the voice coil and then wind this same amount of turns in antiphase on the centre polepiece right down away from the voice coil. Then put this winding in *series*with the voice coil.
The purpose is that any effort by the voice coil to modulate the main magnet is exactly opposed by the same ampere-turns in the extra winding. Sort of like an active Faraday ring.
The purpose is that any effort by the voice coil to modulate the main magnet is exactly opposed by the same ampere-turns in the extra winding. Sort of like an active Faraday ring.
phase_accurate said:
Hmm, this is very interesting...but also maybe a bit alarmist and I think it illustrates some of the rationale behind the dynamic range measurement setup.
Let's assume that this statement is true...that there is Barkhausen effect noise that is directly proportional to signal level at a level of -60dB. Now if this is the only noise, then the dynamic range is 120dB! That is, Barkhausen noise is unlikely to be the limiting factor in dynamic range of the transducer...it is probably swamped by other factors.
Can one hear uncorrelated noise that is dynamically modulated to be -60dB below the signal level? Possibly, but it sounds a lot less worrisome than "Speaker S/N ratio is only 60dB!", doesn't it?
Please point out any logical fallacies in this post.
tiroth said:
Let's not assume its true is far more sensible.
I can easily tell the difference between noise sources of 60dB
(e.g. cassette), 75dB (good vinyl with a MC) and >80dB (CD)
over my speakers.
http://physics.queensu.ca/~lynann/mbnoise.html
The phenomena does not seem to be relevant to saturated
loudspeaker poles, tape heads and magnetic tape perhaps.
sreten.Well, I would not be surprised if the the problem is not as described...but if that is the case, what IS the problem?
It is quite obviously very different than the kind of noise we are talking about on tape (60dB) versus CD (>80dB). Our loudspeakers do not quietly hiss while sitting undriven. The noise must be related by some law to the signal level.
There's a difference between constant noise and modulation noise. Try listening to an early 1950s recording and you will hear the noise floor changing with signal - loud climaxes simultaneously bring up a coarse noise, which is a very nasty effect. Early tape was notorious for this modulation noise.
It strikes me that if a loudspeaker voice coil opposes the static flux in the gap in oder to produce a force, surely the instantaneous flux in the gap is changing? And if the pole pieces are a magnetic short-circuit (in order to get all the energy from the magnet into the gap), and the magnet is a permanent magnet, something has to give? Is it perhaps the magnetic equivalent of two Thevenin sources fighting one another via their internal resistances?
It strikes me that if a loudspeaker voice coil opposes the static flux in the gap in oder to produce a force, surely the instantaneous flux in the gap is changing? And if the pole pieces are a magnetic short-circuit (in order to get all the energy from the magnet into the gap), and the magnet is a permanent magnet, something has to give? Is it perhaps the magnetic equivalent of two Thevenin sources fighting one another via their internal resistances?
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