If neodymium is all that great . . .

[usekgb]

Originally posted by Bill Fitzpatrick
I was reading that neodymium makes a much better magnet than ceramic in regards to quality sound.

If true, where are all the great woofer/mids with the new magnets? I found one ScanSpeak for $160 but that's it.

Have you looked at the JBL 2262? This thing is great.

[Timn8ter]

Originally posted by Bill Fitzpatrick
I was reading that neodymium makes a much better magnet than ceramic in regards to quality sound.

If true, where are all the great woofer/mids with the new magnets? I found one ScanSpeak for $160 but that's it.

I thought I'd go back to the original question, although, I don't know where ALL of them are. I have been working with the Extremis 6.8 which uses Neo and it's a very impressive little mid-woof.

[thoriated]

This table should shed some light on the matter. These figures, which I borrowed from magnetapplications.com show that Neodymium suffers far more from temperature related temporary losses in strength than any other type commonly used in speakers when presented with an opposing magnetic field (HC), thus explaining its much lower maximum service temperature than all other types listed and the extensive efforts to dissipate heat from them in loudspeaker applications. Br is each magnet's maximum residual flux density in the absence of an external magnetic field. Alnico, btw, leads the group in both of these categories, although it is more susceptible to permanent flux losses (until remagnetized) than the other types when presented with an extremely high opposing HC.

Reversible Temperature Coefficients of Br and HC

Material....Tc of Br..Tc of HC..Curie Point....Maximum Service Temp.

NdFeB........-0.12......-0.6......310 (590)...........150 (302)
SmCo.........-0.04......-0.3......750 (1382).........300 (572)
Alnico.........-0.02.......0.01....860 (1580).........540 (1004)
Ceramic......-0.2.........0.3......460 (860)...........300 (572)

Perhaps SmCo has not been so widely used for speakers because once the cobalt is paid for alnico gives better performance as long as the speaker is not being greatly abused physically or by overpowering. Mud magnets may have earned their poor reputation partly because of their significant sensitivities in opposite directions in Br *and* HC which probably would tend to create a less coherent sonic presentation than most other magnet types when significant amounts of power are applied to the vc.

[DanWiggins]

SH grade neo is typically rated to 150 deg C, but EH grade is good to 200 deg C. Both of which are really overkill; to get the magnet that hot your voice coil is at 200+ deg C, which is well beyond the point at which the glues holding it together will fail. In other words, the voice coil will fall apart well before you thermally demagnetize modern SH+ grade neo.

The old L and M grades weren't too good, as they started losing magnetic force at just 100 deg C, which is within the realm of what high power voice coils can withstand.

Neo is like any other magnet material - it has its strengths and weaknesses. It does offer some significant advantages in motor size (weight and physical dimensions), and typical pot-core neo motors are inherently shielded as well. If those advantages are desireable, then use it. Otherwise it may be lower cost to go with ferrite.

Dan Wiggins
Adire Audio

[thoriated]

My concerns with neodymium temperature sensitivity would begin long before the speaker would fail a smoke test because of sonic instability resulting from driver parameter shift caused by squirrely magnet system performance. I wouldn't want a heavy bass line knocking a driver's HF sensitivity down even a quarter decibel when the magnet warms just because of any design compromise related to the magnetic material. Even a 30-40C rise will result in some pretty undesirable stuff happening to Neo magnetic performance.

[DanWiggins]

Personally, I wouldn't sweat it. The thermal capacity of the magnet structure is usually so far beyond what the voice coil can take that you will smoke the VC well before the magnet heats up enough to start losing strength.

In my experience, 10-30 seconds of +200 deg C on the voice coil is a death sentence (even with the ultra-high temp epoxy units used in car audio). It takes a few minutes of such delivered power to heat the magnet structure anywhere near that level.

For a 0.25 dB drop, worry more about the heat of the voice coil. That corresponds to ~6% increase in DCR from temperature. With the Tc of Cu being around 0.4%/deg C, that means an increase of the voice coil temperature by ~15 deg C will drop you 0.25 dB. Start at a warm ambient temperature of 30 deg C (warm club environment). You've lost 0.25 dB at 45 deg C on the voice coil from simple heating, well before what the magnet would have any issue.

I'd be more worried about the ability of the magnet to hold up under flux; demagnetization from flux modulation is an actual issue, and one of the reasons why AlNiCo magnets should be avoided for higher powers. The coercive force of Neo is orders of magnitude higher than AlNiCo or ferrite. Even Ferrite is considerably better than AlNiCo (by 2-5X). You can see high instantaneous flux levels from large peaks that can cause significant permanent loss in magnet strength.

Dan Wiggins
Adire Audio

[thoriated]

Actually, Alnico is the least susceptible of the magnetic materials I have listed to flux modulation. The table makes clear that while Alnico is probably not what you want to place your bets on for high SPL stadium installations, it is still well ahead of neodymium and totally outclasses ceramic for the highest performance sound quality applications where knuckle dragging abuse is not part of the sonic equation.

Speaking for myself, I'm willing to hold my knuckles off the floor to get the best SQ. And intelligent magnet system design, such as, say with an underhung VC, rather quickly obviates that 'problem' with alnico IAC.

VC resistive heating is not as pernicious in its effects IAC, as magnetic system temperature sensitivity because it has no component that corresponds to flux modulation.

[Pan]

The Aura drivers seems to be nice, however compared to the Excel drivers I fail to see the superior performance from these drivers at least by looking at the manufacturers graphs.

Also if these discrete steps in magnet flux exists shouldn´t they show up in a distortion plot then? Meaning in the end the most linear driver will be the best no matter if ceramic or Neo are being used.

The W15CH do not measure better than the old W15CY. Aura woofers don´t seem to measure better than W26/W22 (within physical limits). And the new Accuton Neo tweeters do not seem to measure better than the Diamonds which I believe uses ceramic magnets.

Maybe everything we need to know can be found in bandwith, Q, decay/waterfall and HM/IM plots..?

/Peter

[Bill Fitzpatrick]

Originally posted by usekgb
Have you looked at the JBL 2262? This thing is great.

I haven't and couldn't because I couldn't find reference to it via Google. Could you give me a link?

Originally posted by Timn8ter
Extremis 6.8 which uses Neo and it's a very impressive little mid-woof.

That may be so but they have apparently traded excursion for sensitivity. When you cross at 90 to 110Hz (a rather good bi-amping crossover frequency IMO) as I am doing you don't need all that much excursion even with demanding recorded material - 1/2" pk/pk is way plenty for a 90db, 5 incher. I'd rather have the sensitivity.

Anyway, I've read a lot of opinions about neo here. I was sorta looking for the facts but, as a friend used to say, oh well.

[tomtt]

alnico/neo/mud



http://www.audioroundtable.com/Speak...sages/243.html