Magneplanar magnet pattern?

[Few]

I found this patent assigned to Magnepan and was surprised to see that it states that arranging the magnets in a N-N-S-S-N-N-S-S pattern is superior to the N-S-N-S-N-S-N-S pattern I thought was universally used. Does anyone know which pattern current Magneplanar speakers use?

I'm starting to play with a diy planar-magnetic prototype that I thought I was basing on the Magneplanar midrange and treble system, but this patent has left me questioning whether I'm using the best approach. The current Magnepan website shows an image depicting the N-S-N-S-... pattern.



By the way, I'm planning to use a single-ended magnet system rather than magnets both in front of and behind the diaphragm.

Thanks.
Few

[gootee]

With NNSSNN you would only put conductors between the NS and SN pairs, and not between any NN or SS pairs. But I guess, that way, no NS or SN pair would have to "share" either of its magnets with another pair's magnet, i.e. the field would go from one N to one S, instead of from each N to two S as it would if you had NSNSNS (except for one or two at the edge). I'm guessing that you would get a 2X stronger NS magnetic field with the NNSSNNSS. But you would only have half as many locations, probably twice as far apart. I guess that could still be better.

I don't know of any Magnepan speakers that don't use NSNSNS. I believe that they all use NSNSNS.

[Few]

Hi gootee,
Thanks for the response. The part that seems strange to me is that two N-oriented magnets positioned side by side amount nearly to a single N-oriented magnet of twice the width. The only difference is that there is an air gap through the middle of the wider magnet. Winey claims in the patent that the field projects farther and more uniformly beyond the plane of the magnets so you can cover more the diaphragm with conductors and also use a larger gap between the diaphragm and magnets.That gap allows for greater diaphragm excursion. It seems to me using double-wide magnets may achieve the same goals (without the extra air gap) and if that's true, it's an odd thing to be able to patent. That makes me feel like I'm missing something.
Few

[Marveloudio]

This could be easily proofed by simulating it using FEMM(freeware).

The patent is misleading as you could replace NN-SS-NN with just as a doubled width magnet , the result is still a N-S-N configuration ....

regards

[Few]

you could replace NN-SS-NN with just as a doubled width magnet , the result is still a N-S-N configuration ....

Right. That's the point I was trying to make.

I agree FEMM would be helpful but I'm working on a Mac at the moment and as far as I know there's no Mac version of FEMM. I can play with it when I get to work.

In the meantime, nobody seems to be arguing that some configuration other than N-S-N-S-N-S is used on the Magnelanars.

Does anyone happen to know what diaphragm-magnet distance they use in the midrange and tweeter drivers? (I'm excluding their "true ribbon" tweeter here.) The hint's I've seen suggest it's around 1/16" (a bit over 1.5 mm). Does that sound right?

[gootee]

I happen to have the sock off of one of my Magnepan MG12/QR speakers so I measured it for you. On my MG12s I can push the mylar in by almost exactly 1/8th inch before it bottoms out, in the center of the speaker (the mid-bass, I guess). The quai-ribbon (tweeter) section wasn't measured as precisely but looked like about 1/16th inch.

I actually have a DC Gaussmeter (magnetic field meter) with a directional probe. So I tried measuring the magnetic field strength, too. Halfway between the wires, in most places, I measured about + or - 40 milliTorr or less (sometimes down to 30 mT or even less), with the Hall-effect chip touching the mylar (and measuring left-right field in the plane of the mylar, I think). I think that 1 mT is 10 Gauss. I got about the same readings between the foil runs on the tweeter section. I didn't measure everywhere but spot checking seemed to show that the measurements might have been a little lower in the center of the speaker than near the edges.

I realize that you would probably be more interested in the field measurement at the exact spot that the wire occupies. But the wire thickness changed the measurement significantly. And I couldn't seem to get good measurements directly on the foil of the quasi ribbon, either.

Cheers,

Tom

[Few]

Thanks very much for going to the trouble, Tom. I appreciate it. Your magnetic field measurements were likely in units of millitesla rather than millitorr (which is a measure of pressure). Would that makes sense based on the display of your meter?

Few

[gootee]

Originally Posted by Few

Thanks very much for going to the trouble, Tom. I appreciate it. Your magnetic field measurements were likely in units of millitesla rather than millitorr (which is a measure of pressure). Would that makes sense based on the display of your meter?

Few

Sheesh! Yes, milliTESLA, not millitorr!

[Marveloudio]

In this video at approx 1:06 you can see the new magnet/conductor layout :

YouTube - ‪High End 2011 (1)‬‏