Magnet attached grilles for MA drivers, good or bad idea - diyAudio
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Old 30th August 2011, 03:18 PM   #1
Squeak is offline Squeak  Denmark
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Default Magnet attached grilles for MA drivers, good or bad idea

I thinking about an easy way to do magnet attachable grilles for the Mark Audio drivers.
I've found some grilles that are of a light but quite magnetic metal exactly matching the diameter of the driver.
I was thinking about putting six small neodym magnets (5x2 milimetres) in the cavities at the back of the drivers flange, secured with blue putty.

My question is now: Is there any chance that this will have a bad lasting/non-reversible effect on coil, magnet or diaphragm?
And if they are placed symmetrically, will it have any effect at all?
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Old 30th August 2011, 03:49 PM   #2
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Do you mean attaching the magnets to the back of the grille flange?

It should be easy enough to align the little 1/4" neo magnets with the position of the mounting screws in the driver flanges, but they are very strong and I'd suggest a dab of metal bearing epoxy glue on the back of the grille flange rather than relying on the blue putty.

Mark can answer whether the proximity or polarity of the magnets would affect the speaker's motor, but my intuition is "no".
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Old 30th August 2011, 04:15 PM   #3
Squeak is offline Squeak  Denmark
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Quote:
Originally Posted by chrisb View Post
Do you mean attaching the magnets to the back of the grille flange?
No. I thought of doing that at first. But I figured it would be better to put larger stronger magnets in the curved rectangular cavities on the back of the flange of the driver.
It would be easier to align the grille perfectly that way (although you have to do it again every time you take it off), even though the magnet has to pull through ca. 2mm of plastic that way.

But my guess is also no, since the drivers will tolerate being in the same cabinet as their twins or other unshielded drivers with much stronger and asymmetric fields.
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Old 30th August 2011, 04:32 PM   #4
chrisb is offline chrisb  Canada
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Have you tested magnet's ability to hold through that thick a layer of the plastic flange? And which Mark Audio drivers did you have in mind? To be honest, I've not put a caliper on the depth of the casting web on back of flanges of any of them, and the Alpair7 have a cast integral gasket with no such cavities. You might well find that a magnet with appropriate strength to hold through the flange would be thicker than the cavity's depth and need to be be countersunk into the baffle - still doable, but additional complication.

Would there be an option for a larger diameter grill that would still fit your enclosures for which the magnets could be flush mounted outside the perimeter of the plastic flange?
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Old 30th August 2011, 04:57 PM   #5
Squeak is offline Squeak  Denmark
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Oh sorry, it's just plain old CHR-70s gen. 3.
I have tested and the magnets will hold through that thickness.
The elegant thing about my method is that nothing is fixed. If you find out the alignment is terrible you just move the magnets. My experience is that aligning something with magnets can be very finicky. Esp. with something as irregular as a grille.
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Old 30th August 2011, 05:06 PM   #6
chrisb is offline chrisb  Canada
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If the magnets you've tested will fit within the cavities on back of flange without countersinking , it sounds like your plan should work. Just be careful handling the drivers if you need to remove them to adjust magnet locations - the metal cones are not as rugged as paper!
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Old 13th October 2011, 08:43 PM   #7
von Ah is offline von Ah  United States
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Here's my low-brow approach to simple magnetic grilles. Neo magnets on the driver screws and just the steel screen portion of the inexpensive Madisound metal grilles.

I just use them to protect the drivers when I'm away from the office. I think these particular screens take something away from the EL70s. I'm still waffling on what to do for grilles when these go home (kid protection).

I'd also be interested in the Mark Audio perspective about magnetic fields and whether these powerful magnets might cause something wonky in the drivers' motors/coils.
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Old 13th October 2011, 08:59 PM   #8
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I would be more worried about accidentily placing a credit card on the top with no grills (but magnet still there) in place tahn about the effects of the concentrated magnetic field of the neos.

dave
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Old 13th October 2011, 09:20 PM   #9
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by von.ah View Post
Here's my low-brow approach to simple magnetic grilles. Neo magnets on the driver screws and just the steel screen portion of the inexpensive Madisound metal grilles.

I just use them to protect the drivers when I'm away from the office. I think these particular screens take something away from the EL70s. I'm still waffling on what to do for grilles when these go home (kid protection).

I'd also be interested in the Mark Audio perspective about magnetic fields and whether these powerful magnets might cause something wonky in the drivers' motors/coils.

My name isn't Mark, but after a lot of prompting by Dave I've been using the little 1/4" rod rare earth magnets on grilles for some time now; recessed flush into driver baffle, and generally buried beneath finish veneer, but they can be left exposed on bamboo plywood - careful use of drill press and brad-point / forstner bit will avoid any chip-out on finished surface. Using either 1/4" or 3/8" MDF a very light frame can be fabricated with plenty of clearance to the emitting surface. I honestly can't hear any difference with them on or off, but better ears might. For most enclosures a magnet in each corner will suffice. For my own CastleMTs I made a one piece L-shaped 3/8" frame and set the magnets flush to the inside. Once they're upholstered the fabric will cushion the magnets from scratching the enclosure's finished surface.

These little buggers are pretty strong, but I think it would take quite a few of them very close to the existing drive train motor to wreak any havoc.
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Last edited by chrisb; 13th October 2011 at 09:33 PM. Reason: "clarification"?
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Old 14th October 2011, 02:02 PM   #10
von Ah is offline von Ah  United States
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Noted, thank you both.

Evan actually made me some nice U-shaped frames which I have yet to cover. So the truth is I'm just noncommittal on the fabric-plus-reinforcement idea. I tried cutting some pieces of aluminum window screen, but the threads kept coming loose and I only succeeded in snagging my pants. I imagine fiberglass would be similar, so I'll look for some nylon window screen next.

Cheers!
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