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dual isobaric magnet interaction
dual isobaric magnet interaction
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Old 20th March 2012, 01:27 AM   #1
badman is offline badman  United States
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Default dual isobaric magnet interaction

Howdy crew:

I have an assembly I'm looking to do, using 2 pairs of isobaric subs, mounted at a right angle, very close together. The magnets do not touch but there's enough magnetism to repel each other somewhat.

The concern with this is that it's going to act like a weak bucking magnet, and create some extra motor strength on the interior pairs. This, of course, creates an asymmetrical setup, where the inner driver in either pair will be somewhat stronger than the outer.

Now, the question is-

IS THIS A PROBLEM?

Given that the motion of one cone translates into motion in the other cone, a well-sealed clamshell mount may not actually have a problem here, as the suspension nonlinearities will still track each other.

On the other hand, the whole point of isobaric is to reduce nonlinearity and I don't wish to introduce another source of distortion.

I've been going back and forth on this, and can't seem to reach an internal consensus. Accordingly my plan is to create spacers of 3/4" ply. The cabinets are already built (surplus M&K) so I'm stuck with the format (don't really want to deviate from using them as they're quite nice).

But I'd welcome any feedback from the crew on this.
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Old 20th March 2012, 02:45 AM   #2
hitsware is offline hitsware
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If there was much interaction between driver magnetic systems,
There would be some mention somewhere.
There seems not to be.
It's something about the magnet with associated yoke
forming a sorta shielded system ............ ??
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Old 20th March 2012, 04:42 AM   #3
badman is offline badman  United States
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Hi hits:

What you're talking about is a bucking magnet. The thing is that typically, the magnet interactions are consistent amongst the drivers in the system, where in this arrangement, it's only affecting the inner drivers, the outer ones of each pair don't have that issue, and it's that asymmetry that's the concern. In the case of "push push" subwoofers, where they're opposed for force cancellation, the interaction of the fields is actually a benefit, as it uses some of the stray field and should slightly increase flux density. But the effect is symmetrical for each woofer in that arrangement. My concern is that the inner portions of the drivers would have a slightly stronger magnet system and that would create asymmetrical behavior between inner and outer drivers. Isobaric would seem to rely upon good matching to perform its best, but the effect may be swamped by the other effects.
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Old 20th March 2012, 04:27 PM   #4
weltersys is online now weltersys  United States
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Quote:
Originally Posted by badman View Post
My concern is that the inner portions of the drivers would have a slightly stronger magnet system and that would create asymmetrical behavior between inner and outer drivers. Isobaric would seem to rely upon good matching to perform its best, but the effect may be swamped by the other effects.
The stray field is "wasted" magnetism, and compared to the strength concentrated in the magnetic gap is of no consequence.
The nonsymetrical cabinet layout will have far more acoustical consequence than the magnet proximity.
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Old 20th March 2012, 05:56 PM   #5
badman is offline badman  United States
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Quote:
Originally Posted by weltersys View Post
The stray field is "wasted" magnetism, and compared to the strength concentrated in the magnetic gap is of no consequence.
The nonsymetrical cabinet layout will have far more acoustical consequence than the magnet proximity.
Thanks for your input, certainly the effect would be fairly low level, perhaps I'm chasing too far down the foxhole.

Care to elaborate upon the nonsymmetrical layout? I don't understand your concern.
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Old 20th March 2012, 06:10 PM   #6
weltersys is online now weltersys  United States
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Quote:
Originally Posted by badman View Post
Thanks for your input, certainly the effect would be fairly low level, perhaps I'm chasing too far down the foxhole.

Care to elaborate upon the nonsymmetrical layout? I don't understand your concern.
I'm not concerned, but if you want to chase down foxholes, the interior cabinet reflections from the different isobaric pairs will not be symmetrical, so the cancellation of even order harmonics will not be as effective as a symmetrical layout.

That said, the difference in production driver parameters from unit to unit probably would exceed that difference.
And the effect you room has will make any of these tiny differences look like ants on a mountain.

Don't worry, be happy.
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Old 20th March 2012, 06:58 PM   #7
badman is offline badman  United States
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Why should symmetry of cabinet reflections play a role? The coupling of the inner driver with the outer driver is the method for which the even order distortion cancellation takes place, by virtue of equal but opposite tilts in BL/Suspension curves. While I can see how the airload/reflections on the diaphragm would be different for the inner driver vs. the outer in a given pair, I'm not following how this would mean anything between one pair and the other, since there's no mechanism by which the nonlinearities are coupled from one clamshell to the next, for cancellation.

I appreciate the input, certainly you're right in that I'm being too anal about it, but I'm sure you know how it is- once the gears start cranking...
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Old 20th March 2012, 07:58 PM   #8
weltersys is online now weltersys  United States
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Quote:
Originally Posted by badman View Post
Why should symmetry of cabinet reflections play a role? The coupling of the inner driver with the outer driver is the method for which the even order distortion cancellation takes place, by virtue of equal but opposite tilts in BL/Suspension curves. While I can see how the airload/reflections on the diaphragm would be different for the inner driver vs. the outer in a given pair, I'm not following how this would mean anything between one pair and the other, since there's no mechanism by which the nonlinearities are coupled from one clamshell to the next, for cancellation.
You are correct regarding even order distortion cancellation.
The non symmetrical loading airload/reflections on the inner diaphragm of one iso pair compared to the other would change frequency and phase response compared to a symmetrical loading, and probably not change the second harmonic distortion signature.
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Old 20th March 2012, 08:06 PM   #9
Andrew Eckhardt is offline Andrew Eckhardt  United States
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However, I'll second the idea that the magnetic interaction is below driver to driver tolerance effects.
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Old 20th March 2012, 08:23 PM   #10
badman is offline badman  United States
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Quote:
Originally Posted by weltersys View Post
You are correct regarding even order distortion cancellation.
The non symmetrical loading airload/reflections on the inner diaphragm of one iso pair compared to the other would change frequency and phase response compared to a symmetrical loading, and probably not change the second harmonic distortion signature.
Oh, agreed, though I'd not expect this to be a concern at the lower freq XOs I use for subs, thanks for following up.

Quote:
Originally Posted by Andrew Eckhardt View Post
However, I'll second the idea that the magnetic interaction is below driver to driver tolerance effects.
That was my thought too but I keep thinking about bucking magnets, and how much influence they can have (as much as a 2 dB and a couple tenths of a point of Qes) , but I suppose they're not contstrained by the presence of the motor (which limits the stray magnetism dramatically)

Thanks for all the feedback guys, I think I'll limit myself to one driver spacing ring, just to buy a little extra space, rather than doing 2.
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