High Efficiency Speaker Asylum

RE: Wow - I stand corrected!

68.183.209.38

Steve Schell

In Reply to: RE: Wow - I stand corrected! posted by sser2 on July 12, 2007 at 13:05:01

There is a reason why a field coil would be designed for lower temperature rise than some other devices. The speaker's voice coil has its own heat dissipation to accomplish, all the while living within the motor structure. If there is excessive temperature rise in the motor it will make for a very hostile environment for the voice coil. Although I haven't measured it, I would also expect the dynamic compression of a driver with a hot motor to be greater than one running at normal temperature.

Follow Ups:

RE: Wow - I stand corrected! - John Sheerin 15:58:27 07/12/07 (2)
> Although I haven't measured it, I would also expect the dynamic compression of a driver with a hot motor to be greater than one running at normal temperature.

Hi Steve,
What makes you think that? The resting voice coil temperature will stabilize with the field coil and that will cause different parameters than with the field coil cold but energized, but beyond that, given power dissipations in the coil should cause the same temperature rise in the voice coil which would cause the same increase in DCR. Actually I'd think that a hot field coil might have less compression, as the same increase in DCR would be a smaller percent change relative to rest (with the hot field coil), so would cause less compression. I don't think this would be a very big difference though. However, I must admit it's been a while since I reviewed heat transfer so I could be wrong, and I don't have time to look it up right now.

Other than that, you're definitely right - you're adding the temp rise of the field coil to the voice coil, so depending on what the insulation's like, you could be asking for trouble.

John
- RE: Wow - I stand corrected! - Steve Schell 20:43:10 07/12/07 (1)
  Hi John, great to hear from you.
  
  So maybe that's why field coil drivers sound good... they run warm! You're gonna make me put on my thinkin' cap about this, but what you say makes sense. Hmmm.
  
  There are practical considerations that weigh against running these old drivers at high motor temperatures. At what temperature would a paper former spontaneously combust? The other poster was talking about motor temperatures up to 212 degrees Farenheit. I've only smoked one coil former all these years, but when I was done with it there was nothing left but charcoal.
  
  Running a motor really hot will probably expand the center pole a thousandth or two; not sure what the effect would be on the top plate. The voice coils I've seen that warped out of round probably did so due to high temperatures.
  - RE: Wow - I stand corrected! - amnesiac 23:33:37 07/12/07 (0)
    For what its worth it ran for 6 hours and drifted up to 44 watts and lived.You could put a water cooling block on the back if you where keen enough.Or perhaps just a heat sink.

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