High Efficiency Speaker Asylum

RE: The nominal power for F12N field coil is 25 W.

68.183.209.242

Steve Schell

In Reply to: RE: The nominal power for F12N field coil is 25 W. posted by amnesiac on July 12, 2007 at 22:35:51

That thin coil under the top plate is a humbucking coil, and it is placed in series with the voice coil. Most of these speakers were used in situations where the field coil functioned as part of the smoothing circuit for the amplifier's power supply, so they were fed some gnarly DC. You can either leave it alone of disconnect it; I remove them when taking the drivers apart.

No, those weren't my field coil converted 288s on ebay.

Follow Ups:

This is not a humbucking coil. - sser2 13:45:28 07/16/07 (1)
If it were, then it was to be supplied with a hum signal out of phase with field coil hum.

The extra coil around the pole piece is a demodulator coil. Its purpose is to counter the modulation of magnetic field in the gap by the voice coil. It is connected in series and out of phase with the VC. It makes magnetic field in the gap immune to modulation by the field of the voice coil. Another advantage of the demodulator coil is reduction of driver's Le, which allows better high frequency extension.

With an underpowered field coil that you advocate, demodulation coil has most benefits and should not be disconnected. With high FC power, when the yoke is close to magnetic saturation, demodulation coil becomes magnetically uncoupled from the voice coil and all its benefits disappear.
- RE: This is not a humbucking coil. - Steve Schell 00:02:07 07/19/07 (0)
  Sser2, your comments are most interesting and thought provoking. I have never thought of that little extra coil in this way, but I like your thinking. Do you have any citings from the literature that indicate that this coil functions as a demodulator? It would be fascinating and would open up new avenues of thought if true, and I am all ears when it comes to improving field coil technology.
  
  I have deduced that this coil is a humbucker mostly because the field coils in most of these Jensen units serve as filtering components in the amplifier's power supply. If the audio signal contained some hum components then their presence in this coil, if in opposite polarity to the field coil, would tend to cancel the hum in the speaker's output.
  
  I am not sure why you state that I advocate an "underpowered" field coil. I have stated the recommendations of the manufacturer in response to what appeared to me to be your reckless recommendation of almost three times the nominal field dissipation that these units were designed for. As Paul Klipsch used to say, "Any mechanical or electrical device can be overdriven to the point where failure must occur."
RE: The nominal power for F12N field coil is 25 W. - amnesiac 09:38:25 07/13/07 (0)
Ok thank you.I will try with out it.It running nice and losening up at 20 watts. good bass impact.

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