[HAM] leslie speaker impedance

[Christoph P. Kukulies]

On Sat, Nov 08, 2003 at 04:38:29PM +1100, Randal Muir wrote:
> Thanks for the reply Chris. .. You have piqued my interest with realigning
> the driver.  How does one approach such a procedure??
> cheers -Randal
> 
> > I'm not wise and maybe not so much experienced but I would try to repair
> the
> > buzzing 16 Ohms driver. Have you tried to get rid of the buzz, i.e.
> realigning
> > the driver?

It has been discussed many times and it is probably much in the archives.
I will not recommend the "hammer"-method, which in short is giving
the unit a hit with a hammer on the iron 'U' of the magnet. I have never
done this but I've heard that it sometimes helps. It can cure the symptom
but it also can make things worse. How strong you hit it, well, it depends
on your personal mood of the day.

The 'correct' method is, dismounting the speaker from the cabinet so that
you can hold it in your hand, freed of all wiring etc.

Take apart the horn bearing plate and the black cover under it.
(mark all positions and screws with a felt pen or something - this eases
assembly later). 

When you are at the brown voice coil part, loosen it and take it out
once to inspect the voice coil, whether it has any dents, is burnt or any other
obvious damage that makes further repair superfluous.

Examine the magnet gap whether it contains dirt, metallic parts or
other obstacles. You can wipe with a piece of cardboard through the
gap. It should have even distance all over the whole circumference.

Insert the voice coil cautiously. Connect the speaker to the Leslie
speaker wires (unless you have a separate sine generator lab equipment)

Aim is to center the voice coil. I do it often the following way:

Move the voice coil N(orth) until it touches, get a feeling how much the
travel is now when you move it to S(outh) until it stops. The travel 
back half way. Now move it to W(est), then to E(ast) and then half way 
back to W. Then apply signal to the speaker. If could be helpful if
another person could play single notes (at medium volume) with one
drawbar (4') out. If there is still buzz, move the voice coil
around to minimize or zero out buzz. Fix the voice coil at the best position
and reassemble the speaker.

When fixing the screws things can get worse again requiring to repeat the whole
procedure.

Good luck and sorry for my english. Sometimes I could probably have used better
terms.

--
Chris Christoph P. U. Kukulies kuku_at_physik.rwth-aachen.de