From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Speaker phase and current vs voltage drive
Date: Tue, 29 Oct 2002 13:31:14 GMT
NNTP-Posting-Date: Tue, 29 Oct 2002 05:31:14 PST
John Woodgate wrote:
> I read in sci.electronics.design that Chuck Simmons
> wrote (in <3DBDDB69.3D30001F@webaccess.net>)
> about 'Speaker phase and current vs voltage drive', on Tue, 29 Oct 2002:
> >I think it was Oswald at IBM who came up with
> >the idea of improving mechanical response by the use of a shorted turn.
> The pole-pieces of a moving-coil loudspeaker act as shorted-turns as
> well, but not very low-resistance ones. In order to reduce voice-coil
> inductance, which restricts high-frequency response by causing a rising
> impedance, the centre pole-piece may be thickly copper-plated or be
> encircled by an aluminium (typically) ring.
Interesting. I have never disected a speaker with a shorted turn but I
have never disected expensive ones. In the disk drive motors, the
shorted turn was a long copper sleeve in linear voice coil motors. In
rotary voice coil actuators I have not seen it done. This appears to be
because mechanical response is dominated by moment of inertia rather
than current rise. Of course at one time, high voltages were available
for the actuators and high force constants were used. These days, the
available drive voltage is low and very low motor constants are
required. This means the coil inductance is low as well.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org