From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Cancel speaker resistance?
Date: Tue, 17 Sep 2002 01:27:20 GMT
NNTP-Posting-Date: Mon, 16 Sep 2002 18:27:20 PDT
John Woodgate wrote:
> I read in sci.electronics.design that Simon Byrnand
> wrote (in <firstname.lastname@example.org
> .nz>) about 'Cancel speaker resistance?', on Mon, 16 Sep 2002:
> >nd the frequency response of the speaker is entirely changed, since most
> >(all?) drivers are designed to give their desired frequency response with a
> >constant voltage source, not a constant current source.
> No, not all. KEF, for example, had some constant-current products years
> >Not only would you
> >get a big peak at the fundamental resonance, (which you suggest
> >compensating) but a climbing output at higher frequencies.
> The voice-coil inductance tends to counteract that, if the current
> source is not TOO constant.
> >> This all makes sense only for very high-end sound systems with active
> >> crossovers and built-in amplifiers.
> >And I doubt they drive the actual speaker with a constant current
> >amplifier....(instead of constant voltage)
> It has been done; see above.
It could have advantages. Certainly the impedance characteristics vanish
from the equation. The first principle mode is low Q and could be
equalized away at a low level. Above the first principle mode, the
acceleration of the voice coil is proportional to current. How this sort
of behavior is reflected in acoustic pressure I have not a foggy but if
the function is simple, it could be equalized as well. If it is
desirable to servo the diaphragm using some sort of voice coil position
feedback, current drive is the only way to do it.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com