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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: Mon, 16 Sep 2002 00:13:24 GMT
NNTP-Posting-Date: Sun, 15 Sep 2002 17:13:24 PDT
Kevin McMurtrie wrote:
> Is there any advantage in using current to voltage positive feedback to
> cancel the coil resistance of a single speaker driver? Would
> eliminating the 5-something Ohms improve the sound or is it
> insignificant compared to other factors?
> (This trick is inspired by DC motor drivers which regulate the speed by
> compensating for the losses in a motor.)
You seem to be talking about BEMF bridge feedback. This is not positive
feedback at all. You put the coil in one leg of a bridge and extract the
voltage feedback differentially from the bridge. This is perfectly fine
if velocity control is the goal. There are some challenges.
1) voice coils are usually a spring mass system. You have to match
that impedance in the other leg of the bridge. It can be done.
2) the acoustic impedance reflects into this scheme so that the
bridge balance is not straight forward at all.
3) it is not clear to me at all that for small diaphrams acoustic
pressure is linear with velocity in a large volume.
4) you have to understand the acoustics of the enclosure or horn to
make sense of any speaker driving scheme.
5) speakers are usually used above resonance in the slope 2 regime.
This is the constant acceleration regime. Maybe a current driver
makes more sense.
6) using a technique not specified by the manufacture may require
equalization. This makes sense for any drive scheme once the the
speakers are installed since the room adds "color."
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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