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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: Speaker phase and current vs voltage drive
References: <3DBC76E9.F9DA95C2@managesoft.com> <3DBC7B38.C7EB8A43@webaccess.net> <3j1v9.9211$Fj6.firstname.lastname@example.org>
Date: Mon, 28 Oct 2002 05:04:58 GMT
NNTP-Posting-Date: Sun, 27 Oct 2002 21:04:58 PST
> > Voice coils are usually spring suspended. Below the spring mass
> > resonance, the voice coil displacement is nearly proportional to current
> > (voltage also because the principle electronic resonance is much
> > higher). Above the spring mass resonance, acceleration is proportional
> > to current. This is really the nearly linear regime because sound
> > pressure is proportional to acceleration rather than amplitude or
> > velocity. Cross over is needed because the speaker may have to vibrate
> > in a higher mode than the fundamental.
> > Chuck
> What is the reason that speakers aren't current controlled?
> I seem to remember some experiments done (a while ago) using
> current-controlled amplifiers (i.e., transconductance). As I recall, the
> problem was that the speaker enclosure resonances would have a bigger effect
> on the response -- as compared to the same speaker driven from the low
> output impedance of a voltage amp.
> Any insight into this?
Yes. An ideal transconductance amplifier produces zero damping. It has
infinite impedance. An ideal voltage driver has zero impedance. It has
excellent damping. In a system with no feedback on the variable that is
desirable to control, damping will be very important. On the whole, a
voltage driver works best in this situation even though a current driver
has theoretical advantages given an infinite baffle and so on.
If I were designing a stereo system for me, I would likely go for a very
stiff voltage driver rather than fight a losing battle trying to get all
of the variables under control.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons email@example.com
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