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From: brianr@tekig4.TEK.COM (Brian Rhodefer)
Newsgroups: rec.audio,sci.electronics
Subject: Re: Mercury Filled Speaker Wire
Message-ID: <1953@tekig4.TEK.COM>
Date: Tue, 22-Sep-87 17:33:37 EDT
Article-I.D.: tekig4.1953
Posted: Tue Sep 22 17:33:37 1987
Date-Received: Sat, 26-Sep-87 01:34:16 EDT
References: <3816@watdcsu.waterloo.edu> <578@uthub.toronto.edu>
Reply-To: brianr@tekig4.UUCP (Brian Rhodefer)
Distribution: rec
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 42
Xref: mnetor rec.audio:3386 sci.electronics:1400

The analog guru at the next desk assures me that, with today's
amplifiers, the dominant influence on the transient/frequency
response of the amplifier/cable/speaker electrical-to-pressure
transducing system is the series resistance of the speaker circuit.
He mentioned this by way of pointing out how profitless it is to
worry about small fractions of an ohm's worth of cable resistance
in the face of (typically) 4 ohms of intrinsic speaker coil resistance.

If this is so, why wouldn't it be a good idea to arrange for amplifier
outputs to look like current sources rather than voltage sources?
It ought to be quite simple to implement a current-sensing feedback system
so that the output stages faithfully translate audio program voltage
into speaker current,  within some reasonable (like +/- 60V or so) compliance.

Obviously, this would make the resistance of the speakers, as well as
the comparatively trivial cable effects, "drop out", by pulling these
imperfections inside the amplifier output stages' feedback loops.

It wouldn't be a total loss for the audiophiles, though: they could still
quibble about shunt losses due to distributed capacitance effects in their
cables - why, I'll bet they'd ammount to NANOFARADS!

Moreover, forces generated by currents passing through magnetic
fields tend to be simple products of the currents and field strengths.
A speaker's voice coil, then, should then have a linear current-to-force
transfer function.  As I'd expect voice-coil force to translate directly
into induced air pressure, it seems to me that a current-mode output
signal would also be desirable due to a more nearly linear transduction
of audio voltage signals into air pressure signals.

Am I mistaken in thinking that this is exactly the kind of transducer
that an amplifier/speaker system ought to be?

There must be some reason, though, for amplifier outputs to be made
the way they are;  could someone kindly explain why?



An Inquiring mind which may not really want
to know, but sure loves to ask dumb questions,

Brian Rhodefer