If you do not do something tricky with the amplifier--
and no commercial consumer audio amplifier intended for
universal use does this trickiness, or none I am aware of--
then the cable impedance operates as part of the amplifier
output impedance. This means that the amplifier
will not be flat into the speaker load unless the speaker
load is constant resistive impedance- which effectively
never happens.
It does not take a lot of resistance for this to matter.
I suppose everyone knows how to compute this. In the unlikely
event that anyone does not, it is explained(reasonably clearly
I hope) here:
http://www.regonaudio.com/Why%20Amplifiers%20Don't%20Always%20Sound%20Right.html
This is mostly about amplifier output impedance --the article
could have been subtitled Why you should forget about tube amps!
But cable impedance just adds itself to amplifier output impedance
(or in the case of cable capacitance, it is shunted over,in parallel not
in series). So the calculations are similar.
Do these things matter? Actually , in times past at least, lots of
amplifiers even solid state ones were not in fact flat into actual speaker
loads. Tom Holman had an article (:Manufacturer's Response)in The
Absolute Sound early on--issue 26
as I recall-- measuring the actual response of a bunch of solid state
amps into a real speaker. ALmost none of them was anywhere near
flat to within the (small) threshold of audibility of frequency response
shifts. (Holman's Apt design was the only one that was, in the group
surveyed). There is quite a lot of reason to believe that this sort of
thing is the
main, maybe the only, reason that amplifiers sound different, to the
extent that they do(except for amps with high distortion or clipping at
the operating level).
Robert
On Wed, 27 Jul 2011, Neil Marcia Adams wrote:
Am I right in thinking that the resistive component of the speaker's
impedance is effectively in series with its inductance? Say, 5 ohms for an 8
ohm speaker? If so cable resistance is not so frightening for domestic runs.
It's not so difficult to provide negative output impedance to counter the
wire+speaker resistance. This can significantly increase damping and is
sometimes used in powered 'active' speakers where all parameters can be
controlled.
Neil Adams
At 06:41 7/27/2011, Sampo Syreeni wrote:
On 2011-07-26, Fons Adriaensen wrote:
I certainly don't want you to waste your money on fancy speaker cables.
Never thought otherwise. That's obviously never been what we do here. ;)
But resistance does matter, so a good cross section such as 2.5 mm^2 puts
you on the safe side.
What I was trying to ask is, what's the real problem with resistance,
especially with regard to a passive speaker and a modern, A/B class solid
state end stage? I mean, I don't really see cable resistance shifting their
operating point much, even with feedback, within the audible range.
What is it that I'm missing?
--
Sampo Syreeni, aka decoy - de...@iki.fi, http://decoy.iki.fi/front
+358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
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