In article , Don
Pearce
wrote:
Jim Lesurf wrote:
A while ago there was some discussion about loudspeaker cables and the
relative merits of analysis using the transmission line and AC lumped
element approachs. I've now done a page on this which people may find
interesting. It is at

http://www.st-andrews.ac.uk/~www_pa/...g/howlong.html


Thanks for that, Jim. Pretty much what I expected, with the (for many
counter-intuitive) result that the high capacitance cable had the
flattest response - the expected result of having a better
characteristic impedance match. Doing the usual maths on your table of
cables

A = 8.5 B = 176 C = 153 D = 59 E = 211 G = 48.76

So as far as top end flatness goes, characteristic impedance is the best
predictor of performance.

That is OK if your concern is well above 20kHz for "top end". However the
actual cable impedances are well away from the approximate values you quote
at or below 20 kHz and the behaviour is better predicted there by series
inductance and resistance than by the above nominal values for
characteristic impedance. As the HFN articles will detail... :-)

Despite high capacitance, which might be
thought of as predicting a sagging top end, the high cap cable (A) at
8.5 ohms impedance is the only cable which is actually flat. And of
course a further implication of this is that this cable does not
present a capacitive load to the amp - it connects the speaker almost
invisibly, presenting the speaker impedance to the amp essentially
unchanged.

I'm afraid you make the classic oversight of assuming behaviour is close to
matched. It simply isn't. The reality is simpler. That low series impedance
gives you the flat response in these sorts of situations when the
frequencies are around 20 kHz or less.


And of course this is for cables of 5 metres. There are many audio apps
that use cable considerably longer than this, which makes it important
to think about the applicability of models.

The interest I have is for domestic audio. I doubt that more than a small
fraction of those use cables an order of magnitude longer than 5 metres.

Slainte,

Jim

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