On 2009-08-08, Eeyore wrote:
John Phillips wrote:
Eeyore wrote:
John Phillips wrote:
Don Pearce wrote:
Jim Lesurf wrote:

I've just put up a new webpage that provides some measurements on the
properties of a variety of loudspeaker cables. The page is at

http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html

It is an expanded version of the article published in 'Hi Fi News' a few
months ago.

No conclusions section there, but maybe as follows?

1. If you open circuit the cable at the loudspeaker end, it is better
if the cable is somewhat lossy, as this will prevent the quarter wave
Mod Z dropping to too low (potentially damaging) a value.

Alternatively, perhaps, that a well-designed amplifier will have about
2 uH of good quality inductance in series with its output to avoid such
a case becoming damaging?

Funny, that's very similar to the value I use. And it'll have a series R-C to
ground to stabilise the load the amp 'sees'. This technique has been known for
many decades. It is even used in long line-level drivers.

Yes - I agree. It seems we are in harmony about the need for an amplifer
to see a well-defined load at frequencies well above the audio band. Hence
my use of "good quality inductance" which needs to avoid self-resonance
at too low a frequency to maintain isolation for whatever the user throws
at the amplifier in terms of cable and loudspeaker.

I learned a lot from designing and building my first power amplifier.
I saw undesirable behaviour into the many MHz region whenever I failed
to pay enough attention.

So, I'm surprised at your reaction elsewhere. Even in the audio band,
loudspeakers can present impedances from near zero to high enough to
be considered infinite.

WRONG. Show me one.

That's not relevant. In designing a power amplifier what's important is
the range of possible behaviours over as many 'speakers as the designer
wants to take into account - not just one.

I'm sure you know that and I'm puzzled why you choose to go down that
dead-end road when a little thought should prevail.

Out of the audio band this gets no better,
from what I have seen.

By which time the RLC network in the output stage will be doing its job, so the
point is academic.

That's true only in the consideration of load-related stability problem,
and then only in the case where the "usual" RLC network is present.
Having learned about the RLC solution to the problem I, for one, retain
the academic curiosity to learn how it might otherwise be done. Remember,
that's the way progress lies.

So it seems to me that investigating loudspeaker cables with loads
from zero to infinity, and at frequencies well above the audio band,
is perfectly reasonable.

I do not remotely agree. For most speakers 4 - 60 ohms +/- 4 - 60 j ohms
would suffice.

I guess you meant to write that differently since the minimum of that
range as written, (4 +/- 4j) Ohms, would only do for designing an
amplifier intended to drive loudspeakers labelled "8 Ohms" or above
(assuming the relevant DIN standard had been observed).

You might like to consider, for example, figure 4 from this page:
http://www.stereophile.com/features/99/index4.html.

I trust you know the meaning of the j

Graham, this style of argument is very reminiscent of another
contributor to this news group. It's not very helpful.

--
John Phillips