In article , mick
wrote:
On Fri, 07 Aug 2009 17:31:43 +0100, Eeyore wrote:




I'm unsure about drawing any conclusions from graphs that start at 5x
the accepted maximum audible frequency. I hope Jim has included tests
on VHF coax as speaker leads too - it makes as much sense to me... ;-)

The problem is that some amplifier designs can be upset by having a load at
RF which does not suit them. The classical symptom is either sustained
oscillations in the region around a MHz or above, or bursts of oscillations
with particular audio waveforms. This can alter the audio behaviour. The
effects are measurable as well as audible.

Alas, the amplifier designer has no control over what loads the user
connects. And this will change with the choice and length of the
loudspeaker cables.

*If* your amp has much output above 100kHz then it is faulty and needs
looking at - seriously.

I agree. However some commercial amps *have* produced oscillations like
this with some loadings. For all I know, some still do.

And one of the points of the RF measurements is that it allows you to
determine the cable properties which you can then apply at audio
frequencies to assess what changes may occur *in* the audio band even when
the amplifier is stable and happy. So the measurements are useful - if you
understand why they were made and how to use the results. :-)

Slainte,

Jim

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