John Phillips wrote:
On 2008-07-14, Jim Lesurf wrote:
In article , Dave Plowman (News)
wrote:
In article , Eeyore
wrote:
You need to know the R, L and C of cable. It makes a complex filter.
With the output impedance of a decent amp being 2 10ths of FA, the
capacitance of any practical cable doesn't matter.
This assumes the amp is stable into whatever the resulting load may be
presented to its output terminals. Also that loading at ultrasonic
frequencies has no other effect on its performance which may show up in the
audio range. I'd expect that for a decently designed amplifier. But I am
less confident it will apply for every design that people sell. :-)

Nor should the inductance with a properly designed amp.
Erm... the problem with cable impedance is that it is a series
contribution. May not bother the amplifier, but can change the signal
patterns at the load at the other end of the cable. Particularly with
speakers that are essentially capacitive at HF.

Some LS cables have inductances of the order of 1 microH/m or more. FWIW
I've been measuring LS cables recently, and cables with inductances of the
order of 0.5 microH/m seem to be more common than people might expect! :-)

From some of my amp-cable-speaker modelling (using GNUCAP):

Belden 9718 12 AWG:
R = 10.8 mOhms/metre; C = 72.2 pF/metre; L = 755 nH/metre

Maplin's "Shark 12 Gauge" (it's actually much beefier than 12 AWG):
R = 4.8 mOhms/metre; C = 59.6 pF/metre; L = 660 nH/metre

The Belden is from manufacturer specs (I think). The "Shark" is
calculated by me from the actual cable's geometry.

Both of these show a *small* high treble droop across the load, with
5 metres connected to a complex load modelled on my own rather benign
'speakers. It's a fairly broad band droop so it's just concievable it
might be audible to a good, young set of ears (but not mine, I think).

Paralleled cat 5 has much lower inductance (at the expense of a lot more
capacitance) and is very good in the high treble.

(At least as far as GNUCAP calculates - the real world is often
different.)


As ever with cables, what determines the response is the square root of
the ratio of the inductance to the capacitance. It matter nothing what
each is individually.

The closer you can get that figure to 8, the flatter the speaker
response will be.

d