In message , Rob
writes


Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

I'm sure it doesn't matter, just curious :-)

Rob

The conventional way is to get a long length of the cable (I mean
electrically long at the frequency of interest) and then vary the
termination until you get the minimum reflected wave from the far end.
The termination that gives no reflected signal is the characteristic
impedance at that frequency. Easy to do at HF by sending a narrow pulse
down the cable and looking at the reflected pulse on a 'scope, but
essentially meaningless at audio frequencies as we never use cables long
enough for the characteristic impedance to affect things. The simple
'lumped' capacitance and inductance are all that is needed to determine
how a cable will affect the response. (Not allowing for other real
low-order effects like the piezo-electric effect, and with dielectric
absorption of course).
--
Chris Morriss