MadSci Network: Engineering

Re: Please explain bi-wiring and after market power cords for home audio...

Date: Thu Nov 2 04:03:20 2000
Posted By: Bruno Putzeys, Staff, Electrpacoustics and Analog Electronics, Philips ITCL
Area of science: Engineering
ID: 972681912.Eg

Hi again,

The "power cords question" is a simple one that doesn't need any 
scientific skills to debunk. Suppose one wants to use some special cable 
($$$ per meter) to get the power from the wall into one's equipment, 
shouldn't one be concerned about the other 100m of "normal cord" to the 
electricity cabin and the 200km of high-voltage distribution?

Technically (and stretching the argument a bit), there could be a 
difference between a shielded and a non-shielded cable if any of your 
equipment happens to cause a immense lot of electromagnetic interference 
along the power inlet. By shielding the cable for the first few meters you 
could keep the resulting radiation from entering other devices. Ergo: if a 
power cord should make any difference to equipment's performance, the 
equipment manufacturer has done an extremely lousy job...

About biwiring: This is not placing cables in parallel, far from it. When 
loudspeakers have two sets of terminals, one set is for the woofer and 
associated crossover, the other set is for (midrange and) tweeter, again 
with their part of the crossover filter. If you connect with one cable, 
the voltage drop across the cable's resistance caused by the current 
through the mid+hi section will appear as input to the woofer section and 
vice versa. If the crossover filter has been designed with this in mind, 
no problem. If on the other hand the crossover was designed with the 
assumption that the source impedance to the loudspeaker is zero, 
eliminating this "common leg coupling" by using biwiring is necessary to 
make the speaker perform as intended.
This means that biwiring is not a surefire recipe for improving sound 
quality. Sometimes (i.e. when the loudspeakers were optimised with one 
cable) biwiring will actually give less optimal sound quality. In any case 
the difference is readily explainable using basic electronics.



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