# Very specific Bi-wiring question.

Discussion in 'Archived Threads 2001-2004' started by Philip Hamm, Mar 22, 2002.

1. ### Philip Hamm Lead Actor

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Saurav wrote in this closed thread

2. ### brucek Second Unit

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Philip & Saurav,

I agree with Saurav's quote except that the effect from capacitance in speaker cables is so small it can be ignored. I think he must have meant inductance. A speaker interface is a low impedance connection. Capacitance is only a concern in interconnects, which is a high impedance connection.

The loss from parallel capacitive reactance in a low impedance interface isn't even worth deriving because it's so insignificant.

The output impedance of a typical amplifier is around .02 ohms connecting usually to a load of about 8 ohms. This is a very low impedance circuit where the amplifier acts as a voltage source. Unlike inductance, capacitance provides us with a "parallel" reactance. This frequency dependant resistance is "across" or in parallel with the load. The load is 8 ohms. A typical parallel load that the capacitance of zip cable provides is many, many orders higher than 8 ohms. It's in the thousands of ohms. If you want to do the math - go ahead. It's not significant enough to even talk about. If we were discussing interconnects, of course the opposite is true, because it is a high impedance connection.

Inductance though, is quite significant in a speaker circuit because it provides a series reactance that can be an appreciable portion of the 8 ohms that the speaker provides. This acts as a low pass filter and will indeed roll off high frequencies.

As far as bi-wiring is concerned, there is simply no scientific support (other than anecdotal evidence) for using bi-wiring.

I'm afraid as far as bi-wiring is concerned, you'd probably be better off using bi-wire cables with your speaker straps reinstalled. At least then you'd take advantage of the lower gauge realized by combining two cables to each speaker. It would certainly help the LF drivers damping path to ground through the amplifier.

I've read all the explainations of bi-wire and they all are meaningless when you apply the superposition theorem and know that all those signals can co-exist on a single wire quite nicely without interfering with each other. If you like bi-wire, then use it, no harm done......It's ineffective, others will disagree.

Speaker cable length and phase differences? Forget about it. Yes, electricity does travel near the speed of light in a wire depending on the wires velocity factor, but that's not important here. This speed is approximated to about a nanosecond a foot. The accepted explaination would be that if you had one speaker wire 50 feet longer than the other, then that signal would arrive about 50 nanoseconds later than the other. Well, this is about 1000 less than human hearing can even begin to detect, so don't worry about the lengths of your cables and phase differences.

brucek

3. ### Saurav Cinematographer

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Phil,
I just realized today that I have private messages on this forum I know this one is almost a year old, but I'll respond anyway
Biwiring - I don't have an opinion on it.
And I think Bruce is right, capacitance shouldn't be a big factor in a low impedance situation, so it's the inductance that one should be concrned with. Thanks for correcting that statement, Bruce.

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