Have your say & ask the experts

At the risk of "teaching your grandmother to suck eggs”, speaker cable impedance consists of resistance, capacitance and inductance. When you put cables in parallel (as you have suggested in other posts to get the impedance down) you increase the capacitance, which has a direct effect on the sound (it will also cause instabilities in some amplifiers like Naim)

The sort of capacitance we are talking about here (500pF max) will have no effect on any well designed amplifier. I have encountered instability on a system when a strange cable with woven enamelled wires in a clear sleeve was being used (can't remember the make) but that's exceptional. Inductance would be very low too (maybe a few uH) so for speaker wires resistance more or less equates with inductance at audio frequencies.

Speaker cables are typically between 100-400 ohms. Isolda has a characteristic impedance of eight ohms!

 I don't know where on earth you get that idea from. Your grandmother? A speaker cable with an impedance of 400 ohms wouldn't really transfer any signal at all and one of 8 ohms would still sound awful. I would be looking at achieving an impedance of around 0.1 ohm maximum over the entire length.

Max Townshend strongly believes in Impedance matching

So what does that have to do with speaker cables? Nowt.

He'll believe in anything that helps to convince the credulous to part with their cash.

Do you not think its strange that Max takes this trouble to employ a standard electronic practice with his cable

It is a bit. Maybe he should forget such technicalities and concentrate more on making the outside as pretty as possible for the maximum "mug's eyeful" effect.
 

 

 I just read where you got your impedance info from.

What a hoot.:O)

http://www.townshendaudio.net/index.php?option=com_content&task=view&id=32&Itemid=86

This may be Wikipedia but it does at least explain the true position:

 http://en.wikipedia.org/wiki/Speaker_wire

 And a testing site:

http://www.provide.net/~djcarlst/abx_wire.htm

 

 
 

 
 

[quote user="oldphrt"]The sort of capacitance we are talking about here (500pF max) will have no effect on any well designed amplifier. I have encountered instability on a system when a strange cable with woven enamelled wires in a clear sleeve was being used (can't remember the make) but that's exceptional. Inductance would be very low too (maybe a few uH) so for speaker wires resistance more or less equates with inductance at audio frequencies.[/quote] For the given cap=500pF and Ind few uH how do you calculate an impedence 0.1 ohm ?

[quote user="Anton90125"][quote user="oldphrt"]The sort of capacitance we are talking about here (500pF max) will have no effect on any well designed amplifier. I have encountered instability on a system when a strange cable with woven enamelled wires in a clear sleeve was being used (can't remember the make) but that's exceptional. Inductance would be very low too (maybe a few uH) so for speaker wires resistance more or less equates with inductance at audio frequencies.[/quote] For the given cap=500pF and Ind few uH how do you calculate an impedence 0.1 ohm ?[/quote] 

 Because the inductance and capacitance values are negligible at audio frequencies the impedance of the cable is equal to the resistance.
 

[quote user="oldphrt"]Because the inductance and capacitance values are negligible at audio frequencies the impedance of the cable is equal to the resistance.[/quote] Mmmm... I copied this from another site:The Characteristic Impedance depends upon the ratio of the values of the capacitance per metre and inductance per metre. To understand its meaning, consider a very long run of cable that stretches away towards infinity from a signal source. The source transmits signals down the cable which vanish off into the distance. In order to carry energy, the signal must have both a non-zero current, and a non-zero potential. (i.e. both the E-field and the H-field must exist and propagate along, guided by the cable.) Since the far end is a long way away, the signals transmitted from the source can’t initially be influence by the properties of any destination before they finally arrive. Hence the ratio of the field carried along the cable (and hence the current/voltage ratio) are determined solely by properties of the cable. The result, when the signal power vanishes, never to be seen again, is that the cable behaves like a resistive load of an effective resistance set by the cable itself. This value is called the Characteristic Impedance, ImpedenceZ, of the cable. In general, for a loss-free cable, its value is given by equation : ImpedenceZ=Squareroot(Impedence/capacitance) Using your figures 500pF and a few uH say 3uF we get: 77 Ohms (ish).

[quote user="Anton90125"][quote user="oldphrt"]Because the inductance and capacitance values are negligible at audio frequencies the impedance of the cable is equal to the resistance.[/quote] Mmmm... I copied this from another site:The Characteristic Impedance depends upon the ratio of the values of the capacitance per metre and inductance per metre. To understand its meaning, consider a very long run of cable that stretches away towards infinity from a signal source. The source transmits signals down the cable which vanish off into the distance. In order to carry energy, the signal must have both a non-zero current, and a non-zero potential. (i.e. both the E-field and the H-field must exist and propagate along, guided by the cable.) Since the far end is a long way away, the signals transmitted from the source can’t initially be influence by the properties of any destination before they finally arrive. Hence the ratio of the field carried along the cable (and hence the current/voltage ratio) are determined solely by properties of the cable. The result, when the signal power vanishes, never to be seen again, is that the cable behaves like a resistive load of an effective resistance set by the cable itself. This value is called the Characteristic Impedance, ImpedenceZ, of the cable. In general, for a loss-free cable, its value is given by equation : ImpedenceZ=Squareroot(Impedence/capacitance) Using your figures 500pF and a few uH say 3uF we get: 77 Ohms (ish).[/quote] 

 

For gawds sake we are talking audio here, not RF. Say the cable measures 0.1 ohm dc resistance from end to end. With negligible capacitance and inductance at audio frequencies the cable will also have an impedance of 0.1 ohm from end to end. It's the end to end figure that matters and which needs to be minimized. Many speakers even quote the maximum recommended impedance of the cable in the spec.

[quote user="oldphrt"]For gawds sake we are talking audio here, not RF. Say the cable measures 0.1 ohm dc resistance from end to end. With negligible capacitance and inductance at audio frequencies the cable will also have an impedance of 0.1 ohm from end to end.[/quote] There is no frequency component in that equation so audio or RF is not an issue.

[quote user="Anton90125"][quote user="oldphrt"]For gawds sake we are talking audio here, not RF. Say the cable measures 0.1 ohm dc resistance from end to end. With negligible capacitance and inductance at audio frequencies the cable will also have an impedance of 0.1 ohm from end to end.[/quote] There is no frequency component in that equation so audio or RF is not an issue.[/quote] 

You're confusing parallel impedance with series impedance. The characteristic impedance of the cable is of no consequence on a speaker cable. Presumably Mr. Townshend quotes it to muddy the waters.
 

 Enjoying this, and wondering how long it will be before someone mentions The Amazing Randi...