Propeller Head Plaza

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You're missing the point

Posted by Presto on February 2, 2011 at 12:39:35:
Ideal cables have zero impedance, but in real life have a small inductance, a very small capacitance and relatively higher (yet still very small) series resistance.

Ideal inductors are pure inductive reactance, but with them it's DC resistance that is the culprit.

The trick to understanding inductors is that current in AC system does not flow. Electrons migrate back and forth, depending on the frequency of the waveform. Unless there is a significant DC offset to the signal, electrons don't flow at all in AC circuits. They sort of jiggle back and forth - this is an oversimplification, of course, of what is really happening at the atomic level. The free electrons in metal move en-masse, like a long line of marbles moving to and fro in a tube. Except they move back and forth - not continually in one direction as with DC current.

SO! Why is the 'inductor sold wire justifies cheap speaker cable' a myth? It has to do with the two devices having different function, and being located in different places in the circuit. An inductor is DESIGNED to have increasingly higher AC impedance (not DC resistance) as frequency goes up. DC resistance is not affected by frequency - only reactive components, like inductors or capacitors are. This is why it is used in series in a lowpass filter and in parallel (as a shunt) in a high-pass filter. It passes lows (in series) and shunts lows (in parallel). Either way, lows go through, mids go though less and highs go through even less. But as long as the designer sizes the inductor correctly to get the desired corner frequency, and has either made the inductor large enough to limit DCR or has incorporated the DCR into the crossover design (which is very commmon), this is not an issue. However, putting a significant series resistance BEFORE a network/driver combo CAN be a bad thing. But you'd need a silly amount of series resistance (in the ohms or at least tenths of ohms) to make even a slight difference. Even in bi-amping, with very low resistance cables, even different cables have virtually no effect on the how the low and high-pass filters operate. (There was a long thread about this in the Speaker Asylum - search for bi-amping there).

So - I do agree that very high-buck cables are not really necessary, but some things ARE necessary. You need good clean copper at electrical connections and good mechanical connections between wire, crimp-on parts, binding posts etc. You need a certain amount of copper depending on the amount of power you're using and the length of the wires. Although there are "scientific" battles about self-inductance, capacitance, there are a few things that are generally agreed upon.

1. High resistance cables decrease low frequency damping factor. This is bad. Google this to find out more about what damping factor is and why it's important.

2. High capacitance (silly high) can cause certain amp designs to go into high-frequency oscillation. Again, this topic is well represented here and the search feature is your friend.

BUT (big but) the use of inductors with 16 gauge wire does not mean you should go out and buy 16 gauge solid wire or use coat hangers for speaker cable. Speaker cables are supposed to be a pathway to move signal at all frequencies. Inductors are supposed to move signal less and less as frequency goes up.

So, in that light, the use of inductors and their various gauge sizes and solid wire construction has nothing to do with speaker cable size and quality. Just like it has nothing to do with the hair-like wire used for a loudspeaker voice coil. A speaker wire has a series resistance that is a few millo-ohms. An inductor can be anywhere from a tenth of an ohm to a few ohms. Speakers are 4 or 8 ohms nominal with impedance bumps of 50 ohms or more.

Speaker drivers, inductors, and speaker cables all have wire in them, but they all serve different functions electrically and thus the attributes of the wire used in one has really nothing to do with the attributes of the wire used in another.

"Inductors mean I can use coathangers or 100' of house wire for speakers."

Dude, myth busted.

You can use 24 gauge hook up wire in a twisted/unshielded pair for your speakers and not change the transfer function of your crossovers all that much. You can even run + and - in separate runs and raise the inductance a whole bunch. But the biggest drawback is the fact your going to reduce the effective damping factor of your amp to astonishingly low levels.

If your amp had a less-than-great damping factor to begin with, you really don't want to be doing this, especially if your speakers are capable of really low frequency reproduction and you want it to remain fidel.

Cheers,
Presto