Editor’s Note: This article was written for PSW/LSI at least a decade ago, but it provides a great deal of “evergreen” information that’s still just as relevant today. Enjoy.
Too many good folks have been separated from their hard-earned money by hyperbolic claims about loudspeaker cable. There will always be people with more dollars than sense, but they don’t last very long in professional audio. I speculate there aren’t many (if any) of you who would pay thousands, or even tens of dollars per foot for it.
A very basic practice in merchandising is called differentiation. Marketers must come up with reasons for why you should buy their wire. To claim that their wire is better, they must first identify, in some cases invent, a difference. This search for a selling proposition has sometimes focused on “skin effect.” It’s a real effect and describes how at very high frequencies, electrons travel in the outer layer or “skin” of signal conductors.
Another related property is that high-frequency signals travel faster than low frequency signals through the same cable. These phenomena are dealt with appropriately in very high frequency applications with several techniques. “Litz” wire is made up of a large number of very small conductors braided or woven into one cable, producing a large surface area or “skin” for a given cross sectional area.
Another approach for high-power, high-frequency power transfer is to use a hollow conductor, resembling a section of copper tubing. If the electrons are going to ignore the center of the conductor, why pay for it?
This is not an issue for audio professionals, working at mere audio frequencies of 20 Hz to 20 kHz. Perhaps it would be if we were sending audio over many miles, like the telephone company in its pre-digital days. They had to periodically correct for waveform smear. But at the speed that electricity travels, our typical path distances are much too short to be an issue.
Out Of Perspective
Cable is not very sexy or easy to create real marketing hooks for, but it can actually make an audible difference. The dominant mechanism is simple resistance. It’s perhaps ironic that the “snake oil” markers of loudspeaker wire will exaggerate some real but insignificant parameter far out of perspective while compromising the real deal.
Forget the hype, what’s important is that it exhibit low impedance that is resistive in nature. If the wire has a significant impedance component (reactance) that changes over the audio frequency spectrum, this can form a simple divider with the loudspeaker’s resistive impedance and cause a frequency response error.
In addition, since loudspeaker impedance will vary quite a bit over frequency, even a perfectly resistive speaker wire will cause errors. The magnitude of this frequency response error will increase proportionately as the wire’s resistance increases.
Purveyors of “funny wire” don’t bother to make claims about useful metrics like resistance since that is already defined by the wire size or gauge (known as “American Wire Gauge” or AWG for short). That would be like advertising how many quarts were in their gallons! However, frequency response errors caused by wire resistance are one of the very real things that people actually do hear.
I find this following anecdote instructive. From a discussion with one individual who was certain that he heard a significant improvement when using his “Snake-O Special” loudspeaker cable (name changed because I don’t remember it), I determined that the gauge he was using was marginal for the length of his run. The wideband loss of volume caused by a wire’s resistance will be very difficult to hear without a side-by-side comparison.
But the difference in amount of loss caused by the loudspeaker’s changing impedance at different frequencies can easily cause a frequency response error, which is probably what he heard. It’s easy to imagine how a rising impedance at high frequency could cause a pleasant-sounding treble boost. Just listen to how clean and clear these “Snake-O Specials” sound!
There are several strategies to manage these real losses from wire resistance. The obvious one is to throw more copper at the problem. Heavier gauge wire with lower resistance will exhibit lower losses for a given run length. Another fairly obvious approach is to locate the amplifiers as close as possible to the loudspeakers to keep the run length as short as possible. A third less obvious approach is to scale up the intermediate signal voltages.
There are cases, such as in large distributed sound systems, where neither of the first two approaches is cost effective. You can’t afford to put a separate amplifier at every loudspeaker location and sending sound sources over long distances with acceptable losses would require very heavy gauge wire. The solution borrows a strategy from high-voltage power distribution systems such as the one used by utilities to bring electrical power to our homes.
The power developed within a given load increases with the square of the terminal voltage (E^2/R). However, wire’s losses only increase linearly with current flow, because the voltage developed across the wire is a simple function of its resistance times that current. Power engineers determined that by raising the voltage carried by transmission lines they could increase the power being carried exponentially while simultaneously reducing the losses due to current flow.
The utility company accomplishes this magic with step-up/step-down transformers. By “transforming” a typical 100-amp at 240 volts residential service, up to tens of thousands of volts at the transmission line the 100-amp draw is reduced to the far more manageable level of 1 amp or so. Wire losses are 1 percent of what they would otherwise be.
Similar manipulations go on in “constant voltage” distributed sound systems but rather than stepping up the voltage to thousands of volts the standard for U.S. systems is 70-volt, with Europe using a slightly higher 100-volt standard. The rest of the world tries to conform to one of those two standards.
Of course, the audio signal isn’t actually held constant. The voltage at rated power is. Both 5 watts and 500 watts constant voltage systems deliver the same nominal voltage for distribution.
The goal in any effective distribution system is to deliver as much power as possible to do useful work in the load and waste as little as possible heating up the wire. In a simple distributed sound system, sending a few watts of announcements across a few hundred feet of factory floor, the typical low-voltage system could drop as much power in the wire as would reach the loudspeakers. By stepping up to 70 volts and back down again at each loudspeaker, the balance of power delivered versus lost is more respectable.
To put numbers to this concept, say we are trying to deliver 1 watt each to two loudspeakers located 100 feet distant from an amplifier using 24 AWG (American wire gauge or just gauge) wire. Because we must count wire losses from the feed coming and going, 200 feet total of 24 AWG exhibits resistance of approximately 5 ohms.
To realize 1 watt at each loudspeaker, there would need to be more than 4 watts into the wire at the amplifier end. (Over 2 watts gets wasted as heat in the wire). If we first step up the audio to a nominal 70-volt level the current drops to such a low level that the same wire would only waste 0.14 watts while delivering the same 1 watt each to the two loudspeakers. (See Figure 1)
As useful as constant (high) voltage systems are for managing wire losses, they don’t make sense for point-to-point runs in sound reinforcement systems. The main drawback is the size of the step-up and step-down transformers required. To put this in perspective, the size of the transformer has to double every time you drop the frequency an octave. To cleanly pass 20 Hz both step-up and step-down audio transformers would have to be three times the size of a conventional amplifier’s 60 Hz power supply transformer.