Why Speaker Cables Are More Than You Think They Are
by Roger Skoff
What the heck is a "damping factor," and who cares?
Every audiophile has heard the term "damping factor," and most know that it has something to do with power amplifiers or with the amplifier section of a receiver. How many of us, though, actually know what a damping factor is or why it's important?
Here's a clue: "Dampness" has nothing to do with it.
The "damping factor" of an amplifier is the number that indicates how well it can control ("damp out") unwanted movement of a loudspeaker diaphragm, and the bigger that number is, the better.
One of the problems with speakers is that the moving part (the "diaphragm") of all loudspeaker drivers, even ribbons, electrostatics, and other "planars", has mass, and that mass, once it starts moving, wants to keep on moving, even after the force driving it stops. That is one of the aspects of the phenomenon we call "inertia" ("the tendency of a moving object to stay moving and an object at rest to stay at rest"), and it can have a profound effect on the sound of your system.
The greater the mass of the diaphragm (the "cone", for most speakers) and the more or farther that mass is moving, the greater the inertia that has to be overcome in accelerating and decelerating it to follow (and only follow) the signal fed to it by the amplifier. Because the biggest (most massive) drivers in a speaker system are its woofers, and because bass signals require the most cone movement to produce, bass response is the thing most affected by an amplifier's damping factor.
To calculate your amplifiers damping factor (at least as it is given on amplifier spec' sheets) is easy: Just divide 8 Ohms, the nominal "standard" loudspeaker impedance, by the stated output impedance of your amplifier. If the amplifier's stated output impedance is .01 Ohm, it has a damping factor of 800 (8 divided by .01 = 800), which is very good but not exceptional for a solid-state amplifier. (Tube amplifiers tend to have higher output impedances, and therefore lower damping factors)
In reality, though, the calculation method just given overlooks two very important facts: First, not all or presently even most loudspeakers have nominal impedances of 8 Ohms. Second, and even more importantly, no true calculation of amplifier damping factor can be complete without including the speaker cable into the equation
Three elements are involved in driving a speaker; the speaker itself, the speaker cable, and the amplifier. In calculating an amplifier's actual damping factor, all of them must be considered.
What makes it interesting is that the three elements act as if they were just two, and, surprisingly, those two are not what you might think: Instead of the loudspeaker and the cable being one element and the amplifier being the other, in reality it's the loudspeaker that stands alone, and the combination of the speaker cable and the amplifier is the other element.
To understand how this can affect the amplifier's true damping factor, and, ultimately, the sound of the entire System, consider this: The resistance (not the impedance, but just the measured DC resistance) of a 10 foot run of a typical cheap 24 gauge "speaker cable" is about .51 Ohms. If we add this to the .01 Ohm output impedance of the amplifier I mentioned earlier, we come up with an effective output impedance of .52 Ohms. If we then divide this into the "standard" speaker impedance of 8 Ohms, we get a true damping factor of only 15.4, instead of the 800 shown on the amplifier's spec sheet. To make things even worse, if we're using a speaker's with a nominal impedance of 4 Ohms, instead of the "standard" of 8 Ohms, the true damping factor is reduced even more -- to just 7.7. (4 divided by .52 = 7.7)
This is a fine example of why using cheap or bad speaker cable can make a speaker's bass sound "flabby" or uncontrolled... it actually is uncontrolled.
By contrast, a 10 foot run of one quality high end 10AWG gauge cable can have a total resistance of just .02 Ohm. Adding this to the amplifier's output impedance of .01 Ohm gives a total of only .03 Ohms, which, divided into the 8 Ohm standard speaker impedance gives a true damping factor of 267 -- better than 17 times the speaker control available from the lesser cable. That's one of the key reasons why high end speaker cables sound better.
About Roger Skoff
Roger Skoff is the founder of XLO Cables. The company was sold in 2002. Roger is not currently affiliated with any audiophile companies directly but is still passionate about the hobby of audiophilia.