Debunking the Myth of Speaker Cable Resonance

It has recently come to my attention that some exotic cable vendors (Transparent Cable immediately comes to mind) and esoteric audio magazines (Stereophile comes to mind) claim that speaker cables exhibit electrical resonance at audio frequencies and that the RLC nature of the cable drastically changes at these frequencies causing the alleged cable resonance. I believe this claim was fabricated either because of a lack of understanding of basic principles of electronics, or an attempt to initiate a false scare tactic to rationalize how an exotic cable vendor can justify slapping an RLC network on the cable and charge consumers high asking prices.

Let's model a speaker cable using a single RLC lumped element analysis.

• Rdc -Commonly referred to DCR which is the series resistance of a cable at zero frequency.
• Rac - The resistive portion of the cables series resistance as a function of frequency due to skin effect.
• Rs - Total Series Resistance (milliohms) measured tip to tip at one end of the cable while the other end is shorted. Note: Rs = Rac + Rdc (minus instrumentation slight inaccuracies)
• Ls - Series Inductance (uH) measured tip to tip at one end of the cable while the other end is shorted.
• Cp - Parallel Capacitance (pF) measured tip to tip at one end of the cable while the other end is open circuited.

Many exotic cable vendors enjoy promoting the fallacy that their audio cables eliminate electrical resonance at audio frequencies. The reality is unless the cable is so deliberately poorly designed with added passive elements, it will not resonate at all until frequencies exceed human audibility by well over a decade, and usually in MHz region, as can be seen below.

Thus cable resonance is a function of cable inductance and capacitance!

To demonstrate an excessive and uncommon case for an esoteric set-up, we shall apply our calculations for a 50ft length of a cable we reviewed in Speaker Cable Face Off I.

Most high end set-ups keep cable lengths to a minimum (usually 12ft or less) else how could one afford such expensive cabling? (also, every audiophile knows the shorter the cable, the better!) However, let's do a non typical worse case analysis to determine if there is any validity to the electrical cable resonance claim set forth by some exotic cable vendors and supported by subjective reviewers of some esoteric audio publications.

Cable Resonance for 50ft length of 10AWG Cobalt Cable

Hmm, the Stereophile Reviewer Wes Phillips claimed that audio cables resonate at around 1.5 kHz. The basic laws of Electronics and Physics seem to dictate otherwise. Here we see an ordinary 10AWG Zip Cord cable of 50ft length NOT resonating until 2.02 MHz, which is over two decades past human audibility. In fact, if we re-evaluate cable resonance for a typical cable length of 12ft in a high performance audio system, we find the cable resonance gets pushed up to 8.5 MHz!

In reality cables DO NOT resonate at all! The model represented here is single RLC lumped circuit for simplicity and is only accurate at audio frequencies for circuit analysis. A speaker cable is actually a distributed element and should be represented as infinite number of lumped RLC models. As an infinite number of lumped RLC circuits are modeled becoming its true distributed form factor, we see the resonance frequency go to infinity.

In addition, once we approach much higher frequencies such as in the RF region we must re-evaluate the cable as a transmission line. In that respect the characteristic impedance becomes the SQRT (L/C) =SQRT(8.8*10^-6/700*10^-12) = 112 ohms. So if our source and load terminations at transmission line frequencies (1/6th the wavelength) do not match, we see reflections in the line, which can appear like a resonance behavior, but in reality are simply reflections or power loss down the line.

Also note that when an exotic cable vendor claims Inductance, Capacitance and Resistance dramatically varies within the audio band, that this is more total and utter nonsense as can be seen in the following real world measurements on the same 10AWG Cobalt Cables.

Note: Null Measurement below 100Hz. Notice how steady inductance is in the audio band.

Note: Null Measurement below 100Hz. Notice the relatively stead measurement of AC Resistance in the audio band with a meager 0.44 milliohms increase in resistance due to skin effect .

Note: Null Measurement below 100Hz. Again cable capacitance is rather uniform. The slight downward trend by a meager 0.7pF at the threshold of human audibility is an instrumentation error. The more accurate measurement of capacitance of a speaker cable is at lower frequencies since the inductance of the cable is not masking the measurement.

Conclusion

Claims of speaker cable resonating at audio frequencies, or drastic changes in RLC properties at these frequencies are both false and unwarranted. So much so, that these two points are worthy of adding to our Top Ten Signs a Cable vendor is Selling You Snake Oil. Next time an exotic cable vendor, retailer, or audio publication claims otherwise, tell them you know better and be sure to point them to this article.