Speaker Cable Length Differences: Do They Matter?
More often than not, I see the common question pop up in our forums regarding speaker cable length differences between two or more speakers. Folks often wonder if the cable length between the main front channels need to be identical or close to identical. They are often misinformed by exotic cable vendors or cable forum cult hobbyists that cable lengths need to be kept identical to a void amplitude or phase/time delay differences between the two. They often go one step further and misapply transmission line relevancy at audio frequencies.
In our article on Debunking the Myth of Dielectric Absorption in Cables we learned that even conservatively considering transmission line effects on cables up to 100kHz ( 5 times the audio bandwidth ) with 1/10 wave approximation, it would take a cable of over 500 feet to become relevant! At that point, the RLC losses alone of a typical 12AWG zip cord cable would attribute to over 11dB of attenuation of the upper frequencies, not to mention over 3dB of insertion loss!
So what does matter in speaker cables? The RLC losses do. Below is a basic lumped model for one foot of speaker cable.
Cable Metric Definitions
- 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 (mohms) measured tip to tip at one end of the cable while the other end is shorted. Note: Rs = Rac + Rdc (minus instrumentation inaccuracies identified below)
- Ls - Series Inductance (uH) measured tip to tip at one end of the cable while the other end is shorted. Check out our article on Cable Inductance for more info.
- Cp - Parallel Capacitance (pF) measured tip to tip at one end of the cable while the other end is open circuited.
- G - G represents conductance ( 1 / Rdielectric). The major relevancy roles of the dielectric in this application are to serve as isolation between the two conductors and control the capacitance of the cable based on the conductor spacing and dielectric constant.
The typical 12AWG zip cord has about 3.4 mohms of loop resistance per foot, .200uH/ft of Inductance and about 20pF/ft of capacitance. As the cable length increases, these three parameters increase proportionally. However, it takes very long lengths of cable to cause measurable, let alone audible differences. If we examine the data from our various Speaker Cable Face Off articles, particularly Speaker Cable Face Off I, we see that a 10ft length of 12AWG zip cord terminated into a 4 ohm load only experiences -.088dB of loss at 20kHz and about 2nsec of group delay. Increase the cable length to about 50ft and we do see losses surmount to about -.745dB and 209nsec. Note that at 20 kHz, a phase shift of 36 degrees represents 5 microseconds (almost 24 times larger than our 50ft cable delay), this delay being considered as close to the limit of human directionality perception. Further examining the data from our article Skin Effect Relevance in Speaker Cables we illustrated that model for human hearing is highly insensitive to ultra high frequency response and also discussed that music above 8kHz is harmonic in nature with minimal content at the high frequency extremes. It is a good idea however to use lower gauge wire (10 AWG or less) for runs greater than 50ft to minimize these losses especially when driving loudspeakers with a low impedance (4 ohms or less) profile.
Editorial Note by Audioholics Staff
"Note that at 20 kHz, a phase shift of 36 degrees represents 5 microseconds (almost 24 times larger than our 50ft cable delay), this delay being considered as close to the limit of human directionality perception."
This sentence highlights one of the main problems with the non sequitor "logic" seen on so many audio websites and magazine publications. A 20KHz harmonic note (because that's what it is) represents the 5th harmonic of the highest fundamental frequency on a concert grand piano, 4,156Hz. Frequencies in this lofty realm can be heard by a very young, small percentage of the world's population. Typically this frequency will be over 20dB down from the fundamental which means that relatively close proximity to the reproducing system in a very quiet acoustical environment is required to hear these frequencies by the select few who have the capability.
A 5 microsecond delay has only been detected with any degree of certainty, under controlled laboratory conditions, within the approximate 3500Hz region where the ear is most sensitive. Again this detection must be in an extremely quiet environment, certainly below NC20, almost anechoic in fact.
The reality here is that the beginning statement, though it may be technically true, is ludicrous by nature of its construction which may and I fear does lead most of the hangers-on of such debates toward yet another thread of hopefulness in their trivial cable pursuits. We know what constitutes a "good" cable for any given length based on their associated lumped RLC parameters and construction defined in many articles on this very website. All that's left now for the reader should be to simply read our cable reviews over the past decade and buy the cables that measure within those parameters which are priced at a level of affordability-to-quality-of-construction that makes sense. Done deal.
It seems ironic that with all of the advances in digital room equalization and passive room treatments, which literally transforms the listening experience on a monumental scale, to comment on such trivia matters as cables. But the fact that such controversy continues among those who would like to identify themselves the audio cognoscenti serves only to illustrate, to us at least, that we've got a long way to go in understanding and putting into proper significance the percentage importance of cable (which is miniscule) to that of the speaker/room interaction conundrum as experienced at the listening seat, the only place any of this matters.
There are NO reasons why cable lengths between pair channels (ie. Main Left, Main Right, Rear Left, Rear Right, etc) need to be kept identical, but avoiding a ratio greater than 4:1 of identical wire gauge is good measure for minimizing RLC losses which can affect system damping factor and attribute to frequency response variations. If cable runs need to be much longer, selecting a cable of lower gauge is advised provided that the geometry and conductor spacing is conducive of keeping Inductance (recommended < .200uH/ft) and Capacitance (recommended < 50pF/ft) in check.
Note, simply moving from 12AWG cable to 10AWG cable of similar design reduces resistance by 30% which effectively makes a 50ft 12AWG zip cord cable look like 35ft (assuming all other things equal).
As a rule of thumb, we always recommend keeping cable lengths as minimal as possible, but not too short that it compromises accessibility to equipment. Follow our Cable Budget Guidelines when selecting the right cables for your applications. Avoid the typical Cable Snake Oil often purported by exotic cable vendors as gospel truths.
The bottom line is the resistive losses are far more a dominant factor to consider when choosing loudspeaker cables. The associated electrical delay of a "long" cable vs a "short" cable is simply not a real issue to concern yourself with.
Recommended Reading: Speaker Cable Lengths vs Gauge Guidelines
And always remember our motto “only poorly designed cables are sonically distinguishable”.