20 foot long speaker cable: is it ok?

A number of members here have reported good results using speaker cables in the area of 20 to 25 feet.  Also, generally speaking, the higher the impedance of the speaker the less sensitive it will be to speaker cable effects.  I found an impedance curve for the JBL speakers you indicated you will be getting, which shows that their impedance doesn't go below 5.5 ohms at any frequency, and is significantly higher than that at most frequencies.  So that seems encouraging.

Best regards,
-- Al  

I would respectfully disagree with an earlier comment in this thread by a member who appears to have subsequently deleted his post. In addition to the actual experiences with long speaker cables that have been reported by other members, such as Stereo5 above, I’m pretty certain that the Magico speakers used by the author of that deleted post have much lower impedances than the JBLs you will be getting. Most Magico speakers have nominal impedances of 4 ohms, and are closer to 3 ohms at many frequencies. That will significantly increase their sensitivity to cable effects compared to the impedance characteristics of the JBLs.

Regarding power cords, I have used two 13 foot lengths of 12 gauge Signal Cable Magic Power Digital Reference cords to power the two channels of a dual mono 70 watt class A tube amp, with fine results, even though that cord is nominally intended for use with digital components. I chose that model because I wanted the double shielding it provides, in part because the cords are routed near my phono stage.

The 215 watt class AB Kinki Studio solid state amplifier you are getting is a very different animal, of course, but I would still expect that cord to be a reasonable choice. Even if your amp were to be delivering full power on both channels at times, which is very unlikely considering the 94 db sensitivity of the speakers and your relatively small room size, the combined voltage drop of the two current-carrying conductors of a 12 gauge 12 foot power cord would be only around 1/4 of a volt. Probably less than the voltage of the incoming AC fluctuates between different times of the day and night.

Good luck!

-- Al

P.S: Speaker cable capacitance, that was mentioned in the post that was subsequently deleted, will not affect the speakers. Since it presents itself in parallel with the speakers if it affects anything it would be the amplifier. And in any event the 10 gauge Belden cable you indicated you would be ordering from BlueJeans has low capacitance (26 pf/foot). Many speaker cables have vastly higher capacitances.

It is the cable’s inductance and resistance that are presented in series with a speaker, and can sometimes affect the sonics of the speaker. But as I mentioned those effects are likely to be negligible for a 20 foot length in the case of a speaker having the impedance characteristics of your forthcoming JBLs.

Best regards,
-- Al

@Cakyol

If you perform some quantitative calculations regarding speaker cable capacitance, such as I describe below, I think you will conclude that what I said is correct.

The high frequency rolloff you refer to results from the low pass filter formed by the combination of the capacitance of the cable and the output impedance of whatever is driving the cable. The bandwidth of that filter, defined as the frequency at which 3 db of rolloff has occurred, is:

3 db bandwidth = 1/(2 x pi x R x C)

If R is specified in ohms and C in farads, the calculated frequency will be in Hz.
Since the output impedance of a power amplifier is very small, the resulting rolloff will occur at a frequency that is so high as to be totally insignificant in the case of an analog audio signal, under any reasonable circumstances.

For example, a 20 foot length of the cable the OP is considering has a total capacitance of 520 pf. The Kinki-Studio amp the OP is obtaining has a specified damping factor of 2000, so its output impedance is approximately 8/2000 = 0.004 ohms. But let’s assume a MUCH worse situation than that, say 2000 pf and 1 ohm. Even in that case , which is vastly more extreme than the OP’s, the 3 db bandwidth calculates to 79.6 MHz. In other words, it is high enough to be totally irrelevant to analog audio signals.

On the other hand, as I had mentioned, the inductance and resistance of a speaker cable might have some significance in certain situations, especially if the impedance of the speaker is very low at some frequencies.

In contrast, in the case of a line-level analog interconnect the fact that the cable may be driven in some cases via output impedances of hundreds or even thousands of ohms can sometimes result in the effect you referred to being significant. While in that case inductance and resistance are unlikely to be significant. The impedances presented by inductance ("inductive reactance") and resistance are presented in series with the input impedance of the destination component, and that input impedance is almost invariably vastly higher than the resistance and the inductive reactance of a line-level interconnect at relevant frequencies, even if the cable is particularly long.

It is also true, as I mentioned, that if a speaker cable has extremely high capacitance it can adversely affect the performance of the amplifier, depending in part on the gain, feedback, and bandwidth of the amp. Effects such as overshoot, ringing, oscillations, and on rare occasions even damage have been known to occur when some amps are used in conjunction with speaker cables having ultra-high capacitance.

Regards,
-- Al