Speaker Cable Different for 8ohm vs 4ohm

Al, your voltage divider example does clear things up I think.

Let me just clarify one point, is the goal for Vin and Vout to be equal (ie in perfect world where the speaker cable would have no resistance or inductance) such that the voltage output by the amp (Vin) would be the same at driver (Vout)?

Thus in the real world as Z1 increases then for a given Vin the Z2/(Z1+Z2) ratio decreases and reduces the value of Vout.

Thanks

Hi Nick,

Yes to both questions. However, the most significant issue is not the voltage loss in itself, but the fact that the amount of the voltage loss will vary as a function of frequency, and thus it can affect tonal balance. While the Maggies that Stickman is asking about have a relatively flat impedance curve, as you no doubt realize the impedance of many speakers (Z2 in the equation) will vary widely over the audible frequency range. So even if Z1 is constant (i.e., a pure resistance), if Z1 is not small enough frequency response flatness may be affected to a perceptible degree. And Z1 can also vary as a function of frequency at least slightly, due to the effects of its inductive component at high frequencies. Also, excess resistance can degrade bass damping, especially for speakers having cone-type woofers.

That dependency of the effects of the cable on the impedance vs. frequency characteristics of the speaker is one example of why cable effects tend to be system dependent.

Regards,
-- Al

Al,

Where can I find an impedance curve graph for Magnepan 3.6's? I 'Googled' this but could not locate any graphs.

This page of Stereophile's review shows the impedance curves of the MG3.6/R.

Regards,
-- Al

As four ohm speakers go, Maggies usually have a fairly benign curve and are usually not that hard to drive.

All other things being equal, if you have a 4 ohm speaker and an 8 ohm speaker, you will always find the speaker cable to have a greater effect on the 4 ohm speaker.

About 25 years ago I saw a nomograph published by RCA (if I recall right) that showed the impedance of the speaker, the output impedance of the amp, DC resistance of the cable and the damping factor the amp is able to express (Crown publishes something similar in one of their amplifier manuals). What you see is that in 4 ohm speakers if the cable has DC resistance of more than a few 100ths of an ohm, that the effect on damping factor is rather profound- much more so than one would intuit.

Essentially with 4 ohm speakers the cable becomes critical and should never be long- in most cases less than 6 feet (bass impact and resolution can both suffer)! By contrast a cable for a 16 ohm speaker can by much longer and not be nearly as heavy with no worries. That's why a lot of us old-timers got away with using zip cord in the old days...