Do speaker cables make any difference?

[planet10]

Originally posted by panomaniac
Changing the series resistance of the cable will not only affect the overall level - but it should affect the speaker Q- right?

Qe goes up.

dave

[macgyver10]

Originally posted by panomaniac
Changing the series resistance of the cable will not only affect the overall level - but it should affect the speaker Q- right?

It kind of depends where you want to place the speaker cable in the circuit. If you consider it part of the amplifier, then it lowers the damping factor of the amp (because you can now consider the output impedance to be greater than the amplifiers original design spec.)

However, if you consider it to be part of the speaker, then it will affect the Q of the speaker. In the end, it would essentially be the same result, but two different ways of approaching it.

[Johan Potgieter]

Originally posted by panomaniac
Changing the series resistance of the cable will not only affect the overall level - but it should affect the speaker Q- right?

That would sound different. But that should be easily imitated by a resistor in series with a low R cable.

Just mentioning this because there were a couple of posts talking about the minimal influence of 100 mili-ohm cables vs. higher R cables. The higher series R shouldn't affect a purely resistive load, but a reactive load would be another matter. Right?

Panomaniac and others,

The qualitive observation is correct. It is when one looks at the quantative picture that the real situation becomes clear.

The equivalent diagram of any output circuit contains the loudspeaker as a generator with its complex generation of V and I, with a total resistance loading that, of the amplifier output impedance, cable impedance and loudspeaker (voice coil) resistance all in series. If we take the amplifier output impedance as negligible (folks are always boasting high damping factors) - or, let us say, for a DF of 40, as 200 m.ohm. Normal domestic cable resistances are of the order of another 200 m.ohm maximum if one does not use bell wire. The loudspeaker voice coil resistance for an 8 ohm system is about 5,6 ohm minimum.

This gives a total of 6 ohm resistance in the circuit. (We will ignore the reactive part of that, not to complicate matters - such would make the following argument worst case.)

The effect of the cable resistance mentioned above would have a worst case influence of 3,5% or 0,29dB. Now if anyone can prove that this would make a significant or even audible difference at all, I would like to see that. This, disregarding the order of magnitude larger variation in normal loudspeakers' impedances over the audio range, which makes cable parameters even less significant.

What some of us have tried to show for a long time now, is that if things are negligible, they are ... well, negligible.

Regards

[Johan Potgieter]

Hi Quasi, (your post #885)

So Uriah Heep then. Thanks, a nice lyric.

Regards

[Pano]

Hey John- I think you're missing something. The added series resistance will attenuate the signal a little- but the main thing is that it will change the effective Qts.

That change in Qts will change the way the driver and the box behave. It will change F3 and it can change the frequency and size of any resonance peak in the box. It may have an effect on other things like pulse response, group delay, etc.

You should be able to hear those things - and much more easily than simple attenuation.

A 10 foot 24 gauge cable (Cat5 strand) will have a DCR of about 0.5 Ohms for both legs combined. A 12 gauge cable will have a DCR of about 0.064. That can do a lot to change the system Q.

However, if the same changes can be duplicated with a simple resistor in series, then who cares? Use the wire if the changes work for you, or a resistor, if you like. But remember attenuation is not the only change happening.

[Johan Potgieter]

Not to belabour this, Panomaniac -

but a cable series resistance of 0,064 ohms will affect the Q under 2% (24 gauge is a little thin for my liking). A system Q of 0,7 will become 0,714. You say this will have an audible effect, plus all the other things you mention? (No two loudspeakers of identical make are even this consistent.)

[Dumbass]

Lessee . . . viewed as part of the speaker, series resistance increases total resistance, but doesn't increase reactance (much).

Qe is ratio of resistance to reactance, so series resistance increases Qe, and therefore increases Qts.

Correct?

[anatech]

Hi Johan,

but a cable series resistance of 0,064 ohms will affect the Q under 2%

How about the change in voicecoil resistance as it heats up under power? That'll mess things up a little more maybe.

How dare I let the real world in here!!

-Chris

[Johan Potgieter]

Dumbass,

That is as I see it (but I have not had to do with this for over 2 years - still).

I understood from reputable loudspeaker manufacturers that characteristics of the same model loudspeaker can vary by up to 10% in production. The cable resistance quoted by Panomaniac will make a 1,14% difference. Then one disregarded amplifier output impedance, but which will also make a very small difference. (However, it is not constant in phase in many amplifiers, but let us not open that - it can be a can of snakes, not worms).

Anatech,
I would believe so. I am still not at home with my books and tables, but you could easily calculate the resistance increase. I understand that 100 degrees are not much for some drivers. The magnets can get hot.

Regards.

[macgyver10]

Originally posted by panomaniac
But remember attenuation is not the only change happening.

Panomaniac,

Can we assume, then, that the same changes to sound quality that we'd notice due to a change in Q of the speaker because of added series resistance (probably an amount less than the tolerances of DCR in inductors and drivers within the speaker itself), would be the same as what we would notice if we considered the series resistance to be part of the output impedance of the amplifier?

What I'm trying to get at, is what seems more significant: Lower damping factor due to the cable, or modified Q of the speaker due to the cable? It seems it can only be one or the other depending on what you consider "where the amplifier ends, and the speaker begins"....

I'd hazard to guess that it would seem less important if the DF of the amplifier was modified slightly, rather than considering that the speaker's Q has been changed? Would this, again, not be a case of the psychology of the matter, rather than the reality?