The resistance, capacitance and inductance of the sort of cables under discussion will have zilch affect as the values of this stray stuff is so small. The values of the components that make the speaker will change by a much more significant amount during warm up - yes the speaker and its crossover will heat up and their values drift.
However some amplifiers e.g early Naim are affected by these small values. Transistor amps employ emitter followers in their output stages and these are unstable and tend to oscillate in the UHF. To counter this a Zobel network is placed at the output that connects to the speaker. Naim thought they were being 'clever' and removed a critical component from the Zobel network a series inductor of around 5μH. So with a 'normal' speaker cable the output stage would oscillate in the UHF and heat up and might actually burn out. This loss of power to UHF may cause distorted output.
Now the 'clever' bit. Naim used the inductance of the speaker cable to replace that missing in the Zobel network and this in effect from the amps perspective means that the speaker is not 3.5m or so away but rather connected directly i.e. the speaker cable 'disappeared'. Before the NACA4 became available Naim used to advise something like RS components 79 strand wire loosely twisted (3 turns per meter) to give the necessary inductance.
Cheers,
DV
I'm afraid much of that is quite wrong...
It's all down to NFB (Negative Feedback, the most important "thing" in amplification and largely ignored by non technical people).
Emitter followers are not used in all SS amplifiers and the instability you mention is a negative resistance oscillation that can happen in certain conditions only and is not really any issue in audio power amplifiers. It is also a local to the actual follower phenomena and not global, plus in the case of output transistors if it were to happen it would be very much lower in frequency than UHF! As I say it's not an issue though and even if it were, in the case of Naim amps they are quasi-complementary and so the "push" and "pull" halves of the output stage are not the same... one is an emitter follower and one is common emitter.
The network you mention is not actually a Zobel network... although it is often misnamed as such! A Zobel network consists of a resistor and capacitor in series and in the case of an audio power amp goes from the output to ground. Naim amps DO have these. The network in line at the output (not used in Naim and quite a few other amps) is usually an inductor of a few uH with a damping resistor in parallel, it is sometimes known as a Thiele Network (yes as in Thiele-Small parameters) but this appellation is not widely used and it is usually not referred to by any name... or wrongly called a Zobel Network!
The purpose of the Thiele network is to prevent the load, including cable capacitance, from affecting the NFB loop parameters in such a way as to cause oscillation (instability) and ringing due to "gain peaking" as the point of instability is approached. This network can actually ring separately from any NFB issues though (L-C resonance) hence the damping resistor as a part of it...
The Zobel Network has more to do with keeping the amp stable without a load and/or with a load of rising impedance with frequency but is much less relevant to this discussion.
Now primarily the effect of this Thiele Network is that it's inductance causes rising impedance with frequency so as to partially isolate the feedback point at the output of the amplifier from capacitive loading. It should be understood that we are generally talking in terms of frequencies well above human hearing when considering all these effects.
The beauty of the Thiele network is that at low frequencies it has very low resistance and so has negligible effect on speaker control and damping factor but as frequency rises its AC impedance starts to come into play and it provides the required isolation at high frequencies.
Now Naim and several other companies (for certain models anyway) don't use a Thiele Network but put a resistor at the output to give the required isolation... and in Naim's case still get it wrong as there is insufficient isolation for the characteristics of the NFB used!
The only advantage of using a resistor here is that it can give some
reverse isolation from the back EMF of speakers coming into the amplifiers NFB network via its output. Disadvantages are that it adds to the resistance in line with the speaker and reduces damping factor. In Naim's case the resistor is 0.22Ohm which is about the biggest resistance found in such an application and on its own limits damping factor to 18 with a 4 Ohm speaker...
In the case of Naim amps it is simply very bad engineering that the 0.22 resistor on its own is not enough isolation to guarantee stability with all cables and loads. There are no advantages in things being as they are and it does not in any way shape or form "remove the speaker cable" between amp and speaker. The only amps that make any attempt to do this that I know of were the Trio/Kenwood "Sigma Drive" models and some later models from DPA that did the same thing. They both worked by having extra cores to the speaker cables to allow the NFB to be derived from the speaker terminals directly and hence the NFB theoretically compensates for the speaker cable.
In the Avondale amps, which are closely related to the Naim circuitry and in effect a reworking of them to remove the more glaring faults, a Thiele Network IS used and the resistor removed... jobs a gud 'n.
The only reason I can think of as to why Naim have never corrected this glaring engineering error is that it has become a part of "Naim lore" and to many non technical people possibly looks like the unit is "so special", "such a thoroughbred" that it needs "special cable"
A corollary to all this is that in the case of low or no NFB amps often no Thiele Network or resistor is required as the feedback is low/non existent and so it can't be "messed with" by the load/cable to cause any instability.
