Short signal paths? What short signal paths?

[petercom]

In reply to Ianm2 and others in the crossover debate, I thought it might be pertinent to continue this discussion in a dedicated thread.

I doubt that you should consider the length of wire in a transformer as strictly being 'in the signal path'. The trouble with electromagnetism is that we are working with things we really don't fully understand. We work with amplification by visualising what is going on as current and waves and 'potential' or voltage. None of these really exist as what we are actually working with are changes in charge fields in, and around, structures that channel the movement of charge and energy. Once you get into quantum theory you begin to realise that our concept of 'electricity' is ridiculously simplistic and doesn't at all describe what is really happening. But it is, obviously, a useful paradigm as the electromagnetic theory is built on practical examples and allows us to use it to design.

So, to my mind, the signal doesn't travel 'through' the winding of a transformer to get out the other side! Instead the signal develops in the primary of the transformer a field which creates a potential in the secondary. It does this near instantaneously and this practical application of magnetic field transfer makes transformers very useful things indeed. Having grown up with transistors I tended to regard transformers as bad things to put in the signal path. However once I had heard a few good transformer designs I realised how good they can be. For example there is common consensus that a good MC transformer is better than an amplifying stage 'head amp'. And interstage transformers offer a good alternative, though the design is hairy, to valve driver stages.

Now from that we can start to look at inductors. You would imagine, using the simplistic view of electricity, that the signal has to travel 'through' the wire in a series inductor in order to get to the drive unit. I would like to promote another way of looking at this. When the signal is present in the inductor coil it creates a field which affects every part of the conducting parts of the inductor at once. The creation and collapse of this field is restricted by the core such that the strength of the field is reduced as the frequency increases. The signal at the output end of the core is therefore a result of the field within the core. We can experiment with this idea by putting, say, a shorted coil in the inductor which dramatically alters the field behaviour. The coil also has a resistance to the transfer of charge potential, but this is a DC effect and is, invariably, mixed up with the AC field effects. Whatever, it is probable that the signal is present at the input and output ends of the coil but doesn't have to travel 'through' the metres of cable in the inductor in the way we like to think it does based on the concept of 'current'.

Of course you can also think of the same thing happening within a moving coil speaker drive unit. If it was really the case that loudspeaker cables have a different sound because of the 'goodness' of the materials used for the transfer of 'electrons' then their sound should, of course, be negated by the rubbish wire we use for crossover inductors and speaker voice coils. But the fact is that many of us can hear the difference speaker cables make and, therefore, there is something else going on. So, for example, if we reduce the speaker cable to an impedance and see how this acts as an interface between the speaker/crossover and amplifier then we can start to see that the interface effects are more important than the quality, or 'goodness', of the materials used.

It makes me smile to look at the BS promoted by some cable companies as to the 'goodness' of the materials in their products to enhance the 'flow of electrons' when inside the equipment these cables are connected to all the signals have to travel through all sorts of 'not good' materials, PCBs being a prime example. In my view it is far more instructive to consider all the components and methods of signal routing as impedance transfer devices which, to my mind, fits theory and practice together in a more practical way.

(continued)