Do materials alter frequencies and speed?

Aball, please enlighten us:

How do materials used in cables affect frequencies and speed?

What is speed?

Which materials affect frequencies, the conductor or dielectric or both?

If both, in what measure are such effects produced by one or the other?

Are we dealing here with measured differences in frequency response or subjectively perceived ones?

Thanks.

Wow...questions, questions ;)

Ok, I will simplify things to keep it under control so bear in mind that it is more complex than I am making it sound.

I am doing some work right now involving modeling of cables and their impact with various loads (mostly inductive ones like motors and speakers). All cables have what is called the "characteristic impedance" which is a function of the series parasitic inductance (L) and parallel parasitic capacitance (C). The former is mostly wire-material dependant and the latter is dielectric/sheath-material dependant.

The speed is the "signal propagation speed" which theoretically is the speed of light but (also) due to the L and C of the cable, it is lower in actuality. The speed is inversely proportional to the product of inductance and capacitance - in other words, the higher the inductance and capacitance, the slower the signal will travel through the cable. This obviously impacts dynamics.

Now, here is the fine line that causes confusion. The frequency issues due to these parameters are mostly in the MHz to GHz regime which is of course not audible by humans. However, harmonics are produced by electrical interactions between the L and C which will produce sidebands that theoretically extend ad infinitum in both directions which means they reach the 20-20kHz region as well. Whether or not they are large enough in signal magnitude to be heard is still under hot debate everywhere. My personal opinion is that in some freaky way, we are able to hear this effect which accounts for the differences in sound between various cables and equipment.

The frequency response really doesn’t register these effects because it is a time-domain function. If you look at it in the frequency domain (via the often mentioned Fourier transform), you can see the harmonics involved in the signal. BUT, current measurement techniques don’t really have good enough resolution to get everything so part of the information is missing.

This leads to my “infinite variable” dictum which goes something like this: everything affects everything all the time. All we can “see” is our resolution capability – very similar to our stereos. The information is infinite in quantity and so the amount we experience is a factor of this resolution. What happens outside the resolution is unknown. What we do know is that the effects of parasitic L and C of cables (and don’t forget all the wires in your components too) add up to something that falls within human ear resolution.

Anyway, I blab about this forever so if you have any questions, feel free, but don’t forget that no one knows everything that goes on in our systems. Arthur

Aball is right - there always is a time delay in all Inductive and/or Capacitive circuits with AC signals passing through them. This is because the electromagnetic/electrostatic fields induce a counter voltage back in the wire After the original signal has passed. A good example is when you pull the plug on a running vacuum cleaner, you get a spark at the socket because the magnetic field collapses when you pull the cord and it induces a high voltage in the wire. Also, this is basically how your computer monitor gets its high voltage to power the CRT.

The "counter voltage" is actually a traveling wave and doesn’t only go counter to the signal. When a signal passes through the cable, waves are induced by the electromagnetic image of the wire and are dependant on the reference ground - which is generally very nebulous in a mess of wires behind a stereo and winds up using system parasitic capacitances to sink the voltage (typically).

The problem is that the voltage and current proportionality MUST BE MAINTAINED in any system, from input to output. This is the key to understanding what I am talking about and some of you are probably already familiar with this since it is a direct repercussion of Ohm’s Law. When there is a discontinuity in the line - like a connection to an amp or speaker with differing impedances - the signal has to maintain this proportionality and to do this, it compensates for the differing interface resistances by creating traveling waves which are duplicate signals but travel at different speeds from the original one and go in both directions. This means you can have multiple signals, all phase shifted and arriving at different times at the speaker! All this is havoc on an audio system and is why low capacitance and inductance are desirable.

However, you still have impedance problems at the ends regardless of the cable properties. I believe that the majority of the problem lies in these impedance mismatches. I was very surprised to see the DarTZeel 108 amp and matching preamp use 50 Ohm cable connections between them to precisely eliminate this problem. Finally, a hifi equipment manufacturer trying to correct this obvious issue! It will be very interesting to see if other manufactures adopt this concept in the future. I think they will.

The vacuum cleaner spark is actually a somewhat different reason. The spark is not strictly due to traveling waves but because the vacuum cleaner motor is very inductive, you cannot interrupt the current instantaneously. When you pull the plug (without switching it off first), you see the uninterrupted current continue to flow until it goes through a zero crossing and extinguishes itself.

Anyhow, it is all very interesting and I plan on looking into these issues a lot more. It is turning into (yet another!) hobby for me. Arthur

TIme delay is also caused by wives and girlfriends.