Goal:  Perfect Transfer of Signal at Power Amp Output
Terminals to Input Terminals of Speaker

Conditions:
Very Low Output Z Voltage Source,
Output Voltages up to 100V,
Output Frequencies up to 21 kHz/70 kHz at close to full power,
8 ohm nominal load, 1.6 ohm dynamic load (or lower) with
reactive components at phase angles up to +/- 60 degrees.
Current up to ten's of amperes.

Minimum Performance Requirements:
Dynamic Range > 100 dB.
Simple Distortion < -80 dB.
Complex Distortion <-60 dB
(Preferably much better, of course)

Important Design Considerations:
Minimum Resistance (less than 0.1 ohms for run to speaker)
Minimal Cable Inductance (try to keep to 2X resistance @ 20 kHz,
this controlled through geometry)
Use Least Distorting Materials (bare copper/silver free from
oxidation and a dielectric with minimal capacitance aberrations
and the most linear capacitance)
Maintain Physical Geometry under signal conditions (minimum
"magnetostrictive effect" or motor action between hot and ground
strands causing motion and induced EMF's)
Long Term Stability (lack of oxidation/corrosion effects)

Relatively Unimportant Design Considerations:
Capacitance (under 0.1 uF to avoid modern amplifier instability)
Overall Impedance or load matching (a cable Z of 8 ohms) is not
required.
Appearance/Handling/Cosmetics (obviously, a retail product has
to worry about those things!)

Specifics (my own theories and speculations):
Tinned conductors:  The question has been raised, why bother with
bare copper if the components inside an amplifier, etc. are
constructed with tinned leads, etc.?

My take on this is to consider that the speaker cable carries the
most current of any single component for the longest distance
(anywhere from 10 feet up to 30-50 feet as needed), so that any
effects due to surface "contaminants" would be at a maximum.
I consider "tinning", nickel plating, silver plating, or any other
material on the surface of the conductor to be a contaminant.

It is also instuctive to realize that most of the amplifier wiring is
inside a negative feedback loop, and that the individual wire links
or traces are only an inch or less.

How is a tinned conductor a contaminated surface?  Pure metals
have a crystalline internal organization molecularly, this is
basic metallurgy.  Platings or coatings do not get applied in a
manner so as to totally avoid disrupting the surface of the base
metal.  And the plating/coating itself is highly disordered, with
a large region where the two metals are mixed haphazardly,
severely disrupting the normal crystalline structure of both
materials.  Any plating or worse, a coating, further disorders
the copper/silver metal's crystal structure at the surface,
making worse whatever disorganization is already present due to
wire drawing, extrusion into an insulator, bending, etc.

The skin effect/self-inductance pushes the current flow out
towards the surface.  Skin depth is defined as the depth at
which the current flow is down to 1/e, or 37% of the total, and
the phase lag is one radian.  But the distribution of the other
63% of the current flow is not linear in distribution towards
the surface of the conductor.
It is heavily skewed toward the outermost layer of conductive
material, with a very high proportion of that 63% of the
current, estimated at around 90%, forced toward the
very outermost surface.  Hence the surface purity/linearity
of the conductor becomes important to passing a low distortion
signal, especially at high frequencies where the skin effect/
self inductance comes into play even more.

The skin effect is also going to be responsible for the
effect known as 'strand jumping', see the AudioQuest
web site for an explanation.

One other fact about tin plated wires.  For commercial wires,
a tin plated wire has 6% higher DC resistance than a bare
copper wire of the same gauge.  The tin plating isn't as
conductive as the copper, and is placed where it will do the
most harm to conductivity at high frequencies.

Geometry, Inductance and Surface Coatings:
The inductive reactance in a typical zip cord wire causes the
AC resistance to begin to rise above the baseline DCR level
somewhere in the midrange, usually by 1 to 3 kHz.  It is at this
point that the self-inductance/skin-effect comes into play and
causes not only the cables effective resistance at this frequency
to rise, but the forcing of most of the current towards the
surface of the conductor.  This aspect is often overlooked.
It is implicit in the relationship between the inductance of the
cable vs. the DCR of the cable.

Low-inductance cable designs not only minimize the variation in
frequency response due to amp/cable interaction with the speaker
system impedance, but helps reduce any dielectric nonlinearity
effects.  Inductance by itself shows up as a direct effect in
the frequency response, these material problems are secondary,
and would manifest in low-level nonlinearities.

Magnetostrictive or Motor Effects:
The common reference to magnetostriction uses the term incorrectly,
as true magnetostriction would have the conductor itself changing
dimensions.  This is not the case to any degree.  What does occur
is movement of the conductors relative to one another due to peak
current flow, and the induced back EMF due to the motion while
carrying current.  This is one reason soft insulator/spacer
materials should be avoided, stiff dielectrics like teflon or
polypropylene or even polyethylene will allow less movement and
reduce any magnetostrictive/motor effects.

My first introduction to this effect was with a pair of the old
Discwasher Smoglifters, a very loosely braided cable that would
show a pulse of motion with amplifier turn-on thumps.

A simple demonstration of the presence of this effect is to take
a loop of thin limp wire several feet long, lay the wire out in a
long skinny "U", with the spacing about 1/2" and pulse some
current through it (a car battery or such), with the usual
precautions and disclaimers, i.e., don't put the wire in your
pants and do this, always wear safety glasses, and have a fire
extinguisher handy.  A pulse of current should cause the wires
to twitch or move noticeably.

Vinyl Insulation (dielectric) Concerns:
Vinyl as an insulator/dielectric has a high dielectric
coefficient and a large amount of dielectric absorption.  The
dielectric coefficient of vinyl varies with frequency, that is,
the coefficient does not remain constant.
For some evidence of this, see:
http://bwcecom.belden.com/college/Techpprs/ciocahalf.htm
Fig. 3
Note that polyethylene is realtively constant over the range
shown here.  Teflon is also quite linear up to very high
frequencies.  Also note that the dielectric constant for black
PVC is worse than that of white PVC!

While the dominant
action of concern in a speaker cable is the current flow, and
related inductive effects, there is still a fairly high voltage
present too, one of the highest in the system (unless the power
amp is a tube amp).  This voltage can be corrupted by the
delayed discharge involved with dielectric absorption.

A simple demonstration of D.A. can be had with a hand full of
parts: a power supply (could be a battery), an electrolytic
capacitor of several hundred uF, a pair of (alligator) clip leads,
and a high impedance voltmeter.  If you don't own these or know
anyone who does, you could probably talk the local Radio Shack
counter dude into a demo with store parts.  Charge the
electrolytic capacitor up with the power source (observe proper
polarity and stay within the voltage rating of the cap, easy if
your using a 9V battery) and then remove the source.  Measure the
voltage stored on the cap with the voltmeter.  It should be close
to the voltage of the power supply/battery.  Now discharge the cap
with one of the test leads, holding the wire on the cap terminals
for a good couple of seconds, while the voltmeter is still
connected .  The cap will have been completely discharged to some
extremely small voltage, perhaps 0.001 volt.  After removing the
shorting wire, watch the voltage reading.  Not only will it start
rising in spite of the load from the voltmeter, but it should rise
to an appreciable % of the original applied voltage, if 9 volts,
it could ultimately reach a volt with some caps.  Now that's
distortion, something for nothing.

Most electrolytic caps have at least several % D.A., some even
higher.  Vinyl has so many different formulations, that it is
difficult to even state a range, but generally in the one to
several % region.

From the results of a lot of listening, the following
materials preferences have been established.

-Speaker Cable Materials-
================================
-Preferred Conductor Materials-

In descending order of preference:
Bare copper
Enameled copper
Tinned copper
Silver plated copper

NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL:
Cadmium copper, beryllium copper and other copper alloys.
Nickel plated copper
Silver plated copper clad steel
Copper clad steel (Also called Copperweld)
Tinned steel
Bare steel

-Insulator Materials-
================================
-Inner Conductor Insulation-

In descending order of preference:
Foamed Teflon (TFE)
Solid Teflon (TFE)
Foamed FEP Teflon
Solid FEP Teflon \
Foamed Polypropylene /  These two are real close
Solid Polypropylene
Foamed Polyethylene

NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL:
Solid Polyethylene
Rubber
PVC (Polyvinylchoride) \   These two actually attack most conductors
Polyurethane  /      over a period of time, the severity
    depending on the exact formulation.

-Filler or molded insulation-

Fillers with lots of air are best.
SEE "Inner Conductor Insulation" for order of plastic style fillers
Cotton
Rayon
Nylon
The above fibers would all be placed just below foamed
polyethylene, but above solid polyethylene.

Summary
My ideal speaker cable would have low series resistance across the
entire audio band in order to minimize the variation in frequency
response due to the amplifier/speaker cable impedance interactions
with the speaker impedance.  This would be achieved by utilizing
any one of a number of low-inductance geometry's with a sufficient
equivalent AWG.
It would have the most linear materials available in terms of
conductors and insulators, in order to avoid any materials related
non-linearities.
It would have the rigidity to minimize self-motor action
"magnetostriction", to avoid any potential for generating it's own
motion related distortions.
Finally, it would have the proper material formulations to avoid long
term degradation effects from reducing the performance over time.

Cont'd in Part 2

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