high end audio

Not Causing More Problems Than We Solve The Trouble With Strands: Since a good speaker cable
needs to have more metal than a single 0.8mm (20 awg) strand, our challenge is to provide a larger
electrical pathway without introducing new problems. If we take a group of strands and put them into a
bundle, the entire bundle will suffer skin-effect. The strands on the outside present an ideal electrical
pathway, but the ones on the inside have different electrical values. This causes the same information
to be distorted differently in different parts of the cable. The bigger the bundle of strands, the bigger the
problem. If resistance is to be lowered by using a bundle of strands, the bundle size must be kept small.
Possibly several separate bundles will be needed.
There are many ways in which skin-effect
causes more distortion in a bundle than in a
single over-sized strand. Strands are constantly
changing positions over the length of a
cable. Some leave the surface and go inside,
others are "rising" to the surface. Since the
current density distribution in a conductor cannot
change, some of the current (particularly at
higher frequencies) must continually jump to a
new strand in order to stay at or near the surface. Unfortunately, the contact between strands is less
than perfect. The point of contact between strands is actually a simple circuit that has capacitance,
inductance, diode rectification-a whole host of problems. This happens thousands of times in a cable,
and causes most of the hashy and gritty sound in many audio cables. This distortion mechanism is dynamic,
extremely complex, and because of oxidation will become worse over time.
Magnetic Interaction is the other primary problem in cable design, both with a stranded conductor,
and between conductors. A strand carrying current is surrounded by a magnetic field. In a bundle,
each strand has its own magnetic field. These magnetic fields interact dynamically as the signal in the
cable changes. On a microscopic level, a stranded cable is actually physically modulated by the current
going through the cable. The more powerful magnetic fields associated with the bass notes cause
the greatest magnetic interaction, which modulates the electrical characteristics of the cable, which in
turn modulates the higher frequencies. Because the music
signal modulates the contact pressure between adjacent
strands, it also modulates the distortion caused by current
jumping between strands.
Reducing magnetic interaction is the primary reason speaker biwiring helps so much. Biwireable speakers
have separate inputs for the bass and upper frequency ranges. These speakers simply allow separate
access to the two halves of the "crossover". A crossover is simply a low-pass filter which allows low
frequency energy to pass to the woofer, and a high-pass filter which allows higher frequency current
to pass to the tweeter, or midrange and tweeter. These filters block the undesired signal by causing
the amplifier to "see" an essentially infinite impedance (resistance) at the frequencies which are to be
blocked. Because there is no closed circuit at the blocked frequencies, current at these frequencies
does not travel in the cable-just like a light bulb which does not light when the electric switch is turned
off, no matter how many megawatts are available.
Taking high frequency energy out of the cable feeding the bass does not significantly affect bass performance.
However, taking the bass energy out of the cable feeding the tweeter or midrange/tweeter
causes a big improvement. The magnetic fields associated with the bass notes are mostly prevented
from interacting with and distorting the fields associated with the higher
frequencies. While the fundamental bass frequency is not affected, the
bass sounds better because the bass instrument’s harmonics are in the
midrange. The harmonics define the bass note and describe the instrument
which created the note. Even if we could ensure absolute mechanical
rigidity in a stranded cable, the interaction between magnetic
fields would still be a prime source of distortion. Current within a conductor
is directly proportional to the magnetic field outside the conductor.
In most cables, the magnetic field of any given strand encounters a complex and changing series
of interactions as it travels through a constantly changing magnetic environment. As the magnetic field
is modulated, the audio signal becomes confused and distorted.
Distortion due to both magnetic interaction and from bare strands touching can be dramatically reduced
by using Semi-Solid Concentric-Packing. In such a construction the strands are applied in a layer or
layers spiraling around a central strand. Each layer is packed perfectly tight, exactly fitting around the
strand or layer underneath. The strands in a given layer are uniform and never rise or fall to a different
layer. This construction mimics many of the most important attributes of a solid conductor, while maintaining
most of the flexibility of a stranded cable. The complete solution is solid conductors.
Magnetic interaction between conductors is also an area of major concern. This is discussed in the section
following Material Quality.
Material Quality also dramatically affects the performance of cables and their terminations. By material
quality we mean both the intrinsic quality of the metal, such as gold, nickel, brass, aluminum, copper or
silver, and we mean the way the metal has been refined and processed. Pure silver is the very best performing
material for audio, video or digital. However, if silver is not carefully processed, even low grade
copper will sound better. Silver has also earned a confused reputation because sometimes the term
"silver" is used to describe silver-plated copper. When carrying an analog audio signal, silver-plated
copper causes a very irritating sound, sort of a "tweeter in your face" effect. In a different application,
such as video, RF or digital, good silver-plated copper becomes an extraordinary value, out-performing
even the highest grades of pure copper.
Why no gold wire? Because gold has neither low distortion nor low resistance. Gold is used on connectors
because it is a "noble" metal, it doesn’t corrode easily. Because gold is "noble" it is ideal for pro-
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tecting more vulnerable materials like copper and brass. The nature of gold’s distortion is mellow and
pleasant, which makes it preferable to the irritating sonic signature of nickel. A bare copper or brass part
will outperform a gold plated part, but only until the metal corrodes. In comparison, high quality thick
silver plating actually improves performance. Silver is not noble like gold, but it does resist corrosion
and it enhances performance.
As for conducting materials, normal, high purity (tough pitch) copper has about 1500 grains in each
foot (5000/m). The signal must cross the junctions between these grains 1500 times in order to travel
through one foot of cable. These grain boundaries cause the same type of irritating distortion as current
crossing from strand to strand.
The first grade above normal high purity copper is called Oxygen-Free High-Conductivity (OFHC) copper.
In fact, this copper is not Oxygen-Free, it should more properly be called Oxygen-Reduced. OFHC
is cast and drawn in a way that minimizes the oxygen content in the copper: approximately 40 PPM
(parts per million) for OFHC compared to 235 PPM for normal copper. This drastically reduces the
formation of copper oxides within the copper, substantially reducing the distortion caused by the grain
boundaries. Additional improvement can be attributed to OFHC copper having longer grains (about 400
per foot), further reducing distortion. The sound of an OFHC copper cable is smoother, cleaner, and
more dynamic than the same design made with standard high purity copper.
Not all OFHC is the same. If the poorest copper were given a value of one, and the best was a ten,
then OFHC ranges from two to four-it is actually a range rather than a single performance level. Since
the most important audible attributes are due to the length of the grains, we use the name LGC (Long
Grain Copper) to describe the very best OFHC.
The next higher grade is an elongated grain copper sometimes
called "linear-crystal" (LC-OFC) or "mono-crystal". These coppers
have been carefully drawn in a process that results in only
about 70 grains per foot. Cables using LC-OFC have an obvious
audible advantage over cables using the same designs with
OFHC or LGC. From 1985 to 1987 several AudioQuest models
benefitted from this quality material.
In 1987 AudioQuest introduced FPC (Functionally Perfect Copper) in the higher models. FPC was
manufactured by a process called Ohno Continuous Casting (OCC).Through this process, the metal
is very slowly cast as an almost perfect single crystal small diameter rod. This near-perfect rod is then
carefully drawn to maximize grain length. However, OCC is a process, not a material. The metal (usually
aluminum or copper), the purity, and the size of the cast rod all make a tremedous diference. FPC
copper was drawn from a smaller rod, causing less damage to the near perfect cast state, a single grain
was over 700 feet long. The audible benefits were very obvious.
A couple of years later the "nines" race began. This refers to how many times the number "9" can be
repeated when specifying a metal’s purity. In 1989 AudioQuest introduced FPC-6 in the highest models.
FPC-6 had only 1% as many impurities as FPC. The prime contaminants in very high purity (99.997%
pure, four nines) copper, like LGC and FPC, are silver, iron and sulfur, along with smaller amounts of
antimony, aluminum and arsenic. FPC-6 was 99.99997% (six nines) pure with only 19 PPM of oxygen,
0.25 PPM of silver and fewer than 0.05 PPM of the other impurities. The improvement was dramatic.
As with OFHC and OCC, the nomenclature "six nines" or "eight nines" has almost no meaning. All else
being equal, higher purity is a straight forward benefit. However, grain structure, softmess and surface
finish can each make more difference than a "nine" or two. Then there is the matter of measurable purity.
Due to contamination caused by the measuring process, there is a serious question as to whether
any metal can be verified as having greater than six nines purity. Also, since "nines" became a selling
point, some quite absurd and dubious claims have been made. Let the ears beware.
Once copper has been processed and refined to the Nth degree, the only improvement left is to go
to a long-grain high-purity silver. AudioQuest FPS (Functionally Perfect Silver) is just such a superior
material. It was expensive, but the results were transparency, delicacy, dynamics and believability that
weren’t possible any other way... until PSC copper. FPS silver is still used to excellent effect in many
CinemaQuest (from AudioQuest) wideband cable.
In the previous several paragraphs a number of important metallurgical concerns have been litsed,
such as purity, grain structure, softness and surface finish. Earlier in the discussion of skin-effect it was
mentioned that the only place with 100% magnetic field and current density is at the surface of a conductor.
This means that the surface purity and smoothness does more to define the sonic character,
or hopefully lack of character, than any other part of a conductor. This is why AudioQuest’s recently
introduced new range of metals are called "Perfect Surface."
Perfect Surface Copper (PSC) is drawn and annealed though a novel proprietary integrated process
which creates an exceptionally soft copper conductor with an astonishingly smooth and uncontaminated
surface. Ever since the beginning, AudioQuest cables have improved over time. Starting in 1987
with FPC copper, a foundation was created by four levels of superb conducting materials. On this foundation,
refinements such as SST continually provided further discrete improvements. With the introduction
of PSC copper, a whole new foundation has been laid. For a price not much higher than FPC, PSC
offers more natural and accurate performance than even FPS silver. AudioQuest’s CV-4 speaker cable
is identical to Type 4 in every way, except for the use of PSC copper instead of LGC. Coral interconnect
is identical to the previous Ruby and Quartz designs, except for using PSC instead of FPC (Ruby) and
FPC-6 (Quartz).