Thursday, October 2, 2008
RUNNING IN OF CABLES
Important Cable Facts Running-In: As with all audio components, audio cables require an adjustmentperiod. This is often mistakenly referred to as “break-in”. However, break-in is properly used todescribe a mechanical change-engines break-in, loudspeaker and phono cartridge suspensions breakin.A cable’s performance takes time to optimize because of the way a dielectric behaves (the way theinsulating material absorbs and releases energy), changes in the presence of a charge. Cables willcontinue to improve in sound or picture quality over a period of several weeks. This is the same reasonamplifiers, preamplifiers and CD players also require an adjustment period. The key difference between“adjusting” and “breaking-in” is that things don’t “un-break-in”, however, electrical components do “unadjust”.Several weeks of disuse will return a cable to nearly its original state.The run-in time is essentially the same for all cables. However, the apparent need for run-in varieswildly. As with amplifiers and other components, the better the cable, the less distortion it has, andtherefore the less there is to cover up the obnoxious distortion caused by being new. Since human perceptionis more aware of the existence of a distortion than the quantity, the better the cable, the worsein some ways it will sound when new, because the anemic forced two-dimensional effect reulting frombeing new will not be ameliorated by other gentler distortions. Please be patient when first listening toany superior product.Directionality: All cables are directional, from hardware store electrical cable to the finest pure silvercables. All AudioQuest cables are marked for direction. With other cables it might be necessary to simplylisten to the cables in one direction and then the other. The difference will be clear-in the correctdirection the music is more relaxed, pleasant and believable. While cable directionality is not fully understood,it is clear that the molecular structure of drawn metal is not symmetrical, providing a physicalexplanation for the existence of directionality.CABLE THEORYBiwiring: Many of today’s speakers can be biwired. This type of speaker has one input for the wooferand a separate input for the upper frequency ranges. This often leads to the question “is biwiring soimportant that I should spend twice as much on cable?” Maybe it is worth spending twice as much oncable in general, but that’s a separate question. Biwiring is a way to save money, to get higher performancefor the same price. The biwiring question is not about how much money to spend, but abouthow to get the most performance for one’s money. Biwiring is done in order to substantially reduce thedistortion caused by speaker cable. In a biwire set-up the cable feeding the higher ranges no longerhas to handle the large magnetic fields caused by the high current needed to produce bass. The bassfundamentals are not affected by biwiring, but the treble signal now travels a less distorted path. Alittle like the difference between swimming through waves versus through smooth water. The bass willsound better because bass difinition is in the midrange and higher. It is worthwhile to take advantageof the benefits of biwiring when the speaker manufacturer has gone to the extra expense of includingthis capability. At the very least, please connect a single set of speaker cables to the treble input, andthen use even a modest cable like AQ F-14 to jump down to the woofer. Please replace the jumperssupplied by the speaker manufacturer. These are self sabotage, by the speaker manufacturer and byany listener who uses them. Just like better electronics do not come with poor interconnect cables, it isbest to pretend your fine speakers did not come with stamped metal jumpers. When biwiring, the twocables used must either be identical, or have essentially identical designs. If the cables have differentinductance or capacitance, they will cause different amounts of phase shift. The integrity and coherenceof the speaker will be compromised.
Friday, September 26, 2008
high end audio
Directionality:
All cables are directional, from hardware store electrical cable to the finest pure silver
cables. All AudioQuest cables are marked for direction. With other cables it might be necessary to simply
listen to the cables in one direction and then the other. The difference will be clear-in the correct
direction the music is more relaxed, pleasant and believable. While cable directionality is not fully understood,
it is clear that the molecular structure of drawn metal is not symmetrical, providing a physical
explanation for the existence of directionality.
All cables are directional, from hardware store electrical cable to the finest pure silver
cables. All AudioQuest cables are marked for direction. With other cables it might be necessary to simply
listen to the cables in one direction and then the other. The difference will be clear-in the correct
direction the music is more relaxed, pleasant and believable. While cable directionality is not fully understood,
it is clear that the molecular structure of drawn metal is not symmetrical, providing a physical
explanation for the existence of directionality.
high end audio
Important Cable Facts Running-In:
As with all audio components, audio cables require an adjustment
period. This is often mistakenly referred to as "break-in". However, break-in is properly used to
describe a mechanical change-engines break-in, loudspeaker and phono cartridge suspensions breakin.
A cable’s performance takes time to optimize because of the way a dielectric behaves (the way the
insulating material absorbs and releases energy), changes in the presence of a charge. Cables will
continue to improve in sound or picture quality over a period of several weeks. This is the same reason
amplifiers, preamplifiers and CD players also require an adjustment period. The key difference between
"adjusting" and "breaking-in" is that things don’t "un-break-in", however, electrical components do "unadjust".
Several weeks of disuse will return a cable to nearly its original state.
The run-in time is essentially the same for all cables. However, the apparent need for run-in varies
wildly. As with amplifiers and other components, the better the cable, the less distortion it has, and
therefore the less there is to cover up the obnoxious distortion caused by being new. Since human perception
is more aware of the existence of a distortion than the quantity, the better the cable, the worse
in some ways it will sound when new, because the anemic forced two-dimensional effect reulting from
being new will not be ameliorated by other gentler distortions. Please be patient when first listening to
any superior product.
As with all audio components, audio cables require an adjustment
period. This is often mistakenly referred to as "break-in". However, break-in is properly used to
describe a mechanical change-engines break-in, loudspeaker and phono cartridge suspensions breakin.
A cable’s performance takes time to optimize because of the way a dielectric behaves (the way the
insulating material absorbs and releases energy), changes in the presence of a charge. Cables will
continue to improve in sound or picture quality over a period of several weeks. This is the same reason
amplifiers, preamplifiers and CD players also require an adjustment period. The key difference between
"adjusting" and "breaking-in" is that things don’t "un-break-in", however, electrical components do "unadjust".
Several weeks of disuse will return a cable to nearly its original state.
The run-in time is essentially the same for all cables. However, the apparent need for run-in varies
wildly. As with amplifiers and other components, the better the cable, the less distortion it has, and
therefore the less there is to cover up the obnoxious distortion caused by being new. Since human perception
is more aware of the existence of a distortion than the quantity, the better the cable, the worse
in some ways it will sound when new, because the anemic forced two-dimensional effect reulting from
being new will not be ameliorated by other gentler distortions. Please be patient when first listening to
any superior product.
high end audio
The Challenge Of Interconnect (Low-Current) Cable Design
If you haven’t read the previous discussion of problems in speaker
cables, then please read that first. The following is meant to build
on that foundation. The same problems exist in both high-current
(speaker) and low-current (interconnect) applications. However, the
hierarchy among these problems differs.
In low-current cables; skin-effect, electrical interaction, magnetic interaction
and conductor quality are still primary problems. The negative
sonic effect of internal mechanical modulation due to magnetic
fields is greatly reduced.
The electrical behavior of the dielectric (insulating material) is much
more important in low level cables. Dielectric involvement (the way
in which a particular material absorbs and releases energy), has a
profound effect on an audio or video signal. Dielectric constant, the most often quoted specification for
insulating material, is actually not very helpful in understanding the audible attributes of different materials.
The coefficient of absorption value is more relevant, and the dissipation factor and the velocity of
propagation are even more useful.
The problem is that any insulating material next to a conductor acts like a capacitor which stores and
later releases energy. This is true of circuit board materials, cables, resistors and of course capacitors.
The ideal wire is one with no insulation except for air. When a solid material must be applied, it should
be electrically invisible, meaning that the less energy it absorbs, the better. The energy which is absorbed
should stay absorbed (turned into heat, a high dissipation factor), and the energy which does
come back into the metal conductor should have minimal phase shift and not be frequency selective
(a high velocity of propagation, independent of frequency). All dielectrics absorb more energy at higher
frequencies, but some are more linear in their overall behavior relative to frequency.
The most commonly used insulations are PVC, polyethylene, polypropylene and Teflon. These can be
mixed with air (foamed) or applied in ways which maximize the amount of air around the metal strands.
Which material is used and how it is applied will dramatically affect the performance of a low-level cable.
Capacitance is more important in low-level than high-level cables for two reasons. If a long, "over the
cliff" high capacitance cable is used, many preamplifiers, CD players, tuners, surround processors, etc.,
will not be able to "drive" the cable. The resulting distortion does not happen within the cable, but is
caused by using the cable. There is never a disadvantage to using low capacitance low-level cables.
The other important reason for low capacitance is that high capacitance causes greater field strength
between the positive and negative conductors (and the shield). This means more energy is put into the
dielectric material. There
is always a priority to minimize dielectric involvement, through proper selection
of materials and low capacitance design.
If you haven’t read the previous discussion of problems in speaker
cables, then please read that first. The following is meant to build
on that foundation. The same problems exist in both high-current
(speaker) and low-current (interconnect) applications. However, the
hierarchy among these problems differs.
In low-current cables; skin-effect, electrical interaction, magnetic interaction
and conductor quality are still primary problems. The negative
sonic effect of internal mechanical modulation due to magnetic
fields is greatly reduced.
The electrical behavior of the dielectric (insulating material) is much
more important in low level cables. Dielectric involvement (the way
in which a particular material absorbs and releases energy), has a
profound effect on an audio or video signal. Dielectric constant, the most often quoted specification for
insulating material, is actually not very helpful in understanding the audible attributes of different materials.
The coefficient of absorption value is more relevant, and the dissipation factor and the velocity of
propagation are even more useful.
The problem is that any insulating material next to a conductor acts like a capacitor which stores and
later releases energy. This is true of circuit board materials, cables, resistors and of course capacitors.
The ideal wire is one with no insulation except for air. When a solid material must be applied, it should
be electrically invisible, meaning that the less energy it absorbs, the better. The energy which is absorbed
should stay absorbed (turned into heat, a high dissipation factor), and the energy which does
come back into the metal conductor should have minimal phase shift and not be frequency selective
(a high velocity of propagation, independent of frequency). All dielectrics absorb more energy at higher
frequencies, but some are more linear in their overall behavior relative to frequency.
The most commonly used insulations are PVC, polyethylene, polypropylene and Teflon. These can be
mixed with air (foamed) or applied in ways which maximize the amount of air around the metal strands.
Which material is used and how it is applied will dramatically affect the performance of a low-level cable.
Capacitance is more important in low-level than high-level cables for two reasons. If a long, "over the
cliff" high capacitance cable is used, many preamplifiers, CD players, tuners, surround processors, etc.,
will not be able to "drive" the cable. The resulting distortion does not happen within the cable, but is
caused by using the cable. There is never a disadvantage to using low capacitance low-level cables.
The other important reason for low capacitance is that high capacitance causes greater field strength
between the positive and negative conductors (and the shield). This means more energy is put into the
dielectric material. There
is always a priority to minimize dielectric involvement, through proper selection
of materials and low capacitance design.
high end audio
Importance Of Overall Speaker Cable Geometry
We have been discussing problems within a single conductor, solid or stranded, regardless of polarity
(+ or -). The relationship between conductors is also very important. If this relationship is not consistent,
then the electrical parameters (such as capacitance and inductance) of the cable will be constantly
changing and the signal will be distorted. Conductors can be parallel, spiraled (twisted), or braided.
These various geometries have certain inherent qualities. Parallel construction is inexpensive. Spirals
have good RFI (radio frequency interference) rejection and usually lower inductance. Braids have good
RFI rejection and low inductance, but suffer the consequences of a constantly changing electrical environment
for each conductor.
A cable may have two or more conductors. The arrangement of these conductors dictates the magnetic
interaction, the capacitance and the inductance of the cable. Both capacitance and inductance cause
predictable and measurable filtering and progressively more phase shift at higher frequencies, though
neither is a magic key leading to optimum performance. The effect of capacitance is somewhat like a
cliff, you can go near the edge as long as you don’t go over the edge. In a given application there is a
value at which capacitance becomes a problem. At a lower value, away from the edge of the cliff, there
is not much penalty. On the other hand, inductance is always a problem-a constantly accumulating
problem. Capacitance and inductance are not the only important variables in cable design. However,
it is productive to create cables whose capacitance doesn’t "go over the cliff" while also designing for
minimum inductance.
One theory of cable design holds that the characteristic impedance of a cable should match the impedance
of the loudspeaker (When an antenna cable is referred to as 75 or 300, that is the characteristic
impedance). Impedance matching is a valid concept which only applies when the impedance of the
source, the cable and the load are all the same, and when the cable is longer than the wavelengths
of the frequencies to be transmitted. Amplifiers do not have 4 or 8 ohm output impedances, in fact
amplifier designers try to have as low an output impedance as possible. Speakers are all different and
never have the same impedance at all audio frequencies. Since characteristic impedance equals the
square root of the ratio of inductance to capacitance, very high (over the cliff) capacitance is a necessary
corollary of a low characteristic impedance. Such high capacitance can severely affect amplifier
performance and should be avoided.
Some of the first generation of specialty speaker cables had a characteristic impedance of about 8.
These very high capacitance cables sounded better or worse because of their ability or inability to deal
with the problems discussed earlier. However, many of these cables were accused of being extremely
bright and irritating. It was not the cables which were so bright, it was the sound of the amplifier,which
had been encouraged into instability by the cables.
Such false conclusions could be avoided if products were judged on their merit and then methodically
analyzed. Consumers, store buyers, and reviewers each need to discover what sounds good. Unfortunately
the desire to understand "why" can cause more confusion than insight if not pursued empirically
as well as theoretically.
We have been discussing problems within a single conductor, solid or stranded, regardless of polarity
(+ or -). The relationship between conductors is also very important. If this relationship is not consistent,
then the electrical parameters (such as capacitance and inductance) of the cable will be constantly
changing and the signal will be distorted. Conductors can be parallel, spiraled (twisted), or braided.
These various geometries have certain inherent qualities. Parallel construction is inexpensive. Spirals
have good RFI (radio frequency interference) rejection and usually lower inductance. Braids have good
RFI rejection and low inductance, but suffer the consequences of a constantly changing electrical environment
for each conductor.
A cable may have two or more conductors. The arrangement of these conductors dictates the magnetic
interaction, the capacitance and the inductance of the cable. Both capacitance and inductance cause
predictable and measurable filtering and progressively more phase shift at higher frequencies, though
neither is a magic key leading to optimum performance. The effect of capacitance is somewhat like a
cliff, you can go near the edge as long as you don’t go over the edge. In a given application there is a
value at which capacitance becomes a problem. At a lower value, away from the edge of the cliff, there
is not much penalty. On the other hand, inductance is always a problem-a constantly accumulating
problem. Capacitance and inductance are not the only important variables in cable design. However,
it is productive to create cables whose capacitance doesn’t "go over the cliff" while also designing for
minimum inductance.
One theory of cable design holds that the characteristic impedance of a cable should match the impedance
of the loudspeaker (When an antenna cable is referred to as 75 or 300, that is the characteristic
impedance). Impedance matching is a valid concept which only applies when the impedance of the
source, the cable and the load are all the same, and when the cable is longer than the wavelengths
of the frequencies to be transmitted. Amplifiers do not have 4 or 8 ohm output impedances, in fact
amplifier designers try to have as low an output impedance as possible. Speakers are all different and
never have the same impedance at all audio frequencies. Since characteristic impedance equals the
square root of the ratio of inductance to capacitance, very high (over the cliff) capacitance is a necessary
corollary of a low characteristic impedance. Such high capacitance can severely affect amplifier
performance and should be avoided.
Some of the first generation of specialty speaker cables had a characteristic impedance of about 8.
These very high capacitance cables sounded better or worse because of their ability or inability to deal
with the problems discussed earlier. However, many of these cables were accused of being extremely
bright and irritating. It was not the cables which were so bright, it was the sound of the amplifier,which
had been encouraged into instability by the cables.
Such false conclusions could be avoided if products were judged on their merit and then methodically
analyzed. Consumers, store buyers, and reviewers each need to discover what sounds good. Unfortunately
the desire to understand "why" can cause more confusion than insight if not pursued empirically
as well as theoretically.
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-
Page
COPYRIGHT © 2006 THE QUEST GROUP, ALL RIGHTS RESERVED
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).
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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COPYRIGHT © 2006 THE QUEST GROUP, ALL RIGHTS RESERVED
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).
High end audio
Misunderstanding Resistance And Other Pitfalls
If a speaker cable used a single 0.8mm strand of copper, it would have too much resistance to do its
job properly. Speaker sensitivity varies, but if the path between the speaker and amplifier has too much
resistance, the sound quality will suffer. Such degradation is not actually distortion in the cable, but is
the result of using too small a cable. For this reason, even a short speaker cable should be at least 18
awg (.82 sq. mm) or larger.
Power loss due to resistance is not usually a significant problem. If a very small cable were to cause
a 10% power loss, the result would be like turning down the volume a fraction of one dB. If a signal
has been robbed of the information that allows you to perceive dynamic contrast, harmonic beauty and
subtlety, we tend to refer to the loss as an "amplitude" loss. However, the signal sounds so dull and lifeless
at the far end of a poor cable not because of lost power, but because of added distortion.
Unfortunately, the language of audio very often includes misleading terms. Many types of distortion are
referred to as making the sound "bright" or "dull", both of which imply a change in amplitude. "Bright" is
often used as a way of saying that harshness in the upper midrange has somewhat the same effect as
turning up the treble. "Dull" is often thought of as turning the treble down, even though it is usually the
result of distortions which obscure information. In most products, and certainly in cables, the amplitude
response (frequency response) is not the culprit.
Probably the biggest obstacle to predictably assembling a high performance audio or video system is
too much thinking and not enough evaluating. It is tempting to follow some logical story as to why some
key ingredient will make all the difference, when in fact, pursuing any one priority almost always means
inadequate attention to dozens of other often more important concerns. Please be careful not to get
seduced by some common myths. Simplistic and ineffective solutions are often "sold" as cures for complicated
problems. Dogma isn’t productive, results are what count. The best phono cartridges aren’t the
ones with the lowest tracking forces, S-video outputs are not necessarily better than composite, two
way speakers are not necessarily better or worse than three way speakers, more powerful amplifiers
are not etc. The most relevant fallacy in this discussion is the one about "the more strands, the bigger
the cable, the better".
If a speaker cable used a single 0.8mm strand of copper, it would have too much resistance to do its
job properly. Speaker sensitivity varies, but if the path between the speaker and amplifier has too much
resistance, the sound quality will suffer. Such degradation is not actually distortion in the cable, but is
the result of using too small a cable. For this reason, even a short speaker cable should be at least 18
awg (.82 sq. mm) or larger.
Power loss due to resistance is not usually a significant problem. If a very small cable were to cause
a 10% power loss, the result would be like turning down the volume a fraction of one dB. If a signal
has been robbed of the information that allows you to perceive dynamic contrast, harmonic beauty and
subtlety, we tend to refer to the loss as an "amplitude" loss. However, the signal sounds so dull and lifeless
at the far end of a poor cable not because of lost power, but because of added distortion.
Unfortunately, the language of audio very often includes misleading terms. Many types of distortion are
referred to as making the sound "bright" or "dull", both of which imply a change in amplitude. "Bright" is
often used as a way of saying that harshness in the upper midrange has somewhat the same effect as
turning up the treble. "Dull" is often thought of as turning the treble down, even though it is usually the
result of distortions which obscure information. In most products, and certainly in cables, the amplitude
response (frequency response) is not the culprit.
Probably the biggest obstacle to predictably assembling a high performance audio or video system is
too much thinking and not enough evaluating. It is tempting to follow some logical story as to why some
key ingredient will make all the difference, when in fact, pursuing any one priority almost always means
inadequate attention to dozens of other often more important concerns. Please be careful not to get
seduced by some common myths. Simplistic and ineffective solutions are often "sold" as cures for complicated
problems. Dogma isn’t productive, results are what count. The best phono cartridges aren’t the
ones with the lowest tracking forces, S-video outputs are not necessarily better than composite, two
way speakers are not necessarily better or worse than three way speakers, more powerful amplifiers
are not etc. The most relevant fallacy in this discussion is the one about "the more strands, the bigger
the cable, the better".
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