Tip #25: IN PURSUIT OF THE PERFECT CONDUCTOR
Note: The is an abridged and updated version of an article originally published in the January 1996 issue of Fi Magazine. Most of the updates are minor in nature, except for the addition of MAC wireand Kimber Kable Select KS 1030 interconnect to the recommended list.
The notion of cable as a high-end component, so contentious in the 80s, is today rather well accepted by most serious listeners. However, the underlying technical foundation for the sonic character of cable remains nearly as controversial and fuzzy today as it was back then. Well...NOT if you're an electrical engineer. Most of these folks look at the corpus of a cable through entirely materialistic eyes; mainly because they are taught to analyze a circuit in terms of a few fundamental electromagnetic quantities. They idealize and model a cable's behavior as a function of its lumped electrical parameters: resistance (R), inductance (L), and capacitance (C). These parameters are ordained by the cable's dielectric materials and "geometry," by which I mean conductor wire gauge, the number of strands, the spacing between strands in each leg, and the spacing between the "go" and "return" legs. On this basis it is possible to calculate a cable's impedance. And because the calculations agree with the meter readings, this model must be judged as physically valid.
Taking this one step further, it isn't difficult to find instances where a cable's basic electrical parameters do make a sonic difference. Adding the loudspeaker impedance to the model, it is easy to show that since the cable impedance is in series with that of the loudspeaker, a speaker cable can actually modify the loudspeaker's frequency response. It soaks up a greater percentage of the amp's output power as its own impedance rises and that of the load decreases. Imagine a worst case scenario where a 2-ohm dip in the speaker's impedance curve meets up with a 1-ohm cable impedance; the result being about a 3 dB drop in output at that frequency. In general, it's fair to say that cable impedance contributes subtle EQ effects to the overall system sound. In addition, a high-impedance speaker cable increases the apparent output impedance of the power amp. The obvious consequence of that is that the amp's damping factor is reduced. Another not so obvious consequence involves the "de-tuning" of the loudspeaker's crossover network. Crossovers are designed to look into specific source and load impedances, so an increase in the amp's output impedance works to shift the actual crossover point from its intended frequency. All of these effects clearly impact the sound, but because their precise nature is unpredictable and usually deleterious, I would therefore be the last guy on this planet to recommend high-impedance speaker cable. On the other hand, it's important to note that a high-impedance interconnect is normally not a sonic detriment because it operates in a high impedance circuit; a power amp's input impedance typically being on the order of 50,000 ohms. But interconnect capacitance can be an issue if the preamp's output impedance is unusually high. The cable capacitance and output impedance form a low pass network that rolls off the treble. Just how critical is this effect? Lets take a look at a typical scenario. The capacitance of most interconnects measures between 100 and 150 pico Farad (pF) per meter. No serious preamp should have an output impedance greater than 500 ohms, but lets stretch that a bit to 2,500 ohms for the benefit of some tube preamps. Using figures of 150 pF per meter, a 20-foot run of interconnect, and a realistic upper limit of 2,500 ohms for the preamp's output impedance, results in a calculated -3 dB frequency of 73 kHz - and that folks is good enough for me. Undoubtedly, it is a cable's electrical "personality" that gives rise to specific system interactions and much confusion about the merits of any given cable. For example, a high-inductance speaker cable, which would be expected to sound dull in a tonally balanced system, may in fact be hailed as "sonic nirvana" in the context of a bright-sounding system.
A Question of Perception
The decisive mistake engineers make is to ascribe ALL sonic differences to a cable's electrical parameters. It's about as absurd as trying to divine a person's character from his weight, height, and rectal temperature. Card-carrying members of engineering societies by and large tenaciously uphold scientific dogma pounded into their heads during many years of schooling (as a reformed engineer, I should know). Put a gun to their head, and they will maintain till their dying breath that the RLC paradigm is the truth, the whole truth, and nothing but the truth. In the past ten years, a handful of investigators have shown that the RLC paradigm just doesn't go far enough, and that there are other factors that do indeed affect signal transmission. This is also true for other passive parts such as caps and resistors where a simplistic test-bench measurement oriented paradigm has failed to fully account for sonic differences. Turn a Meter Head loose with an Audio Precision System and have him try to differentiate between a mass-market receiver and a Mark Levinson, or for that matter, between a run of #16 awg zip cord and an equal length of high-end cable. It's like trying to judge fine wines on the basis of a chemical analysis. Such measurements are in general not predictive of human perceptions.
To paraphrase Rene Descartes, I hear, therefore I am. Meaning, that the whole is greater than the sum of the parts. While it is possible to dissect a sound field with a variety of frequency and time domain measurements, these meter readings or waterfall plots in no way add up to reflect the emotional reaction I might experience. No wonder science has had such a hard time defining perceptual attributes. Take timbre, for example. The American National Standards Institute defines timbre as "that attribute of a tone by which a listener can judge that two sounds of the same loudness and pitch are dissimilar." Pretty vague if you ask me. The following layman's definition is no better: the perceivable difference between a clarinet middle C and a violin middle C is timbre. To quote Handel (Listening: An Introduction to the Perception of Auditory Events: MIT Press), "timbre is not reducible to an acoustical property that automatically yields a clarinet note or a violin note." Timbre [has] to be judged subjectively. Human vision presents us with a similar perceptual dilemma. The wavelength of visible light can be measured very precisely with a spectrometer. At a wavelength of 520 nm, light is perceived as green; at 470 nm it is blue. But at what wavelength does it change from green to blue? That's a question that measurements cannot settle. There's an infinite number of blue-green shades between these wavelengths, so in the end the answer depends totally on the observer.
It is precisely because sound perception is nearly impossible to predict on the basis of objective measurements that subjective audio reviewing was invented some 40 years ago by J. Gordon Holt. And that's why the ear must be the final arbiter in all things musical.
Beyond the RLC Paradigm
My main thesis is that cable sound is profoundly influenced by its constituent materials. In hindsight, this assertion strikes me as not only sensible but also as self evident. A long-standing audiophile tenet holds that a component's sound is determined to a large extent by its parts quality. Hence, in the case of an active component such as a power amp, we can safely state that identical circuits executed with different ingredients will sound dissimilar. Ditto for passive components such as caps where, for example, the choice of dielectric makes a world of difference. By extension, it is logical to expect that the following factors would impact cable sound: conductor type, its purity, crystal granularity, and choice of cable insulation or dielectric. As with capacitors, the quality of the dielectric is critical in determining the harmonic lucidity of a cable. A fraction of the signal soaks into the dielectric, to be released later in time with a rather slow decay. This has the effect of smearing musical transients and causing textures to turn grainy or gritty. Certainly, dielectrics with small "memory" effects are best for audio applications. The main issue then revolves around the choice of conductor material, which brings to mind questions such as: "is silver superior to copper?" or "is 6N copper audibly better than OFC?"
The Inner View
To understand why factors such as conductor purity are important in signal transmission, it's imperative to examine the conductor's inner world - a microscopic realm inhabited by the ubiquitous electron. Metals are by definition good conductors of electricity. The noblest of these, copper, silver, and gold, are distinguished from insulators by virtue of possessing many more free electrons. These electrons, being detached from atoms in the crystal lattice, are the mobile charge carriers that perform the actual conduction. The poplar view of how a conductor works, has electrons buzzing down Electric Avenue at the speed of light. If that were the case, the cost of a relativistic electron accelerator would be less than a single dollar: simply connect a piece of cable to the terminals of a battery. The truth of the matter is that electrons meander down the length of a conductor at a snail's pace. It is the electromagnetic field associated with the flowing electrons that conducts the signal at the speed of a photon torpedo. This field surrounds the cable, cutting through the space around the conductor. The audio signal travels through the conductor at a fraction of the speed of light in vacuum. The transmission speed increases slightly with signal frequency, so that the bass is slightly delayed relative to the treble. Without the application of an external voltage, free-electron motion is thermal in nature and totally random. In other words, there is no net current flow along the wire. Recall that electric current is defined as the net charge passing a cross section of the wire per second. Thus, in the absence of an applied voltage, there are as many electrons coming and going at any point in the wire, so that the net current is zero. The application of an external voltage to the wire provides a velocity component to the free electron that is parallel to the field. Electrons drift down the crystal lattice, pushed along by the voltage gradient, until they bump into atoms in their path. These atomic collisions stop the forward drift and again deflect the electrons in a random direction. After each collision, the electrons are accelerated again by the potential gradient. The result is random electronic motion characterized by an average drift velocity down the conductor. In a sense it's like a microscopic pin ball game with the electrons (the pin balls) crashing into massive bumpers (the atoms). In both cases, the situation is chaotic; it's impossible to predict the path of either the pin ball or the electron. However, it is possible to calculate the average electronic drift velocity. For a 20-gauge copper conductor and a current of 1 ampere, the actual velocity is on the order of 1 foot per hour. It would in this instance take an electron on average about a day to complete a journey down a 24-foot cable!
The continual scattering of electrons by atoms is a form of friction and constitutes the main source of electrical resistance. The amount of scattering is a function of temperature. As temperature is increased, the atoms vibrate more strongly about their mean position in the crystal lattice and scatter electrons more often. It's a well known fact that the resistivity of a conductor increases with temperature. And as copper, for example, is cooled toward absolute zero its resistance decreases. Ideally, at absolute zero where all thermal motion comes to a screeching halt, its resistance would be zero. I said ideally, because for this to happen requires a perfectly ordered crystal lattice. Quantum mechanics predicts that electrons will not be scattered by a perfect crystal.
Unfortunately a conductor wire is far form a perfect crystal. Numerous lattice defects are introduced during the casting of the metal and drawing of the wire, and these create resistance by interfering with electron motion. A wire, though it may look like a homogeneous mass to the naked eye, is in reality made of a multitude of small crystal grains. Because each grain boundary acts to scatter electrons, metallurgists over the years have invented numerous heat treatments and even a continuous casting process all designed to grow larger grains and thus minimize the number of boundaries.
Just as important an impediment to electron conduction are impurity atoms (mostly oxygen) which lodge in the crystal lattice or precipitate along grain boundaries. The level of impurity is a function of the grade of copper and is often given in parts per million (ppm). Copper as a raw material is available in a number of purity grades. Ordinary Tough Pitch Copper (TPC) is only 99.5% pure. Electrolytically refined copper is 99.9% pure and may be designated as three-nines or 3N in purity. This is the stuff of which common electrical conductors are made of. The next level up is 4N or 99.99% pure. The most significant impurity in 3N copper consists of oxygen atoms at a level of over 200 ppm. Being electronegative, oxygen is adept at latching on to free electrons.
The problems of ordinary zip cord are multiplied by its multi-strand construction. First, there's the problem of strand interaction. Second, by greatly increasing the surface area of the conductor, oxidation of the copper over time is significantly increased over a solid-core design of equivalent gauge. Because copper oxide is a semiconductor material, it behaves as a microscopic diode to rectify low-level audio signals. In terms of purity, Oxygen Free Copper (OFC) represents, in my opinion, the minimum starting purity for audio use. This is a 4N pure material, whose oxygen contamination level is only about a fifth (40 - 60 ppm) of that of TPC.
As an audiophile, the absolutely first question that should come to mind when considering a prospective cable purchase is: what grade is the conductor material?
In 1987 the Nippon Mining company, Ltd., succeeded in implementing copper purification technology suitable for commercial scale production of 6N high-purity copper. The 6N designation, of course, refers to the six nines in its level of purity: 99.99997%. It is a factor of 100 more pure than TPC, with less than 20 ppm oxygen content at crystal grain boundaries. Nippon Mining has also developed the technology for drawing various gauges of 6N copper and of heat-treating or annealing the wire to make it suitable for audio applications. Sold under the trade name of Stressfree 6N, and available for the first time in large quantities and in a variety of forms, the 6N grade has found its way into a diverse cross section of audio products: speaker cable, interconnects, phono cartridge wire, internal component wiring, voice coils, crossover coils, and even power cords. Acrotec's high-purity speaker cable and interconnects remain, to this day, in my stable of reference products.
A New Paradigm
I've already mentioned the use of various heat treatments to increase grain size. However, the efficacy of the various treatments depends on the level of impurities present. Grain growing conditions are optimum when the impurity level is lowest. Hence, OFC wires have much finer grains compared with Stressfree 6N copper. The crystal grains in 6N copper are considerably larger, so that the total number of boundaries is about 80 to 100 times smaller than in 4N copper for similar gauge wire.
It is known that impurity atoms precipitate preferentially at grain boundary sites. Ono and Kato, of Nippon Mining Company, discuss in a 1989 paper (87th AES Convention, October 1989, Preprint 2865) several ideas as to how impurity atoms at such sites may compromise audio signals. First of all, the precipitate impurities act as a nonconductive "wall" impeding current flow by scattering electrons. They also postulate the formation of microscopic "capacitors" at grain boundaries which cause signal phase shifts. Along the same lines, since these impurities attract and trap free electrons, it is possible that trapped electrons are released fractionally later in time and thus in a manner similar to the memory effect of a dielectric act to smear transient detail. At least such theories correlate with my own observations of the sonic impact of decreasing crystalline granularity and increasing conductor purity.
I can still recall Acrotec's demo many years ago at a Winter CES, where they compared 6N copper to 3N or plain vanilla copper. The cables were otherwise identical, as far as geometry and dielectrics. The richer, smoother, and more detailed presentation of the 6N cable still resonates in my memory banks. Over the years, I've had the chance to get to know Acrotec's 6N cable quite intimately, and then the 8N cables arrived at my door step. With the only variable being copper purity and grain size, I was surprised to find that as good as the 6N stuff was, the 8N cable was even more delicate and refined sounding. After all, we're contrasting 99.9999% pure copper with copper that's 99.999999% pure. While those last two nines represent a mere parts per billion improvement in purity, they were sonically audible.
The Silver Bullet
This is about as good a time as any to broach the subject of silver as a conductor material. As a conductor of both heat and electricity silver has no equal. The resistivity of 4N copper is 4.4% higher than that of 4N silver. It is only second to gold in malleability and ductility. One ounce of silver can be drawn into a fine wire about 30 miles long! It is commonly available in a number of grades. A common alloy form is sterling which contains 92.5% silver and 7.5% of usually copper. Jewelry silver is an alloy containing 80% silver and 20% copper. Lab-grade silver is 4N, and 5N as well as 6N grades are available at a significant premium. Outside of the high-end cable industry, silver is used for making printed circuit boards and as a plating for other conductors. High-purity silver wire is clearly a phenomenon of the high-end audio scene, where Siltech, Kimber, Audio Note, and AudioQuest have been the most noteworthy proponents of silver wire.
Available evidence indicates that silver is sonically less affected by oxygen impurity levels than is copper. Silver like copper oxidizes, but unlike copper oxide, silver oxide is a good conductor. That's probably the reason that 4N silver sounds much better than 4N copper. Another practical advantage is silver's greater resistance to mechanical damage. It is more readily shaped and drawn into wire with less crystal damage, so that the granularity of the wire and the number of crystal lattice dislocations is reduced. From this perspective it's easy to argue that silver is superior to copper. My listening tests suggest that when properly annealed and at sufficiently great purity (eg, 8N) copper is sonically the equal of 4N (but not 6N) silver and that other factors beyond materials come into play (see discussion on skin effect). However, OFC and even 6N copper are easily outdistanced by 4N silver in terms of liquidity of harmonic textures, preservation of low-level detail, and microdynamics.
Siltech, the Dutch cable specialist, has adopted the technical position that certain residues in refined silver are instrumental in improving signal transmission. Because Siltech's silver supply is a secondary product of gold mining, Siltech came to realize that gold inclusions in refined silver have a salutary effect on sound quality. That naturally suggests a gold-silver marriage for enhanced signal conduction, which Siltech has implemented in the FTM line.
I do not find silver to be inherently bright sounding, as others have. In my experience, some of the brightest sounding cables have turned out to be stranded copper designs. The worst of the lot could fry a gnat at 10 yards. In contrast, some of the sweetest and most liquid cables I've heard to date have been pure-silver Litz construction. For example, the Audio Note AN-SPX facilitates the upper octaves with remarkable finesse and grace - without even a hint of brightness. Of course, any cable can sound bright under certain conditions, and there were in fact instances where silver cable did sound bright in my system. Take the Kimber 4AG. Its airy and extended top highlights any inherent speaker brightness. Substituted for a rolled off cable and matched with a metal-dome tweeter, I can understand why the finger might be pointed at silver as the culprit. When cable is used as an EQ band aid to correct a tonal problem, substitution of a neutral cable into the chain is bound to cause problems. In the case of the Kimber KCAG interconnect, the situation turned out to be a bit more complicated. Being unshielded, it is prone to RF pickup. Its slightly bright sound in my system was totally mitigated by the application of AudioQuest's RF Stoppers.
Motherhood, Apple Pie, and the Skin Effect
Conductor and dielectric materials impact cable sound in several critical areas. First, the degree to which harmonic textures and colors are retrieved with a semblance of the purity and liquidity of live music is contingent on the level of purity and lack of granularity of the conductor material itself. Second, the "pedigree" of the conductor and dielectric materials influence resolution of low-level detail - including elucidation of the recording venue's reverberant signature. Finally, without the intervention of pure conductors, much of reproduced music's microdynamics would be squashed.
But that's not the end of the story. There's space, the final frontier, and the proper domain of the skin effect. Unless a cable design copes with the skin effect, it will be unable to paint a spatially believable soundstage complete with tightly focused image outlines. Let me go on record publicly to affirm the skin effect's essential role in audio cable design. It has been known for about 100 years that a conductor's self inductance forces high-frequency currents outward, toward the conductor's skin layer. Conductor cross section shrinks with increasing frequency; the electrical consequence being, of course, an increase in cable impedance with frequency. In the time domain, the skin effect may be said to cause phase shifts which delay bass and mid frequencies relative to treble frequencies. Because the skin effect is small over the audio bandwidth, it has been discounted by engineers as a serious factor in cable sound. Yet, listening tests tell another story.
The concept of skin depth is crucial for understanding the implications of the skin effect for cable design. Skin depth is defined for a given frequency and conductor material as the distance into the wire at which the signal decreases by a factor of 2.718. Skin depth obviously decreases with increasing
frequency. The following Table shows calculated values of the skin depth for circular conductors and various materials at a frequency of 20 kHz.
Material Skin Depth in mm at 20 kHz
To minimize the impact of the skin effect, conductor radius should be small relative to the skin depth at the highest frequency of interest. For copper at 20 kHz, the skin depth is 0.47 mm - or about the radius of a 19-gauge (awg) wire. For impedance to remain as [uniform] as possible over the audio bandwidth, 19-gauge or finer wire is indicated. The finer the gauge, the more uniform the impedance magnitude becomes but at the cost of a higher DC resistance, which you should realize by now is almost irrelevant for interconnect design.
Mapleshade/Insound have taken this approach to its practical limit by using a nearly invisible micro-conductor for their interconnect - the thinnest that can be handled by human hands. The conductor is so fine that a good sneeze during assembly, when the wire is still outside the shield, can spell the end.
An important observation to be gleaned from the skin depth Table is that the "worse" the conductor material, the greater the skin depth. Comparing copper to carbon, the skin depth for carbon is a factor of 2.85 larger. That means that a 19-gauge carbon fiber is already small relative to its skin depth. Therefore, at a given frequency, the more resistive the material, the more uniform is the current distribution in the wire. Another way of saying it is that the worse the conductivity, the smaller the skin effect. No wonder then that some Dutch audio pros have embraced the use of carbon in audio cable. In particular, van den Hul has introduced an interconnect based on carbon-fiber technology. As you can see, there is a method to his "madness," but my feeling is that such designs emphasize the skin effect portion of the design formula to the detriment of conductor materials.
High-resistivity interconnects may sport loop resistances in excess of 10 ohms per meter. That's about 100 to 200 times the typical loop resistance of a "normal" interconnect. The world record in this regard (at least for a commercial product) is surely held by Dave Magnan, whose Ultra High-Resolution Signature interconnect uses a conductive polymer for one of its legs. The resultant loop resistance is on the order of 35,000 ohms per meter! Such a level of resistance is bound to cause trouble with some preamps and power amps.
The traditional approach to taming the skin effect while at the same time maintaining low-resistance values involves the use of Litz construction. Litz refers to cables in which many individually insulated strands are used in parallel and the strand radius is smaller than the skin depth at the highest frequency of interest. There is also the requirement for a braiding that allows each strand to occupy as much of a position along the conductor surface as every other strand. In this way, each strand will see the same flux, on average, giving the conductor as a whole better current distribution. Of course, Litz cable opens up a can of worms in terms of interaction or intermodulation between strands, and has provoked some innovative fixes such as the Cardas Golden Section stranding. Cables that have been optimized in regard to impedance uniformity, sound more coherent spatially. Image outlines are brought into sharp focus, massed voices are easier to resolve, and depth perspective is fully resolved. My first exposure to a simple solid-core design was via the TARA Labs Space & Time speaker cable. I was amazed at the time by just how cohesive the harmonic envelope became. The cable's impact was akin to that of a focus knob on a slide projector, as it integrated harmonics into a tight space within the soundstage.
DO's Hall of Fame
Over the years, I've listened to dozens of speaker cables and interconnects, and in a variety of system contexts. Only a few of these cables have withstood the test of time, and have established themselves as sonic leaders either by virtue of offering value for the dollar or by being able to practically walk on water. Well, reference class, is probably a more restrained descriptor for the cost-no-object winners. I won't bore you with the losers; it would simply take up too many pages. The winners are hereby inducted into DO's Hall of Fame. I expect from time to time to welcome new inductees into the Hall of Fame roster - as the state of the art advances.
Please note that these listings merely reflect one man's opinion. And while I've listened to a multitude of cable products, it's fair to say that I haven't listened to everything out there. The intent here is to give you the reader a clear and concise idea of what speaker cable and interconnects I think ought be high on your shopping list. Culled form several dozen contenders, these cables have impressed me in at least one system, and often in the context of several systems. So without any further delay, the winners are...
P.O. Box 3060
The Quartz x 3 ($165/1m pair) interconnect uses 6N copper conductors to convey a detailed, yet unforced impression of the music's harmonic tapestry. Treble detail is also quite refined, accounting for the Quartz's natural flavor.
The Diamond x 3 ($950/1m pair) interconnect is the senior member of the Audio Truth series (I have not listened to the other "gems" in the series - the Opal, Emerald, or the Lapis). FPS silver used in an elaborate "Air-Hyperlitz" construction accounts for the Diamond's astounding level of harmonic textural purity. That such a level of purity comes bundled together with exceptional low-level detail resolution is a miracle indeed. Gloriously sweet and refined!
Did I mention the Diamond's spatial resolution? On some recordings, image outlines were so 3-D as to conjure the Gestalt of being there. However, in my experience the sound of the Diamond has been system dependent - so be sure to audition it in the context of your own system.
The Sterling speaker cable ($1,855/8 ft. pair) is only junior to the all-silver Dragon (which I have yet to hear) in the Audio Truth series. It combines long-grained silver with 6N copper conductors to achieve an exceptionally well balanced sound; warmer sounding than the Clear and much sweeter than the Midnight. Soundstage transparency and spatial focus are strong suites. Ditto for the preservation of harmonic textures. But, really, there are no weaknesses here. I've left the best for last: bass definition is outstanding.
2. Kimber Kable
2752 So. 1900 West
The KCAG ($552/1m pair) interconnect is a proud member of Kimber's AG silver series. Ray Kimber originally intended the silver line as a limited production, ultra high-end line, and never anticipated the universal stir such product would create among audiophiles worldwide. The KCAG has remained in the line essentially unchanged since I first heard it in 1988. Each leg consists of three "hyper-pure" silver conductors of differing gauges (Kimber refers to this as Varistand), Teflon-coated, and braided in the traditional Kimber braid.
Time has not tarnished this cable of the Gods. It still offers a slice of sonic heaven. Soundstage transparency is a joy to behold, and image outlines are forged as if by the hand of Zeus into a cohesive whole. There is a tendency toward brightness, but I'm convinced that its entirely due to the lack of a shield and the resulting susceptibility to RF pickup.
My recent experience with the Kimber Select KS-1030 interconnect ($1,560/1m pair) has convinced me that this unique design using Kimber's "Black Pearl" silver conductor in an orthogonally braided geometry is superior to the venerable KCAG. Its hallmarks are a remarkable textural purity and an absolutely holographic soundstage.
3. TARA Labs
2245 Ashland Street
TARA Labs' Prism 22 ($35/1m pair) easily gets my vote as the best sounding interconnect under $100 a 1m/pair. On the face of it, the Prism is a classic coaxial design which uses a single 1.15 mm diameter solid-core conductor and a braided copper shield as the return leg. Materials are all of good quality: long-grained OFC, polyethylene dielectric, and an anti-static polymer outer jacket. The RCA connectors are 24K gold-plated and are soldered with lead-free silver solder. The RLC parameters are given 0.1 ohm/m, 0.72 micro Henry/meter, and 115 pF/m.
Each Prism interconnect is hand-assembled and individually tested at the TARA Labs Factory in Oregon. Yet, despite (or probably because of) the lack of hi-tech engineering, the Prism 22 delivers big time. The sound is surprisingly smooth and spacious, with particularly sweet upper octaves. This interconnect knows how to cater to violin and female voice. Treble transients are always under control, and there's plenty of low-level detail in evidence. OK, so it isn't perfect: there are slight losses in soundstage transparency, clarity, image outline palpability, and microdynamics. The total sonic signature reminds me of a vintage Dynaco Stereo 70 tube amp - and I mean that as a complement from the bottom of my heart. Considering the asking price and its level of textural liquidity, the Prism 22 undeniably represents a minor miracle. Kudos to the TARA Labs team, and especially cable meister Matthew Bond.
Here's a product that Matthew Bond tells me he dearly loves, and I can understand why. On a tight budget? Well, at $3.95/ft pair ($47.40/6 ft pair plus a $50 biwire termination charge) the Prism Biwire speaker cable fits the definition of an entry-level product... and it's even biwire capable! What that means in no-brainer language is that there's one pair of spades at the amp end and two pairs at the speaker end. If your speaker doesn't have a biwire provision, simply double up the spades at the speaker end. Its sound bears a strong family resemblance to that of the Prism 22. Think of tube gear and you'll begin to form an accurate mental image of the Prism's ability to flesh out image outlines and caress harmonic textures. The speaker cable, however, gives up a bit more than does the Prism 22 in the realm of low-level detail resolution. An enthusiastic thumbs up for this puppy.
It's truly a mouthful: The Space & Time Rectangular Solid Core "Master" Generation 2 - a name befitting a member of the Royal Court. This speaker cable ($45/ft plus $90 termination) basic premise is that rectangular solid core (12 mils by 25 mils - 24 awg) is better than the equivalent 24 awg circular conductor - at least as far as maintaining a more uniform impedance versus frequency. Each leg is physically separate and consists of 14 of these conductors helixed around an inner Teflon tube. The outer jacket is an anti-static nylon braid. The RSC's sonic calling card is an open, deep, and spacious soundstage, replete with superbly sculpted image outlines. The soundstage feels right, being organically whole. The tonal balance is faithfully neutral, but bass definition is system dependent, ranging from tight all the way to lacking in impact with some amps and speakers. Spatial resolution aside, its reproduction of harmonic textures and retrieval of low-level detail retrieval are not quite competitive with the standard set in these areas by the Acrotec 8N-S1080 and silver-based Litz designs.
4. Acrotec/Nippon Mining
I have spent considerable time with some of Acrotec's 6N cables. Thus I can confidently report that the 6N-S1030 speaker cable at $25/1m represents one of the best bargains in the crowded cable sweepstakes. Construction is classic solid-core: a single 1.2 mm diameter 6N copper conductor per leg, covered with a braided fabric inner jacket and a clear PVC outer coating. The two conductors are positioned in a widely-spaced twin-axial (parallel) geometry. While not as liquid sounding nor as transparent and spacious as Acrotec's 8N cable, it is still head and shoulders above OFC-based designs. It will win many friends with its endearing textural smoothness, pristine textures, rhythmically quick bass, and neutral balance.
Another safe recommendation is the Acrotec 6N-A2010 ($500/1m pair). Resolution of low-level detail and clarity are nothing short of exceptional. It loses out slightly to solid-core designs in terms of delineating soundstage depth. But otherwise, it is capable of singing spaciously and sweetly in varied system contexts. Its sound is a tad less liquid and textures are a bit brighter relative to 8N copper. As such it comes across as actually sounding more lively than its 8N cousin in some systems.
The sonic leaders in the Acrotec cable clan are clearly the 8N interconnect and speaker cable. The interconnect is available in both unbalanced (8N-A2080,$850/1m pair) and balanced versions (8N-A2090, $895/1m pair). The 8N-S1080 speaker cable comes terminated with gold-plated 6N copper spades. At $1,395/2m pair it isn't cheap, but neither are silver cables. But, as with all things, quality costs. Simply put, as a family the 8N cable possesses startling clarity and transparency. Yet harmonic textures flow with stunning liquidity and with an expressive flair that is guaranteed to elicit the music's full emotional power. The manner in which these cable define the rhythmic underpinning of the music is just exemplary. And retrieval of micro detail is phenomenal. As with the Acrotec 6N cable, however, these 8N products fall slightly short of fleshing out a totally organic soundstage. Spatial information, for example, isn't sculpted in the incisive manner managed by the Siltech FTM cable family and the Fadel Art Products cable.
5. Fadel Arts Products
Fadel cable first came to my attention via Bel Canto Design's John Stronczer. "From France with love" was his basic message. Did he know that I couldn't possibly refuse the siren call of a French product? Jay Bertrand, the US importer, was even more animated about the sonic virtues of FAP: it's thrashing some of America's best cable (he specifically mentioned MIT and Transparent) was the crux of his feedback. What a challenge to the status quo! The man behind the cable turned out to be Dr. Jean M. Fadel, who had a distinguished engineering career with the Thomson company in France. Dr. Fadel tells me that his work should not be regarded as a scientist's attempt to predict sound quality from a set of formulas, but rather as that of a music lover's attempt to solve a concrete problem by artfully using his scientific knowledge. When he launched the company in 1985, his idea was to design a cable with a constant characteristic impedance over the audio bandwidth. You should know that characteristic impedance is a critical parameter in transmission line theory. His colleagues (all engineers I might add) laughed at him. After all, conventional engineering wisdom maintains that transmission line models are valid for signal propagation over mile-long distances (e.g., telephone lines), and clearly inappropriate for distances less than 1/30th of a wavelength. In realm of RF or VHF, wavelengths are in meters, so even fairly short cable would qualify. But for audio signals, electromagnetic wavelengths are typically several miles long, which defines a lower limit for the model of about 1,000 feet. Over distances of less than 1,000 feet, a transmission line model for audio makes no conventional engineering sense. And I need not tell you that a 1,000 foot run is considerably longer than your typical domestic cable run. Undaunted, and encouraged by the fact that none of these engineers could explain sonic differences between cables, he proceeded with just such a design. The sonic results were so amazing that he was immediately convinced that he was on the right design path.
Fadel Art cable is said to be based on the technical premise that independently of the quality of the conductor material itself, and independently of the structure of the conductors inside the cable, phase and impedance corrections are absolutely necessary to realize perfect signal transmission. A sophisticated electrical network mounted inline with both legs of the cable provides the requisite phase and impedance compensation. Resistors together with both series and shunt coils are used in the compensation network. The coils use a core of carbonyl-iron powder. This material features a low permeability (about 35), high saturation, and efficiency up to a frequency of 300 MHz.
The IC 15S interconnect ($1,250/1m pair) employs a balanced geometry. The construction of each leg is unique in that both solid-core and tubular conductors are used in tandem. Specifically, a 0.6 mm diameter, solid-core silver wire is positioned inside a silvered 4N OFC tube (0.3 mm thick). The copper tube is encased in Modified Teflon insulation, 0.2 mm thick. This is a special material created by Dr. Fadel by mixing Teflon with carbonyl-iron powder, and is patent pending. An outer PVC jacket encases both legs. Gorgeous locking WBT RCA plugs are standard.
The Streamflex Plus speaker cable ($1,500/1m pair) uses separate legs. Each leg consists of two concentric silvered 4N copper tubular conductors, 0.2 mm thick, with Teflon insulation. A 1-mm diameter carbonyl-iron core is located in the center of each leg. This core is not used to handle any signal, but rather to increase the inductance of the cable as part of the phase and impedance correction.
The FAP line attempts to address all of the pertinent issues in cable design, from A to Z. Just how well did it succeed? The Fadel cable first made its appearance in the reference room, where it was used with the likes of the Sound Lab A-1 loudspeakers and Fourier Components' Panthere OTL power amp. In this realm of ultra-high end, every little nuance of a systems change seems to make a difference. So I fully expected that the Fadel's sonic signature would be readily exposed. What I found out in a flash was just how poorly previous cables managed to portray the soundstage. Image outlines were absolutely unwavering and so solidly anchored within a totally convincing spatial perspective, that I sat for several minutes in stunned silence. The impact was that dramatic with just the substitution of the speaker cable. With the addition of the interconnect to the system, spatial precision was such that every instrument within the soundstage - both laterally and front to back, became untangled and individually distinct. These cables redefine what 3-D palpability is all about. Granted the Fadel isn't perfect; textures are a bit sweeter and more liquid sounding through the Siltech FTM4-SG and the Audio Note AN-SPX. And the Siltech's upper octaves are also more refined and lucid. But it is by virtue of delivering such a convincing all-around performance that the Fadel is hard to beat.
The Omega Mikro Planar-Active speaker cable ($995/5ft pair) is the world's first active speaker cable. A battery power supply is included with the cable! For what purpose you ask? Well, let me explain. The cable consists of separate legs, with each leg made of a bare copper ribbon inside an open-mesh polypropylene sleeve or shield. The shield is "floating" electrically; it isn't connected to the conductor at either the source or component ends. The function of the power supply is to apply a DC bias voltage to the shield. Two 9-volt batteries in parallel bias each shield. The idea according to Mapleshade's Pierre Sprey is to electrostatically isolate the conductor from external electro-magnetic energy. This technique was apparently used many years ago to reduce noise induction in telephone lines. He attributes the sonic gains to the reduction of RF noise pickup, though I'm inclined to think that the actual physical basis has more to do with improved current distribution in the ribbon conductor.
While the cable is available in a "passive" version at a savings of $400 for a 5-foot set, the active version sounds so much better, that I wouldn't consider a second best in this context. A similar biasing scheme is used with the Omega Mikro Active interconnect ($795/1m pair). There's almost no current drawn from the power supply. Therefore, the battery lifetime should be approximately equal to the battery shelf life. Mapleshade suggests checking the battery voltage every two months with a voltmeter. The instructions call for changing batteries when the voltage drops below about 18.8 volts. Only Carbon-Zinc dry cells (e.g., Radio Shack Heavy Duty) are recommended; apparently Ni-cads and alkalines don't sound as good.
Because Mapleshade/Insound have found no limits to the benefits of ever-thinner wire, the interconnect's conductor diameter here has been taken to the limit. A nearly invisible solid-core copper conductor is used. It is so thin, that its resistance is about 150 ohms per meter. A bare bi-metallic shield is used to protect the conductor. Because of the materials used, the interconnect is limited in length to a maximum of two meters. Mapleshade believes that they have gone further than other manufacturer in reducing not only the skin effect, but also dielectric absorption. In addition to using low-absorption materials, they use a factor of 10 to 100 less mass than other designs. For example, the speaker cable uses a loose fitting mesh sleeve with lots of air gaps, as opposed to the industry practice of molding dielectric material directly onto the skin of the conductor.
Note that neither of these products is particularly user friendly. The interconnect is stiff and requires care in bending. The speaker cable is fragile, and can easily be crushed by being stepped on. Mapleshade chose not to compromise sound quality by bullet proofing the product. Mapleshade warns prospective users that their cable should not be used around young children, pets, or careless wielders of vacuum cleaners.
The Active cables imbue the midrange with liquid textures. In particular, the lower mids glow with a natural warmth that does wonders for string tone. The body of a cello or double bass is exquisitely portrayed, with the lyrical quality of these instruments fully intact. Disconnect the power supply and join the shield leads together (to simulate the passive version of the cable), and much of the midrange warmth vanishes into thin air. Resolution of microdynamics is exceptional. Dropping these cables into the reference system, felt like juicing up a Honda with a 200 horsepower engine. The soundstage all of a sudden resonated with energy. Instrumental outlines ebbed and flowed with gusto. And, of course, in matters of spatial resolution the Actives are most convincing. Image outlines are forged into a tight focus with excellent 3-D palpability.
Along with the Acrotec 8N, the Mapleshade Actives represent the best all-copper cables money can buy. Although the Actives are not quite as smooth sounding nor as detailed as the Acrotec, they outshine other copper cable in the areas of microdynamics and imaging.
7. Audio Note Japan (web site: http://www.audionote.co.jp/)
Audio history was made in 1976 when Hiroyasu Kondo, president of Audio Note Japan, unveiled the world's first 4N pure silver cable (the AN-V). Mr. Kondo, the "Audio Silversmith," is single-handedly responsible for putting silver technology atop the high-end totem pole. The current reference interconnect, the AN-VX ($900/1m pair), and the reference speaker cable, the AN-SPX ($400/1ft pair), were introduced in the early 90s. And it's really a shame that it has taken this long for these products to find their way into the reference room. My listening impressions to date, however, are almost entirely limited to the AN-SPX speaker cable. Audio Note uses 4N silver exclusively in all of their silver-wired products. This is lab-grade silver, and much more expensive than the garden variety silver which is alloyed with copper, such as sterling silver (7.5% copper) or jewelry-grade silver (20% copper). Each silver strand receives six coats of polyurethane at "birth," as the wire leaves the final diamond die. This process not only prevents any surface oxidation from taking place, but also controls surface vibrational energy. Audio Note believes that even silver oxide is detrimental to signal transmission because of its low-level signal rectification. Litz construction is used together with small-diameter strands (0.2-mm diameter for the AN-SPX) to control skin-effect related phase shifts.
Sonically, the AN-SPX sets new standards in several respects. Its voicing is utterly natural. Harmonic textures ebb and flow with a lyrical majesty, as if fashioned by Mother Nature herself. The AN-SPX conjures a mental images of pure silk and velvet. Just listen to how this cable preserves the textural purity and integrity of a soprano's upper registers. Folks, it doesn't get any more liquid or pristine than this. The treble is well integrated with the mids, but is a bit softer sounding than the upper range of the Kimber 4AG or AudioQuest Diamond. And neither is it as quick as that of the Siltech FTM. Relative to the Kimber, the AN-SPX is tonally a tad more laid back through the midrange. However, the body and natural warmth of stringed instruments is properly preserved. Image outlines are portrayed incisively with exceptional focus and plenty of reach-out-and-touch-someone palpability, though soundstage transparency falls short of the standard set by the Siltech FTM4-SG and FTM4 GOLD. A benchmark product in terms of harmonic integrity and purity.
The AN-SP speaker cable ($200/1ft pair) bears a strong sonic resemblance to its more expensive brother, the AN-SPX. It isn't quite as sweet nor as spatially focused, but at half the price it represents a great value in silver cable.
US Distributor: Siltech America, Inc.
Siltech stands for Silver Technology, and although the company was founded in 1985, it has already established a pre-eminent position in silver and gold metallurgy for audio cables. From the start, silver became the focus of attention by virtue of its superior conductivity, chemical stability, and ability to maintain its crystalline integrity when subjected to mechanical stress.
The current president, Edwin Van Der Kley, joined Siltech in 1991. An experienced electronics engineer with an addiction to music, he set up a research program based on the premise that the secret of cable performance lies mainly in its conducting properties. As part of this program, Siltech designed an analog measuring system capable of -150 dB resolution relative to the primary signal. The payoff came in 1992 when Van Der kley discovered an enhanced conductivity state which he has dubbed as the gold-silver marriage. That very same year, the first FTM-4 GOLD was born. The GOLD uses 6N silver, 24-K gold, and Teflon.
Why gold you ask? Gold is even more malleable and ductile than silver, and even more resistant to damage under mechanical stress. A single ounce can be drawn into a wire 35 miles long! Gold is resistant to most naturally occurring chemicals so it doesn't oxidize or tarnish. The yellow metal is quite dense, being almost twice as heavy as lead. However, its electrical conductivity is not as good as that of either silver or copper. I'm sure that if conduction electrons could talk, they would sing praises for both silver and gold wire. Lack of granularity and oxygen contaminants make the electron's passage more efficacious from an audio standpoint, as there is less opportunity for time smearing and loss of low-level detail.
The following cable products represent the "Crown Jewels" of cable kingdom; the most perfect means known to me of conducting an audio signal. Let me start with the LS 4-180 ($1,550/1m pair). It is only second to the LS 4-240 (which I have yet to audition) in the LS speaker cable series, and is considerably better than the LS 4-120 ($990/1m pair) which I have auditioned. The 4-180 already uses 84 pure silver strands (0.5 mm diameter) in a Star-Quad geometry. The latter term refers to the use of four individual bundles of strands per channel, with the diagonally opposing bundles connected in parallel to define symmetrical "go" and "return" legs. The shield is silver coated, and gold-plated spade lugs are standard. However, I'm told that solid silver-gold spade lugs of increased conductivity are now in production.
As with other Siltech cable, the LS 4-180 is directional and should be connected so that the lettering on the jacket points or reads from the source to the target component. This is the only cable that can match the flesh and bone image palpability and spatial resolution of the Fadel Streamflex Plus. Yet, it is even more transparent than the Fadel. The soundstage is accessible through an absolutely pristine window. The Siltech cuts through several layers of haze, and thereby dramatically heightens the illusion of being there. The window is so clean that it's possible to resolve every layer of depth and explore every recess as if a the stage were suddenly flooded by the midday sun. Spatial resolution is such that massed voices or instruments in a complex passage are allowed to breath individually. Spatial detail is painted with a fine brush. Harmonic textures bubble forth from a velvety background - without even a hint of grain. It is precisely this combination of textural purity and spatial finesse that coaxed the Sound Lab A-1 to new heights of concert-hall realism.
The Siltech sounds fast. Microdynamics appear to be "turbo-charged." The attack and decay portions of each transient are digested without any time smearing. The harmonic envelope ebbs and flows organically, shifting gears from pianissimo to fortissimo levels without a glitch. It becomes mere child play to discern the precise moment when a mike overloads or when compression is used on a recording. Bass lines are exceptionally tight, as good as I've ever had it. And best all, the upper bass range is imbued with a natural warmth that does magical things for cello and double bass timbres.
The FTM-4 SG ($1,600/1m pair) interconnect delivers even more. All of the FTM products are similar in construction, which is based on a co-axial toroidal ribbon geometry. The ribbons are spiraled around an inner core, creating a low-inductance and low-capacitance signal path. Impedance is kept very low ( below 0.003 ohm per foot) to prevent interference from ground loop current. The FTM-4 SG uses two 4.0 x 0.3 mm silver ribbons, and an inner core of 28 0.3-mm diameter silver strands together with a single 24-Karat gold strand. That works out to about a 3% pure-gold cross-sectional area. Gorgeous WBT-0150 locking RCA connectors are standard for all Siltech interconnects. The treble range is startlingly transparent, fast, and lucid. The delicacy with which struck and brushed cymbals are resolved is without equal. The Siltech is a fountain of low-level detail. It's all there, in a totally natural manner; much unlike the artificial, "in your face detail" presentation realized by cables which etch treble transients. These false gods may impress at first, but after a prolonged exposure to such demons of brightness my ears start to bleed. The Siltech delivers the goodies all right, but it's cat like in its demeanor. The Siltech's richness of detail is not immediately obvious. But as soon as you decide to focus on a particular instrument or passage, you begin to download nuances that you never realized were hiding on your favorite records. The Siltech allows you to dig as deep as you want. In particular, the ambient signature of a hall, and treble nuances were more faithfully resolved than with any other interconnect I've heard to date.
8. Music Advancement Company Wire (MAC wire)
You don't really have to mortgage the house in order to pay off that high-end cable purchase. MAC wire offers cost-effective, high-purity copper, cable products that are worth checking out. MAC's Ray Bauman has provided me with samples of 6N copper hook-up wire that I highly recommend, after having used this wire in the context of the BassZilla loudspeaker project. The 22 gauge solid-core yields wonderful image focus and spatial bloom, yet allows you to stay within budget.