April 1, 2003
The Wonder of Wire
So youve visited your local high-end audio emporium and put together a ne plus ultra system that includes the latest digital front end, show-stopping amplification, and premium speakers, all of which are boxed and invoiced and ready to load into the car. Think youre done? Think again. Those components will need to be connected to the wall and to each other, and the reason the salesperson is coughing and looking at the floor is that he doesnt know whether to throw in a few junker cables for free and let the customer go home happy, or tell the truth about how much good wire is going to cost.
Ever wonder how manufacturers can possibly justify charging more for a pair of interconnects than you paid for your amp? Or ask yourself what kind of customer would actually pony up at those prices? I have. Just after I maxed out my credit card on a pair of MIT 350 interconnects at $2500.
If you believe that audiophiles are mostly made and not born, and I do, then every audiophile must have a teacher. My own stereo spirit guide, lets call him Brian, is an employee at a distinctive boutique audio shop in my area. Hes about three feet tall, green in color, and claims to be several hundred years old. I dont believe the age bit, but the green color looks natural. His selling technique is simple and effective: loan the customer a couple of products that are in the price range he wants to pay, and throw in a higher-priced model "for comparison" purposes. Almost inevitably, the higher-priced item blows the doors off the competition sonically, and the sale is made. With regard to wire, this technique has been devastatingly effective. Good wire, you see, really has to be heard to be believed. Manufacturers are making wire at a dozen price points in this fiercely competitive market, there is no clear winner in terms of technology, and you cant look at the fitnfinish or peek under hood to compare build quality the way you can with electronics.
What can wire do to the sound? It is, after all, a passive component, right? Well, maybe passive-aggressive. Even imaginary, ideal, perfectly uniform wire has capacitance, inductance, and resistance, which depend on the conductor material used, the geometry of the arrangement of conductors (coaxial, twin wires, braided, woven, et cetera), the kinds of dielectric materials used in the insulation and the shielding, which is designed to keep the cable from acting like an antenna by rejecting radio-frequency noise. Capacitance in series acts as a high-pass filter, shutting out bass, while capacitance between the hot wire and the ground wire can shunt high frequencies to ground, which has the effect of rolling off the treble. Worse, since we are dealing with a signal that is analogous to sound, it is in fact alternating current (AC), and the capacitance we are talking about is really reactance -- the proper term for the AC version of DC capacitance. Similarly, the resistance is actually impedance, the AC version of DC resistance. Both of these properties, as well as inductance, vary depending on the frequency in real wires. As a result some cables have a bright tonal balance and sound "tipped up," while others emphasize the bass and sound dark. Ditto midrange emphasis, midbass hump, and other lumpy non-linearities.
So cables can alter the tonal balance (i.e., amplitude spectrum) of music. Big deal, you say, throw in a tone control or use an equalizer. Unfortunately, this is just the tip of the iceberg. Mechanical waves, such as sound waves, travel at a speed that is fixed by the elastic properties (the elastic modulus) of the medium in which they travel, so a 20kHz sound travels through air at exactly the same speed as a 20Hz sound. Now consider that the propagation of electricity is an electromagnetic (EM) wave, and not a mechanical wave. It arises from the mutually reinforcing action of perpendicular electrical and magnetic fields, and hence provides its own medium. Thats why light, which is a form of EM, can travel through a vacuum, as can radio waves, which are just light at sub-visible frequencies. Different frequencies of light, unlike sound, however, do travel at different velocities when moving through a medium other than a vacuum. In a glass prism, for example, lower-frequency light (at the red end of the spectrum) travels more slowly than high-frequency light (at the blue end). If a beam of white light, which contains both reds and blues, hits the prism surface at an angle, the whole beam will be bent toward the perpendicular because the first corner of the beam front to hit the glass is slowed down before the last corner hits. Since the reds will slow more than the blues, these colors will be bent to a greater degree than the blues, causing the colors to separate from one another in the prism. This effect, called dispersion, is generally a pleasing pattern of pretty multicolored lights that delights children.
Now think of your audio cable, which consists of a medium through which the EM waves of your music is passing, and imagine that the various frequencies in it are being transmitted at different speeds. When the separated frequencies arrive at their destination, the phase changes and outright transient delays that result will likely not be so pretty to your ears. Some cables distort transients, making them soft, while others exaggerate them. Cables can give the impression of being fast or slow in terms of their transient response, or even in terms of the perceived tempo of the music. A fellow named Heaviside established a clever way of making the various frequencies traveling in a wire go at the same speed by balancing the speed-increasing effects of capacitance with the speed-slowing effects of inductance. This is called Heavisides Condition. Cables in which the ratio of conductance to capacitance equals the ratio of resistance to inductance (G/C = R/L) satisfy Heavisides Condition and may sidestep this problem (assuming all the other sources of distortion are controlled). Companies that use network boxes, such as MIT and Transparent, for example, introduce capacitors, inductors, and resistors in the boxes in part to make the cable satisfy Heavisides Condition.
Then theres the dreaded skin effect. Though most of us think of wire as passing electrons through it under voltage the way a pipe passes water molecules under pressure, the reality is that most of the energy traveling through the cable resides in the EM fields generated around it, not the electrons themselves. The wire functions not as an electron pipe, but as a wave-guide (though that is a term usually reserved for tubular conductors guiding very high-frequency EM). Since high-frequency EM penetrates a conductor less than low-frequency EM, the result is that the high frequencies tend to be confined to the skin or outer surface of a solid-core conductor. As they travel through a smaller cross-sectional area of conductor, and impedance is inversely proportional to area, they experience greater impedance. Hence the high frequencies experience more signal-power loss and travel slower. The sonic result is high frequencies that are rolled off and delayed; again, not a happy situation for your music. The imaging, realism, and accuracy of the high frequencies can be, and often are, compromised. Skin effect can be combated through the use of a higher-conductivity material, such as silver, plated on the outside of a lower-conductivity material such as copper, or with a Litz wire configuration, in which the conductor consists of multiple strands insulated from one another by a thin varnish-like coating, a technique often used by Cardas, for example. Other companies try to increase the surface-area to volume ratio of the conductor by using oval, rather than round wire.
Speaking of cable geometry, did you know that cables could be microphonic? Yes, indeed. Small alterations in the spacing between wires can alter capacitance and inductance, resulting in a cable that picks up sound from the room and modulates the signal with it. Ouch.
Finally, the "nines race" and the issue of grains deserve mention. The conductance of materials is strongly affected by the presence of impurities, particularly oxygen, which tend to react chemically with the conductor and form metal oxides, so some cable manufacturers go to great lengths to use super-pure metals. High-purity copper, for example, is 99.9% pure and contains 235 parts-per-million (ppm) of oxygen. In addition, the way the wire is worked also affects its sub-microscopic structure. Copper wire is ordinarily cold-drawn through a mill. That is, transformed from a solid copper billet of the sort produced by Inco into a wire of the desired diameter by rolling and stretching it. This process jumbles-up the crystal-lattice arrangement of the copper atoms that occurs as molten metal solidifies at the smelter. The result is a bunch of crystal fragments called grains that abut one another randomly. These structural discontinuities are said to distort the sound by interfering with the passage of electrons and the uniformity of the EM fields. The high-purity copper mentioned above might have 1500 of these grains per linear foot. Enter oxygen-free, high-conductivity copper (OFHC), which is 99.99% pure. It contains only 40ppm of oxygen, and has 400 grains per foot. The grains are reduced by annealing the wire (reheating it after drawing to near molten temperatures, and allowing it to cool and form uniform crystals in a low-oxygen environment). A Japanese man by the name of Ohno (oh yes) has taken the nines race even further with his Ohno Continuous Casting (OCC) process, which is said to result in 99.9997% pure copper containing single-grain "monocrystals" that are over 700 feet in length. (Of course, the nines do start to become a bit hard to verify because of the limitations of measuring techniques at this level of purity.) Companies such as Acoustic Zen tout their use of OCC copper as central to the sound of their cables.
What does all this mean? Do you need a crash course in metallurgy and electromagnetism to purchase cables intelligently? No, but you do need to listen to them carefully, preferably under the tutelage of a suitable pointy-eared sensei who can emphasize the virtues of good cables -- wide soundstage, precise imaging, accurate tonal balance, speed, dynamics, lack of blur, and accurate high-frequency reproduction -- and guide you away from the dark side of hyper-detail, graininess, thinness, slowness, bloated bass, and phony phase effects. Though cables do tend to work better with some components than others because they may compensate for deficiencies, beware the trap of buying ever-more-expensive cabling, when what you should really do is upgrade your amp. That said, thankfully cables tend to have an identifiable signature that is relatively consistent, even with different components, so the task of choosing one in the face of multiple other system variables is not impossible. The kind of rules tossed around by audio salespeople such as "you shouldnt spend more than 25% of your stereo budget on cables" are pretty much tripe. If a $2000 cable makes your $3000 system sound as if its worth $6000, then it may be a bargain. And dont forget power cords. Remember that ultimately all the electricity that makes the music comes from the wall. All the properties discussed above apply, though the sonic signature of power cords is often even more consistent than with other wire. Imagine how surprised I was when the sonic signature of a power cord plugged into my amp could also be heard when I used that cord on my CD transport! Sometimes power cords can even impose their signature on your system when plugged into an unused outlet because of their effect on the house circuit. Happy listening, and may the forge be with you.
Ultra Audio is part of the SoundStage! Network.