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Bigger is not always better

By Roy Johnson, loudspeaker designer, Green Mountain Audio, Inc.

If you were looking for a quick tip about how to choose the best speaker cables, we believe it is more cost effective to first improve the 'front end' of your audio system -- the CD player and its cables -- before upgrading the speaker cables. This is because any distortions introduced at the beginning of the chain are always magnified (multiplied) by the rest of the system, including poor speaker cables. If a new speaker cable does not dramatically improve your musical experience or emotional involvement in a soundtrack, try another.

Otherwise, it seems each variety of speaker cable has its own group of evangelists. This article will help you better understand today's cables, burn-in, wire length, bi-wiring, connections, and how to select a reputable manufacturer.

The state of the art

The first insulated wires were made to 'just carry electricity,' such as the first successful trans-Atlantic telegraph cable pictured above.

Since copper smelting and refining had been mastered on a large scale by then, new research centered around improving copper's conductivity (less resistance) and determining which wire sizes and layouts best carried high-frequency signals over long distances. Until the late 1970's, not much thought was given to how speaker cables might affect the music. And even today, theory is still insufficient to completely explain what is heard when different gauges (diameters) of wires are used or when the wires are twisted together -- to name only two variables.

Advertising

To cut through the advertising hype, it helps to know something about the technology of speaker cables. Manufacturers usually promote a few technical aspects as meaningful, and we have yet to hear direct correlations. Many variables of cable design affect the sound, though. For example, bass is not necessarily better with thicker wires. However, it is easy to advertise a few, high-tech concepts because that is all most of us need to read. Communicating exactly what the average consumer wants to know also depends upon the time in history. Henry Ford knew the best thing to imply about his first car was that it did not break down.

Metals

Some cable designers believe silver makes the best-sounding conductors while others feel copper is best. There are those who use a silver-plated copper and some think alloys are the way to go. Some feel a single, solid round conductor is best, and still others believe a flat ribbon conductor makes the best sound. Some find that many smaller round conductors are best and a few have used hollow metal tubes.

Each has its advantages according to physics. There can be no 'best' one metal for conduction, nor one best method for arranging the conductors. What one hears is always the resulting synergy between all aspects of a speaker cable's design, including its insulation. The best-sounding speaker cables consistently come from designers who pay attention to all areas of design and conduct controlled experiments to probe further into each variable. Indications of this attention to detail might be seen in their literature and on their websites, if they are willing to make such things known.

Metallurgy of the raw wire

Physics indicates and lab experiments show that the process of forming a single wire affects how smoothly the electrons literally can be shaken back and forth inside the wire by the amplifier's signal (those electrons never traveling much beyond about 100 atoms distance, back and forth).

Forming a wire begins by decreasing the diameter of a metal rod. For copper, that rod is about 12mm in diameter. It is heated and slowly pulled through a series of ever-smaller rollers and precision-shaped diamond dies which are highly polished and well-maintained. There is much more to this process, including annealing (heating to semi-softness) the wire to reduce impurities and micro-fractures. The wire's surface might be finely-polished as it is wound onto its reel. Perhaps the insulation is added at that time.

The first micro-photograph of copper (left) shows how it looks after casting. Notice the many air bubbles?

The middle image shows the crystal structure after the rod has been drawn down to a fine wire. Note the difference in scale?

The third image shows how annealing reduced the individual grains.

Wire can be cryogenically-cooled to further reduce fractures and drive out or consolidate impurities. The slowness of that cooling process, the time spent down at temperature, and the time taken to come back up to room temperature are each important.

Purity of metals

That original copper rod already contains oxygen. Considered an impurity at the end, it was intentionally injected into the molten copper where it combined with impurities to form water vapor and sulfur dioxide. The subsequent removal of the remaining oxygen during the rod's draw-down process prevents the formation of copper oxide, a molecule which does not allow electrons to pass neither smoothly nor equally in one direction versus another. One result is a grainy-sounding harshness added to the signal. Copper oxide is also the green tarnish seen on copper objects.

'Oxygen-free copper' (OFC) is thus widely advertised, such as '99.9999% oxygen-free' (or 'six nines' purity). The actual trademarked name, OFHC (for high conductivity), is held by the Phelps-Dodge Corporation.

However, neither OFC nor OFHC is a guarantee that the newly-formed surface of the wire was not exposed to oxygen during the draw-down process, but only refers to the interior of the wire. Any copper wire also has some amount of secondary-metal content which is very difficult to remove, such as a few percent of silver and smaller amount of other metals, and some sulfur. Those are not part of an OFC or OFHC specification.

Insulation

Any insulation affects the signal, because the electron-orbits around the insulator's molecules are easily warped by the signal passing by in the wire. To pull the electrons into those new orbital paths requires energy -- energy drawn from the signal. It is then released back into the wire after the signal has passed, when the electrons are free to assume their usual orbits. The energy stored in the insulation is calculated using the insulation's 'dielectric constant.' The time for that energy's release depends upon the insulation's 'dissipation factor.' Lower numbers for both are better, but are measured only on very high-frequency test tones, never on the dynamics of music.

What can be heard from some plastic insulation is a smearing of the signal, especially on complex music. Teflon is considered by many as the best-sounding plastic insulation, but it must be extruded around the wire at a very high temperature which can push oxygen and other compounds into the surface of the wire. However, Teflon is more rigid than polyethylene or polypropylene, so it does not mechanically damp a wire's internal vibrations as well. Vibrations are caused by the electron motions inside the wires, and by the magnetic fields attracting and repelling the +/- conductors to and from each other.

Some manufacturers surround their wires with a great thickness of plastic, which leads to a smeared sound in the treble, with reduced detail and dynamic contrasts elsewhere.

But perhaps that makes up in some way for speakers that are too 'sharp-sounding,' or too 'edgy.'

There are wide, flat, thin wires covered with tight-fitting plastic insulation. Those sound much different than the same insulation material covering the same mass of round wire, because many more plastic molecules are in contact with that flat wire's metal atoms.

Layout of the conductors

When the two +/- speaker conductors are placed near each other, they vibrate through the changing magnetic field surrounding each one attracting and repelling that of the other. Twisting those two wires together does not prevent this interaction, in fact it strengthens the forces because the two wires are close together. Twisting only reduces how much of the magnetic fields are broadcast out into the room. The wire vibrations are difficult to damp, and for example we have heard them add resonance to certain notes in the bass.

The best solution is to keep the +/- conductors separated by a few inches, and run not completely parallel to each other. Many choose to lift their cables off their carpet, and again the sound is a little more clear, because the signals are less affected by the dielectric constant of the carpet fibers.

Speaker cables with their +/- conductors woven (not twisted) together can be very flexible. This flexibility has been heard to rob the bass drum of its impact. Cables that are very rigid have been heard to resonate on high notes.

Length

Left and Right speaker cables need to be the same length, no matter how long. When there is more than a 10 percent difference between the two, a dynamic inequality will be heard between the two speakers which no balance control can correct. Any extra cable should lay in a loose, non-organized coil to avoid magnetic restriction of the signal.

Long speaker cables can greatly change the sound of many speakers (not so much ours). When the cables are long, it is common wisdom to use a heavier gauge, for less resistance between the speaker and amplifier. It is thought that the higher resistance of a smaller-diameter wire reduces the amplifier's control of the speaker's woofer, causing some speakers to become 'boomy' in the bass. Again, we have heard speaker cables of smaller diameters that do not create this effect, so perhaps the smaller diameter is not the real culprit. Trust your ears!

Some believe short speaker cables sound better. This may be true with certain brands, but we have heard many examples where a longer length has less resonance in a particular tone range, a resonance seemingly caused by the magnetic fields of the signal interacting between the +/- conductors, or by the current flow inducing a vibration inside a single conductor. We have heard short speaker cables resonate in the voice range. We have heard an 8' (2.5m) pair resonate on drums and on one note of a string bass, but not in its 11' (3.5m) version.

Connections

To make quick connections, many retailers use 'banana plugs' on the end of their speaker cables. This is only for convenience, as they do not connect as well as 'spade lugs.'

Speaker cables can also be terminated in metal 'pins.' However, those do not provide much surface area for connection and are to be avoided.

Bare wires need to be connected very tightly and checked every year for corrosion. We recommend spade lugs on both ends of the wires.

On most speaker binding posts, a finger-tight connection is not good enough, so tighten them with a nut driver. Avoid using a wrench, as the additional leverage will break most binding posts, especially the plastic ones.

Check your new speaker cable connections at both ends a few times during the first month of ownership, until you are satisfied that they are solidly tight. Clean those connections at least once a year with denatured alcohol. Even gold-plated connections can become contaminated by the oils and sulfurs from cooking. We recommend the cleaners made by Caig Laboratories.

Break-in or burn-in

Speaker cables do 'break in' and become clearer and less 'electronic sounding,' especially on complex music and soundtracks. While there are many explanations for what is going on, the process takes about 300 hours to fully complete. We find that break-in is best accomplished with varied music instead of test tones or noise because the dynamics of music have a far greater effect.

Bi-wiring

Bi-wiring means running separate wires from the amplifier to the woofer section, and to the midrange and tweeter section. The idea is that distortion in the wires is reduced, which is true.

However, for our speakers, bi-wiring is not worth doing, as that money is better spent on one set of truly extraordinary speaker wires. This is because bi-wiring disrupts the careful blend we have achieved between the drivers.

Recommendations

When trying new speaker cables in your system, relax and play a wide variety of music. Take advantage of your retailer's experience with many different brands. In website chat rooms, look for extreme consistency of very positive reports, regardless of the systems in which that cable is used. Avoid fads and speaker cables that have a large 'filter network' box.

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