Technical White Papers
Cables White Paper
Electrostatic loudspeakers (ESLs) are different. The load they present to an amplifier and speaker cables is quite unlike that of conventional magnetic speakers.
To an amplifier or speaker cable, ESLs appear as a capacitor, while magnetic speakers appear as a combination of a resistor and inductor. It therefore is not surprising that cables for ESLs have different requirements than those for magnetic speakers.
The electrical parameters of cables are inductance, capacitance, and resistance. Let's look at these elements more closely and see how they should be optimized for ESLs.
An ESL is driven by a high-voltage, step-up transformer. This transformer is inside the speaker where you don't see it. It converts the relatively low voltage of an amplifier to the several thousand volts needed to drive an ESL.
All transformers have leakage inductance. This inductance interacts with the capacitance of an ESL to form an L/C (inductance/capacitance) resonant circuit. This produces an undesirable, high-frequency, resonant peak in the frequency response of the ESL.
It is essential that this resonance be kept in the supersonic region (well above 20 KHz) so that it doesn't alter the high frequency response of the speaker. Since the capacitance of the ESL is fixed, the only way to get the resonance high is to build a transformer with very low leakage inductance.
Designing and building very low leakage inductance transformers that will operate over a wide frequency range and at high voltages is extremely difficult. One of the reasons that some ESLs sound better than others is the design and quality of their transformers.
Inductance is a big problem with ESLs due to the L/C resonance described above. ESL manufacturers expend great effort to obtain transformers with low inductance. So it is very important that the cables have low inductance too. If the cables add a lot of inductance to the circuit, they can undo the transformer designer's best efforts and drag the high frequency resonance down into the audio range where it will adversely affect the sound of the speakers.
Inductance in a speaker cable is largely determined by the area between the conductors. Most speaker cables have conductors that run side by side ("twin-lead"). These conductors are separated by a small distance, so have moderate inductance. Therefore, twin-lead cables do not have the low inductance desired for the best performance when driving ESLs.
Some cables use many small wires that are woven together. This reduces inductance greatly, but at the cost of increased capacitance.
Capacitance should be low. This is not as critical as inductance, but it is important.
Remember that an ESL is a capacitor, and amplifiers find capacitors very hard to drive. If the cable adds more capacitance, it only makes things that much worse for the amplifier.
Capacitance is a function of how close the conductors are to each other. So to keep the capacitance low, the conductors must be widely separated. Note that this is just the opposite of what we need for low inductance.
Many cable manufacturers deliberately add a lot of capacitance to their cables. For example, you will find a box at the end of MIT cables, which contains capacitors. Alpha Core (Goertz) cables are made as a sandwich with two ribbon conductors very close together, which produces high capacitance and often, amplifier instability. Woven wires are close together so have high capacitance. These types of high-capacitance cables are best avoided when operating ESLs.
Resistance is the tendency for the wire in a cable to oppose the flow of current. Most cables are designed to have low resistance so that they don't significantly reduce the damping factor of the amplifier.
Some manufacturers deliberately use high resistance cables to alter the sound of the magnetic speakers by both interacting with the speaker's crossover and reducing the damping factor. When the damping factor is reduced, the amplifier cannot keep the woofer under good, tight control. The result is that the bass becomes "loose" and poorly controlled.
In the case of an ESL, it is best to use a medium resistance cable as this will "damp" the L/C resonance and reduce its magnitude. Since the L/C resonance should be supersonic, this damping effect may not be audible. But reducing even a supersonic resonance will make life much easier for the amplifier.
Of course, if the ESL's transformer is poor, the L/C resonance will be in the audio range and damping it with a medium resistance cable will help smooth out the high frequencies.
For all the above reasons, the best type of cable for driving ESLs will have very low inductance, low capacitance, and moderate resistance. How is this done?
Because the conductors need to be close together for low inductance, but wide apart for low capacitance, simultaneously obtaining low inductance and low capacitance seems impossible. But surprisingly, there is a solution to this problem.
Coaxial cable construction places one conductor inside the other. So electricity "sees" the conductors in the same place. This results in very low inductance.
But what about capacitance? Doesn't a coaxial design place the conductors close together forming a high-capacitance cable?
Not necessarily. The conductors can be physically separated by a significant distance using a thick, high-value dielectric to produce very low capacitance while maintaining ultra-low inductance.
The resistance is determined by the size and length of the conductor. To achieve moderately high resistance (1/4 to 1/2 ohm) a relatively small cable should be used. The cable gauge should be somewhere between 15 and 18 for best results.
This type of cable design should only be used for ESLs. It is not ideal for magnetic
Unlike electrostatic speakers, conventional speakers use magnetism for their operation. Therefore cable requirements for these are different than for ESLs. Cable manufacturers know that capacitance, inductance, and resistance interact with the passive crossovers found in most magnetic speakers and can alter the frequency response of the speakers. So they deliberately juggle these elements to get their cables to make your speakers sound slightly differently than other cables.
Because each speaker design is different, various cable designs will interact with each one differently. So it is impossible to say that any particular cable is "better" than another. All you can say is that you like or don't like the way a particular cable sounds in your room and with your speakers. This fact is the reason that there is so much controversy regarding cables.
To avoid interactions with your speaker's crossover, a cable must have very low inductance, very low capacitance, and very low resistance. Most commercial speaker cables have very low resistance, but their inductance and capacitance will vary widely.
There is a great deal of misinformation, hype, and marketing nonsense surrounding interconnects. This makes it very confusing to know what is important in the design of interconnects. The purpose of this paper is to explain the facts so you can make intelligent decisions. The facts can be quite surprising as you will soon see.
There is no doubt that speaker cables can exert a small influence on the sound of your audio system. But interestingly, all well-designed interconnects sound identical.
The above statement sounds absurd, since interconnect manufacturers all claim that their products will make your system sound better. They also claim that different types of wire material (copper, silver, oxygen-free copper, etc.) sound different, how skin-effect causes transient smearing, how different dielectrics change the sound, etc. So the idea that all interconnects sound identical is outrageous.
Or is it? Have you actually done a well-controlled test to verify the claims of manufacturers? I strongly urge you to do your own testing rather than taking my word for it. To understand how to do good testing, please refer to the "Testing White Paper" on my website. For now, I will give quick instructions on how to test interconnects because it is relatively simple and easy to evaluate interconnects. Let me explain how.
The idea behind the test is to make it possible for you to switch back and forth between interconnects instantly and repeatedly while all other components in your stereo system remain the same. You can then listen very critically for any difference in sound between the interconnects you wish to test.
You cannot accurately test interconnects by listening to one for awhile, then unplugging it, connecting another set, and listening again. Our "audio memory" for subtle details is too short (scientifically proven to be about two seconds) to accurately remember subtle differences in sound in such a test; and we cannot check repeatedly to be sure of what we hear -- so we are easily deceived. You must be able to switch instantly and repeatedly to hear real differences between interconnects (and any other components as well).
To test interconnects; you do not need any test equipment. You can use your preamplifier to do the switching. You will need a "Y" connector so you can connect the two interconnects under test (let's call them "A" and "B") to the same component -- probably your CD player.
Note that the "Y" connector is the same for both interconnects, so even if you believe that the "Y" connector somehow corrupts the sound (they don't), the same signal will pass through both interconnects so the test will still be valid. We will only be listening for any differences between the interconnects, and you can hear that difference (if present) on any signal, even a corrupted and distorted one.
Inexpensive "Y" connectors can be obtained from Radio Shack. If you want audiophile grade "Y" connectors, Sound Connections International (phone 813-948-2707) sells beautifully-built, gold-plated units at reasonable prices.
Plug your "Y" connectors into the left and right outputs of your CD player. Connect one end of interconnects "A" and "B" to the "Y" connector. Do so for both channels.
Connect the other ends of interconnects "A" to one of your preamp line-level inputs (such as "CD"). Connect the other end of interconnect "B" to your tape monitor input. Do so for both channels. Be sure you don't reverse the channels. All line-level inputs on a preamp are identical, so it doesn't matter which ones you use.
You could connect the interconnects to any other line-level input on your preamp instead of "Tape." But the tape monitor inputs will allow to switch back and forth between interconnects by toggling the tape monitor switch instead of having to press different input switches, or rotating a knob.
Toggling a single switch like a tape monitor is more convenient and makes it easy to do the test "blind" so you don't know which interconnect you are listening to. Doing the test blind is desirable so your personal prejudices don't influence the test results.
I understand that some audiophiles do not believe in blind testing. But really now, why do you need know the brand of the interconnects to hear differences between them? If they sound different, they sound different. You can hear such differences even with your eyes closed.
Blind testing offers the advantage of eliminating psychological expectations and bias. Human nature is such that if you believe that a particular component will sound "better" (for whatever reason), then it WILL sound better. So to be sure that you do not deceive yourself, you must not know which interconnect you are listening to.
The test is easiest to do if you have a remote-control preamp so you can sit in your listening chair and simply push the Tape Monitor button on the remote whenever you want to switch interconnects. If you don't have a remote control preamp, then you may need an assistant to switch for you whenever you signal them (just wiggle a finger) to do so.
To do the test blind, press the tape button several times quickly so you get confused and don't know which interconnect you are listening to. If your preamp has an indicator light showing what you are listening to, then either put a piece of black electrical tape over the light or close your eyes while you do the test.
Testing is done by listening to music while switching back and forth between the two sets of interconnects whenever you wish. The idea is to try to hear any difference between the interconnects.
There is no time limit, you may switch whenever you wish and take as long as you want. If you think you hear a difference, you can go back and listen to the same section of music over and over and switch back and forth several times to be sure.
Some audiophiles believe that only long-term listening tests will reveal differences. If you believe this, then take as many days as you want to do your tests.
All you should do is listen for any difference between the interconnects without knowing which one you are hearing. If there is a difference, then you can later decide which sounds better to you. But initially, just listen for differences.
If you hear differences, others should hear them too. You will find that both "golden ear" audiophiles as well as non-audiophiles will be able to hear the same thing you do. In other words, this test is very accurate and if differences are present, everybody will be able to hear them and agree.
After doing this test, you will discover that all the hype surrounding interconnects is just that. The fact is that all well-designed interconnects sound identical. Only poorly designed interconnects will reveal differences in sound.
But please carefully note that I said all WELL-DESIGNED interconnects sound identical. Some interconnects are badly designed and do indeed sound different. So just what is a "well-designed" interconnect?
The first requirement is that the interconnect must be shielded. Shielding prevents RFI (Radio Frequency Interference) and EMI (Electromagnetic Interference) from corrupting the sound. RFI can take several forms with the simplest being a buzzing sound (usually caused from light dimmers in your room), to actually hearing radio or TV program transmissions faintly in the background of your music.
EMI is caused by magnetic flux lines cutting across the interconnect and inducing currents in it. This can take the form of hum if the interconnect is near an electrical transformer or motor, or will be crosstalk if the interconnect is near another interconnect that is active with a different signal.
Shielding is usually done by braiding a fine wire mesh around an internal conductor, making the interconnect coaxial in design. Although this mesh is usually adequate, there are small spaces between the wires in the mesh so that there is not 100% coverage. To obtain the greatest shielding, very fine wires with very tight mesh is needed.
The best shielding is made with solid foil, which has no gaps in it. Unfortunately, foil is prone to cracking and breaking if it is flexed, so the foil (usually aluminum) is often deposited on Mylar film that is wrapped around the wire to improve flexibility. But still, foil-shielded cables should only be used in stationary applications since frequent flexing will eventually crack the shield. Because interconnects are flexed a lot, very fine, braided-mesh shielding is best used for interconnects in home audio systems. In the vast majority of cases, a braided-mesh shield is completely satisfactory.
The second requirement is that the interconnects have low resistance. High resistance can cause loss of output at either high and low frequencies depending on the loads presented by the components connected to the interconnect. When the frequency response is altered, the effects are indeed audible.
Some interconnect manufacturers use extremely tiny wire, and this does adversely affect your system's frequency response. But why would you want to limit your system's frequency response? By definition, "high fidelity" music systems must produce the entire audio spectrum linearity without distortion or noise.
The third requirement is that the connectors at the ends of the wire be practical and trouble-free. This encompasses several factors:
1) They must not oxidize or corrode as this eventually will cause a high resistance contact and restrict the frequency response. This means that the conductor must be plated with an inert metal. Most connectors are gold-plated to meet this criterion, although tin or iridium plated connectors also work well. If they are gold plated, it is important that the plating be of high quality so it doesn't easily chip or flake off.
2) The outside contacts (the "ground" contact) of an RCA connector should not be tapered. If they grip only on their tips, they can put great pressure on your components' jacks and can gouge or scratch their relatively delicate gold plating.
Along these lines, it is best to avoid connectors that have clamping mechanisms that you tighten after insertion. These can put enormous pressure on your components' jacks and then the slightest motion can tear off the gold plating. And note that it is virtually impossible to tighten the clamps without moving the contact and damaging the plating.
The best contacts are those that have precision-machined, parallel walls in the shape of a cylinder. These produce smooth, even, firm pressure on the jack without damaging the gold plating. Such connectors are rare, but they are available if you search for them.
3) The connector should have a strain relief. The purpose of the strain relief is to prevent tension on the interconnect cable from being transferred to the delicate connections inside the connector. This requires some kind of clamping mechanism so that the connector is solidly anchored to the outer covering of the interconnect cable, while the wires inside the connector are slack.
Most RCA connectors don't have any strain relief. Some have springs around the cable near the connector to prevent excessive cable bending, but it doesn't prevent tension from damaging the internal connections. Some RCA connectors have a small metal strap inside the connector that is pinched around the cable, but this is weak and grips very poorly. The best connectors will have a clamp that can be screwed down and that gets a really solid grip on the wire's outer cover. These are rare, but are available if you search for them.
4) The connector should have a tough, scratch-resistant, attractive exterior surface. Most are painted, and paint is easily scratched and damaged. Some are gold-plated. But gold is soft and easily scratched. The best connectors have industrial hard-chrome surfaces. Although uncommon, this type of coating has an attractive, matte silver color and is very durable.
5) The connector, particularly small RCA connectors, should have a "grippy" surface so that you can grasp it firmly to remove it so you don't have to pull on the cable. A thick ring is nice to grip, but often interferes with other connectors that are close by. So the best option is deep knurling on the surface that produces a rough, easily gripped surface, without increasing the size of the connector.
6) The connector needs to be highly conductive to keep the resistance low. Steel is not a suitable material. Brass or copper with gold plating should be used.
Amazingly, many very expensive interconnects fail to meet these basic criteria. In particular, many have no shielding at all! This is inexcusable in an expensive interconnect.
The manufacturers of such poor interconnects only get away with this because most home environments have little RFI and EMI. But this isn't always the case and there are many systems that are plagued with buzzing and other noises due to the lack of shielding. The owner is very frustrated that he can't eliminate the noise and never suspects that his exotic, expensive interconnects are the cause.
Some interconnects have very high resistance. This is because the interconnect uses extremely tiny wire. The manufacturers of such interconnects claim that very small wire prevents "transient smearing" due to "skin effect" or some other arcane reason.
The facts are that wire size and type does not affect the sound (unless the resistance is too high). There is no such thing as "transient smearing" in interconnects, this is totally a marketing ploy. "Skin effect" does not alter the sound at audio frequencies (it may affect radio frequencies, but not audio frequencies). Some of these interconnects with tiny wires have high enough resistance to adversely effect the frequency response of your system.
Very few interconnects have connectors that meet the "practical and trouble-free" criteria outlined above. There are too many connector types to discuss here, but if you will examine them, you will see that few meet the criteria outlined above. Vampire wire interconnects meet all the above criteria, so you may want to consider them.
XLR connectors are much more standardized than RCA connectors. All the good ones have strain reliefs. The only thing you really need to look for is that they have gold plated pins and sockets. Most are tin plated, which is generally satisfactory. But for the best in long-term reliability, gold is better.
ABOUT CABLES AND DIRECTIONALITY
Wire is not directional. It has no magnetic polarity and has no rectifier properties like diodes. It behaves the same regardless of current flow direction. It has identical resistance, capacitance, and inductance regardless of the direction of current flow. If you doubt this, then I encourage you to actually measure wire and see for yourself.
Even if wire did have some sort of directional quality to it, it wouldn't matter in an audio cable because the audio signal is AC (alternating current), not DC (direct current). This means that the musical signal reverses direction at the frequency defined by the music -- it does not "flow" from your source components to your speakers.
So even if you could find wire that actually did flow current better in one direction than the other, its orientation would always be wrong half the time and right half the time, no matter which way you connected it because the signal is constantly changing directions. So orientation wouldn't matter.
Cable manufacturers who claim otherwise are operating outside the realm of science. They are either ignorant of the facts or trying to deceive you. In either case, you should have nothing to do with them.