Sanders Sound Systems Speaker Cable for Electrostatic Speakers

15 AWG, 7 foot coaxial speaker cable, spade terminated on both ends

Impedance: 0.019 Ohms per 7 foot cable
Capacitance: 539pF per 7 foot cable (pF is picoFareds or 1 trillionth of a farad)
Inductance: 0.84uH per 7 foot cable (uH is microHenry or 1 millionth of a Henry)

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From the Sanders Sound Systems Cables White Paper:

SPEAKER CABLES

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.

Inductance

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

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

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
speakers.

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.