If you have spent enough time running around as a stage technician or a sound engineer, you will most probably be no stranger to speaker cables. Even if you are a beginner or just an enthusiast, you would still have at least seen or heard of it. However, the wires used for speaker cables are unlike other audio cables. So what is a speaker wire? How is it different?
Now you must be thinking (yes, I can read your mind), is it really that important to know about this? Well, I would express my strong personal opinion that yes, it is crucial. You would be surprised to find out about the various factors that affects the quality of the speaker wire, which in turn, affects the audio signal travelling through it. Now tell me its not important! (no, seriously, don’t do that)
Speaker Wire – Tell me about it!
The function of this wire is to make a successful electrical connection between loudspeakers and its amplifiers. Today, you will find that most speaker wires consists of two or more electrical conductors, each insulated by plastic (normally PVC, PE or Teflon) or, sometimes rubber. The two electrically identical wires, will usually be marked to indicate the correct audio signal polarity.
If you buy a brand new set of speaker wires, they will usually come in the form of “zip cord”. People in the audiophile and high fidelity industry, always debate about the effect of speaker wire upon the signal it carries. There are many advertising claims (regarding speaker wires) that have been refuted by expert engineers, who believe that by and large, simple electrical resistance is the most important characteristic of a speaker wire.
History – How it used to be
During the early days, speaker cables were typically just stranded copper wires which are insulated with either cloth tape, waxed paper or rubber. To make it easy for portability, the common lamp cord was utilized, often twisted in pairs for mechanical reasons.
To make an electrical connection, cables were often soldered in place at one end. Other connectors used were binding posts, terminal strips, and spade lugs for folded connections. Soon after, the two-conductor, ¼-inch tip-sleeve phone jacks were widely used in the 1920s and 30s for convenience.
Some of the earlier speaker cables were designed to include another pair of wires for carrying direct current to supply electrical power for an electromagnet in the loudspeaker. However, from 1940s onwards, all loudspeakers that are manufactured till today, use permanent magnets, which replaced the field electromagnet speakers.
So what affects its performance?
A speaker wire is known as a passive electrical component, which is measured by its electrical “impedance”. This “impedance” can be further broken down into three properties which determine its performance:
Ideally, a speaker wire should have no resistance, capacitance, or inductance. You should know that the electrical resistance of a wire, increases as the wire gets longer and decreases as the wire gets thicker. Therefore, the shorter and thicker a wire is, the lower is its resistance, which means better performance.
It is important to take note that the wire’s resistance, is the biggest factor in affecting its performance. Both capacitance and inductance of the wire, does not have a big impact as they are considered to be insignificant, in relative to the capacitance and inductance of the loudspeaker.
Now lets talk more about the three factors that are mentioned above. (Bare with me for a little longer yeah?)
A speaker wire’s most important determining factor (in terms of performance) would be its resistance. This is because, low-resistance wire will allow more of the amplifier’s power to drive the loudspeaker’s voice coil. In order to optimise the performance of a conductor (in this case, speaker wire), its length is often limited while maximising its cross-sectional area (thickness).
Resistance of speaker wires will begin to have an audible effect when the resistance exceeds 5% of the speaker’s impedance. Although this heavily depends on the hearing ability of the listener.
A speaker wire’s “impedance” is affected by the wire’s resistance, path, and the dielectric properties of local insulators. The first two factors mentioned, also determines the wire’s frequency response. As a general rule, the lower the impedance of the speaker, the greater a significance the speaker wire’s resistance will have.
Just for your information, most large buildings use a constant voltage speaker system, in order to reduce losses in the wiring. This is because, long runs of wires are used to interconnect speakers and amplifiers around the facilities and this will definitely have a detrimental impact on the audio signal.
There are two main factors that affects the resistance in speaker wires:
- Wire Gauge
- Wire Material
The fundamental understanding here is that, thicker wires will reduce resistance. A 16-gauge speaker wire (or thicker), with a length of around 15m (or less), will have almost zero detectable effect in terms of resistance. This holds true for standard loudspeaker connections with a typical 8 ohm speaker at home. However, as speaker impedance drops, a thicker wire (lower gauge) is needed to prevent a reduction in its “damping factor” (a measure of the amplifier’s control over the position of the voice coil).
The insulation thickness or material, will also not have an audible effect as long it is a good quality insulation and will not chemically react with the wire itself (low-quality insulation may sometimes accelerate the oxidation of copper conductors, increasing resistance as a result). Just take note that high-powered, car audio systems with 2-ohm speaker circuits will need thicker wires as compared to 4 to 8-ohm home audio systems.
The majority of consumer audio systems use two conductor wires. A general rule is that the resistance of the speaker wire should not exceed 5% of the rated impedance of the system.
You will come to realize that copper is the most widely used material for speaker wires worldwide. This is due its low resistance and lower cost as compared to other suitable materials. Both copper and aluminium will oxidise, but the oxides of copper are conductive, while the ones from aluminium are insulating. Oxygen-free Copper (OFC) are also frequently offered today, which are sold in various grades. These grades are advertised as having better conductivity and durability, but with no significant benefits in audio applications.
Some types of copper wires include the “C11000 Electrolytic-Tough-Pitch (ETP)” which is identical to its higher-cost counterpart, “C10200 Oxygen-Free (OF)”, in speaker cable applications. The much more costly C10100, which is a highly refined copper wire with its silver impurities removed and oxygen reduced to 0.0005%, only has a one percent increase in conductivity rating, not significant in audio applications.
Silver on the other hand, has a slightly lower resistance than copper, allowing a higher-gauge wire (thinner) to have the same resistance. But silver is expensive, so a copper wire with the same resistance will be considerably cheaper. On top of that, silver tarnishes to form a thin surface layer of silver sulphide.
Gold, as compared to copper or silver, has a higher resistance. But, take note that pure gold will not oxidise, so it can be used for plating wire-end connectors.
Capacitance is a phenomenon that can happen with any two conductors that are separated by an insulator. For example, in audio cables, capacitance will occur between the two conductors within the cable, which results in the loss of current. This loss is called “dielectric losses” or “dielectric absorption”.
Capacitance can also occur between the cable’s conductors and other conductive objects nearby, including domestic wiring and damp foundation concrete. This is known as “stray capacitance”. Parallel capacitances will add up, which means that both “dielectric loss” and “stray capacitance” loss, adds up to a net capacitance.
Since audio signals are alternating current, it will be attenuated by such capacitances. Take note that attenuation is in direct proportion to frequency. This means that the higher the frequency, the easier it is to leak through a given capacitance.
Inductance refers to a conductor’s (speaker wire) inherent resistance to the changes in current. Every conductor will have inductance. That resistance is often known as “inductive reactance”, which is measured in ohms.
Inductive reactance is dependant on the speed in which the current is changing. Which basically means that, faster changes in current (i.e. high frequencies) will lead to a higher inductive reactance than slower changes (low frequencies).
Audio signals are alternating current and so are attenuated by inductance.
The “Skin Effect”
The tendency for high frequency signals to travel more on the surface than in the centre of the conductor is known as the “skin effect”. Just imagine a hollow metal pipe as the conductor. This effect is caused by “self-inductance” which makes the conductor more resistant of higher frequencies, thus reducing its ability to transmit those frequencies with as much power as the low frequencies.
As the diameter of conductors increase, they will have less overall resistance, at the expense of increased skin effect. In this case, the material of the conductor makes a difference. For instance, silver has a greater skin effect than copper, and aluminum has less. Skin effect is a big problem for radio frequencies or long-distance (miles and kilometres long) high-tension electrical transmission lines, but not at audio frequencies travelling over shorter distances (often measured in feet or meters).
Usually, speaker cables are made with stranded conductors. However, bare metal strands (which are in contact with each other) do not mitigate skin effect, as the bundle of strands actually functions as a single conductor at audio frequencies.
Some solutions include the “Litz wire” (individually insulated strands held in a particular pattern), which is a type of high-end speaker wire designed to reduce skin effect. Another method that has been tested, is to actually use silver (which has less resistance) to plate the copper strands.
Contrary to marketing campaigns, skin effect is mostly inaudible, thus making it negligible, especially in typical affordable cables for loudspeakers or other audio uses. For common audio connections such as in home stereo systems, the resistance for the frequencies at 20,000 Hz is just under 3%, which makes it an insignificant and inaudible degree of attenuation.
There you go. An explanation on the various aspects of speaker wires. I hope it was not too difficult to grasp for you people who are still new to this!
Either way, thanks for reading and do leave comments!