Speaker wire
Encyclopedia
Speaker wire is used to make the electrical connection between loudspeaker
s and audio amplifier
s. Modern speaker wire consists of two or more electrical conductor
s individually insulated
by plastic
such as PVC, PE or Teflon. The two wires are electrically identical, but are marked (e.g. by a ridge on the insulation of one wire, the color of one wire, a thread in one wire, etc) to help easily identify the correct polarity.
Some historic designs also featured another pair of wires for electrical power for an electromagnet
in the loudspeaker. At least one such speaker design is still in production (in France), but essentially all speakers manufactured now use permanent magnets, a practice which displaced field electromagnet speakers over half a century ago.
The effect of speaker wire upon the signal it carries has been a much-debated topic in the audiophile
and high fidelity
worlds. The accuracy of many advertising
claims on these points has also been a matter of much debate.
, capacitance
, and inductance
. A theoretically perfect wire has no resistance, capacitance, or inductance. The shorter a wire, the closer it comes to this, because resistance increases with the length of the conductor (except superconductors). The wire's resistance has the greatest effect on its performance. The capacitance and inductance of the wire has less effect because they are insignificant relative to the capacitance and inductance of the loudspeaker. Larger conductors (smaller wire gauge) have less resistance but increased skin effect
. As long as speaker wire resistance is kept to less than 5% of the speaker's impedance
, the conductor will be adequate for home use.
Speaker wires are selected based on quality of construction, price, aesthetic purpose, and convenience. Stranded wire is more flexible than solid wire, and is suitable for movable equipment. For a wire that will be exposed rather than run within walls, under floor coverings, or behind moldings (such as in a home), appearance may be a subjective
benefit, but it is irrelevant to electrical characteristics. Better purification of oxidizing materials such as copper is said to result in more consistent conductive properties throughout the length of the wire, but this is a non-issue in terms of its effect on sound quality. Better jacketing may be thicker or tougher, less chemically reactive with the conductor, less likely to tangle and easier to pull through a group of other wires, or may incorporate a number of shielding techniques for non-domestic uses.
Even with poor-quality wire, an audible
degradation of sound may not exist. Many supposedly audible differences in speaker wire can be attributed to listener bias or the placebo effect
. Listener bias is enhanced in no small part by the popular manufacturers' practice of making claims about their products either with no valid engineering or scientific basis, or of no real-world significance. Many manufacturers catering to audiophiles (as well as those supplying less expensive retail markets) also make unmeasurable, if poetic, claims about their wire sounding open, dynamic, or smooth. To justify these claims, many cite electrical properties such as skin effect, characteristic impedance
of the cable, or resonance
, which are generally little understood by consumers. None of these has any measurable effect at audio frequencies, though each matters at radio frequencies.
is by far the most important specification of speaker wire. Low-resistance speaker wire allows more of the amplifier's power to energize the loudspeaker
's voice coil
. The shorter the cable and the greater the conductor's cross-sectional area, the lower its resistance. Depending on the hearing ability of the listener, this resistance begins to have an audible effect when the resistance exceeds 5% of the speaker's impedance.
A speaker wire’s impedance takes into account the wire’s resistance, the wire’s path (coiled wire acts as an inductor
), and the dielectric properties of local insulators. The latter two factors also determine the wire's frequency response. The lower the impedance of the speaker
, the greater a significance the speaker wire's resistance
will have.
or heavier speaker connection cable has no detectable effect in runs of 50 feet (15 meters) or less in standard domestic loudspeaker connections for a typical 8 ohm speaker. As speaker resistance drops, lower gauge (heavier) wire is needed to prevent degradation to damping factor
—a measure of the amplifier's control over the position of the voice coil.
Insulation thickness or type also has no audible effect as long as the insulation is of good quality and does not chemically react with the wire itself (poor-quality insulation has occasionally been found to accelerate oxidation of the copper conductor, increasing resistance over time). High-power in-car audio systems using 2-ohm speaker circuits require thicker wire than 4 to 8-ohm home audio applications.
Most consumer applications use two conductor wire. A common rule of thumb is that the resistance of the speaker wire should not exceed 5% of the rated impedance of the system. The table below shows recommended lengths based on this guideline:
* While in theory heavier wire can have longer runs, recommended household audio lengths should not exceed 50 feet (15 m).
The gauge numbers in SWG (standard wire gauge
) and AWG (American wire gauge
) reduce as the wire gets larger. Sizing in square millimeters is also common.
is more or less universal for speaker wire; it has low resistance and less cost compared to other suitable materials. Copper
and aluminum both oxidize
, but oxides of copper are conductive, while those of aluminum are insulating. Also offered is Oxygen-free Copper
(OFC), sold in several grades. The various grades are marketed as having better conductivity and durability, but they have no significant benefit in audio applications.
Silver
has a slightly lower resistivity
than copper, which allows a thinner wire to have the same resistance. Silver is expensive, so a copper wire with the same resistance costs considerably less. Silver tarnishes to form a thin surface layer of silver sulfide
.
Gold
has a higher resistivity than either copper or silver, but it does not oxidize, so it can be used for wire-end terminations. Suitably specified gold flashing has its uses for appropriate tasks, but in domestic use such flashing is not normally functional, for several reasons.
occurs between any two conductors separated by an insulator. In an audio cable, capacitance occurs between the cable's two conductors; the resulting losses are called "dielectric losses" or "dielectric absorption". Capacitance also occurs between the cable's conductors and any nearby conductive objects, including house wiring and damp foundation concrete; this is called "stray capacitance".
Parallel capacitances add together, and so both the dielectric loss and the stray capacitance loss add up to a net capacitance.
Audio signals are alternating current
and so are attenuated by such capacitances. Attenuation occurs in direct proportion to frequency: a higher frequency can more easily leak through a given capacitance. The amount of attenuation can be calculated for any given frequency; the result is called the capacitive reactance, which is an effective resistance measured in ohms:
...where:
This table shows the capacitive reactance in ohms—higher means lower loss—for various frequencies and capacitances; highlighted rows represent loss greater than 1% at 30 volts RMS:
The voltage on a speaker wire depends on amplifier power; for a 100-watt-per-channel amplifier, the voltage will be about 30 volts RMS. At such voltage, a 1% loss will occur at 3000 ohms or less of capacitive reactance. Therefore, to keep audible (up to 20,000hz) losses below 1%, the total capacitance in the cabling must be kept below about 2700pF.
Ordinary lamp cord has a capacitance of 10-20 pF per foot, plus a few picofarads of stray capacitance, so a 50 foot run (100 total feet of conductor) will have less than 1% capacitive loss in the audible range. Some premium speaker cables have higher capacitance in order to have lower inductance; 100-300 pF is typical, in which case the capacitive loss will exceed 1% for runs longer than about 5 feet (10 feet of conductor).
, which is their inherent resistance to changes in current. That resistance is called inductive reactance, measured in ohms. Inductive reactance depends on how quickly the current is changing: quick changes in current (i.e. high frequencies) encounter a higher inductive reactance than do slow changes (low frequencies). Inductive reactance is calculated using this formula:
...where:
Audio signals are alternating current
and so are attenuated by inductance. The following table shows the inductive reactance in ohms—lower means lower loss—for typical cable inductances at various audio frequencies; highlighted rows represent loss greater than 1% at 30 volts RMS:
The voltage on a speaker wire depends on amplifier power; for a 100-watt-per-channel amplifier, the voltage will be about 30 volts RMS. At such voltage, a 1% loss will occur at 0.3 ohms or more of inductive reactance. Therefore, to keep audible (up to 20,000hz) losses below 1%, the total inductance in the cabling must be kept below about 2μH.
Ordinary lamp cord has an inductance of 0.1-0.2μH/foot, likewise for shielded cord, so a run of up to about 5 feet (10 total feet of conductor) will have less than 1% inductive loss in the audible range. Some premium speaker cables have lower inductance at the cost of higher capacitance; 0.02-0.05μH/foot is typical, in which case a run of up to about 25 feet (50 feet of conductor) will have less than 1% inductive loss.
are optional and largely for convenience. Bare wire ends work just as well electrically and may work better mechanically, as adding a termination introduces another potential point of error in installation or failure over time. The most common termination types are solder-tinned wire ends, soldered or crimped pin or spade lugs, banana plugs
, and 2-pin DIN connector
s. Which type to use is determined by the connectors on the equipment at each end of the wire.
Some terminations are gold plated
, which is of no functional use on consumer equipment speaker lines, except to help market equipment to end users unfamiliar with the relevant principles. In a moist environment, gold-plated connectors can resist corrosion better than some other materials, although they should only be mated with other gold-plated connectors as galvanic corrosion may otherwise occur.
Many speakers and electronics have flexible five-way binding post
s that can be screwed down or held down by a spring to accept bare or soldered wire and pins or springy banana plugs (through a hole in the outward-facing side of the post).
There are also several types of proprietary connectors, though these are largely on all-in-one entertainment centers and bookshelf stereo systems.
In recent years, the Neutrik
Speakon connector
is appearing more and more on professional audio equipment. One reason is simple: in many European countries the banana plug can fit into 230 V main electrical sockets. A mistake will damage equipment, and could possibly injure or kill someone as well. Recent EU
regulations prohibit banana plugs in non-AC equipment, unless equipped with a safety pin mechanism preventing insertion into a wall outlet; there is such a connector available (from WBT Connectors), but it is not widely used.
Additionally, the Neutrik speakON connector twists to lock in place, preventing one cause of intermittent failure, and accidental disconnection common in well-used banana plug connections. The speakON also carries more current than heavy-duty 15 A 0.25 in (6.4 mm) phone plugs (originally used in the telephone
industry), and does not short two conductors together at insertion/removal.
high-fidelity systems. For analog audio interconnecting cables, basic system frequency response can be calculated from the electrical properties of the cables and components on either side of the cables. These properties include electrical resistance
, capacitance
and inductance
. For small-signal applications the degree of shielding
is also important. All of these qualities are taken into account in the design of commercial and broadcast cables. High-end cables for the audiophile
market often involve intricate construction geometries and exotic materials such as silver
and oxygen-free copper
(long-crystal, high-purity copper
).
Cables carrying digital signal
s such as S/PDIF
and HDMI
are effectively immune to signal degradation for the short lengths used in consumer audio. HDMI
uses error correction which makes errors even less likely.
s surrounding the impact that high-end cables have on audio systems with audibility of the changes central to the discussion.
"quality". While some speaker wire marketers claim audible improvement with design or exotic materials, skeptics say that a few meters of speaker wire from the power amplifier to the binding post
s of the loudspeaker
s cannot possibly have much influence because of the greater influence from complex crossover
circuits found in most speakers and particularly from the speaker driver voice coil
s that have several meters of very thin wire. There is however agreement that the overall resistance of the speaker wire should not be too high.
An accepted guideline is that the wire impedance should not exceed 5% of the entire circuit. For a given material, resistance is a function of length and thickness (specifically of the ratio of length to cross-sectional area). For this reason, lower impedance speakers require lower resistance speaker wire. Longer cable runs need to be even thicker.
Once the 5% guideline is met, thicker wire will not provide any improvement.
Roger Russell—a former engineer and speaker designer for McIntosh Labs—details how expensive speaker wire brand marketing misinforms consumers in his online essay called Speaker Wire - A History. He writes, "The industry has now reached the point where [wire] resistance and listening quality are not the issues any more, although listening claims may still be made....The strategy in selling these products is, in part, to appeal to those who are looking to impress others with something unique and expensive."
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s and audio amplifier
Audio amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification,...
s. Modern speaker wire consists of two or more electrical conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s individually insulated
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
by plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
such as PVC, PE or Teflon. The two wires are electrically identical, but are marked (e.g. by a ridge on the insulation of one wire, the color of one wire, a thread in one wire, etc) to help easily identify the correct polarity.
Some historic designs also featured another pair of wires for electrical power for an electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
in the loudspeaker. At least one such speaker design is still in production (in France), but essentially all speakers manufactured now use permanent magnets, a practice which displaced field electromagnet speakers over half a century ago.
The effect of speaker wire upon the signal it carries has been a much-debated topic in the audiophile
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
and high fidelity
High fidelity
High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...
worlds. The accuracy of many advertising
Marketing
Marketing is the process used to determine what products or services may be of interest to customers, and the strategy to use in sales, communications and business development. It generates the strategy that underlies sales techniques, business communication, and business developments...
claims on these points has also been a matter of much debate.
Explanation
Speaker wire, like any other linear electrical component, has three properties which determine its performance: resistanceElectrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
, capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
, and inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
. A theoretically perfect wire has no resistance, capacitance, or inductance. The shorter a wire, the closer it comes to this, because resistance increases with the length of the conductor (except superconductors). The wire's resistance has the greatest effect on its performance. The capacitance and inductance of the wire has less effect because they are insignificant relative to the capacitance and inductance of the loudspeaker. Larger conductors (smaller wire gauge) have less resistance but increased skin effect
Skin effect
Skin effect is the tendency of an alternating electric current to distribute itself within a conductor with the current density being largest near the surface of the conductor, decreasing at greater depths. In other words, the electric current flows mainly at the "skin" of the conductor, at an...
. As long as speaker wire resistance is kept to less than 5% of the speaker's impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
, the conductor will be adequate for home use.
Speaker wires are selected based on quality of construction, price, aesthetic purpose, and convenience. Stranded wire is more flexible than solid wire, and is suitable for movable equipment. For a wire that will be exposed rather than run within walls, under floor coverings, or behind moldings (such as in a home), appearance may be a subjective
Subjectivity
Subjectivity refers to the subject and his or her perspective, feelings, beliefs, and desires. In philosophy, the term is usually contrasted with objectivity.-Qualia:...
benefit, but it is irrelevant to electrical characteristics. Better purification of oxidizing materials such as copper is said to result in more consistent conductive properties throughout the length of the wire, but this is a non-issue in terms of its effect on sound quality. Better jacketing may be thicker or tougher, less chemically reactive with the conductor, less likely to tangle and easier to pull through a group of other wires, or may incorporate a number of shielding techniques for non-domestic uses.
Even with poor-quality wire, an audible
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
degradation of sound may not exist. Many supposedly audible differences in speaker wire can be attributed to listener bias or the placebo effect
Placebo effect
Placebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...
. Listener bias is enhanced in no small part by the popular manufacturers' practice of making claims about their products either with no valid engineering or scientific basis, or of no real-world significance. Many manufacturers catering to audiophiles (as well as those supplying less expensive retail markets) also make unmeasurable, if poetic, claims about their wire sounding open, dynamic, or smooth. To justify these claims, many cite electrical properties such as skin effect, characteristic impedance
Characteristic impedance
The characteristic impedance or surge impedance of a uniform transmission line, usually written Z_0, is the ratio of the amplitudes of a single pair of voltage and current waves propagating along the line in the absence of reflections. The SI unit of characteristic impedance is the ohm...
of the cable, or resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
, which are generally little understood by consumers. None of these has any measurable effect at audio frequencies, though each matters at radio frequencies.
Resistance
ResistanceElectrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
is by far the most important specification of speaker wire. Low-resistance speaker wire allows more of the amplifier's power to energize the loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
's voice coil
Voice coil
A voice coil is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it...
. The shorter the cable and the greater the conductor's cross-sectional area, the lower its resistance. Depending on the hearing ability of the listener, this resistance begins to have an audible effect when the resistance exceeds 5% of the speaker's impedance.
A speaker wire’s impedance takes into account the wire’s resistance, the wire’s path (coiled wire acts as an inductor
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
), and the dielectric properties of local insulators. The latter two factors also determine the wire's frequency response. The lower the impedance of the speaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
, the greater a significance the speaker wire's resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
will have.
Wire gauge
Thicker wires reduce resistance. The resistance of 16-gaugeAmerican wire gauge
American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
or heavier speaker connection cable has no detectable effect in runs of 50 feet (15 meters) or less in standard domestic loudspeaker connections for a typical 8 ohm speaker. As speaker resistance drops, lower gauge (heavier) wire is needed to prevent degradation to damping factor
Damping factor
In audio system terminology, the damping factor gives the ratio of the rated impedance of the loudspeaker to the source impedance. Only the resistive part of the loudspeaker impedance is used. The amplifier output impedance is also assumed to be totally resistive...
—a measure of the amplifier's control over the position of the voice coil.
Insulation thickness or type also has no audible effect as long as the insulation is of good quality and does not chemically react with the wire itself (poor-quality insulation has occasionally been found to accelerate oxidation of the copper conductor, increasing resistance over time). High-power in-car audio systems using 2-ohm speaker circuits require thicker wire than 4 to 8-ohm home audio applications.
Most consumer applications use two conductor wire. A common rule of thumb is that the resistance of the speaker wire should not exceed 5% of the rated impedance of the system. The table below shows recommended lengths based on this guideline:
| Wire size | 2 Ω load | 4 Ω load | 6 Ω load | 8 Ω load |
|---|---|---|---|---|
| 22 AWG (0.326 mm2) | 3 ft (0.9 m) | 6 ft (1.8 m) | 9 ft (2.7 m) | 12 ft (3.6 m) |
| 20 AWG (0.518 mm2) | 5 ft (1.5 m) | 10 ft (3 m) | 15 ft (4.5 m) | 20 ft (6 m) |
| 18 AWG (0.823 mm2) | 8 ft (2.4 m) | 16 ft (4.9 m) | 24 ft (7.3 m) | 32 ft (9.7 m) |
| 16 AWG (1.31 mm2) | 12 ft (3.6 m) | 24 ft (7.3 m) | 36 ft (11 m) | 48 ft (15 m) |
| 14 AWG (2.08 mm2) | 20 ft (6.1 m) | 40 ft (12 m) | 60 ft (18 m)* | 80 ft (24 m)* |
| 12 AWG (3.31 mm2) | 30 ft (9.1 m) | 60 ft (18 m)* | 90 ft (27 m)* | 120 ft (36 m)* |
| 10 AWG (5.26 mm2) | 50 ft (15 m) | 100 ft (30 m)* | 150 ft (46 m)* | 200 ft (61 m)* |
* While in theory heavier wire can have longer runs, recommended household audio lengths should not exceed 50 feet (15 m).
The gauge numbers in SWG (standard wire gauge
Standard wire gauge
British Standard Wire Gauge is a set of wire sizes given by BS 3737:1964 , and is generally abbreviated to SWG. It is also known as: Imperial Wire Gauge or British Standard Gauge. Use of SWG sizes has fallen greatly in popularity, but is still used as a measure of thickness in guitar strings and...
) and AWG (American wire gauge
American wire gauge
American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...
) reduce as the wire gets larger. Sizing in square millimeters is also common.
Wire material
Use of copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
is more or less universal for speaker wire; it has low resistance and less cost compared to other suitable materials. Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
and aluminum both oxidize
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
, but oxides of copper are conductive, while those of aluminum are insulating. Also offered is Oxygen-free Copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
(OFC), sold in several grades. The various grades are marketed as having better conductivity and durability, but they have no significant benefit in audio applications.
Silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
has a slightly lower resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...
than copper, which allows a thinner wire to have the same resistance. Silver is expensive, so a copper wire with the same resistance costs considerably less. Silver tarnishes to form a thin surface layer of silver sulfide
Silver sulfide
Silver sulfide, Ag2S, is the sulfide of silver. This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of...
.
Gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
has a higher resistivity than either copper or silver, but it does not oxidize, so it can be used for wire-end terminations. Suitably specified gold flashing has its uses for appropriate tasks, but in domestic use such flashing is not normally functional, for several reasons.
Capacitance
CapacitanceCapacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
occurs between any two conductors separated by an insulator. In an audio cable, capacitance occurs between the cable's two conductors; the resulting losses are called "dielectric losses" or "dielectric absorption". Capacitance also occurs between the cable's conductors and any nearby conductive objects, including house wiring and damp foundation concrete; this is called "stray capacitance".
Parallel capacitances add together, and so both the dielectric loss and the stray capacitance loss add up to a net capacitance.
Audio signals are alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
and so are attenuated by such capacitances. Attenuation occurs in direct proportion to frequency: a higher frequency can more easily leak through a given capacitance. The amount of attenuation can be calculated for any given frequency; the result is called the capacitive reactance, which is an effective resistance measured in ohms:
...where:
-
is the frequency in hertz; and -
is the capacitance in faradFaradThe farad is the SI unit of capacitance. The unit is named after the English physicist Michael Faraday.- Definition :A farad is the charge in coulombs which a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second...
s.
This table shows the capacitive reactance in ohms—higher means lower loss—for various frequencies and capacitances; highlighted rows represent loss greater than 1% at 30 volts RMS:
| Capacitive Reactance | 100hz | 200hz | 500hz | 1,000hz | 2,000hz | 5,000hz | 10,000hz | 20,000hz | 50,000hz |
|---|---|---|---|---|---|---|---|---|---|
| 100pF (0.1nF) | 15,915,508 | 7,957,754 | 3,183,102 | 1,591,551 | 795,775 | 318,310 | 159,155 | 79,578 | 31,831 |
| 200pF (0.2nF) | 7,957,754 | 3,978,877 | 1,591,551 | 795,775 | 397,888 | 159,155 | 79,578 | 39,789 | 15,916 |
| 500pF (0.5nF) | 3,183,102 | 1,591,551 | 636,620 | 318,310 | 159,155 | 63,662 | 31,831 | 15,916 | 6,366 |
| 1,000pF (1nF) | 1,591,551 | 795,775 | 318,310 | 159,155 | 79,578 | 31,831 | 15,916 | 7,958 | 3,183 |
| 2,000pF (2nF) | 795,775 | 397,888 | 159,155 | 79,578 | 39,789 | 15,916 | 7,958 | 3,979 | 1,592 |
| 5,000pF (5nF) | 318,310 | 159,155 | 63,662 | 31,831 | 15,916 | 6,366 | 3,183 | 1,592 | 637 |
| 10,000pF (10nF) | 159,155 | 79,578 | 31,831 | 15,916 | 7,958 | 3,183 | 1,592 | 796 | 318 |
| 20,000pF (20nF) | 79,578 | 39,789 | 15,916 | 7,958 | 3,979 | 1,592 | 796 | 398 | 159 |
| 50,000pF (50nF) | 31,831 | 15,916 | 6,366 | 3,183 | 1,592 | 637 | 318 | 159 | 64 |
| 100,000pF (100nF) | 15,916 | 7,958 | 3,183 | 1,592 | 796 | 318 | 159 | 80 | 32 |
| 200,000pF (200nF) | 7,958 | 3,979 | 1,592 | 796 | 398 | 159 | 80 | 40 | 16 |
| 500,000pF (500nF) | 3,183 | 1,592 | 637 | 318 | 159 | 64 | 32 | 16 | 6 |
The voltage on a speaker wire depends on amplifier power; for a 100-watt-per-channel amplifier, the voltage will be about 30 volts RMS. At such voltage, a 1% loss will occur at 3000 ohms or less of capacitive reactance. Therefore, to keep audible (up to 20,000hz) losses below 1%, the total capacitance in the cabling must be kept below about 2700pF.
Ordinary lamp cord has a capacitance of 10-20 pF per foot, plus a few picofarads of stray capacitance, so a 50 foot run (100 total feet of conductor) will have less than 1% capacitive loss in the audible range. Some premium speaker cables have higher capacitance in order to have lower inductance; 100-300 pF is typical, in which case the capacitive loss will exceed 1% for runs longer than about 5 feet (10 feet of conductor).
Inductance
All conductors have inductanceInductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
, which is their inherent resistance to changes in current. That resistance is called inductive reactance, measured in ohms. Inductive reactance depends on how quickly the current is changing: quick changes in current (i.e. high frequencies) encounter a higher inductive reactance than do slow changes (low frequencies). Inductive reactance is calculated using this formula:
...where:
-
is the frequency in hertz; and -
is the inductance in henrys.
Audio signals are alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
and so are attenuated by inductance. The following table shows the inductive reactance in ohms—lower means lower loss—for typical cable inductances at various audio frequencies; highlighted rows represent loss greater than 1% at 30 volts RMS:
| Inductive Reactance | 100hz | 200hz | 500hz | 1,000hz | 2,000hz | 5,000hz | 10,000hz | 20,000hz | 50,000hz |
|---|---|---|---|---|---|---|---|---|---|
| 0.1μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 0.2μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 |
| 0.5μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.2 |
| 1μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.3 |
| 2μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.3 | 0.6 |
| 5μH | 0.0 | 0.0 | 0.0 | 0.0 | 0.1 | 0.2 | 0.3 | 0.6 | 1.6 |
| 10μH | 0.0 | 0.0 | 0.0 | 0.1 | 0.1 | 0.3 | 0.6 | 1.3 | 3.1 |
| 20μH | 0.0 | 0.0 | 0.1 | 0.1 | 0.3 | 0.6 | 1.3 | 2.5 | 6.3 |
| 50μH | 0.0 | 0.1 | 0.2 | 0.3 | 0.6 | 1.6 | 3.1 | 6.3 | 15.7 |
| 100μH | 0.1 | 0.1 | 0.3 | 0.6 | 1.3 | 3.1 | 6.3 | 12.6 | 31.4 |
| 200μH | 0.1 | 0.3 | 0.6 | 1.3 | 2.5 | 6.3 | 12.6 | 25.1 | 62.8 |
| 500μH | 0.3 | 0.6 | 1.6 | 3.1 | 6.3 | 15.7 | 31.4 | 62.8 | 157.1 |
The voltage on a speaker wire depends on amplifier power; for a 100-watt-per-channel amplifier, the voltage will be about 30 volts RMS. At such voltage, a 1% loss will occur at 0.3 ohms or more of inductive reactance. Therefore, to keep audible (up to 20,000hz) losses below 1%, the total inductance in the cabling must be kept below about 2μH.
Ordinary lamp cord has an inductance of 0.1-0.2μH/foot, likewise for shielded cord, so a run of up to about 5 feet (10 total feet of conductor) will have less than 1% inductive loss in the audible range. Some premium speaker cables have lower inductance at the cost of higher capacitance; 0.02-0.05μH/foot is typical, in which case a run of up to about 25 feet (50 feet of conductor) will have less than 1% inductive loss.
Terminations
Speaker wire terminationsElectrical termination
Electrical termination of a signal involves providing a terminator at the end of a wire or cable to prevent an RF signal from being reflected back from the end, causing interference...
are optional and largely for convenience. Bare wire ends work just as well electrically and may work better mechanically, as adding a termination introduces another potential point of error in installation or failure over time. The most common termination types are solder-tinned wire ends, soldered or crimped pin or spade lugs, banana plugs
Banana connector
A banana connector is a single-wire electrical connector used for joining wires to equipment. The term 4 mm connector is also used, especially in Europe, although not all banana connectors will mate with 4mm parts...
, and 2-pin DIN connector
DIN connector
A DIN connector is a connector that was originally standardized by the , the German national standards organization. There are DIN standards for a large number of different connectors, therefore the term "DIN connector" alone does not unambiguously identify any particular type of connector unless...
s. Which type to use is determined by the connectors on the equipment at each end of the wire.
Some terminations are gold plated
Gold plating
Gold plating is a method of depositing a thin layer of gold onto the surface of another metal, most often copper or silver , by chemical or electrochemical plating...
, which is of no functional use on consumer equipment speaker lines, except to help market equipment to end users unfamiliar with the relevant principles. In a moist environment, gold-plated connectors can resist corrosion better than some other materials, although they should only be mated with other gold-plated connectors as galvanic corrosion may otherwise occur.
Many speakers and electronics have flexible five-way binding post
Binding post
A binding post is a connector commonly used on electronic test equipment to terminate a single wire or test lead. They are also found on loudspeakers and audio amplifiers as well as other electrical equipment....
s that can be screwed down or held down by a spring to accept bare or soldered wire and pins or springy banana plugs (through a hole in the outward-facing side of the post).
There are also several types of proprietary connectors, though these are largely on all-in-one entertainment centers and bookshelf stereo systems.
In recent years, the Neutrik
Neutrik
Neutrik is a Liechtenstein company which manufactures connectors which are used in audio and video recording studios and concert sound systems. Their product range includes XLR-type connectors, speakON connectors, powerCON connectors, patch bays, BNC connectors and special connectors for industrial...
Speakon connector
Speakon connector
The Speakon is a type of cable connector, originally manufactured by Neutrik, mostly used in professional audio systems for connecting loudspeakers to amplifiers. The same manufacturer produces another connector dubbed PowerCon, which is designed to carry mains power rather than audio signal...
is appearing more and more on professional audio equipment. One reason is simple: in many European countries the banana plug can fit into 230 V main electrical sockets. A mistake will damage equipment, and could possibly injure or kill someone as well. Recent EU
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
regulations prohibit banana plugs in non-AC equipment, unless equipped with a safety pin mechanism preventing insertion into a wall outlet; there is such a connector available (from WBT Connectors), but it is not widely used.
Additionally, the Neutrik speakON connector twists to lock in place, preventing one cause of intermittent failure, and accidental disconnection common in well-used banana plug connections. The speakON also carries more current than heavy-duty 15 A 0.25 in (6.4 mm) phone plugs (originally used in the telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
industry), and does not short two conductors together at insertion/removal.
High-end cables
High-end audio cables are claimed by their manufacturers to improve the sound quality of high-end audioHigh-end audio
High-end audio is a term used to describe a class of consumer home audio equipment marketed to audio enthusiasts on the basis of high price or quality, and esoteric or novel sound reproduction technologies. High-end audio can refer simply to the price, to the build quality of the components, or to...
high-fidelity systems. For analog audio interconnecting cables, basic system frequency response can be calculated from the electrical properties of the cables and components on either side of the cables. These properties include electrical resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
, capacitance
Capacitance
In electromagnetism and electronics, capacitance is the ability of a capacitor to store energy in an electric field. Capacitance is also a measure of the amount of electric potential energy stored for a given electric potential. A common form of energy storage device is a parallel-plate capacitor...
and inductance
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
. For small-signal applications the degree of shielding
Electromagnetic shielding
Electromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world' and to cables to isolate...
is also important. All of these qualities are taken into account in the design of commercial and broadcast cables. High-end cables for the audiophile
Audiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
market often involve intricate construction geometries and exotic materials such as silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
and oxygen-free copper
Oxygen-free copper
Oxygen-free copper or Oxygen-free high thermal conductivity copper generally refers to a group of wrought high conductivity copper alloys that have been electrolytically refined to reduce the level of oxygen to .001% or below....
(long-crystal, high-purity copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
).
Cables carrying digital signal
Digital signal
A digital signal is a physical signal that is a representation of a sequence of discrete values , for example of an arbitrary bit stream, or of a digitized analog signal...
s such as S/PDIF
S/PDIF
S/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high...
and HDMI
HDMI
HDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...
are effectively immune to signal degradation for the short lengths used in consumer audio. HDMI
HDMI
HDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...
uses error correction which makes errors even less likely.
Quality debate
There is debate among audiophileAudiophile
An audiophile is a person who enjoys listening to recorded music, usually in a home. Some audiophiles are more interested in collecting and listening to music, while others are more interested in collecting and listening to audio components, whose "sound quality" they consider as important as the...
s surrounding the impact that high-end cables have on audio systems with audibility of the changes central to the discussion.
Digital cables
One of the more contentious areas is in digital cable design, with high-end cables being sold with claims of "distortion-free signal transfer."Speaker wire
Another area of debate is speaker wireSpeaker wire
Speaker wire is used to make the electrical connection between loudspeakers and audio amplifiers. Modern speaker wire consists of two or more electrical conductors individually insulated by plastic such as PVC, PE or Teflon. The two wires are electrically identical, but are marked Speaker wire is...
"quality". While some speaker wire marketers claim audible improvement with design or exotic materials, skeptics say that a few meters of speaker wire from the power amplifier to the binding post
Binding post
A binding post is a connector commonly used on electronic test equipment to terminate a single wire or test lead. They are also found on loudspeakers and audio amplifiers as well as other electrical equipment....
s of the loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s cannot possibly have much influence because of the greater influence from complex crossover
Audio crossover
Audio crossovers are a class of electronic filter used in audio applications. Most individual loudspeaker drivers are incapable of covering the entire audio spectrum from low frequencies to high frequencies with acceptable relative volume and lack of distortion so most hi-fi speaker systems use a...
circuits found in most speakers and particularly from the speaker driver voice coil
Voice coil
A voice coil is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it...
s that have several meters of very thin wire. There is however agreement that the overall resistance of the speaker wire should not be too high.
An accepted guideline is that the wire impedance should not exceed 5% of the entire circuit. For a given material, resistance is a function of length and thickness (specifically of the ratio of length to cross-sectional area). For this reason, lower impedance speakers require lower resistance speaker wire. Longer cable runs need to be even thicker.
Once the 5% guideline is met, thicker wire will not provide any improvement.
Roger Russell—a former engineer and speaker designer for McIntosh Labs—details how expensive speaker wire brand marketing misinforms consumers in his online essay called Speaker Wire - A History. He writes, "The industry has now reached the point where [wire] resistance and listening quality are not the issues any more, although listening claims may still be made....The strategy in selling these products is, in part, to appeal to those who are looking to impress others with something unique and expensive."
External links
- http://procosound.com/education/99-white-papers Pro Co Sound Inc. white paper
- Speaker Wire - Roger Russell (former McIntosh LaboratoryMcIntosh LaboratoryMcIntosh Laboratory is an American manufacturer of high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh,. The "classic" vacuum tube components of the 1960s include the MC275 power amplifier, the C22 preamplifier, and the MR67 tuner...
loudspeaker designer) opinions on loudspeaker wiring - Audioholics - Speaker wire gauge - "audiophile" opinion
- Crutchfield Advisor advice on standard domestic speaker installations
- Understanding In-wall Speaker Cable Ratings
- Solving Signal Problems - Belden Corp article for Broadcast Engineering magazine
- Speaker Wire - Roger Russell (former McIntosh LaboratoryMcIntosh LaboratoryMcIntosh Laboratory is an American manufacturer of high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh,. The "classic" vacuum tube components of the 1960s include the MC275 power amplifier, the C22 preamplifier, and the MR67 tuner...
loudspeaker designer) opinions on loudspeaker wiring