Speaker wire
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Speaker wire is used to make the electrical connection between loudspeakers and audio amplifiers. Modern speaker wire consists of two electrical conductors individually insulated by plastic. 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.
Explanation
Speaker wire, like any other linear electrical component, has three parameters which determine its performance: resistance, capacitance, and inductance. If a perfect wire were possible, it would have no resistance, no capacitance, and no inductance. The shorter a wire is, the closer it comes to being perfect, as resistance decreases as length decreases in all conductors (except superconductors). Resistance is the property which has the most effect on speaker wire performance,[1] whereas capacitative and inductive characteristics of speaker wire are insignificantly small relative to the loudspeaker itself. Larger conductors (smaller wire gauge) have smaller resistance. 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 effects 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[2].
Resistance
Resistance 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.
Wire gauge
Thicker wires reduce resistance. The resistance of 16-gauge 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.[3] 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 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 contuctor wire. Based on a guideline is that the resistance of the speaker wire not exceeding 5% of the rated impedance of the system the table below illustrates recommended lengths.
Maximum wire lengths for two conductor copper wire[3]
| 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).[3]
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.
Wire material
Use of copper 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 capacitative and insulating.
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. Like copper, silver is also subject to oxidation.
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.
Capacitance and inductance
Speaker wire capacitance and inductance normally have no effect on audio quality, though extreme examples using unusually high-impedance speakers and exceptionally long wire runs can show a small effect.
Terminations
Speaker wire terminations 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 connectors. Which type to use is determined by the connectors on the equipment at each end of the wire.
Some terminations are plated in gold, 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.
Many speakers and electronics have flexible five-way binding posts 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 230v 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.[citation needed]
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 15A 1/4" phone plugs (originally used in the telephone industry), and does not short two conductors together at insertion/removal.
See also
References
- ^ ProCo Sound. Whitepapers. Understanding Speaker Cables
- ^ http://sound.westhost.com/cables.htm
- ^ a b c Russell, Roger (1999–2007). "Speaker Wire - A History". Roger Russell. Retrieved 17 July 2009.
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External links
- Understanding the speaker cable Pro Co Sound Inc. white paper
- Speaker Wire - Roger Russell (former McIntosh Laboratory 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