There is an opinion among some lovers, or rather fanatics, of audio equipment that the wires in circuits should not be made of oxygen-free copper alone, but preferably of silver-plated copper. Some audiophiles go even further and even recommend gold-plated cables. Where did this opinion come from and to what extent is it correct? I am already explaining it to you.
At first glance, the myth about silver's positive effect on sound is due to the fact that silver has lower resistivity than copper. This is true, but the difference between the resistivity of copper and silver is only about 6% (1.72×10-⁸ Ω-m for copper and 1.59×10-⁸ Ω-m for silver). From this it can be concluded that it would be cheaper to increase the diameter of the cables by 6% than to make them entirely of silver. On the other hand, silver plating of the conductors itself has a completely negligible effect in terms of reducing resistivity.
But the myth lives on. In my opinion, its origin is in professional communications equipment, mainly military, from the tube era. At that time, silver-plated wires were indeed widely used, but this was only for high-frequency circuits and it was never intended to be used in acoustic circuits. It is true that in old equipment you can find silver-plated contacts in switches and relays, but there silver has a completely different role.
In the analogue communications era, short-term and long-term stability was an important parameter and depended heavily on the quality of the coils in the resonant circuits. This is where silver-plated wires were used extensively. The operating frequencies of these circuits usually exceeded 3 MHz. At such frequencies, the skin effect, which occurs in AC circuits and causes the current density near the surface of the conductor to be greater than inside the conductor, becomes very evident.
The thickness of the skin layer for non-magnetic metals is inversely proportional to the square root of the frequency and resistivity. For silver, it is approximately 65 µm at a frequency of 1 MHz. In practice, however, the thickness of the silver layer on such conductors is usually much less. This means that silvering the conductors is not intended to reduce their resistivity.
Anyone who has dealt with copper products knows how quickly copper oxidises and becomes covered in patina, requiring regular cleaning and polishing to maintain its shine. In electronic equipment, especially in resonant circuits, 'shine' refers to the quality of the epidermal layer. Copper oxides and their derivatives quickly reach a thickness of a few nanometres at room temperature, and moisture further accelerates this process.
After a few years, the oxide layer increases the resistivity of the epidermal layer - not because the oxides themselves have higher resistivity (in fact, copper oxides are dielectrics), but as a result of an increase in the effective path length of the current in this layer. Instead of flowing along as straight a path as possible, the current must bypass the irregularities created by the oxides. This leads not only to a reduction in the circuit's goodness, but also to a deterioration in resonance performance.
Silver and gold are not susceptible to oxidation, at least under terrestrial conditions. And it is precisely silver that is used as a protective agent for copper against oxidation. Admittedly, silver is also sometimes used as an epidermal current conductor on metals other than copper, or even on non-metals, but these cases are rather rare.
On the other hand, silver reacts with sulphur compounds present in the air, leading to the formation of a dark tarnish. However, this is very thin and does not significantly affect the properties of the conductors. In electronic equipment, this tarnish can be found especially in the immediate vicinity of insulators, which in former times were often made of rubber containing sulphur.
The conclusion is simple: silver plating of conductors in acoustic circuits makes no sense from the point of view of sound quality, because at acoustic frequencies the skin effect is negligible. Gold in such circuits even worsens the performance, as it has a resistivity about 30% higher than copper (2.44×10-⁸ Ω-m). This is of little significance in circuits with small currents, but in power circuits this difference already becomes significant.
At first glance, the myth about silver's positive effect on sound is due to the fact that silver has lower resistivity than copper. This is true, but the difference between the resistivity of copper and silver is only about 6% (1.72×10-⁸ Ω-m for copper and 1.59×10-⁸ Ω-m for silver). From this it can be concluded that it would be cheaper to increase the diameter of the cables by 6% than to make them entirely of silver. On the other hand, silver plating of the conductors itself has a completely negligible effect in terms of reducing resistivity.
Typical coil from a military radio. Photo by Tadas (LY1CE)
But the myth lives on. In my opinion, its origin is in professional communications equipment, mainly military, from the tube era. At that time, silver-plated wires were indeed widely used, but this was only for high-frequency circuits and it was never intended to be used in acoustic circuits. It is true that in old equipment you can find silver-plated contacts in switches and relays, but there silver has a completely different role.
In the analogue communications era, short-term and long-term stability was an important parameter and depended heavily on the quality of the coils in the resonant circuits. This is where silver-plated wires were used extensively. The operating frequencies of these circuits usually exceeded 3 MHz. At such frequencies, the skin effect, which occurs in AC circuits and causes the current density near the surface of the conductor to be greater than inside the conductor, becomes very evident.
The thickness of the skin layer for non-magnetic metals is inversely proportional to the square root of the frequency and resistivity. For silver, it is approximately 65 µm at a frequency of 1 MHz. In practice, however, the thickness of the silver layer on such conductors is usually much less. This means that silvering the conductors is not intended to reduce their resistivity.
Anyone who has dealt with copper products knows how quickly copper oxidises and becomes covered in patina, requiring regular cleaning and polishing to maintain its shine. In electronic equipment, especially in resonant circuits, 'shine' refers to the quality of the epidermal layer. Copper oxides and their derivatives quickly reach a thickness of a few nanometres at room temperature, and moisture further accelerates this process.
After a few years, the oxide layer increases the resistivity of the epidermal layer - not because the oxides themselves have higher resistivity (in fact, copper oxides are dielectrics), but as a result of an increase in the effective path length of the current in this layer. Instead of flowing along as straight a path as possible, the current must bypass the irregularities created by the oxides. This leads not only to a reduction in the circuit's goodness, but also to a deterioration in resonance performance.
Silver and gold are not susceptible to oxidation, at least under terrestrial conditions. And it is precisely silver that is used as a protective agent for copper against oxidation. Admittedly, silver is also sometimes used as an epidermal current conductor on metals other than copper, or even on non-metals, but these cases are rather rare.
On the other hand, silver reacts with sulphur compounds present in the air, leading to the formation of a dark tarnish. However, this is very thin and does not significantly affect the properties of the conductors. In electronic equipment, this tarnish can be found especially in the immediate vicinity of insulators, which in former times were often made of rubber containing sulphur.
The conclusion is simple: silver plating of conductors in acoustic circuits makes no sense from the point of view of sound quality, because at acoustic frequencies the skin effect is negligible. Gold in such circuits even worsens the performance, as it has a resistivity about 30% higher than copper (2.44×10-⁸ Ω-m). This is of little significance in circuits with small currents, but in power circuits this difference already becomes significant.
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