Skin effect exists

Is the term “skin effect” in the world of audio-only “woo-doo deceit”, or has the skin effect that was described in 1892 by J.C. Maxwell really affect music reproduction?

Where is the truth?

In 1884, the famous inventor Nikola Tesla used the skin effect for his engaging show, where he let flowing electricity trough his body, shooted lightnings from him and turned on light of tubes filled with rare gases by bare hands. Using the Tesla transformer, he demonstrated to his audience at that time unprecedented power transmission possibilities. How is it possible that electricity did not Tesla kill?  Thanks to the skin effect. Tesla’s transformer is a high-voltage high-frequency generator. The current, thanks to the high frequency in the hundreds of KHz, flowed only on the surface of his body. Still using some illusionist skin effect with Tesla’s transformer at their spectacular shows (http://www.highvoltagemagic.cz)

What a skin effect is?

Skin effect (surface effect) is a physical phenomenon in which the electrical current is ejected to the surface of the conductor. The electric alternating current (I) passing through the conductor closes around the magnetic flux streams (H) around it which form the vortex streams (Iw). The winding currents are closer to the center of the conductor opposite the original electrical current and are therefore read. Closely to the surface of the conductor, the directions are consistent. Therefore, the whirling currents are added together. The most skin effect is applied to the full circular cross-section of the conductor, the strand (braiding more thin wires), or the flat cross-section of the eddy current limitations. At a 50 Hz transmission frequency for copper wires, the skin effect does not exceed a loss more than 1%.

The skin effect increases

– current frequency
– conductor cross section
– conductivity of conductor material
– relative conductivity permeabilityWhere does the skin effect in audio technology apply?

Where large AC currents flow. From the amplifier current source, through the amplifier element of the transistor or the tube to the speaker. Thus, the skin effect most applies to speaker cables due to their length. Although some manufacturers do not care about the distance and quality of the cables inside the speaker system (the distance between the terminals and the loudspeaker), the length of the interconnecting speaker cables is usually several times larger and therefore has a greater impact.

According to Malcolm Raven’s 2015 study, the skin effect is certainly applied at low frequencies. The author compares the theoretical assumptions with actual copper, aluminum and brass wire impedance measurements and copper wire of 0.5 and 4mm cross sections at frequencies from 100Hz to 1MHz. It states that the measurement results are comparable to the theoretical assumption and apply to audible frequencies up to 20 kHz.

Does the skin effect have a major impact on the speaker cable?

Influence yes, but definitely not. From the point of view of the purely electrical connection of the audio string (amplifier – cable – speaker), each of these components has its own parasitic (unwanted) properties. The simplest of them – of course, the cable is. An obscure reader (electrician) knows that each cable has the electrical resistance that is also temperature dependent as the main parasitic property. This parasitic property, however, is not the only one. The speaker cable consists of two insulated conductors. One flows to the speaker, the other to the opposite direction. They are therefore influenced by mutual inductance, which is applied as a second parasitic effect right after resistivity. There is also a capacity between drivers. As an electrical substitution diagram of the cable, it is possible to consider the connection of two resistors (impedances), which also have inductive and capacitive coupling.Conclusion from practise

On highly sensitive speaker systems, the differences in cable production technologies are audible. But it’s just one part of the whole audio chain, in which the most overwhelming role is often played by the neglected acoustics of the listening space. But that’s the next time.


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References:

http://www.highvoltagemagic.cz/
https://cs.wikipedia.org/wiki/Skin_efekt
Malcolm Raven
http://www.audioholics.com/audio-video-cables/skin-effect-relevance-in-speaker-cables