Why Does Power Cable Length Affect Sound Quality?
Last year I met Steve Dickinson who was reviewing some Black Rhodium cables for Hi-Fi Plus magazine. During our many discussions, Steve mentioned some manufacturers who claimed that there was an optimum length for power cables. Although at first sceptical, I realised that the wavelength of a 50 Hz mains supply was 6.8 metres and that the quarter wavelength of 1.7 metres was a useful length for power cables.
Curious to test this theory, I assembled a batch of power cables of some 15 different lengths from 0.8m to 4m, all with the same cable (Black Rhodium Fusion) and connectors. All cable lengths were cut accurately to the required length. These were tested on my own systems and also on systems of interested friends. We all agreed that the best sound came from a cable of length 1.65m. When unwound, a 1.65m length of cable measures 1.68m, very close to the quarter wavelength of sound at 50 HZ.
Further testing of the many different lengths revealed that lengths very close to fractions of 1.7m (0.85m, 2.5m, 3.3m) all tended to sound slightly better than other lengths such as 1m, 2m, 3m and 4m. Whilst the 3.3 metre length might have been expected to sound better than 1.65m, it did not. I have to assume that as the lengths increased, those distortions that increase with a cable length such as RFI or magnetic field effects were having a greater effect.
Comparing the difference in sound between 1.7m and 2m cables lengths, reviewer Christiaan Punter of Hi-Fi Advice says “The 1.7m Stream cable sounds tighter, more controlled and more focused with a tightly locked center image. This is a very well balanced sound and highly refined with just the right amount of bite. The 2.0m Stream cable sounds more spacious at first and even more relaxed but is less articulate overall, less well defined in the bass and less precise in terms of imaging. Swapping back to the 1.7 indeed it seems obvious why they have chosen this length.” The full review can be found at http://www.hifi-advice.com/blog/review/cables-reviews/power-cable-reviews/black-rhodium-stream-power/
Since testing different lengths of power cables, I have looked at many power cable manufacturer web sites. Only two have actually stated their optimum cable length and these were 1.5m and 1.8m. Which means that we are only at the very start of discovering why power cables appear to have an optimum length for sound quality.
From the science, it does seem that the passage of 50 Hz power through the cable is causing minute changes in electrical and magnetic fields that are translated into mechanical vibrations at this frequency. These vibrations will occur at 50 Hz and for some reason their effect on the sound quality of the system may be minimised as a result of the cable length being close to fractional lengths of the wavelength.
19 October 2017