The question comes from a discussion I had years ago with a keyboard player who had perfect pitch. His problem came from the fact that he lived in a very small appartment in an old building and he had to play at a very quiet level. So quiet that he could hear the 60hz humm (we are in north america) coming from electric appliances and that would bug him a lot. He thought about it a lot and he realized that the electricity itself was actually out of tune. Since most modern occidental music is based the reference not of A=440Hz, if you go 3 octaves below that, you get to 55Hz. But AC around the world is either 60Hz or 50Hz. When he made that calculation, he declared that 55Hz would be a very convenient and musical average if there is ever a worldwide standard.

So here is the question. Is there a reason for 50 or 60 Hz? Or it might as well be 55Hz?

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    \$\begingroup\$ Pretty sure it would be OK if it was 55 Hz. Note, this is theoretical. Like, if you go back in time to before there were standards, and convince everyone to adopt the 55 Hz standard. In the real world, changing to 55 Hz would cause a lot of problems for certain types of machines that rely on either 60 or 50 Hz. Especially induction motors and transformers. \$\endgroup\$ – mkeith Jun 14 '17 at 3:50
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    \$\begingroup\$ Related (but not a duplicate): electronics.stackexchange.com/questions/310150/… \$\endgroup\$ – MarkU Jun 14 '17 at 3:51
  • \$\begingroup\$ @MarkU : so from what they say there it's because of the induction motors that happened to work better at frequencies between 50 and 60Hz. So the answer would be yes, in theory, 55Hz would work too? \$\endgroup\$ – BadgerBadger Jun 14 '17 at 4:05
  • \$\begingroup\$ I'm not convinced that a 55Hz hum (be it in tune with the standard scale) would be less annoying for music than a 60Hz hum. What about no hum at all? \$\endgroup\$ – dim Jun 14 '17 at 7:00

Frequency directly affects the speed of some kinds of motors so you can't just change it willy-nilly without affecting a lot of expensive equipment. Low power electronics usually can work with any frequency from 50 to 60Hz (and in fact may work over a much wider range). Making a transformer (mains frequency type) work at either 50 or 60Hz incurs a small (but significant) cost and mass penalty on each unit.

The hum from pickup of AC line power can be at mains frequency (eg. 60Hz), perhaps plus some harmonics, but the audible hum directly from electrical transformers, old-school fluorescent ballasts, motors and so on is typically double mains frequency (plus some harmonics).

Don't worry, there will not be a worldwide standard any time soon. The trend is for more and more relatively small devices to accept either frequency. The biggest factor preventing changes in the supplied power is probably the billions of dollars worth of turbines, generators and utility distribution transformers that are optimized for one frequency or the other. Until relatively recently 25Hz was (maybe still is) still used in a few isolated industrial applications.

  • \$\begingroup\$ I'm not expecting to see one anytime soon! I'm aware that a lot of equipment relies on the AC frequency for their proper operation. But if we take that out of the equation, it could be possible to have AC at 55Hz. In his case he probably was not hearing the 60Hz itself, but when you go up in the scale, you are still out of tune and the higher you you, the larger the gap between the real pitch and the electricity. I was just curious about the feasibility of 55Hz AC. Thanks! \$\endgroup\$ – BadgerBadger Jun 14 '17 at 4:01
  • \$\begingroup\$ How about a typical generator turbine, say in a hydroelectric plant. Is it going to be happy running 10% faster or slower? \$\endgroup\$ – The Photon Jun 14 '17 at 4:07
  • \$\begingroup\$ @ThePhoton Yes, just added that. It may be happy enough but it won't be optimized. 20% is a pretty big frequency change to not affect the efficiency. \$\endgroup\$ – Spehro Pefhany Jun 14 '17 at 4:11
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    \$\begingroup\$ Don't forget clocks! Believe it or not, almost all mains-powered clocks are designed to keep time using the mains power as a time standard. It turns out mains frequency has extremely little drift (I've heard as good if not better than quartz crystals) \$\endgroup\$ – Jay Carlson Jun 14 '17 at 5:31
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    \$\begingroup\$ The mains frequency has plenty of drift. It's just that it is routinely adjusted back and forth so that over time the frequency (cycles per day) is very accurate. \$\endgroup\$ – gbarry Jun 14 '17 at 5:53

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