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How many different frequencies have or are being used, and what for? Also, what do they sound like? I have heard of 25, 16.66, and 400 to 500hz in planes. Are there others?

bobiscool
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    google "tone generator", sine wave to hear them. heard of 50 and 60? – dandavis Jan 26 '18 at 05:41
  • @dandavis You don't understand, I mean the recordings of transformers on said frequencies, not pure tones. – bobiscool Jan 26 '18 at 06:09
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    Then what do you mean 'what do they sound like'? Transformers don't make any sound, theoretically. Yes, they might vibrate and thus make sound, but do you really expect every transformer to sound similarly, according to frequency? How could they? – MrGerber Jan 26 '18 at 06:14
  • They do sound different, I find it interesting so why not? https://www.youtube.com/watch?v=jtk_1Pi30nk – bobiscool Jan 26 '18 at 06:19
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    you can generate AC @ nHz with a webapp, then feed the AC to a transformer via an amp ;) – dandavis Jan 26 '18 at 06:27
  • I dont have the equipment to do so. – bobiscool Jan 26 '18 at 06:34
  • @MrGerber they say each bean has its tone, so each transformer has as well? –  Jan 26 '18 at 07:27
  • Of course, but how do you expect we should tell you generally how they sound? Find a transformer and listen to it. – MrGerber Jan 26 '18 at 07:51
  • In theory, they should all have a fundamental frequency that matches the mains frequency that they're transforming, so listening to the frequencies on youtube should give you a sense of what theyll sound like. – BeB00 Jan 26 '18 at 09:51
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    My point exactly. If you want to listen to the theoretical sound of a mains voltage at a specific frequency, listen to the pure tone. If you want to listen to the sound of a specific frequency of a specific transformer - please do. But practically, transformers will sound different, because of different harmonics (mechanically and electrically), so I don't understand how EE.SE could explain how each frequency sounds, generally – MrGerber Jan 26 '18 at 13:31
  • As the second answer below states, what I am looking for is the sound of transformers running X frequencies, when said transformers produce harmonics and create interesting sounds. – bobiscool Jan 27 '18 at 04:35
  • @bobiscool if your asking about harmonics on the line there are infinitely many, it depends on what the loads and sources are locally. Mostly 60,120 and multiples of these (unless your in a 50Hz country). If you want to hear them, take an AM radio and put the antenna near a mains line – Voltage Spike Jan 28 '18 at 01:42
  • I don't leave near any 16.7hz or 25hz mains. Just 60. – bobiscool Jan 28 '18 at 03:36

2 Answers2

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For a detailed list of utility frequencies, see this article from Wikipedia.

The frequency of mains electricity is strongly related to the rotational speed of the machines used to generate it (usually alternators connected to some form of turbines). That's why frequencies are somewhat lowish.

The world has somewhat standardized, along the way, on 50Hz/60Hz systems (with most of the world using 50Hz). Some higher frequency are indeed used (e.g. 400Hz), but the main problem with them is they cause more problems when transmitted over long lines. Therefore they are used when their advantages are paramount, e.g. when space is limited (aircrafts, submarines, etc.), because higher mains frequency means, for example, more efficient and less bulky transformers.

Some relevant excerpts from the Wikipedia article (emphasis mine):

Several factors influence the choice of frequency in an AC system. Lighting, motors, transformers, generators and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise between contradictory requirements.

[...]

There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse).Once AC electric motors became common, it was important to standardize frequency for compatibility with the customer's equipment.

[...]

Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at a higher frequency.

Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency.

Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in a grid, providing reliability and cost savings.

As for the "how do they sound like part", the usual frequencies lie in the audible spectrum, therefore google for a free signal generator program to run on your PC. Your sound card is well able to generate sounds at those frequencies. Remember to set the generator to produce a sine wave, since that's the waveform of mains voltage. Different waveforms will sound different.

LorenzoDonati4Ukraine-OnStrike
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    @bobiscool Please, avoid accepting my answer so soon, even if it was good for you. On this site we have a guideline of waiting about 24h before accepting an answer, so that other users across the world have a chance to post their answers. You can unaccpet my answer and return here later and accept it again if no better answer has been posted. – LorenzoDonati4Ukraine-OnStrike Jan 26 '18 at 06:22
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All the terrestrial mains frequencies are so low that 'what they sound like', any interesting differences from what a pure tone sounds like, will be governed by their higher harmonics. While the 'ideal' mains waveform is sinusoidal, in practice it is distorted.

When you hear a recording of a particular transformer in a particular situation, you are hearing the distortion caused by its non-sinusoidal generation, and departures from ideal resistive loading, as much as its pure underlying 16.66 to 60Hz fundamental. Rectifier capacitor input loads and phase shift loads, as well as iron cores going into distortion, will all create swathes of odd harmonics going up well beyond mid C. Should there be any DC bias to the current, from a faulty load, or an illicit half-wave rectified load, then there will be even harmonics generated, which sound quite different in character to odd harmonics.

The audible noise from a transformer is interesting. There are two main components. There's magnetostriction of the core, where the core changes size according to the flux. As it responds to the magnitude of the flux, it produces even harmonics. Then there are Lorentz forces between current-carrying conductors. These are square-law (current times magnetic field) and so also produce even harmonics.

Neil_UK
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