Results 1 to 9 of 9

Thread: Two basic questions about noise due to electrical set-up

  1. #1
    Kyriakos's Avatar Praeses
    Join Date
    Nov 2012
    Location
    Thessalonike, The Byzantine Empire
    Posts
    9,816

    Default Two basic questions about noise due to electrical set-up

    Two connected questions about electricity and noise (unwanted sound) :

    1) Sometimes you get a very unpleasant, continuous sound/noise when you operate a machine which normally is mostly silent. Eg speakers connected to your computer. Is it correct to generally refer to this as an electrostatic phenomenon? (I understand it has to do with grounding -??? not sure if the correct term in english - of wires).
    2) I am also thinking of a similar, but a lot more pronounced, noise which seems to be the result of nearing a wire to a socket in a similar set-up (eg computer socket and some wire for the speaker). Is this due to mistaking the polarity of the edge of the wire, and in effect trying to insert the edge with the wrong polarity? (electrical charge?). If so, is the phenomenon again tied to grounding the system or is this something entirely different?
    If possible I'd like to avoid technical terms (I read about Ω difference and "ground loop", but I just need general terms as in the ones I mentioned above ).

    I just need this for a passing simile in a short story. A terrible sound is likened to that. (story isn't in english, so what I want is just to verify the generals for the simile)...
    Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
    "While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
    Anaxagoras of Klazomenae, 5th century BC










  2. #2

    Default Re: Two basic questions about noise due to electrical set-up

    The fundamental frequency of that noise is twice the rate of your local alternating current = usually 60 Hz in the North America, 50 Hz in Europe. I believe the ultimate cause is magnetostriction - tiny changes in the of shape of the iron in transformers in reaction to changes in the magnetic field. The related grounding issue is that a loop can occur amplifying the sound by feeding back into itself to some degree. I don't really dislike the sound at low levels. It's the backing track to nearly all modern music.
    Quote Originally Posted by Enros View Post
    You don't seem to be familiar with how the burden of proof works in when discussing social justice. It's not like science where it lies on the one making the claim. If someone claims to be oppressed, they don't have to prove it.


  3. #3
    Kyriakos's Avatar Praeses
    Join Date
    Nov 2012
    Location
    Thessalonike, The Byzantine Empire
    Posts
    9,816

    Default Re: Two basic questions about noise due to electrical set-up

    Thanks Is it the same phenomenon in the second case as well? Cause there the noise is a lot more powerful. A bit like (maybe tied) to what microphones sometimes produce when moved (a nasty and loud noise).
    Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
    "While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
    Anaxagoras of Klazomenae, 5th century BC










  4. #4

    Default Re: Two basic questions about noise due to electrical set-up

    Part of it can be looping back noise which amplifies it, same principle as microphone feedback, but from a different original sound source. Also, audio equipment tends to have various power filters to reduce this noise, so in the second case you're also introducing more which is bypassing the filters. As the noise gets louder it will also get to an amplitude where the line starts to saturate causing more harmonics relative to the fundamental frequency. That's why it's not just louder, but also harsher. We call the base sound "60 cycle hum" or just "hum" in the US, although "hum" is probably a too mild descriptor for what it sounds like saturated out of control.

    By the way, a controlled level of saturation is what overdrive/distortion on an electric guitar is. The harmonics produced by saturation are natural harmonics which can be out of tune with the tempered tuning of Western scales. That's why rock/metal guitar parts are usually very simple harmonically, limited to root, fifth, and octave if you know music theory. These chords are neither major nor minor, because major and minor tonalities come from the third of the chord which is omitted for the reason that saturation on a third is often really out of tune with the rest of the chord. Guitar cabinet speakers also roll off the high end. The direct sound of distorted electric guitars not being filtered through speakers or speaker emulation has a similar harshness to the saturated hum you're talking about.
    Quote Originally Posted by Enros View Post
    You don't seem to be familiar with how the burden of proof works in when discussing social justice. It's not like science where it lies on the one making the claim. If someone claims to be oppressed, they don't have to prove it.


  5. #5
    Kyriakos's Avatar Praeses
    Join Date
    Nov 2012
    Location
    Thessalonike, The Byzantine Empire
    Posts
    9,816

    Default Re: Two basic questions about noise due to electrical set-up

    Thank you! +1

    Last question: is it ok (ie not wrong) to term this in passing (cause it is only a passing simile; I cannot include that much info) as an "electrostatic phenomenon"?
    And tied to that: doesn't incorrectly connecting the wires (in case they have different polarity on their edges) contribute to this? (eg with computer socket+ speakers+ cord to power the speakers).
    Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
    "While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
    Anaxagoras of Klazomenae, 5th century BC










  6. #6

    Default Re: Two basic questions about noise due to electrical set-up

    There may be a little electrostatic noise in the signal, but mostly it’s transformer hum from magnetostriction. Electrostatic noise is caused by parasitic capacitance. The trouble for your simile is that electrostatic is technically semi-wrong. Although it would sure sound better than any term I can think of, and probably get the point across. I feel like I may have heard electrostatic used in the way you’re thinking. I suppose it just comes down to whether you want to open yourself up to pedantic criticism from the few who will notice. I know the the difference, but it would probably fly past me without being an issue.

    At 1:06, this is pure unsaturated transformer hum:



    Now the following is mostly transformer hum with a little bit of electrostatic noise (in the upper mids you should hear the electrostatic noise as an added sizzle):



    The polarity thing can effect the volume of the noise by defeating the filters. One way to filter the noise is actually to sum two versions of the noise out of phase so that they cancel each other out. If they are no longer out of phase, the amplitude of the noise is doubled rather than cancelled out.

    For the sake of simplicity, these are sine waves:



    Adding blue and green gets you red. If you reverse the polarity of either blue or green, then adding them together will get you a wave with twice the amplitude of either on its own.
    Quote Originally Posted by Enros View Post
    You don't seem to be familiar with how the burden of proof works in when discussing social justice. It's not like science where it lies on the one making the claim. If someone claims to be oppressed, they don't have to prove it.


  7. #7
    Kyriakos's Avatar Praeses
    Join Date
    Nov 2012
    Location
    Thessalonike, The Byzantine Empire
    Posts
    9,816

    Default Re: Two basic questions about noise due to electrical set-up

    Excellent information!
    You are right, the electrostatic noise is not that noticeable. But yes, it will be tricky to reference "transformer hum" in passing. I will see how I can alter the short phrase...

    Btw, are cords incorrectly connected (opposite polarity) an issue at all? (iirc in the ground loop article I read, they just added to the hum, because they prevented the usual means of the system to lower or cancel it). But I recall a terribly loud and nasty hum one time I neared the cord of the speaker to the wrong socket in the PC - that is exactly the type of sound I wanted to allude to, so if you can name it I would be beyond grateful!!!
    Last edited by Kyriakos; October 18, 2019 at 01:47 PM.
    Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
    "While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
    Anaxagoras of Klazomenae, 5th century BC










  8. #8

    Default Re: Two basic questions about noise due to electrical set-up

    If you have everything connected reverse polarity in your system, it usually isn't a problem, but if something is reverse and something isn't, it can cause problems like amplifying noise you don't want and partially cancelling out sound you do want.

    Speaker cables carry waves of electrical current analogous to sound pressure waves in the air, so that speakers move in such a way as to reproduce those sound pressure waves. When you put the speaker cable connector near a power source it picks up current that is just straight up noise. I don't think there is any particular name for that, but the particular structure of the noise is mostly a product of the aforementioned phenomena.
    Quote Originally Posted by Enros View Post
    You don't seem to be familiar with how the burden of proof works in when discussing social justice. It's not like science where it lies on the one making the claim. If someone claims to be oppressed, they don't have to prove it.


  9. #9
    Kyriakos's Avatar Praeses
    Join Date
    Nov 2012
    Location
    Thessalonike, The Byzantine Empire
    Posts
    9,816

    Default Re: Two basic questions about noise due to electrical set-up

    Thanks, your answers were really excellent and helpful
    Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
    "While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
    Anaxagoras of Klazomenae, 5th century BC










Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •