repetitious hum from Acer a715-74g

Mike000
Mike000 Member Posts: 22

Tinkerer

edited September 2023 in 2019 Archives
Experiencing repetitious hum from a715-74g with fan. One fan doesn't spin all the time and blade idles back and forth when not functioning. Is this normal?

Best Answer

  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    Answer ✓
    Nope. It simply means the CPU & GPU are at different temperatures causing the fans run at different speeds. The higher the temperature the higher the fan speed to keep it cool. Entirely normal. And the varying beat frequency (hum) you hear as a result is entirely normal. Jack E/NJ   

    Jack E/NJ

Answers

  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    Yes. The hum you hear is probably a beat frequency when the fans are NOT running at the same rpm. For example, if the CPU fan is running at 4000rpm and the GPU fan is running at 3000 rpm, the beat frequency is about 1000rpm or 17Hz multiplied by the number of fan blades. 6 blades would yield about 100Hz beat. This would definitely sound like a low pitched hum. And a variable pitched hum too depending on the difference between fan speeds. The fix is earplugs or a headset to dampen the drone.   :)   Jack E/NJ     

    Jack E/NJ

  • Mike000
    Mike000 Member Posts: 22

    Tinkerer

    Probably isn't certain, I need to know if I should return the laptop or not. One fan completely stops by the way, not one going slower. Would one fan completely stop in an acer laptop? It isn't a matter of 2 Hz frequency's, it only is a matter of a repetitious tone that turns on and off.
  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    >>> Probably isn't certain, I need to know if I should return the laptop or not. >>>

    Sorry. No 100% guarantees from this forum. Accordingly, return it to the vendor for a refund or exchange ASAP before the vendors RMA period expires. Jack E/NJ

    Jack E/NJ

  • Mike000
    Mike000 Member Posts: 22

    Tinkerer

    Can you elaborate on "beat frequency" thing you're talking about? Do you mean fan hum or something else?
  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    The low pitched beat is the numerical difference between the frequency of one fan and the frequency of the other fan. If one fan for example is emitting a 2000Hz tone,  and the other a 2200Hz tone, (which are both fairly high pitched tones that some people like me with high pitch hearing loss can't hear), they will indeed also hear a 200Hz low frequency tone --- the difference between 2000 and 2200 Hz.   This is called a 'beat' or 'resonant' frequency response between 2 sound emitters. You can often hear this type of beat in a twin engine prop plane when the two engines are NOT running at precisely the same rpm or "synched" This beat can often sound more like an annoying and varying pitched drone that some folks can't tolerate. This is one of the drawbacks of trying to cool both a CPU and a GPU in a congested hiperformance laptop vs a desktop. Jack E/NJ

    Jack E/NJ

  • Mike000
    Mike000 Member Posts: 22

    Tinkerer

    Ya, the fans run at different speeds when the sound comes on but what's the cause? Is the sound a warning to tell tell you the fans are broken?
  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    Answer ✓
    Nope. It simply means the CPU & GPU are at different temperatures causing the fans run at different speeds. The higher the temperature the higher the fan speed to keep it cool. Entirely normal. And the varying beat frequency (hum) you hear as a result is entirely normal. Jack E/NJ   

    Jack E/NJ

  • Mike000
    Mike000 Member Posts: 22

    Tinkerer

    I know theres an option to turn off the Nvidia Graphics card. Could it be the fan hasn't been running because the graphics card has been off up until this point?
  • JackE
    JackE ACE Posts: 45,098 Trailblazer
    edited August 2019
    The GPU fan may still run even if the GPU is completely turned off just by being indirectly heated by other mainboard components. Thus the beat frequency hums between the two fans may still be heard from time to time but probably not as much. Jack E/NJ

    Jack E/NJ