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How to minimize acoustic mike<loudspeaker feedback?

Discussion in 'General Electronics Discussion' started by FuZZ1L0G1C, Jul 22, 2017.

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  1. FuZZ1L0G1C

    FuZZ1L0G1C

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    Mar 25, 2014
    To prevent howl, would delaying the signal-path help?
    Low volume or headphones helps, but play guitar "live" and problem of feedback surfaces.
    An idea I had is to use a passive analog delay-line in the input circuit.
    I have a circuit for this, somewhere...
    Hopefully this would decrease the feedback frequency to sub-audible (my theory anyway).
    Would this work in practice?
    Otherwise how do stage performers overcome this problem?
    Guitar is nylon-string acoustic, fed to amp up to 4m away via several alternate methods:
    600 ohm balanced mike on stand, into FM transmitter,
    acoustic clip-on soundboard pickup (in hole),
    also tried an old turntable pickup, sensor pressed on soundboard (poor audio response).
    If I remember, the delay-line used multiple inductors / caps in a "pi" network.
    Cheers, Clive.
     
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Audio feedback suppression is usually achieved by frequency-shifting the mic input - I have a number of construction articles that describe the process and offer a solution in hardware.

    Here's the schematic of one solution - lots of op-amps but a very basic circuit overall.
     

    Attached Files:

    FuZZ1L0G1C likes this.
  3. FuZZ1L0G1C

    FuZZ1L0G1C

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    Mar 25, 2014
    Perfect!
    Thanks i'll try it out. :D:D
     
  4. Audioguru

    Audioguru

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    Sep 24, 2016
    Frequency shifting or having a delay sounds very odd to the performer.
    Usually a speaker is more sensitive at its resonant frequencies, which can be equalized to not have a peak. Then there will be less feedback.

    Speakers are usually directional, point them away from the mic. A directional mic can also be used and pointed away from the speakers.
     
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  5. kellys_eye

    kellys_eye

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    Jun 25, 2010
    The shift (or delay) is measured in Hz and/or milliseconds and would be unnoticeable by most.
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    If the frequency shift fixes a sound system that is on the edge of feedback then the shifted frequency obviously sweeps up (or down). It sounds funny. Many singers cannot sing properly when they hear an echo of their voice.
     
  7. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Which is why they use earpieces! Well the pro's do..... or you see them standing with a finger poked in one ear!
     
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    The pros use an earpiece to hear the drum beat and the pitch of the accompaniment music.
    But some pros do not actually sing, instead they play a recording of their singing then pretend to be singing.

    Some pros make many mistakes when recording so they record a song many times (takes) and pick the best parts that are joined together for the finished recording.
    Some pros cannot sing, instead they use auto-tune (for correct pitch) and just talk the lyrics. I can hear a lot of auto-tune in recordings of Drake. But RAP isn't singing anyway.
     
  9. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Understatement of the century :D
     
  10. xryz

    xryz

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    Jun 24, 2013
  11. Audioguru

    Audioguru

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    Sep 24, 2016
    A sound system with a half decent microphone and good speakers is usually equalized for a flat frequency response without any peaks. Then acoustical feedback can occur at any frequency if the mic can hear the speaker. The automatic notch technique will be trying to notch all sounds which sounds funny.
     
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