Effect of 180 degree phase inversion in audio amp

Discussion in 'The Projects Forum' started by rick5, Aug 22, 2008.

  1. rick5

    Thread Starter Member

    Jul 17, 2008
    I have designed an audio circuit but haven't breadboarded it yet. I'd like to know how does the human ear perceive 180 degree phase inversion? Is it perceivable at all? I'm thinking if you haven't got a reference sound where the phase is the same as the input then maybe you can't tell.
  2. bertus


    Apr 5, 2008
  3. Wendy


    Mar 24, 2008
    If it is your only source then you can't tell the difference. Where you stand in a room will cause all the signals to be phased differently than output by a speaker, every one of them different, speed of sound being a constant and wavelength being the variable.
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    With most audio sources we don't know what the correct phase was to start with and any number of inversions may have taken place in the recording chain. Of course, if your circuit ultimately feeds a pair of loudspeakers it's easy to invert the phase (if there is a preferred phase), although slightly more difficult with headphones.
  5. Audioguru


    Dec 20, 2007
    A good audio amplifier has negative feedback to establish the voltage gain, to reduce the distortion and to reduce the output impedance for good damping of resonances of the speaker.
    Negative feedback is an input that is 180 degrees from the input.

    Billions of amplifiers have negative feedback. Did you design another one?
  6. SgtWookie


    Jul 17, 2007
    I think he's simply talking about the amplifier's output being inverted from the input.

    I think that percussion instruments is where the difference will be most noticeable; it won't be audible necessarily, but it will have a different "feel".

    If you watch a bass speaker when a bass drum is struck, you'll see the cone deflect outwards. If the signal is inverted, the cone will deflect inwards. Rather than feeling a "thwack" to the body, there will be a low-pressure region.

    It'll be subtle, but it literally won't "feel" quite right.
  7. rick5

    Thread Starter Member

    Jul 17, 2008
    Thanks for these responses. I think the last post is what I was thinking. Deliberate phase inversion may be perceivable to a listener, but detecting a difference from the same signal amplified with no phase shift is going to be highly subjective - it's a very unscientific comparison.

    I'm going to have my i/p and o/p in phase in the frequency ranges I'm designing for, as far as possible.
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    The most noticeable effect you can easily demonstrate is in reversing the connection to on of a pair of stereo loudspeakers. There will be a marked reduction in bass ans lower midrange sounds.

    As far as phase shift through an amp goes, it's hard to see how anyone could perceive it.
  9. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    This should be quite any easy thing to test either by physically swapping wires around or by electronic inversion. With electronic inversion, the circuit must process inverted and non-inverted in exactly the same way in order not to introduce any more variables.

    Devise a blind-test whereby the music is paused and an inversion may be introduced, the subject then records if they perceive a change in sound. Examine the results to see whether the perceived changes correlate with an inversion.
  10. Buck Rogers

    New Member

    Apr 18, 2013
    The perception of Absolute Phase is called the Woods Effect. You can Google it for more info.