Audiosonic Noise Cancelling Headphones bought for $9 @ Kmart

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  wharlie on 10/06/2013 - 10:53

  Yeah that's how noise canceling works.
  The louder the external noise the louder the hum.
  In the expensive models you can switch between a hum and a screech.

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  TheAviator on 10/06/2013 - 19:36

  Noise cancelling headphones work by essentially listening to the same sound you hear and then sending sending an extra soundwave to your ears. This extra soundwave is meant to cancel out the ambient noise.

  However it only works if the external sound is rather constant, e.g. the sounds of jet engines or perhaps a train. If the sound is constant the soundwaves follow a constant pattern and can be cancelled out easily by the noise-cancelling headphones.

  On the other hand, if the external sound is someone speaking, it won't be able to cancel it out very well at all because the external soundwaves aren't constant.

  So I suppose the best way to check if the noise cancelling is working is to find a YouTube video or something of jet engines, turn on your headphones and see how it goes :)

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    [Deactivated] on 11/06/2013 - 11:45

    +1

    Sorry, don't mean to sound like a smart alec, but the reason you can still hear people speak is not because they are unable to cancel out non-constant noise. Because the noise cancelling effect is virtually instantaneous. The reason is because that's the way they're designed. i.e. You want to be able hear someone speaking, over say, the noise of an angle grinder.

    The way it works is a microphone picks up the noise (sound waves). They know the sound waves of unwanted noise are mostly in a certain frequency band. They also know other noise such as human voices are outside that range. Noise in the unwanted band is picked up by the microphone, inverted (reversed in amplitude), fed into an amplifier circuit, and finally into speakers inside the ear cups. So you "hear" the opposite waveform to the noise.

    So when you twiddle the dial, you're adding or reducing the amount of amplification in the opposite direction.

    A very simplified example is, if an unwanted noise had a level of +5, the circuitry reverses that to -5. So +5 and -5 added together = 0 (no noise).

    Obviously you get what you pay for with these. The more expensive versions (generally) mean better noise-cancelling circuitry.