Active Noise Control with a surface transducer

Discussion in 'The Projects Forum' started by oc161993, Apr 26, 2016.

  1. oc161993

    Thread Starter New Member

    Apr 26, 2016
    3
    0
    Hi there, I am currently looking into Active Noise Control and its potential applications as part of my Honours for Industrial Design. From what I have looked into Active Noise Control, it seems it is easier to achieve if you have direct access to the source that is creating the noise. So my project question is if surface transducers (or maybe speakers) were put on an object producing noise (such as a kettle or even a power tool) and have played the inverted sound of the object via them being connected to an ANC circuit, and microphones to pick up the objects noise in the first place (which would also be placed on the object as well), would you be able to get the noise dampened?

    I came across this circuit on Instructables for Active Noise Cancelling Headphones-
    http://www.instructables.com/id/Analog-Noise-Cancelling-Headphones/
    Would it be possible to adapt this circuit to suit my project question (ie have the surfaces transducers as the outputs instead of the headphones)? Or are they simply too different?

    Thanks for any feedback
     
  2. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    1,438
    368
    It's good that you welcome feedback because, aside from the practical problems of installing the transducers, acoustic feedback will almost certainly make it unworkable. Unlike noise-cancelling headphones, there is nothing to prevent the noise-cancelling signal from reaching the microphone and it won't be out of phase at all frequencies.

    If you really want to understand the problem, build the circuit and try it.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Not only will the original noise plus the noise-cancelling signal reach the microphone, there is also room echo/reverberation to consider. That will have unpredictable phase shifts. If any component happens to be in phase with the original noise you could finish up with howl-around.
     
  4. oc161993

    Thread Starter New Member

    Apr 26, 2016
    3
    0
    Thanks for your feedback. Just out of curiosity what about the case of over ear active noise cancelling headphones that have internal microphones next to the speakers, what is to stop the microphones from picking up the noise cancelling signal? Also, what do you think of the idea of placing surface transducers on a wall and and have them play the inverted signal picked up by microphones from outside? would this be way more likely to work? Thanks again.
     
  5. oc161993

    Thread Starter New Member

    Apr 26, 2016
    3
    0
    Would there be any other way of using Active Noise Control to dampen the noise of loud objects?
    Also, with the idea of placing surface transducers on a wall and have them play the inverted signal picked up by microphones from outside, would this in theory result in the noise from outside being dampened inside? Or is this idea flawed as well? If it isn't, then would it be possible to modify this circuit ( http://www.instructables.com/id/Analog-Noise-Cancelling-Headphones/ ) to suit this scenario (have the surface transducers as the output instead of the headphones)? Or are they too different to each other?

    Thanks to anyone who replies again! And sorry if I have come across as a bit of a noob - I am still very much a beginner in the field of electronics and am still learning the limitations of Active Noise Control technology.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Have a re-read of post #2. Like blocco, I think you'll need to do some preliminary experiments to test the feasibility of this project. I doubt that a simple circuit will be anywhere near adequate. In view of all the possible routes by which sound can reach the microphone I think you would need some very sophisticated real-time signal processing to get even modest noise cancellation. But I hope you can prove me wrong :).
     
Loading...