Fan Noise cancelling Issue

Hi ADI's

One of my customers is considering developing a fan noise reduction solution.

she wants to reduce fan noise on equipment (air purifier) to reduce noise in work area.

The devices under consideration are planned to be placed next to the already installed equipment.
I think it should be designed in such a way that it receives the fan noise from the side and generates the opposite phase noise.

So I'm trying to design an ADAU1772 ANC part

Question

1. Is the output of the ADAU1772 the opposite phase of the noise signal? Or is it a noise-canceled signal?

2. Is there any other solution available besides the ADAU1772 assuming that I know the noise frequency?

   

Thank you in advance

Parents
  • +1
    •  Analog Employees 
    on Mar 26, 2019 6:53 PM

    Hello Andrew,

    I think technically this is very difficult to do. Fan noise has a lot of higher frequency signals and they are somewhat random. This is all very difficult to cancel out in an acoustic environment. The wavelengths are short so the amount of cancellation will differ with the angle between the source and the speaker differs depending on where the listener stands. 

    As far as your questions, The 1772 will output whatever signal you would like to output. Normally this part is used to drive headphones so the output is the noise cancelled signal. However, nothing is stopping you from just developing the cancellation signal and sending that out without the original signal. 

    We have the acoustic noise canceller and the noise reduction algorithms that we license for the ADAU1452 family of parts. It is available in trial form in SigmaStudio. The 1452 had PDM inputs so it can receive audio from a PDM output microphone. Then you can interface it with a codec for other inputs and outputs. The ADAU1372 would be a good choice. It is basically the converters from the 1772 without the DSP. 

    Dave T

  • +1
    •  Super User 
    on Mar 27, 2019 7:27 PM in reply to DaveThib

       Dave is quite correct; a look at this Wikipedia article demonstrates what such a noise reduction problem is up against.  The finite speed of sound (about 1K feet/second) means that sound added to cancel the noise at a particular location, may actually reinforce the noise a few inches or feet away.  Noise cancellation is easier if when when operating right at the listener (headphones), or at the source (inside the fan's duct).  Anywhere else is extremely difficult.  Also it's a lot easier when the undesired noise is a tone or hum of one or a few frequencies.  It's much harder for a fan sound, which typically covers a wide frequency band as does pink noise.  Thus, anything you can do to make the fan quieter in the first place would be more effective than an add-on cancellation system.  Mechanical features such as motor shock mounts, deadening material in ducts and enclosures, and the lowest fan speed that does the job usually provides sufficient noise reduction.

         Best regards,

         Bob

Reply
  • +1
    •  Super User 
    on Mar 27, 2019 7:27 PM in reply to DaveThib

       Dave is quite correct; a look at this Wikipedia article demonstrates what such a noise reduction problem is up against.  The finite speed of sound (about 1K feet/second) means that sound added to cancel the noise at a particular location, may actually reinforce the noise a few inches or feet away.  Noise cancellation is easier if when when operating right at the listener (headphones), or at the source (inside the fan's duct).  Anywhere else is extremely difficult.  Also it's a lot easier when the undesired noise is a tone or hum of one or a few frequencies.  It's much harder for a fan sound, which typically covers a wide frequency band as does pink noise.  Thus, anything you can do to make the fan quieter in the first place would be more effective than an add-on cancellation system.  Mechanical features such as motor shock mounts, deadening material in ducts and enclosures, and the lowest fan speed that does the job usually provides sufficient noise reduction.

         Best regards,

         Bob

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