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Author Topic: Active Noise Cancellation System  (Read 493 times)

Josh Rawls

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Active Noise Cancellation System
« on: August 11, 2021, 09:04:59 PM »

I have a unique opportunity to put in an active noise cancellation system in up to 24 locations. The problem is I can't find any active noise cancellation systems that I can get by the end of the year.

Here is the situation; these will be installed in a power utility's substation control rooms. The noise is from Cisco fiber switches with very loud fans. They do vary in loudness and pitch depending on the temperature. It seems to very between 70dB at the low end at as much as 85-90dB on the high end. Measured A weighted, slow response, at a few feet away.

We already ruled out putting them in a proper noise reducing rack as we can't take them offline to move them to a new rack.

The other option is sound absorbing panels on stands to surround the rack. We may also do both the sound panels and the active noise cancelling.

I'm looking for other ideas or active noise cancelling options.

Thanks!

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Josh Rawls

Caleb Dueck

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Re: Active Noise Cancellation System
« Reply #1 on: August 12, 2021, 03:23:04 AM »

I have a unique opportunity to put in an active noise cancellation system in up to 24 locations. The problem is I can't find any active noise cancellation systems that I can get by the end of the year.

Here is the situation; these will be installed in a power utility's substation control rooms. The noise is from Cisco fiber switches with very loud fans. They do vary in loudness and pitch depending on the temperature. It seems to very between 70dB at the low end at as much as 85-90dB on the high end. Measured A weighted, slow response, at a few feet away.

We already ruled out putting them in a proper noise reducing rack as we can't take them offline to move them to a new rack.

The other option is sound absorbing panels on stands to surround the rack. We may also do both the sound panels and the active noise cancelling.

I'm looking for other ideas or active noise cancelling options.

Thanks!

I'm curious to see what the rooms look like.  As long as airflow is accounted for, you can get some pretty impressive results with a mixture of absorption (facing the racks) and blocking (facing away from the racks). 

I'm working on a portable drum booth right now, so a lot of this is fresh in mind.  Shoot me a message if you'd like and I'd be happy to help.
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Ivan Beaver

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Re: Active Noise Cancellation System
« Reply #2 on: August 12, 2021, 04:20:04 PM »

I have a unique opportunity to put in an active noise cancellation system in up to 24 locations. The problem is I can't find any active noise cancellation systems that I can get by the end of the year.

Here is the situation; these will be installed in a power utility's substation control rooms. The noise is from Cisco fiber switches with very loud fans. They do vary in loudness and pitch depending on the temperature. It seems to very between 70dB at the low end at as much as 85-90dB on the high end. Measured A weighted, slow response, at a few feet away.

We already ruled out putting them in a proper noise reducing rack as we can't take them offline to move them to a new rack.

The other option is sound absorbing panels on stands to surround the rack. We may also do both the sound panels and the active noise cancelling.

I'm looking for other ideas or active noise cancelling options.

Thanks!
The problem with active noise cancellation is freq (size of the wavelength) and location.

In the case of headphones, you don't have a position issue, since the headphones and your ear remain a constant distance from each other. 

In order to cancel, you need opposite phase of the original source, or close to it.

As you go higher in freq and are in different relative positions of the source and the "cancelling" speaker, it gets harder and harder, because different listening positions will have a different phase relationship, due to the physical distance difference.

Down low it is much easier, because the wavelengths are much larger.  So there is more room to "move around".

Up higher, the areas of cancellation get to be really small, and in the other areas it is actually LOUDER.
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Ivan Beaver
Danley Sound Labs

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Re: Active Noise Cancellation System
« Reply #2 on: August 12, 2021, 04:20:04 PM »


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