Mysterious 30 Hz signal

Hi RS Forum

I moved my RS to a new location and there is now a persistent 30 Hz signal in the spectrogram
day and night.
What would produce 30 Hz?
How can I get rid of it?
Please see attached:

Most likely an electric motor, or some device driven by one (assuming you are in a country with 60Hz power).

As for getting rid of it, I see two options: 1) Find the motor and turn it off. 2) Put your Shake somewhere else.


Hello rmurawsk,

Yes, as Philip said, that is clearly something relatively close-by which is always on (at least for the duration of the spectrogram window).

If you cannot find anything in your house, then it may be something in a neighbouring one, so you can experiment with different locations in your home to see and find the one in which this constant noise is absent, or, at least, minimized. It would be an interesting “hunt”.

Let us know what you discover, as it could be useful to other Shakers in the community!

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Yes, US AC at 60 Hz. So it suspiciously looks like a sub harmonic.

Would a make shift Faraday cage help, maybe?

I am checking out new locations for a quiet spot.

Thanks for the reply.


Hi Stormchaser,

I am currently trying out different spots on my campus looking for the least noisy.
I found a quiet noise level (mostly yellow on the Station View Map), but it introduced this 30 Hz signal.
Must have placed the RS near a mechanical room.

Thank You.



I think that is vibration, not an EM signal. Probably a synchronous motor.
When I first installed mine I thought I had an ideal spot, but was just not aware how far the vibration from the heat pump and air handler motors travelled.


You’re very welcome rmurawsk, I agree with Philip about that 30Hz signal being generated by some kind of motor.

For example, I have a similar waveform on one of my Shakes at around 37Hz, which is generated by the external cooling fans of my laptop.

But, if you want to test a Faraday Cage, one of our Shakers has created an RF-shielded vault that maybe can inspire you: Amateur Radio & My RF Shielded Raspberry Shake Vault Experiment

My refrigerator causes a 30hz signal while the compressor is running. I put damping pads underneath the refrigerator to try and reduce the signal. The signal was still there slightly less, but various harmonics were eliminated. It was helpful but not perfect. The damping pads are 1"x1" and normally meant to be placed under speakers. The simple rubber dampeners with nubbies had no effect on reducing the signal.


The refrigerator no longer touches the floor, just the pads.


Hello PerMartin, and welcome to the community!

Thank you for your feedback and description of your experience. I’ve never tried adding pads so that vibrations from “heavier” equipment (fridge, washing machine, etc.) would be diminished.

It would be interesting to see, using your experience as a starting point, how big/thick those pads would need to be to actually see a definite vibrations reduction on the Shake.

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Correction, the pads that I am using are 2" cubes, BXI Subwoofer Isolation Pads. There is a larger version of these at a much higher price. I did get the larger ones, but the 2" cubes were sufficient. This does not solve any issues of radiated sounds from the refrigerator such as transfer through the air. All it does is reduce the direct contract transmission from the feet to the floor. For me, that helped. My compressor noise line at 30hz looks more crisp and less energy. My refrigerator is in a 3 wall cubby hole in the kitchen. Thus there is probably a lot of air transmission to the walls.

The rubber pads that did not work were BXI Exercise Equipment Mat 4x4x0.8 Non Slip Noise Reduction Anti Vibration Treadmill Stationary Bike Mats.