Ground Loop

[Gordon Palmer]

I guess this is not strictly a REW question

Spectrogram and Waterfall graphs both clearly show a spike at 50Hz (I'm in the UK)
I assume this is a ground loop issue but its not audible when no content is playing
My crossovers are all 100Hz so I assume its the subs (4)
If I put my ear to each sub there is the very faintest noise (I wouldn't characterise it as a hum as such)

Should I ignore it or not?

 

[John Mulcahy]

It can also be acoustic pickup from other devices, hum is pervasive. You can ignore it.

 

[Gordon Palmer]

Update
Unplugging the subs from socket made no difference
Muting the receiver made no difference
Unplugging receiver, power amp made no difference
Switching off the lighting made no difference

I conclude it something else in the room generating a very low level hum

 

[Gordon Palmer]

It can also be acoustic pickup from other devices, hum is pervasive. You can ignore it.

Ok thanks

 

[ddude003]

In the UK the power grid is 50Hz... So you could be hearing any home appliance or HVAC or even lights... Or if in an apartment other folks appliances...

 

[Lid9497]

Update
Unplugging the subs from socket made no difference
Muting the receiver made no difference
Unplugging receiver, power amp made no difference
Switching off the lighting made no difference

I conclude it something else in the room generating a very low level hum

Currently dealing with similar problem, however I narrowed it down to ground loop. My subs are silent when nothing is connected, but as soon as I plug in RCA, hum is there. What helped a bit was putting everything on the same power outlet, now I can increase amp on subs and there is barely any hum. I tried RCA isolator (ART DTI) but that introduced very high distortion at ultra low-end (25Hz showed 15% distortion with ART DTI vs 0.6% without). My last attempt will be high-powered usb isolator for my DSP, since the ground loop is coming through it.

If there is still hum coming from your subwoofer when nothing is connected, that probably means an issue with the subs internal wiring, if the hum goes away, it's a ground loop.