Eliminating subwoofer hum/buzz

[marconi]

For my Item 2 I meant AV plugs and sockets not mains ones.

No doubt you have thought of checking if the hum is worse with the g9 lamps switched on.

Could you measure the supply N-E voltage at the CU with the Main Switch on and then off.

 

[Midwest]

If it’s making a noise just sat, take round somebody else’s house, see what happens.

 

[static zap]

@marconi Love the bit , Kettle on you RFC ... If broken 2X ,
For when its now a giant induction loop !

 

[telectrix]

if you're going to play current pop music. the hum will be an improvement.

 

[marconi]

We are exploring mains pick up through cabling and connectors, earth loops when AV items are plugged in at different places (- one should use star configurations and linearly linked stars for earths to avoid earth loops), and mains frequency potential differences (differential/transverse mode) - through volt drop along the supply Neutral - between local earth mass and the supply Neutral which results in - electrically - the waggling at 50Hz of the potential of the double insulated sub woofer electronics assembly with respect to its casing which is at ambient/local earth potential - not the same potential as the incoming supply E. For the latter waggling the isolation transformer removes/reduces the galvanic connection to neutral and as reported reduces the hum but does not erradicate it because there is still some capacitative linkage and the lines (L and complement L*) of the shaver output are floating with respect to local terra firma. Sometimes an NTS supply can be used for audio equipment - a bit like an I-T but with the line complement L* connected to local terra firma to make a N* - a neutral with respect to local earth through an electrode in the ground- and this connection used to provided a local terra earth for the cpc of the audio equipment.

(Or something along these lines - being nagged to serve dinner now. Others can correct or amplify.)

 

[kropaske]

@Midwest
I'll definitely try this

@marconi
N-E shows 0v with mains switch on or off.
None of the appliances affect the noise at all.
Sub is on RingFC up+down.
I also tried the sub with all MCB off except for that 1 socket just to exclude any potential noise from other devices in the house - still no luck.

I will see what the tech support say

In the meantime I'll relax listen some ACDC "noise"

 

[static zap]

I was similarly disappointed with Hum+hiss from a Hi fi loving mates new sub.
(and now fully understand why the diagram has placement of Sub -behind the listener -( and covered in a curtain !))

 

[marconi]

Prompted by Static Zaps #22 I pondered the physics of the low frequency sound from your sub woofer. The speed of sound in air is about 350m/s so a 50Hz sound wave has a wavelength of about 7m. This wavelength is much longer than the dimensions of your sub woofer speaker and box meaning the sound it emits is largely omni-directional. However, being comparable to the dimensions of your room there may well be the effects of constructive and destructive interference between sound bouncing off your walls, floor and ceiling. Such interference for a steady 50Hz tone will produce stationary regions/directions of peaks and nulls in sound amplitude. Where you normally sit in relation to the sub woofer may well be in a peak accentuating the 50Hz hum - you said it sounded less in the showroom. I wonder then if you might experiment with the position of your subwoofer in relation to the walls and the listener. Corners will be good reflectors so perhaps try locating the woofer away from them. Lastly, maybe put some sound absorbent material behind the sub woofer - a curtain? - so the predominant sound is from the speaker towards the listener than from reflections off near walls behind it. So, some trials. Top end Hifi buffs will be able to provide their experience on locating speakers and room acoustics.

 

[Squid]

What make is the Sub?

 

[kropaske]

It's Polk Audio

 

[Midwest]

Have you contacted the manufacturers tech dept?

 

[mattg4321]

I've had this on 2 subs now. Neither of which are particularly cheap. One of which I still own and it still does it.

I have a few ideas to try out, but it's not yet bothered me enough to do so.

Mine sounds very similar to yours:

• Lighting/appliances etc etc make no difference
• It's done it in two different houses - very similarly
• The sub is double insulated
• I've tried plugging all into same lead etc and it made no difference

The only thing that seems to help is if I touch the sub metal casing whilst simultaneously touching the tv metal casing (also double insulated) it gets a fair bit quieter. Unplugging the TV doesn't help! Touching something that is earthed doesn't help. I think touching the bluray player or amp at the same time may have helped a bit too but can't remember now.

 

[Midwest]

Thats very helpful. You have the same problem as the OP, and standing on one foot with your finger in your ear is the solution

I've had a couple of subwoofer's, none made any audible noise when not connected to sources, think I would get a replacement or @kropaske did you post on here Home Cinema Speakers - https://www.avforums.com/forums/home-cinema-speakers.45/ as I previously suggested; or am I talking to myself again, Mother!

 

[marconi]

Based on mattg4321's helpful #27 I'd try bonding the casings of all equipments together so they all share the same ambient earth potential at 50Hz.

 

[Midwest]

Based on mattg4321's helpful #27 I'd try bonding the casings of all equipments together so they all share the same ambient earth potential at 50Hz.

Marconi much respected, but bits of green/yellow wire looping around ones cinema room, doesn't look particular stylish