Subwoofer hum has just started - possible reasons outlined

xar

Well-known Member
Hi all,

I have read the various threads about subwoofer hum, but seem to have slight odd set of circumstances as follows:

- had no issues with hum before in any capacity - the subs are only a few months old
- was a power outage last night in my area while I was mid-movie and playing it loud - came back on a few hours later and all seemed fine, including when finishing the movie this morning
- this afternoon, 2 things happened;
1) I removed some driveway lighting that was wired to my garage circuit (the same place the cinema room is, separate from the house)
2) I accidentally broke the rca connector into the back of the sub - its a long one that converts an XLR cable running from the amp - the end of the rca connector stayed stuck in the sub, but I managed to get it out (eventually)

After removing the rca connector, fitting to another I had an plugging back in, there was fairly loud hum from the sub. Turning on the other sub, it was also humming the same (loud) amount.

Note that I have 2 identical subs, there was no damage to the connector on the 2nd sub.

The hum does NOT occur when the subs are turned off. It does hum the same regardless of whether the amp is turned on or off, albeit I have not tried removing the cables from the amp.

I have tried plugging the subs into a different plug point which has reduced the sub considerably, and plugging it into the house seems to remove it entirely.

All of this suggests to me its a ground loop of some sort in the garage wiring, and is occurring from removing the driveway lighting, as I only broke the connector on one sub but both subs are humming.

Unfortunately running an extension to the house is not a viable option, so any thoughts are welcomed on how to solve a ground loop within the garage...!
 

cottonpickers

Active Member
I think an early step is to unplug the rca to see if the sub hums even when not plugged in to the amp. Then confirm if it’s speaker hum vs amplifilier him. (Is the speaker vibrating)
 

xar

Well-known Member
Thanks - have tried the following:

- No hum at all when the rca is disconnected from the sub (but is connected to the amp)
- Normal hum when the rca is disconnected from the amp but is still connected to the sub

Other things I have tried are:
- plugged into my normal plug points - normal hum
- plugged into same bank of plugs as my amp/all other equipment - lower hum
- Louder hum when the rca is disconnected from the amp but is still connected to the sub for both options above
 

xar

Well-known Member
Not sure - would need to check that one tomorrow
 

Conrad

Moderator
Does is rise and fall with gain as well, that's another useful thing to check.
 

xar

Well-known Member
Sorry, super busy day. No speaker vibration, and dies not change with gain.

I have since plugged both subs into an extension cable which runs to my mains conditioner at the other end of the room. Result: no hum.

Doing the same into the ‘normal’ plug points at the front of the room: loud hum

Doing the same into a normal plug point elsewhere in the room: medium hum

current plan is to try and run an extension from my main conditioner at the rear of the room to the front of the room and connect both subs

No idea why this has started and continues to happen though
 

mcbainne

Distinguished Member
How were the driveway lights connected, Is there an issue where you disconnected them?

Have you tried connecting one sub RCA at a time? Does the sub that you didn't break the connector on still hum when the sub that you did break it on is disconnected from the mains and RCA?
 

xar

Well-known Member
The driveway lights went into the same junction box and fuse as the garage mains as far as I can tell. i.e. the lights and mains go into the same fuse. Didn't seem to be anything special about the connections, but the hum did start after (albeit I also broke the RCA connector after removing the lights but before using the subs)

I have tried connecting both subs individually and separately. They both exhibit the same behaviour regardless, hence my conclusion its an electricity problem...
 

ggwoodland

Well-known Member
As they say I am no expert here. But I did have subwoofer hum for a while and went down a few rabbit holes trying to figure it out. Seems to be two main causes ground loop or D.C. noise. I think mine was caused by D.C. noise and is reduced just due to the fact that less people are working from home now than back in March April - george
 

xar

Well-known Member
Thanks. Might just be that. Very annoying!
 

thatpaddle

Standard Member
This won't be directly for OP's problem but I want just share my very strange humming case. All of my subs have been humming more or less, but strange thing is that the humming starts on September and stops at the end of May on every year. I have tried to disconnect all other devices from our houses electric grid except subwoofer(s), even then subs keep humming on 15-30sec cycles. There were two engineers from local electric company at our home inspecting this issue for two days, but they couldn't find anything even with their professional tools. Only way to stop humming were to plug subwoofers to UPS and not to connect UPS to wall power outlet. I have done seriously everything to get rid of this humming but it just don't want to go away.
Have tried 2x BK mono, 2x Chario subs and one DIY sub, same problem with every one of those.
 

rccarguy2

Well-known Member
What brand is it? If bk they do appear to have this common fault
 

xar

Well-known Member
They are almost brand new REL212SX's - its not the subs at fault though, as they were fine for weeks before all this started. I have managed to mostly negate the issue by running extension cables from both subs to the mains conditioner at the rear corner of the room where the main gear is plugged in, so that will do for now.
 

Cliff

Distinguished Member
So you broke the xlr to rca connector and fitted another one. Have you checked the Earth is good on the replacement rca ?
 

Ormy

Member
Seems like the broken RCA connector is the more likely cause compared to removing a lighting circuit. You may have damaged the internal connection to the RCA jack inside the sub.

Or it could be power outage damaged something (or a surge when the power came back).

I have a slight hum in my subs that does increase with sub gain and only happens when the graphics cards in my HTPC are working hard. I bought some 2-core + shield cable and DIYed some new interconnects with the shield connected to a common earth and that reduced but did not eliminate the hum.
 

xar

Well-known Member
I assumed it was the RCA initially, but the hum occurs on both subs equally (I only broke the connector on one of them), so have since ruled it out.

The new RCA connector is fine - have checked it also.

After lots of testing of different plug points, I think it is something do do with the fact that my cinema room in the garage is on a spur rather than a ring connection. The subs usually connect to the very first plug point in my room coming from the junction box. I have 3 more points round the room, and the hum seems to reduce the further from the initial plug point I go. Plugging it into a main conditioner connected to the final plug point almost removes it.

For reference there is no hum when I plug the subs into a point in my main house which in on a separate junction box.

I think I will just need to get a sparky round to rewire or turn the spur into a ring.
 

Saul Goodman

Distinguished Member
I had a hum with both of my PSA S18ipals with just the mains cable connected. A quarter turn on the crossover dial on the amp completely removes the hum.
 

xar

Well-known Member
Thanks. A quarter turn on the subwoofer x-over amp panel itself?
 

xar

Well-known Member
Thanks. Will give that a try tomorrow.
 

xar

Well-known Member
Afraid not. Had 2 electricians round, 12 new plug points installed, tried a power transformer in the mix to check input / output levels, and some XLR ‘bungs’ on the spare slot on the subs.

I have narrowed it down to the xlr feed from the amp, so I think it’s running hot after the power cut for some reason, but can’t seem to solve...
 

ggwoodland

Well-known Member
Hi - I would try and borrow a DC filter and see if that helps. JL provided one for me and my sub hum has pretty much gone. So try and check whether REL can provide or recommend one to use - george
 

Conrad

Moderator
I have a DC blocker from ATL hifi. It helped with my transformer hum in my power amps. Something on my mains is kicking DC back in, I suspect the Hue lights or the fridge. I had a second CU installed with 4 spurs, I tried a sine wave UPS and power conditioners, nothing fixed it. Maybe your power conditioner has a DC filter in it which is why it's helping?

I have a spare one I'm not using that I'd be happy to send up if you want to try it.
 

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