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Old 4th July 2011, 01:01 AM   #1
DDRRE is offline DDRRE  Israel
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Unhappy Subwoofer Humming

While I know many others have posted this issue, my case is a bit different.

I have 2 active subwoofers (not identical), located at opposite sides of the room. One subwoofer works just fine, the other hums whenever it is turned on.

BUT! this only happens in my room. When I take it to the kitchen, for example, no humming is heard.

I tried unplugging all the devices in my room (UPS (PC, TV), stereo amplifier, cable RF amplifier, DSL router, ethernet switch, mobile phone charger, DTV) and then plugging in the subwoofer, but the humming stayed.

Then I tried covering the subwoofer's power cable with aluminum foil and isolation tape, which actually helps, but only when my hand touches the cable and the cable is closest to the ground as possible. When I step away from the subwoofer the humming comes back.

The thing is, before I put the subwoofers apart from each other, I used to have them side-by-side, and I had no humming whatsoever.

Any ideas as to how I could get rid of the humming noise?

More info that might help those trying to assist me with this issue:
My AC is 50Hz 220V,
The humming comes from the driver itself, and has nothing to do with whatever's connected to the subwoofer.
Remember that I unplugged all electronic devices in my room, and the humming remained.


Any replies would be very appreciated.
Thanks, DDRRE
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Old 4th July 2011, 01:39 AM   #2
18Hurts is offline 18Hurts  United States
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Try plugging it into the UPS, just to check for hum.

If only that room causes hum, you might have an issue with the grounding in that room. If you have grounds on the outlets, run a wire to a known good ground and plug into the ground of the outlet. If your hum vanishes, that is the issue.

The other thing is you might have a bad ground on the amplifier which will cause hum.
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Old 4th July 2011, 02:05 AM   #3
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Did you try swapping positions of the two subs? That would tell you if it was the one of the subs or something else, like problem with outlet wiring, bad interconnect or a ground loop. If hum moves with the sub that was oiginally having problem, it's most likely something wrong with that sub. If so, try sub with nothing connected except power cord to see if hum remains, if hum goes away it's not the sub, but something wrong with sorce or interconnect. Just approach problem logically and try to isolate down to the sorce.
Hope this helps.

Mike
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Old 4th July 2011, 09:20 AM   #4
rabbitz is offline rabbitz  Australia
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Make sure they are powered from the same power point or power board. Had a similar issue where the sub was plugged into a different power point to the rest of the system.

For safety ensure that ground pins to the power outlet are connected.
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Old 4th July 2011, 12:54 PM   #5
HK26147 is offline HK26147  United States
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Quote:
Originally Posted by DDRRE View Post
...Any ideas as to how I could get rid of the humming noise?...
If you cannot get both devices at the same ground potential; then get an isolation transformer.

Last edited by HK26147; 4th July 2011 at 12:58 PM.
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Old 4th July 2011, 01:40 PM   #6
DDRRE is offline DDRRE  Israel
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I'd like to thank everyone for replying.

Connecting the subwoofer to the UPS isn't an option at the moment, because it has computer power supply outlets (I suppose I could buy an adapter).

The subwoofer isn't grounded, it has a proprietary 2-pin AC socket, and its own cable. It does look a lot like a computer power supply, but it isn't.

Could you direct me to solving this problem, when all devices are unplugged and the subwoofer isn't connected to the amplifier? how do I check the grounding? The subwoofer is connected to an AC splitter, with 6 sockets.
I have 3 wall outlets in my room, I've tested the subwoofer with two (directly, meaning no other devices were plugged in). I haven't tested it with the third (quite unreachable, behind furniture).
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Old 4th July 2011, 02:22 PM   #7
HK26147 is offline HK26147  United States
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Quote:
Originally Posted by DDRRE View Post
The subwoofer isn't grounded, it has a proprietary 2-pin AC socket, and its own cable.
That is less than ideal...
Get an audio ground loop isolation transformer.

Last edited by HK26147; 4th July 2011 at 02:30 PM. Reason: Clarity
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Old 4th July 2011, 03:19 PM   #8
DDRRE is offline DDRRE  Israel
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Isolation transformers cost 45$ for the a 50W model, 60$ for 100W, 70$ for 150W and so forth. Which one should I buy? I'm no laboratory, I can't tell how much the subwoofer consumes. It's an active 100W RMS subwoofer.
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Old 4th July 2011, 03:49 PM   #9
HK26147 is offline HK26147  United States
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You are looking at the wrong devices.
Audio isolation transformers work at line level and don't have wattage ratings.
They work by running the line level signal through a transformer which breaks the physical connection.
Audio isolation transformers
Radio Shack should have them as well as MCM.
Jensen makes some of the best, with a correspondingly high price tag.
Since it's for a sub the HF performance ( of a transformer ) is not critical in this scenario.
Example: Cables To Go 41163

Last edited by HK26147; 4th July 2011 at 04:15 PM. Reason: Addition
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Old 4th July 2011, 04:17 PM   #10
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by HK26147 View Post
You are looking at the wrong devices.
Audio isolation transformers work at line level and don't have wattage ratings.
They work by running the line level signal through a transformer which breaks the physical connection.
Audio isolation transformers
Radio Shack should have them as well as MCM.
Jensen makes some of the best, with a correspondingly high price tag.
Since it's for a sub the HF performance ( of a transformer ) is not critical in this scenario.
Example: Cables To Go 41163
But is it humming just sitting there with nothing plugged into it at all?

Is it possible to reverse the direction that the plug is in the wall socket or is it bladed on one side (polarized)? It's possible that this wall socket is wired backwards perhaps. It's also possible that it's getting interference from a power cable that runs through the wall on that side of the room. Have you tried pulling it out away from the wall?

Also, do you have a dimmer switch on that side of the wall perhaps for a light fixture? I've had problems with those types of devices introducing hum and buzz.

Last edited by DrDyna; 4th July 2011 at 04:21 PM.
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