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Aargh! Speaker Hum!

561 Views 12 Replies 9 Participants Last post by inti, Nov 6, 2002

Tom_Bombadil

Discussion Starter · May 2, 2002

Okay, I complete re-arrange my audio & HT room. It took a few days to get everything setup. After turning everything on, I hear a hum out of all speakers. So I start isolating component after component, wire after wire. A good deal of the hum drops out after isolating one of my power cords with a cheater plug. A couple of hours later, and after pulling about 40 wires, I find an interconnect with a bad solder joint.

At this point, the only remaining hum is coming from my center channel speaker. I eventually find out that it disappears when I turn my TV off. So I start messing around with the placement of the speaker cable, but no results. I turn off my amp and the hum is still there. Then I yank the speaker cable out of the speaker, so that I have an unconnected, unpowered speaker resting on top of the TV. To my dismay, there is still an audible hum coming from it. I pick up the speaker and vary it's distance to my set. I find that once it gets about 2' from the set, it starts a low level hum. When it is resting on the TV, the hum is loud enough to hear from 8' away. I can even hear it over the TV's built-in speakers at low volume levels.

So there is so much noise/interference coming off the back of my TV, that the only way to eliminate the hum is to move the center channel speaker at least 2' from my TV. Very annoying.

Tom B.

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JhnZ33

· #2 · May 2, 2002

Do you have cable tv service connected to any of the components?

If so, try disconnecting the cable from the equipment to see if the problem goes away. If it does (which wouldn't surprise me), you have an infamous cable ground loop. To remedy the problem, purchase an inline ground-loop isolator. That should take care of the problem.

JJP

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Tom_Bombadil

Discussion Starter · #3 · May 2, 2002

Yes, I did try that. Didn't have any affect. I reduced it down to having just the TV plugged in and turned on- with no connections coming into it, with the disconnected speaker sitting on top of it, and there was a hum being emitted from the speaker.

I never anticipated running into a problem like this one.

Tom B.

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jbabbitt

· #4 · May 2, 2002

I am not sure I am getting this right. You did not have a problem until you rearranged the theater room? If your TV wasnt causing any problems before, then why would it be now? It might be the beams in the walls, but I have never heard of that before, unless your speaker wire is directly touching it.

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dr150

· #5 · May 2, 2002

Try using insulated cables (interconnect, speaker, power cord, maybe even a line conditioner).

One best quality product for price AND is insulated--unlike most other mfg. which don't insulate this well is LAT Int'l .

Visit their website as they explain insulation in detail.

For me, there is NOTHING worse than hearing speaker hum--especially at low volume settings! I would be prone to throw my sh!t out the window.

I use LAT and their top stuff is reference quality, competing with some cables I've tried in the $10,000+ range. Nuff said!

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Tom_Bombadil

Discussion Starter · #6 · May 2, 2002

I tried insulated and shielded cables. But note that the speaker has a hum with *NO* cable connected! Just a detached speaker sitting on top of the TV. I presume the electrical noise being emitted from the back of the TV is being picked up by the speaker's internal wiring, like a radio. As I move the unattached speaker closer and further from the back of the TV, the sound level of the hum changes with distance. At 3' away, there is no hum. When the speaker is resting on the back of the TV, the hum measures at over 60dB on my Rat Shack SPL meter (measured right at the front of the grill of the speaker).

I had noticed a slight hum in the past, but the speaker was located a bit further from the TV. Once I moved the speaker on top of the TV, in the traditional center channel position, the hum became far more noticable. That's when I started playing around with different speaker cables, presuming that the cable was picking up the hum as it passed over the back of the TV.

I've heard unattached speakers pick up nearby ham radios before.

The only solution is going to be for me to find a new location for the center speaker. Or haul the TV in for repair, assuming it is out of spec.

Tom B.

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Tuomy

· #7 · May 3, 2002

Tom:

Could you tell us what sort of speaker your center ch. is? I assume it's not a powered speaker, but in any case there may be a shielding approach you could try.

JMT

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Tom_Bombadil

Discussion Starter · #8 · May 3, 2002

It's a Von Schweikert LCR-21. Last night I used two other speakers, a Paradigm CC-350 and the upper mid/tweeter module from my Von Schweikert VR-4/mod-5. Both of them picked up the hum too (with no speaker wires attached). In fact the mid/tweeter module had an audible hum at 2' from the TV.

At this point, I'm looking at two alternatives: A) Haul the TV in to have it serviced in hopes of them finding the problem (I'm not opitimistic), B) Position the center speaker at least 2' from the TV.

Tom B.

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HTCrazy

· #9 · May 3, 2002

"If it does (which wouldn't surprise me), you have an infamous cable ground loop. To remedy the problem, purchase an inline ground-loop isolator."

I DO have a hum problem that's solved when the cable's disconnected, but I've heard that ground-loop isolator's don't often work. Regardless, I'll try anything. Where do you get these (rat shack?) and which brand would you recommend?

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Tuomy

· #10 · May 3, 2002

Tom: Since this hum is happening without any wires attached to the speaker, the only cause that I can think of is induction from the high voltage drive circuits of the TV. You could try putting a sheet of grounded metal between the top of the TV and the speaker...the sheet could be fairly thin, even some metal window screening might work. Another "clue finder" might be to take a speaker that is light enough to wave around, and move it all around the TV to see where the field is strongest. Personally, I think that it is a defective TV in the sense that no TV should emit anything that is powerful enough to drive a load as big as an inductor or whatever in an unconnected speaker's crossover. One last thing, try shorting the speaker's input terminals while listening to the hum. If there is a big difference between shorted and not shorted, especially if the hum disappears altogether, then there may be another answer relating to the power amp that ordinarily drives the speaker.

Jim T

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phyre3

· #11 · May 3, 2002

sounds to me like the shielding in the TV became ungrounded or loose during the move or something to that effect. Usually there are is grounded metal casing for the chassis or individually around circuits that emitt interference. I'd say this is a problem for a TV repairman to look at.

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RichardMA

· #12 · May 3, 2002

The grounded metal (steel is superior) sheet might work.

I had a problem with the speaker (Paradigm with less than perfect

shielding) and the method worked.

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inti

· #13 · Nov 6, 2002

Tom - did you solve it?

If not, you should look at option (C): get a projector.

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