Years ago, we had a Runco projector with a noticeable hum that would come and go that was coming out of the chassis.

We spent hours, no days trying to remedy it. Finally got fed up, left the room to go home, turned the lights off at exit of room with the wall mounted slider light dimmer and the friggin hum came back and then went away right away.

It coincided with the motion and place of the dimmer position!!

The client had installed a $9.00 light dimmer and that was the issue!!!!
We installed a Lutron dimmer.....issue fixed.

Same thing happened to a company I was with years ago. The homeowner had a recording studio. Whnever he plugged in his guitar cord he got buzz. We replaced his guitar cord with a fancy assed one. Nope, installed a high end Furhman conditioner, nope... tried all kinds of stuff. It too, was froma cheap light dimmer in the hallway!
We tore our hair out, and made several trips to the house. Lost a lot of $$$ too.

I remember a horrible buzz on an Panasonic plasma back when I started installing. Turns out that the outlet the electrician had moved above the fireplace for us to use was still on the lighting circuit for that room. And there was a dimmer on the lights ...

Very possible. I installed a system years ago and hum was coming through all of the speakers out of no where. spent days on it. Found the light dimmer was bad in the kitchen next to the room. Replaced dimmer and problem went away. Try turning off all dimmers and see if hum persists or changes when dimmer is set to different scenes

Seriously, that's an important distinction to make. We're trying to describe characteristics of sound with words that are approximate at best.

Hum: low pitch, few overtones
Distorted: we usually mean harmonic distortion. Distortion takes the pure single tone of a sine wave or, instrumentally, a flute, and adds buzzes and, well, grunge that comes and goes with the loudness of the sound. Other kinds of distortion are much harder to describe.
Buzz: high pitch or, more often, high overtones of a low pitch such as 60
Hz; the 60 Hz tone is usually not even present, so you hear high frequency sounds being turned on and off 120 times a second.
Tubby: a word I use for sloppy bass with a rise around 100 Hz
Nasal: overly loud in the 2K- 3K region. It's an actual mic adjustment used by recording artists. Elton John does it.
Thumping: low low bass, non repetitive so you can't really hear a tone
Scratchy: random but not too often sounds, each of which might sound like the pop you get when you turn a DC circuit on or off.
Crisp: any percussion sound that starts and stops abruptly. A real kick drum gives a crisp sound, but a kick drum sound played through a crappy subwoofer gives, at best, thump.

I'm out for now.

Sorry it's taken so long to get back to this thread. I finally had a chance to get to his house last night and actually see/hear the issue in person.

He has a Pioneer Elite receiver connected to a 5-speaker system (no separate subwoofer). The two front main speakers are powered Polk Audio speakers. I didn't see a model number on them, but they have four speaker level inputs on each so that they can be biamped. The lower set of speaker connections is for the subwoofers. They also have line-level inputs (stereo?!) for an internally powered subwoofer.

This apparently gives you several options for connecting the speakers:
1. Bridge the speaker level inputs so that the speaker level inputs drive all of the speakers;
2. use the top set of speaker level inputs to drive the mids and tweeters and use the bottom set of speaker level inputs to drive the subwoofers;
3. or, use the top set of speaker level inputs to drive the mids and tweeters and use the line-level inputs to feed the internally powered subwoofer.

The person who set his system up had the speaker-level inputs so that the receiver powered both the mids and tweeters as well as the subwoofers, but they also had them plugged in to a power outlet so that the internal amplifier was powered.

The issue was that his left front speaker had a hum once it had received sound. If the receiver was powered on with the speakers connected, there was no hum until the sound was turned on. This was regardless of whether the sound was on or then muted, whether the receiver was powered on or not, or whether the speaker level inputs were connected. The hum only went away when the speaker was unplugged from the power outlet.

This led me to believe that it was likely an issue with the speaker.

So, I switched the left and right front speakers. The new left speaker had the same issue, whereas the speaker that was moved to the right no longer did.

Maybe it was an issue with the power? To test this, we ran an extension cord from the outlet behind the right front speaker to the left front speaker and plugged the speaker into the extension cord. It still had the same issue!
The good news is, since the speakers were actually driven by the receiver, there was no reason to keep them plugged in, so there is no more hum. However, I'm still wondering what the issue could be?

As an aside, he does have a light dimmer in the room, but changing the dimmer's setting didn't affect the sound coming from the speaker.

Thanks,
CJ

May not necessarily have to be a dimmer in the same room. could be a dimmer in another room. It would be worth trying all dimmers in the house to see if one of the dimmers cause a change in the sound you hear.

Sounds an awful lot like a typical ground loop.

Did you try using the line level sub input? Did the speakers have any marking like 'Subwoofer input", 'LFE' or anything like that? I would bet that the lower pair of binding posts send signal to the woofers, but they may have a down-firing subwoofer, which you're not using. The fact that it hums could mean it has one or more bad capacitors or it could be a lifted/cold solder joint. Get the model number.

But shouldn't that go away when I used an extension cord so that both pairs of speakers were using the same outlet? When I did this, the hum was still there on the one speaker but not the other.


I didn't try the line-level input. From what I recall, the line-level input did say subwoofer input. I'm pretty sure the lower level binding posts said the same. I'll check and get a model number the next time I'm there.

Thanks!
CJ

Take a up-close picture of the equipment with your phone to refer to numbers latter. That's how I combat my long term loss of short term memory. Helps us help you.

Is it possible the speaker is picking up interference from and appliance or something on the other side of the wall, ceiling or floor?

Is the noise there if the speaker wires are disconnected from the speaker and the speaker is free standing.

A/C polarity issues between chassis'

Sounds like a bad output on the amplifier based on your additional troubleshooting. Could just be a bad ground on the amplifier output board/transistor (or a leaky capacitor).

did you try a test run of new speaker wire from old right speaker location to 'old' or 'new' left speaker...and/or a direct speaker wire connection from right amp output to 'left' speaker.

Sounds like a bad output on the amplifier based on your additional troubleshooting. Could just be a bad ground on the amplifier output board/transistor (or a leaky capacitor).

did you try a test run of new speaker wire from old right speaker location to 'old' or 'new' left speaker...and/or a direct speaker wire connection from right amp output to 'left' speaker.

Also, have you tested this on multiple different inputs?

Also, try putting the receiver into 'all channel stereo' mode (or whatever pioneer calls it), and turn off the front speakers to see if the 'hum' jumps around, make sure to set all speakers to large/full range (no low pass crossover) for this test as well.

He said it happens with the receiver off and all sources unplugged, as well it only happens when the built in subwoofer amp in the speaker is plugged in.

The built in subwoofer amp in the speaker would have been a great clue at the beginning but aint no big thing.

I would like to know if the speaker wire was unplugged at the speaker and the subwoofer amp in the speaker was plugged in if the speaker by itself hums.

If you do more places where guitars pick up noise, look at the pickups on the guitar- single coil are susceptible to noise, dual-coil pickups, and this is the reason they're called humbuckers, have a second coil with reverse polarity/winding that's wired in series.