jbl sub - "feedback" sound [Archive] - Audio & Video Forums


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09-18-2008, 02:17 PM
i've had my surround setup for 3-4 years...everything was fine until recently...periodically my sub gets this buzzing, feedback type of sound...it will come for about 5 mins or so (haven't determined a definite length of time) and then goes away...

thoughts? speaker going bad? don't think it's under warranty, but should i be concerned?

09-19-2008, 03:51 AM
As a musician I've always defined feedback as a situation where a tone of a specific hertz comes out of a speaker, is picked up by a microphone or other magnetic pickup and procedes to re-enforce itself. By feeding back on itself the tone becomes louder and louder.

Buzzing is another thing altogether. Really difficult to help you with your description. I don't see how a consumer subwoofer would "feedback" on itself unless you're playing bass guitar or piano through your home theatre system. What you maybe hearing are certain tones being re-enforced by room acousitics and appearing much highter in the mix as a result.

Hope this helps.

Da Worfster

09-19-2008, 02:41 PM
no didn't help, sorry...

what i said was, it's a sound that if you hear it reminds you of feedback - feedback like you hear as a musician...i know that's not what it is, it just sounds that way...maybe some sort of interference? you know, like when you have a cell phone too close to your computer speakers and you get that weird interference sound....

i haven't moved anything in the room, nothing has changed - acoustics or anything...that's why i was wondering if the speaker was going bad...

09-19-2008, 05:50 PM
Does this also happen without a sound source (idling) or when a movie or music is paused? Just a wild guess that you might have a intermittent grounding hum/buzz problem due to a bad or loose sub cable.


09-20-2008, 07:35 AM
haven't tried that..i have tried changing channels and that didn't work (thought maybe it was something with the sound from the channel)...i'll try pausing a movie to see what happens...

would muting a station work as well, essentially give me the same result? meaning, if i hear the sound and mute the station and continue to hear the sound, do you think that would lean towards bad cables or connection? or would pausing give better results?

09-20-2008, 03:38 PM
I presume if you have not already heard it when there is no sound source then that probably answers the question with a no. I had a case once when I got a fairly loud hum when hooking up my sub. It was there intermittently. I finally discovered that I had a bad line connector to the sub. I replaced it and the trouble went away.

I don't think this is probably your trouble unless the vibration from the sub is causing this periodic problem. Just try a new connector to eliminate my guess.


09-21-2008, 12:17 PM
just heard it watching football...muting the sound didn't stop the noise...tried pausing the dvr, didn't stop the sound...maybe a connector then....i will look at getting another and test...

09-21-2008, 12:46 PM
ok, as the sound was happening just now, i unplugged the cable coming from the receiver to the sub....sound continued!

09-21-2008, 09:24 PM
Well, you've obviously narrowed it down to the sub or its power cord. You might be having a grounding problem, internal wiring problem or amp troubles. See if you can isolate it. Good luck. Probably not worth paying anyone to check it since I see from your profile that this is a sub from an inexpensive HTIB system.


09-21-2008, 10:02 PM
ok, as the sound was happening just now, i unplugged the cable coming from the receiver to the sub....sound continued!

I wouldn't recommend doing this. It's hard on the sub's amp and your receiver.

Does the sub have a phase switch on the back? How about a gain or level switch?

You might try these one at a time to see if there's any effect on your problem.

09-22-2008, 06:53 PM
i'll try the "subwoofer level", the only option i have...

@RoadRunner6: hey, that's all i could afford :( i know they're not top of the line, but this should be fixable...should these speakers stop after 3 years use?

09-22-2008, 09:34 PM
Sorry, I wasn't trying to dis your speakers. I was only trying to explain that it wouldn't be worth having a repair center check them because they would charge you more just to look at them than they were probably worth.

Check the power cord for defects and look inside for loose wires etc, if you can open up the sub.

RR6 :)

09-23-2008, 06:13 AM
I'm sure the sound you're hearing is 60HZ hum related to a grounding problem. I understand why you would call it feedback, since you hear it occasionally during a microphone "check". It could be a plug/cable, but could also be a bad solder joint on a capacitor, or a crack in a printed circuit board of the plate amp losing connection from vibration. Since it's intermittent, it's probably mechanical rather than electrical.

As stated earlier, do the easy checks first.

Check/replace sub input cable. Replace because the problem could be internal to the cable.

Check the RCA jacks at both ends (sub/receiver). I had them pull out of a receiver and power amp before, so don't assume it's on the the sub's end.

If not resolved by the easy checks, do the following if you feel comfortable opening the sub and have some troubleshooting skills.

Check in the internal wiring between the plate amp and the speaker. If this doesn't resolve the problem, it's probably a problem with the amp itself.

If you can solder, you may want to "touch" several of the solder joints associated with the large capacitors and any signal wires coming from the input jacks. If you can't solder you may at least try tapping on a suspected component, or use a canned cooling spray on isolated suspect connections. This will contract the connection enough to make contact and show where the problem's located. Once located have a friend or service resolder it.

09-23-2008, 05:03 PM
@RR6: i know, i was just giving you a hard time regarding my cheaper speakers...i figured even though they are cheap, it *should* be fixable - at least i am hoping...

@bfalls: i'll try your suggestions...i'm leaving town tomorrow morning for a week so it will be late next week before i can try...but i'll update everyone what i am able to find

side note - two nights now and no sound!!! :)