Please Help: Vibrating subwoofer - AVS Forum
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post #1 of 9 Old 05-02-2011, 02:31 PM - Thread Starter
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First let me say that I don't know much about audio stuff, just a layman that likes a nice system.

The problem I have is this: I have a surround sound system with a powered sub, and the sub vibrates quite loudly when plugged in and turned on. And it's not the vibration of the sub against the floor per se, it's the actual speaker outputting sound. It's a steady hum that increases when I turn up the gain dial on the back and decreases when I turn down the gain. If I turn up the gain all the way it becomes quite loud...loud enough that somebody would probably hear it a little bit from outside my room with the door closed.

The receiver and RCA cord that connects the two is irrelevant in this situation because the sub does this when completely disconnected from the receiver. As soon as I give it power it does this. When I plug the RCA cord in to connect it to the receiver it continues to make this noise, even when receiving a signal so basically my music is polluted by a continuous bass. It still plays the bass of the music but there's a continuous hum and it sounds terrible! Imagine a song with the bassist sustaining a single note for the ENTIRE SONG!

It wasn't like this fresh out of the box and only recently started doing this. Its a samsung 7.1-in-a-box-kit but unlike the usual cheaper surround-sound-in-a-box-kits the inputs in the back of the receiver and the speaker cords are NOT designed for exclusivity so I could potentially swap out for a new sub but hopefully won't have to

Can anyone please explain what the problem is and if there's any way to fix it without spending 100 bux on a technician?

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post #2 of 9 Old 05-02-2011, 02:54 PM
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Sounds like a bad amp in the sub. Since it increases by turning up the gain, it appears to be a problem with the preamp or the power supply. Fix or replace are the only options.

Given your description, the only external source I can think of is if you recently placed something near the sub that has an electric motor and you're picking up EMI from it.

Randy
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post #3 of 9 Old 05-02-2011, 03:03 PM - Thread Starter
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Sorry for my naïvety but about the EMI thing...is that something that could have caused damage or do you mean that if I move the sub into the hallway for example it might stop the noise?

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post #4 of 9 Old 05-02-2011, 03:17 PM
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Ground loop hum?

Television: Mitsubishi WD65737 DLP
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Amps: Carver AV 806x/Behringer EP4000
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post #5 of 9 Old 05-02-2011, 03:47 PM
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If it's more like a buzzing sound then it's most likely the driver.


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post #6 of 9 Old 05-02-2011, 04:32 PM
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Quote:
Originally Posted by AGENT_P6 View Post
Sorry for my naivety but about the EMI thing...is that something that could have caused damage or do you mean that if I move the sub into the hallway for example it might stop the noise?
Electromotive Interference. The building/collapsing of the magnetic field around the windings of a motor. This is not likely the cause, but I've seen some pretty weird results from EMI. So you are correct that if it is EMI, moving the sub a couple feet will make it go away.

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Ground loop hum?
Since it happens when the sub is isolated, I don't believe it is GLH.

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If it's more like a buzzing sound then it's most likely the driver.
Could be, but I question that it would get louder by turning up the gain.

Randy
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post #7 of 9 Old 05-02-2011, 06:05 PM - Thread Starter
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Quote:
Originally Posted by ransac View Post

Sounds like a bad amp in the sub. Since it increases by turning up the gain, it appears to be a problem with the preamp or the power supply. Fix or replace are the only options.

Given your description, the only external source I can think of is if you recently placed something near the sub that has an electric motor and you're picking up EMI from it.

Ok I moved it and it's not EMI.

One considerable option: My receiver has 2 menu options allowing me to sweep this problem under the rug...there's an output tweak option (-10 to +10) for each channel as well as a general bass and treble tweak option. So since the RECEIVER adjusting the level of output to the sub does NOT increase the annoying hum (only the sub's actual gain dial on the back increases the hum) I could potentially turn the sub's gain dial realllllllly low and just crank
the SW channel output to Max to pick up the slack.

Or...

I could alternatively keep the sub at a normal (on the receiver menu and still the sub gain dial is low) level but
turn everything else down a bit on the receiver channel options and then turn up the receiver's volume dial to get the bass to treble ratio I want without the hum. This might be tricky to get to sound right tho.

And I could also tweak the general bass up a bit but unfortunately I imagine this will give my 7 speakers too much bass and mess up the quality of the sound

I mainly use the unit for gaming and movies so the bass is important. I have two nice Bose front bookshelves and actually prefer to switch to s.direct for music which cuts out everything including the sub except for the FL and FR cuz im not a big fan of crazy bass in my music. Point being that other than in my music, I definitely need some good umph and would need to tweak to extreme channel settings to avoid a big dent in my wallet and I'm worried it could be detrimental to tweak to that extremity

I'm worried the first option might burn out something in the receiver by having too much power continually through a channel and I'm worried that the second might burn something out by continually restricting the flow. In the end I don't know what the hell I'm talking about and maybe it will be just fine and the receiver is meant to handle that type of extreme settings...but I'm worried nonetheless cuz it's my baby <3

Please let me know what you think is my best option: fork out $ for a new sub or a repair, or can I rest assured the receiver will be fine with some extreme channel tweaking?

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post #8 of 9 Old 05-02-2011, 07:21 PM
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You can use the sub trim level in the receiver at higher settings. This is a low level output and doesn't tax the power amp in the receiver. Leave yourself some headroom by not going to +10.

This may or may not work. It depends on where in the signal path the noise is being produced. But it won't hurt to try.

Randy
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post #9 of 9 Old 05-06-2011, 07:42 AM - Thread Starter
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Ok well thanks for the help everybody...I think I might have to just suck it up and buy a new one :S

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