# Occasional subwoofer rumble, possible causes?



## Dominyon (Nov 27, 2010)

Aloha all

I have a JL 10w1v2-4 in a srq customs sealed box behind the seat of my 350z bridged on a vibe audio litebox 4 amp along with polk db6501 comps in custom kicks(by Bing!). I had another issue prior to this that eventually went away but I will tell you about it for background info.

That first issue was the right channel comps & sub (always together) would occasionally cut out if I went hard around a corner or over a bump/bumpy stretch of road. Rapidly turning the volume up 4 or 5 notches and immediately back down would bring them back. Naturally, I checked all my connections and they were solid so I contacted Vibe and their engineers said it could be a cracked solder joint at the RCA input location. I removed the amp from my glove box to see if I could open it up and take a peek for myself as I am competent enough to re-solder a joint on a pcb and wanted to make sure there was a real potential issue before I shipped it back. I wasn't able to get the tiny screws out and didn't want to risk voiding warranty so I tossed it back in my car. This problem never occurred again.

Fast forward a month or two and I have my current problem. At first I thought a plane was taking off behind my seat but there is no runway or room for a commercial jet in my little car so it turns out my subwoofer was rumbling. There doesn't seem to be any trigger to it like the previous problem, it's completely random. The volume or source of the music I am playing doesn't seem to matter, high/low volume, radio, CD or streaming from my phone through FM transmitter. I can also turn the radio off while it is happening and the rumbling persists. It can also be a low almost imperceptible rumble or a almost drowning out my music loud ass rumble. length can also vary and it usually goes away on it's own, only a few times has it lasted so long I had to turn the engine off to kill power to the amp (and a few times it came back when turning the car back on).

It went away for 3 or 4 months and I thought it was over like the last problem but it is now back. I have 2 weeks before the warranty on my amp runs out so I would like some opinions on if you guys think this is an amp problem or could be something else. I don't really want to lose music in my car for a month or two while having the amp repaired but it's better than buying a new amp I suppose. Thoughts?

Oh and thanks for your time and reading all my crap


----------



## thomasluke (Jun 10, 2011)

I do not know what could be causing that other than a problem inside the amp.
If it was me i would lose my tunes for however long to get that taken care of.
It could be just the start of a majer meltdown you know or could just be a ground issue the more i think about have checked your grounds and all other connections?


----------



## ErinH (Feb 14, 2007)

Bad RCA is my guess. Had this problem recently and it was a bad RCA.


----------



## Dominyon (Nov 27, 2010)

thomasluke said:


> more i think about have checked your grounds and all other connections?


The last time I checked them they were solid. This was back when I was trying to diagnose the other problem however, I can check them again.



bikinpunk said:


> Bad RCA is my guess. Had this problem recently and it was a bad RCA.


As I don't have any replacement cables to swap them out with I will switch the RCAs for the comps signal with the RCAs that send the amp signal and see what that does if anything. Otherwise could be like the vibe tech's said and the problem could be at the RCA input on the amp itself. Unfortunately I don't have much time to test, especially considering the problem is random and I can't find a way to duplicate it.


----------



## sqshoestring (Jun 19, 2007)

I'd play the system and gently move the RCA around while plugged into the amp. This is often a bad ground the shield on the RCA, it can be the RCA or the plug or the solder on the board in the amp. If its the amp I'd send it in under warranty or verify and repair it before warranty went out. Might also be a switch or other control on the amp, less likely it could be a short inside the amp. Could also be the RCA to the amp.


----------



## Dominyon (Nov 27, 2010)

sqshoestring said:


> I'd play the system and gently move the RCA around while plugged into the amp. This is often a bad ground the shield on the RCA, it can be the RCA or the plug or the solder on the board in the amp. If its the amp I'd send it in under warranty or verify and repair it before warranty went out. Might also be a switch or other control on the amp, less likely it could be a short inside the amp. Could also be the RCA to the amp.


Good thinking here, not sure why it never crossed my mind. Thanks for the advice, I'll give it a try on thursday when I have some free time.


----------



## sqshoestring (Jun 19, 2007)

Dominyon said:


> Good thinking here, not sure why it never crossed my mind. Thanks for the advice, I'll give it a try on thursday when I have some free time.


Let use know what you find. If not that make sure you check all the switches/gain/etc controls.


----------



## Dominyon (Nov 27, 2010)

sqshoestring said:


> Let use know what you find. If not that make sure you check all the switches/gain/etc controls.


Preliminary findings: Just got home from work and decided to play around with it for a minute since the car was already on playing music. Started wiggling the RCA connections at the amp and it seemed to be producing a small distortion similar to the rumble. Switched the cable with the leads to the comps and nothing. Started to take those off and noticed when the plug was only partly in it would make something similar to the rumble, if I pushed it all the way in then nothing even if I wiggled. I have tomorrow off so I'll play with it more but it looks like it could be a flaky connection. Time to somehow experiment if it's cable or amp that is making it flaky.


----------



## tonesmith (Sep 8, 2011)

Definitely an RCA issue. Something is loose or not soldered correctly. First try a new RCA cable, if that's not it could be the headunit RCA or inside the amp.


----------



## Vanlan (Jul 20, 2011)

actually, i had a friend with TERRIBLE rumble, constant and loud, and he just had to drop his gains a bit, and it fixed it. might have just been a bandaid on the real problem tho haha


----------



## sqshoestring (Jun 19, 2007)

Usually as you plug it in the center of the RCA (the signal) touches inside before the outside (the ground) and that will make a ground loop....which is the problem you get with a fault in the shield ground at any point. Common to cause rumbles and other strange sounds like feedback.

You can take the RCA off the amps and test the shield back to the HU with a DMM, it should read ~0 ohms about the same as to ground. The HU must ground the shields and amp must see that ground for the preamp in the amp to pass the right signal over to the actual high power amplifier section.


----------



## Dominyon (Nov 27, 2010)

Just spent my morning checking every connection, wiggling every cable, taking my dash apart and putting it back together & testing every knob on my amp...came up with nothing. I cannot find a way to reproduce this issue. Lunch is in about an hour so I'll take the car for a ride and crank it up while cruising around.

One thing I forgot to mention, because I've never ended up using it like I thought I would so I forgot about it, is I had channels going to the amp hooked up to a Universal Remote Level Bass Control (potentiometer). As I never used it, I removed it from the loop.


----------

