Why is my subwoofer so quiet all of a sudden??

[malibuboats91 10+ year member]

Hey everyone I have a JL 12W6v2 W4 with a MTX x500d amp in my 2010 Jetta with the stock head unit. I've used this setup for maybe 5 years and have been experiencing some issues. About two months ago my amp kept going into safety mode because it was to close to the back of my seat. MTX also told me to turn my gain down below half. After doing that it worked fine but didn't have the output that it used to have due to the lower gain. Over the past few weeks now I have noticed that the subwoofer output has been fading to a point where it's hard to even tell I have a sub. I haven't changed any settings other than the bass knob on my OEM head unit in my car.

I did some research and started doing some tests. First I tested the sub and both voice could are reading 4 ohms so it's good. Next I downloaded a 50hz tone, played my HU at 3/4 volume and turned down all the settings on the amp (gain, subsonic, LPF). MTX said I should get a reading of 31 volts. With all the filters down I have to turn the gain up almost all the way. With LPF at half my gain is at half. Do you think my amp is failing? What other steps should I take?

Thanks!

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[malibuboats91 10+ year member]

My line output converter is set at about 2/3 volume also. I have my whole car pulled apart trying to figure this out. Any help would be appreciated!

 

[fly_marlin]

Try replacing the speaker wire to the box and within the box.

 

[alienchickenomg]

Also check your fuses. I may be unique in this, but if i remember correctly when i got my first system i had an amp with two fuses and one had blown, and it reduced output dramatically. (my memory could be wrong though lol)

 

[los33]

Why would MTX tell you to turn the gain up all the way???

No matter what thats not a solution to testing a sub setup. If you noticed the sub volume has been jumpy or just plain out low then you should check the ground specifically.

Other then that you should test the amp by doing the dmm method using a 50hz tone 0db. Then watch to see how the dmm measurement stays the same or lowers all of a sudden.

 

[los33]

Why would MTX tell you to turn the gain up all the way???

No matter what thats not a solution to testing a sub setup. If you noticed the sub volume has been jumpy or just plain out low then you should check the ground specifically.

Other then that you should test the amp by doing the dmm method using a 50hz tone 0db. Then watch to see how the dmm measurement stays the same or lowers all of a sudden.

 

[malibuboats91 10+ year member]

Thanks for the replies! I will replace the wires and see. Also, MTX said I should get 31v on my DMM and in order to get that I need to have my gain all the way up. They said it should be about 1/4 of the way up to get that. This is why I think it may be on its way out. I'll update you in a little bit

 

[malibuboats91 10+ year member]

Well boys I think I figured out what it was...bad RCA cable. I picked up a scosche at Walmart just to check and it bumps like before! Is it worth keeping the scosche or should I return it and get a raptor or something better?

 

[los33]

Well boys I think I figured out what it was...bad RCA cable. I picked up a scosche at Walmart just to check and it bumps like before! Is it worth keeping the scosche or should I return it and get a raptor or something better?

If its bumpin just like normal no need to change..

I dont see any quality difference in different rcas other then style.

also good to hear you fixed it.

 

[malibuboats91 10+ year member]

So I tuned my sub and to get 31v gain is at 1/4 and it bumps more than ever. The installer had it at over half 3 years ago when I had it put in and it was never this loud.

 

[What was that? 10+ year member]

So I tuned my sub and to get 31v gain is at 1/4 and it bumps more than ever. The installer had it at over half 3 years ago when I had it put in and it was never this loud.[/quote
Just so you know gain is not a volume control. There is several good tutorials on gain matching with a dmm. Since you have one use it. I am happy to see that you were able to self diagnosis and fix your issue( and cost effectively). That is very satisfying.

 

[malibuboats91 10+ year member]

So I tuned my sub and to get 31v gain is at 1/4 and it bumps more than ever. The installer had it at over half 3 years ago when I had it put in and it was never this loud.[/quote
Just so you know gain is not a volume control. There is several good tutorials on gain matching with a dmm. Since you have one use it. I am happy to see that you were able to self diagnosis and fix your issue( and cost effectively). That is very satisfying.

Yea I do know that gain is not a volume control... I took the proper measures with my DMM to properly set the gain.

 

[What was that? 10+ year member]

I kind of assumed you did but then it seemed there was surprise when you had the gain turned down from the original installers setting and it sounded better. The first thing I tell people I install for is don't touch the gain unless you change parts. I do mine by ear but use the dmm as a guide or reference.

 

[bbeljefe]

Congrats OP. You now know more about gain setting than most car audio installers, lol.

Just to clarify, you mentioned turning all the settings on your amp down when you set the gain. You should have the low pass filter turned all the way up when gain setting and after that, it should be turned back down to ~80Hz.

 

[malibuboats91 10+ year member]

Yeah I left the LPF up last night so I'll do the tuning over again. The only issue I'm running into is that my stock speakers play the 50hz tone when I'm tuning and I don't want to blow them. The LOC is connected behind the radio and if I unplug them then the LOC doesn't have a signal.