bass sound/feedback when starting car

Hello,

The problem is that I have a sporadic issue in which when I start my lexus 06' GX470, the subs will sometimes operate very loudly for 1-2 seconds, regardless of if the stereo is off or on.  I have a JL xd300/1 amp and two 10w1v2 subs.  I thought it was the Pac-Soem T line output converter so I eliminated that, it seemed to work for 2 days but now it's back.  I can replicate the sound problem now when I have the stereo on while the car is off (acc.), then when I turn the car on, the stereo cuts out for a moment while the car starts, then when it comes back on, the subs make the loud sound. 

My installer had the remote turn on wire hooked up to my seat heater fuse, it did the problem then as well.  I just moved it to the acc. fuse so that I can have the subwoofers available when my stereo is on but the car is off.  I couldn't before.  I spoke to JL briefly and they mentioned something about a possiblility of a "noise cancellation mic" in my car and testing to see if it makes the noise with the doors open or closed.  If I am correct, it has done it in either/both conditions.  It seems as if it's some type of voltage change/surge that the amp responds to.  Perhaps there is a better fuse I can use for the amp to turn on?  Or any other ideas as to what could be causing this?

I have some new diagnostic info.  I moved the remote turn on to another fuse (ign) and it fixed the problem, however, now I am back to not being able to have the amp turn on when the car is off but the radio is being used by "acc".  Is there any other fuse that I could use that would have the amp on during the "accessory power" scenario and then NOT make that loud when when i actually turn the car on? 

If your head unit does not have a remote power switch lead (are you using the factory system?) then you will either need to use your meter to find an existing circuit that is on with key in ACC but off during cranking, or you will need to use a low-voltage relay switched by the speaker output of your head unit.

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I forgot to mention, I am using the factory mark levinson stereo.  I think the problem happens when there is a signal on acc. then off during cranking, then back on again.  for some reason, that's the exact condition in which i could replicate the sound problem.  The mystery to me is that it was fine for 2 days on the acc. fuse.  I would have the car off, stereo on and amp on, then turn the car on, it would turn off for a brief moment then turn back on with so sound issue.  Then it started doing it.  I moved it to the ign fuse, so the amp/subs are only on when the car is started but I'm worried that it will do it again in another day or two.  JL didn't seem to be too helpful because he said that the sound will likely come on now when the car is on but the stereo is turned off while I'm driving.  That doesn't make sense to me, that has never happened before.  And, they are saying that it's normal for the amp to get a signal on start up and translate that to the subs.  What is not normal is the extremely loud sound in doing that.  I also have the remote bass nob, maybe I need to bypass that or something? 

okay, now it's doing it again already.  even with the amp just coming on after crank up (ign fuse).  Why is this happening after 3-4 successful start ups?  Could it be connected to my remote bass knob and gain issues?

I am guessing that you installed the soem-t at the rear speakers. Catch the front speakers, or the rear speaker wires behind the radio and it will take care of this problem.

I believe that the original installer used the front speakers, I'll double check by using the fader control to find out.  but for clarification, I have eliminated the line output converter and wired rca's into those tapped signal wires.

more of an update.  So it's confirmed that the problem is there when the remote turn on is hooked into any fuse.  there was a false success at times, lasting 4-5 start ups, then it becomes a constant loud sound again upon start up, regardless of if the stereo is turned on or not.  I disconnected the remote bass knob and it still did it, for now, I have turned the knob all the way down and will turn it up to use the amp/sub.  It just doesn't make sense to me because I know that this is not normal and has progressively gotten worse.  Could it be a ground issue?  Or fault/defect in the amp that has gotten worse? 

You may have a ground issue as well. Check for bare metal with no rust or corrosion. Also you can sometimes have an instant on instant off instant on issue using a 12v accessory wire. Try putting a 1.24k ohm resistor inline between the accessory line and the amp. You should notice a change. It may end the problem or it may reduce it. Try greater ohm resistors until the problem goes away and the amp stays on. No more than say 5.6k ohms max.

any thoughts on if this is connected to noise canceling features and mics inside the cabin? Some say that I need to find these mics and disconnect them. Another thought is that it has to do with tapping into the rear speakers vs. the fronts or factory sub. I sent the amp back to the place where I bought it and they tested it, saying that it's not defective.

I would try putting the remote wire on a switch and see if this solves your problem. Is there a factory amplifier in the vehicle? if there is you may need to grab the signal going into the factory amp before it is amplified.

I can try to resistor idea but something just doesn't seem right to me about having to find ways around this problem. It's just not normal and something is causing it. It didn't do it for a month, then occasionally, now all the time. I can use the remote bass knob to stop the problem if I keep it turned down/off until after I start the car. But, the principle of that bothers me.

Major update!!!!

So, I realized that the installer pulled the signal from my rear speakers to use for the amp/sub. I removed the LOC, wired a set of RCA's directly to the speaker wires of the factory sub, using the sub signal and disconnected the factory sub. Not only did that fix the problem but it made the subs so strong/loud that it was as if I added 4 subs to the system. Now it is working so well that I am just using one sub and it's way louder/deeper than when I was using both subs coming off of the rear signals. Thanks for the input/suggestions. I just wanted to pass this along.

Ah, an improper installation.  Where was it done?

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Hey I forgot to answer your PM, the reason you have to disconnect the factory sub is that when a speaker moves it produces voltage. This would make the LOC think that the radio made that voltage, this in turn would tell your amp to make your woofers move. Then when the woofers moved, they would in turn make the factory sub move. Then it starts over again, causing problems very similar to your original problem.

yup, that make's sense.  the install was done at a local shop, I'm just glad that it's not only fixed, but better than it ever was.  thanks again for the help/input.