Troubleshooting Sub/Amp expert advice needed

[Project-LXi]

Ok, I know this might be hard to diagnose without having the setup in front of you, so I will try to be as specific as possible.

Here is my setup:
Kenwood 40w x4 headunit (im guessing this isnt realated to the problem)
Rockford Fosgate Punch HE2 sub 400w cap, in bandpass box
MTX Thunder Series 280w 4 channel amp, which is bridged to the sub. It is mounted on the back of the box (which I have heard is bad).

Recently my sub began to give me trouble. The trouble is that it only seems to hit occasionally. Here is exactly what happens: When the car is first turned on, the sub hits consistantly for about 15-30 mins. Then it for the most part shuts off, only occasionally (about once every 30 sec, not consistant) it will hit. ie: the music is playing and the bass is like: bump, bump, bump, BUMP, bump, bump, etc...

My first thought was it might be the amp overheating. Nope, amp was ice cold.
Second idea was that it might be a loose connection, and maybe something like a bumpy section of road could have made a cable somewhere come loose. I checked all the connections on the amp to the sub, and on the amp to the deck, all connected properly. Checked the ground wire, also connected properly. checked the power line from battery to amp at all points, connected properly. I did the same to the headunit, and all the wires were in place how they should be.

This is where my knowlege ends, so I talked to 2 different people about the subject:

I talked to a guy who works as a car audio installer, and he thought it might be a loose or frayed voice coil in the sub.

I talked to an electrician, he said that something might be wrong with the amp.

So, I know this might be hard to diagnose, but do any of you car audio buffs have any idea what could be wrong? and how to go about fixing it?

thanks

[NOAHS88accord]

I am not an audio installer or an electrician but i have installed everything from alarms, remote starts, headunits, to amps and etc. my guess your power cable is not big enough. I had a 300 watt jensen amp with a 10gauge power cable and it did the same thing, so i upgraded to 8gauge and it fixed it

my question is, what size cable you using, what size fuse? it could be shutting off because the fuse in the amp is causeing the thermal/short protection to kick in.

ONCE AGAIN, i am not an audio installer or an elec trician these are just guesses and by any means i could be completely wrong. just troubleshoot it

NOah

[Project-LXi]

Not sure on specific sizes, but everything came from a friend of a friend who worked as a car audio installer at The Good Guys. It is all really expensive Monster Cable.

[AccordEpicenter]

make sure your sub is wired correctly and the wires arent loose. If everything checks ok id look into swapping the amp to see if thats the problem. I had a pair of mtx 3000s once and they blew up very badly, when the first one went i didnt smell it but it would play and sound bad but then it would cut out because the VC shorted and the amp went into protection. It did that for like 8 tries because i thought it was just the amp acting up...

[StUpiD8000]

Look at the wires in the sub...The one right by/on the spider that go to the coil. One of them might be messed up.

[88 Accord DX]

it could be the amp is just jacked up. my old amp would be perfect when the car was off but when it was on it would miss sometimes. there are alot of tiny parts that can get jacked up in those little boxes.

[Bobs89LXi]

Does your amp have overload protection? If so, it may be kicking in when the output passes peak. I am not too familiar with the MTX amp, but most have some type of overload indicator on them. This can either be an LED that turns from green to red or an LED that lights only when the amp overloads. What is the peak power rating of the subs? If is less than the rated peak of the amp, there is a distinct possibility that you are in fact overloading it.

[AccordEpicenter]

I know alot of MTX amps would go thermal and into protection if you ran the amp into lower ohms than what it was rated to. For example, my friends 2300x was stable to 4 ohm mono, he ran it at 2 ohm mono and it got soo hot and went into protection in less than 15 minutes

[Project-LXi]

400w capacity on the sub
280w amp
The setup has worked flawlessly for the past 6 months until it started doing this earlier this week.
It is not overheating. And the sub sounds fine up until about 15 min, then it just works every so often in blips here and there.

[AccordEpicenter]

are you sure you dont have a loose connection in ur sub or speaker wiring?

[Project-LXi]

Ok, last night I hooked up my friend's 300w Jensen amp to my sub, and it didnt work. So, I think the problem is with the sub, maybe the VC like the audio installer thought it may be.

[AccordEpicenter]

yeah also you might wanna take a look and see if your tinsel leads to the voice coil are wrecked or somthing. Test the resistance of the voice coil, most are 4 ohm but some are 2 ohm or dvc

[xbi0s]

I had this problem on my civic

It was because my alternator was a peice of shit and my battery was dying..

The amp would drain out the battery

I'd let the car run for a day or two (normal driving w/o amp) and it'd work for awhile

Then my car got broken into and I didnt have to worry about my radio.. cuz I didnt have it anymore :(

[AccordEpicenter]

MY friends civic did that too

[jeffreygivens]

if you have a fuse on the power wire it might be the fuse is to small try a 30 amp one that might work but i dont know

[Project-LXi]

Yeah thats a thought. I think the alternator in there is only 30 amp or something shitty like that. Only thing would be then how come it has worked for so long up to now...

Here is an update of what I have done to troubleshoot this problem:

All connetions from the head unit out have been checked and tested with an osciliscope. All work fine.

The sub, which I have now found to actually have 600w capacity and NOT 400 as originally thought, has been taken out of the box and tested to see if it still works by hooking up a 6 volt battery to the terminals. I appears to work correctly, although I have no idea how I would go about checking the acutal coil.

The amp when hooked up to the sub works properly for about 10-15 min, (less if the car is on) After that it works in spontanious blips. Here is the interesting thing about the amp however: When we hooked it up to the osciliscope, when the sub stops hitting, the amp is not sending the sub any current on any channel. However when it does it's 'blips' of hitting, the amp is of course again sending current at least for a few seconds until it stops sending anything.

So this lead us to believe it could be the amp that is the problem, especially since it has come ungrounded and stayed unground for long periods of time because the carpeting in my trunk does not hold itself down and the box would frequently slide around and rip out the ground cable. HOWEVER: I recently hooked my sub up to my friend's amp, and it still didnt work. So it may not be that.

As for the alternator, it is a piece of shit, and just yesturday my rear right 6x9 mysteriously shut itself off after about 15 min of driving, which would I guess be evidence to support that argument.

Soon I will hook up a 10 ohm resistor to the amp instead of the sub, that way I know if its a sub problem or not. Until then your guy's advice is always appreciated.