I need help figuring out why my system sounds like crap. It's really my woofers that sounds bad. I have 2 12 Rockford Fosgate 12' P1 punch subs in truck boxes behind the seat with a 250 watt amp. Now the thing is they don't thump, just kinda vibrate badly. They also cut out when the truck is idleing or with the key in the accessory postion. Can someone tell me whatI can do to make them thump like they are supposed to? Thanks in advance.

 

Your description sounds almost like a clipping issue...

Did it ever sound like what you wanted with your existing set-up, or is this a new problem?

Fwiw, a friend of mine has a 600watt amp pushing his 2-Rockford 12s with a decent (steady) thump.

 

I was thinking the same thing. Try turning your gain all the way down, putting in a CD you like, turn the volume up to your normal listening volume and turning the gain back up about an 1/8 of a turn at a time until it starts sounding good. This will get you kind of close, then back it off a little so it still sounds good at your maximum listening level and your pretty much set.

I ran an old pair of P1 12" off 200 watts, I had 8ohm speakers in parallel for a 4ohm load and 200w. Without knowing how you have them wired and their impedance it's hard to say what you could do if the gain setting doesn't help.

 

It has always sounded like this. I will try the gain control as suggested. Two different people have "played" with it but it didn't change anything.
I have RCas going from the head unit to the amp. Then heavy guage amp wires going to the boxes. I know the wires from the box connections to the subs are puny compared to the amp wires.
So what about the cutting out problem. I have seen capacitors at the sterio shop, but aren't they for big high power sytems?
I had 4000 watts going to two 15's and two twelves, 8 mids and 4 tweeters in my Trans Am, and I never needed a capacitor in that system, nor did I have the problems I'm having in my truck.

 

I believe you mean clipping. Clipping is when the input is being multiplied beyond the capability of the amp, on an oscilloscope, the normally round sine wave will have a square top rather than a radius. Usually turning down the gain will correct it, unless you have too much voltage in the RCAs for the amp to handle.

If you want to isolate your power supply, unplug the RCAs from the amp. If it still makes noise, then you have an issue with the amp or the power. If it's quiet, then try plugging the RCAs back into the amp and unplugging them from the headunit. If it's noisy then, you are picking up noise on the RCAs. Which means you should try to move the RCAs away from any other wires. However, if it's making noise with the engine off, either of these seem unlikely.

Capacitors can clean up the power coming in, but it's not their intended function.

 

Here's another explanation for clipping (forgive me for using the Wiki..)
Clipping (audio) - Wikipedia, the free encyclopedia The first 2-3 parts seem to have a "simple" explanation.

 

Weird. Um, are the woofers in phase? Are there built-in crossovers in the amp that are set wrong? Are the boxes a suitable size and tuned appropriately for the woofers? If the woofers have dual voice coils, are they wired correctly? Are the woofers connected to the amp correctly?

Maybe that's irrelevant. The cutting out when the engine isn't running suggests a power supply issue more than an amp/woofer/box thing. Putting a voltmeter across the amp power terminals would tell us a lot. If you don't see 12V there in Acc, and around 13 to 14V with the engine running at a high idle, you need to check the power and ground paths.

Finally, has the amp ever worked properly?

 

Well the boxes are store bought with Cerwin Vega subs in them , but I blew them up a long time ago. The amp was bought used and was told it was in working order. All the rest that you asked, I have no clue to any of the answers. But the cutting out thing,, well thats what I was thinking I might need a capacitor for.
The guy I bought my head unit and the amp from also installed everything for me. He owned a car audio business and has won many competitions. So I think he knew what he was doing, whenn he installed everything. I had the boxes already in another truck, but a different amp, and never had a problem like this, but they didn't thump as hard as I thought they should, that why I went with the Rockfords after I blew the Crewin Vegas.

 

With a cap you may get your 13.3-14volts needed to keep it hitting at its hardest, but the amp it self is going to try and get the output needed to get both subs bumping-thus cut/Clip out....

See if you notice the subs getting screaming hot (on the magnet side) while they are on...

Also, see if you can borrow a 600-800watt amp to see if it still does it.

One more thing... what kind of fuse situtation are you running?

 

The only fuse for the amp is on the big cable out by the battery. I'll have to check to see if they are getting hot or not. As for borrowing an amp. virtually not possible. When I'm working again, I may just wait for a sale at the local audio shop and buy a bigger amp.

 

Its your amp. Buy a well known brand amp. A Kicker 300.1 amp will work great for those subs.