Bad noise from sub at certain frequencies

Hello,

I am posting about an issue i am having with my subwoofer. It is a very simple setup:

- Pioneer CD unit
- factory speakers
- MTX TC2002 amp
- Infinity 12-inch subwoofer, in sealed enclosure

I have the amp hooked up to the "front output" RCA connection on the CD unit, and the subwoofer is hooked up as a bridged 4ohm connection from the amp. The amp is grounded to a point on the floor of the vehicle (2002 Honda Odyssey).

The amp is new, however the subwoofer i had used last year in a similar application in the same vehicle. This is a new install, and this issue has just appeared now (the subwoofer has been sitting in my basement for a few months). The problem is, i get a sort of continous "popping"/"cracking" noise at certain bass frequencies and gain levels. It seems like it is not at the really low frequencies, but when the slightly higher bass ones come in a song. For example, in a bass test i have, where the frequency is going from high to low, it will make this noise just before it hits the really low bass. Also it only seems to happen when the gain is up past a certain level, but i don't have to turn it up very much for it to happen. When this noise occurs, the subwoofer amount of movement is very minimal. So i can really turn the gain up, and it will be fine for the low bass, but then all of a sudden when there isn't any low bass and i get a certain frequency, it will make the noise but it will barely be moving.

I have tried playing around with the LP crossover, but even turned all the way down it does it.
I have heard a bunch of songs that this happens, and it will happen everytime at the exact same spot.

Is this a problem with the subwoofer, or something else? I'm not very experienced with car audio, so i apologize if the description is kind of vague.

Any help is appreciated, thanks,
Aaron

One of a few things are happening here.

1: Your gain is set too high, you've already admitted that it only happens "at certain gain levels".
2: Your box is improperly built, and tuned for a bad frequency. It is possible that your woofer is hitting a resonant peak, and with the new amplifier, (if there was a subsonic filter in the old one) you are "bangin' against the stops". You ARE going to destroy your woofer soon, if you dont fix this issue. Try a sealed enclosure, or have your enclosure re-designed FOR the woofer you have chosen.
3: Your voice coil has come unglued - literally... It now has resonanaces in it that are appearing at X frequency, OR it could be possibly rubbing the pole piece. (heheh he said "rubbing the pole piece"...)

or D: a combination of the above.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

thanks for the response.

1. this could be possible, but like i said the gain doesn't even have to be that high for the noise to occur. if i turn the gain down to a point that this noise doesn't occur at all, then the subwoofer is very quiet.

2. this resonant issue might be possible, however i actually built the enclosure myself, and it is a sealed enclosure based on the specs provided by Infinity. is there some way to troubleshoot to find out if a "resonant peak" from the amp is an issue?

like i said, when this noise occurs the subwoofer isn't actually moving that much, so i don't know if that says anything?

hmmm, i guess i can't edit posts after i post them?
anyways,

3. could this have happened from just sitting in my basement for many months? like i said, i did not notice this problem the last time i was using this sub.

(you'll be able to edit posts after you become a standard member)

Still sounds to me, (even more now, though) as though something is mechanically wrong with the woofer. What could have caused it, I can't tell you, but is the amp properly rated, (power-wise) to match your woofer?

Could inactivity, or a period of non-use CAUSE it? Not likely... Was it protected adequately from the "elements"? Was it somehow damaged otherwise?

As far as I know, there is no real way to determine if you have a resonant peak, without some test equipment... at a minimum, you need a signal generator, a precision resistor, and an accurate meter.

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

yup, i'm definetly not disagreeing that the sub is the issue, that is kind of what i am thinking. i just don't want to go out and buy a new sub and find out i still have the problem.

i'm not quite sure if the amp is matched to my sub, but i think it should be fine. 200 watts RMS output bridged is around what the sub can handle i believe.
specs here: https://www.mtx.com/caraudio/products/amplifiers/TC2002.cfm
the amp definetly seems like it is able to pump the sub well enough, it's just this noise issue, which happens even at middle gain, not just high. one thing to note though is that the amp gets hot, more so than the last MTX amp i had which was actually a little less power, but this is probably normal.

there are basically two settings for output level, i haven't really fooled around with adjusting GAIN and BASS BOOST together. should i use a balance of both, or should i crank one up first?

NEVER crank either... ideally, you turn the boost all the way down, FIRST, then set your gain, and never touch it again...

-------------
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

To me this sounds like a mechanical failure of the sub as well. The cracking that you are more than likely hearing is when the sub is playing a specific bass frequency that has enough amplitude behind it to cause the voice coil former to bang the magnet assembly. This amplitude is coming when the gain is too high and the bass boost is turned up. It is source material dependent (how it was recorded) or how it is boosted at the cd player as well. Next time, keep the boost down and keep the gain down as well.

An amp is going to get warm, more so if the amp is small or if it is played for an extended period of time or at full pull. Most people are stuck with this scenario, amp too small, demand for bass too big, improperly set gain and boost = disaster waiting for a place to happen.

-------------
Top Secret, I can tell you but then my wife will kill me.