I installed a new 12" MTX US-XT12-04 on the weekend. Everything sounds good until I turned the volume up to 15+. After that it sounds like the sub is blown(Im thinking there is too much air pressure in the box). I built the box(sealed) with the instructions that came with the sub. It gave me the dimensions to cut the wood out for optimal sound.

Well after I built the box I realized it was too big for where I wanted to put it so I had to trim it a bit. The box is probably about 3/4 the size the instructions said it needed. Started with a 1.25 cubic ft box and now its probably between .75 and 1 cubic ft.

My question is, would porting the box help with this?

 

In my opinion, porting wouldn't help at all here. Ported boxes usually..always need to be bigger than sealed boxes. First, I would check the gain. Turn the gain down a little until it sounds better. Second, you could use poly fill to make up for some of the space you lost by trimming the box. It won't make up for .5 cubic ft, but it will help some. But adjust the gain, I'd guess it's set too high and it's clipping the signal, making the sub bottom out.

 

Would the gain be Level, LPF or Low Boost? I turned all of them down then slowly turned them back up to where it was(level @ .5v, LPF @ 100Hz and Low Boost @ +6dB). I didnt notice a difference at all except there was less bass.

I went on crutchfield and figured out how to correctly wire a 4ohm sub to a 2 channel amp. It seems I had it wired up for 2 ohms instead of bridging the channels to make it 4 ohm.

What is this poly fill you speak of?

 

the only way to try and make an enclosure bigger is to stuff it with polyfill, or pillow stuffing. It reduces the speed of the sound waves in the box and helps it to make the enclosure look a little bigger. A ported box has to be made to specific dimensions just like a sealed box, it isn't just as simple as pokin a hole in the box.

If normally recomend making 2 seperate smaller enclosures that can be loaded individually and it makes it a little easier. You can always screw them together once it is in and then you do not have to worry about them being stolen as easy.

 

Gain=Level. .5 sounds high to me for the gain. unless i'm thinking backwards, .5 is max gain. there is a way to correctly set the gain with a digital multimeter. I'll try to find a link for you real quick. if the level/gain is too high, it won't send a clean signal to the sub, and will cause distortion and eventually damage. what kind of head unit/amp are you using?

 

On my amp .3 is max gain. 6 is least gain.

 

setting gains with a meter is wrong in sooo many ways, does your meter like rock, rap or techno?

once again, polyfill is nothing more then pillow stuffing. Try to put as much of it as possible in the box and the shove the sub in.

 

OK thanks. Ill try that and see if it helps.

 

true, but it's the cheapest way to get at least a ballpark setting. O-scopes cost a lot and years of experience isn't cheap either lol


Personally, I still think the gain is high. I don't think I've ever seen a head unit with .5v preouts. The lowest I remember is about 2v. The gain/level/input sensitivity should match the deck's output voltage. It may not be as loud, but if you blow the sub, it's even quieter.

None of this was meant to be rude, btw, but I'm kinda drunk so it may seem like it was haha

 

you also forgot to mention that he would need to do this with a test cd of 60 hz.

Oscopes are the only tool for tuning a system man, otherwise it is like trying to use a screwdriver as a chisel. It will work but...................... The right tool for the job, do it right do it once.

What are the cross-over setting on the amp set at?