4x mtx thunder 7500 12?

I don't agree with you here completely. Yes he is losing some of the lower frequencies due to box size, but the heat dissipation issue is a little off. A slightly larger sealed box is going hold heat as well.

So back to the issue, your best bet is to build a larger enclosure for your subs. They will perform better that way. And yes these subs do well in vented enclosures but you are going be giving up some major space.

The heat issue is to be expected, I had a pair of those subs and my current subs can get warm to the touch, but know that at that point you might back the volume down a bit.

Those subs have a very high Q and high Fs and are not going to provide very much low end extension (deep bass).  But they will pound out some SPL in a sealed box.  The box could be what you have now or it could be twice as big and you wouldn't see much difference in the response.

You said "...but I lost the low frequency."  I take it from that wording that the low frequency was there for awhile and then something went wrong.  Else, you wouldn't have "lost" it.  So...

Here's what I think might be the problem:  the amplifier is overloaded.  How do you have these four SVC 4 ohm subs wired?  What impedance load is on the amp?  Do I guess right that you have these all paralleled to a 1 ohm load?

And cones getting warm:  an indication of excess heat in the enclosure.  The box size alone will not cause that.  The smaller airspace will just peak the response a little higher and reduce the already very poor low end response.  My suspicion here lies in a clipped signal creating excessive voice coil heat, and that has everything to do with the amplifier gain setting.  I'm willing to bet it is too high.

I looked at these subs using  WinISD.  The MTX website is good about disclosing full parameters so I loaded it up and gave it a look.  Here's the response with the 0.81 ft^3 per sub you now have:    t7512-04at0.81x4.jpg

Compare that to this response with 1.25 ft^3 per sub:  t7512-04at1.25x4.jpg

You see that there is less of a peak in the response but the low end is still not there.  That's just the way this sub works, from what I can tell.  Take your time and set this system up so that the amp is not overworked (if that's a problem) and that the amp's gains are set right with the deck output (so that there is no clipped signal).  After the very precise setup is done, you can open up that enclosure and stuff it with polyfil to bring that peak in the response down a bit.  Other than that, the box size as you have it is fine.

The best use for this sub?  Pure kickass rock and roll!

Hi guys thanks for answer me. yep my problem is that i lost the low frequency that i had when i had 2 Mtx 9510-44 sealbox, when i had the 9500 series it was very loud and low i played songs like: late nite tip, little john and it sounded very good compared now with my 4 mtx 7512-04, now it punch very hard, but no low freq. or that's because of the aiming of the subs? So i will make a new box and gave them 1 cubic feet each. If i make my box larger would i get more spl than with what i have now(0.81)? or if i make it larger i'll only get the low freq.? i'm using the MTX TA81001 that's rated 1500WRms @ 1 ohm, but mine can give me 1958Wrms at 1 ohm, so i think power is not the problem, right? i read that those mtx 7500 can take more than they rated 400watt rms. but i don't know if it's true. another quest. is it ok that the magnet of the subs is flush mounted with the wood of the box? or should it have a space between? i know a guy that have 4 of those mtx thunder 7512-04 in 1.25 cubic feet(seal) per each subs powered by 2 mtx thunder 801d in a Mitsubishi Eclipse, and that thing was freaking loud and also low. but i cannot gave mine 1.25 because i have a Toyota Corolla thus no big trunk space, so mine will not be loud as the Eclipse(hatcback) but can't i be at least closer? anyways guys, thanks very much and i post some picture of what i had before(2x mtx 9510-44) and what i have now(4x mtx 7512-04).

Aruman, look at the data Stevdart was kind enough to provide.  You will never get much more out of these subs.  The difference in Fc between the enclosure size you have now and 1.2 cubes is the difference between 65 and 53 Hz.  These subs are designed mainly for SPL competition, not for deep bass.

Larger enclosures will get you a little more deep bass extension, but these guys cannot hack below 40Hz (look at that fs!) unless, maybe, you remove two of them, keep the same enclosure arrangement but open it up so that each sub can use 1.6 cuft (which is still too small by the way) and port them for 38Hz, which will help reinforce that low end.

Aruman, in my shop, we have done those false floors' with four 12's on several occasions. Some times (such as in a previous gerneration Mustang) they simply make earthquakes, but other times (like when we put that same setup into a Civic sedan), the results were a bit dissapointing.

Also, remember that an Eclipse is a hatchback coupe. Like the old Honda CRX's, hatchbacks are some of the easiest cars to make pound very hard. There is no trunk, so bass response is directed straight into the cabin. It would be difficult for a four door Toyota Corolla to match that kind of immediate response, especially with the amount of sound deadening being placed into the modern Toyota.

The same individual who had the Civic sedan had us take out the four 12's and put three of them into a rear-fire box. The verdict? MUCh better SPL. The three 12's firing toward the rear severly out-pounded the four 12's up-firing. With the limited trunk space available to him in the Civic, placing them to face the rear allowed them to have much more trunk space to play with.

We've seen the same phenomonen with two 12's...firing them back seems to yeild much better bass than aiming them up.

If it isn't too much trouble for you, I would say take them out of that box and put three of them, or even all four if you can find a way to make it fit, into a rear fire box placed roughly in the middle of your trunk. I'll bet that the results please you.

If you are in the Southern Cali area, you are more than welcome to drop by the shop and we'll help you figure it out! Shameless plug...

Good luck,

---Sebastion