4x mtx thunder 7500 12"?

hi guys, yesterday i install 4x mtx thunder 7500 12" in my corolla i have them in sealbox with 0.81 cubic feet for each subs, it sound very hard, but i lost the low freguency they told me that's because that the box is to small for them, they needed 1.25 cubic feet to work fine, but i cannot make a box that big, i can make one that is 1 cubic feet, so my question is should it be a hearing difference if i gave my 4x 7512-04 subs 1cubic feet per subs, that what i have right now(0.81 cubic feet) for them? thus should it be a huge difference between 0.81 and 1 cubic feet? and is it normal that the cones of the woofers get warm? anyways, thanks guys.

um no the cones of the subs should not get warm that is a very bad sine. you NEED to make a bigger box for them, right now there is to little air space for the sub to extend correctly to reproduce the low frequensies. Also there isent enouph air space for the sub to correctly disipate the heat that is created when you play them. I think that those subs need to be in a ported box cause they would be louder and more then likely sound better. that is gust my 2 cents.

Aaron

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On the12volt you give some info and you get in

youngone wrote:

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um no the cones of the subs should not get warm that is a very bad sine. you NEED to make a bigger box for them, right now there is to little air space for the sub to extend correctly to reproduce the low frequensies. Also there isent enouph air space for the sub to correctly disipate the heat that is created when you play them. I think that those subs need to be in a ported box cause they would be louder and more then likely sound better. that is gust my 2 cents.

Aaron

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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.

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Yeah, you definitely need more air space. Though, for SPL using a slightly small box than called for will help acheive that goal, but .81 is definitely stretching the limits. According to SoundDomain's info on this sub it requires a sealed enclosure from 1 - 1.5 cubic feet. What might work for you is building the boxes out to 1 cube and, if you want deeper bass, fill it with a good amount of Poly-fill to "trick" the speaker into seeing a larger volume.

youngone wrote:

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I think that those subs need to be in a ported box cause they would be louder and more then likely sound better.

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Yes, a ported enclosure will typically yield greater SPL if the box/port are tuned properly. However they usually require almost double the volume of the sealed. If you went with a ported enclosure you would probably only be able to run two of your subs. Also, if by saying it'll "sound better" refers to greater SPL, then sure. However, 98% of the time the sealed will have better SQ, because it yields a flater response. With that said, don't worry about it you'll be fine with 1 cu.ft.

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!

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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).

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Shaking The Neighborhood

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.

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i've forgot to mention, now that i read Stevart post.(i didn't see it before) that my subs are wired at 1ohm and no Stevart i don't have the gain to high i have it between 1/4 and 1/2 that isnt to hight right? i think about the low frequency thing is that aiming the subwoofer have a lot to do also, right? because the 2 9500 has a reflected bass. like the picture above, or shouldn't it matter aiming subwoofers? anyways.. thanks again.

Aruman wrote:

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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?

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Yes, if your subs have a vent for the voice coil on the back of the magnet then you should make sure it can breathe. About .5" will do and if you use poly-fill try to keep that way from the magnet vent.

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

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Sebastion K.
So Cal Audio Concepts

If I were you, I would sell two of them, rebuild the box for a decent sized vented enclosure, and rewire them for a 2 ohm load on that amp. That'd help with your low end.

I kinda get the impression you aren't sure of what to look at when you're faced with a response graph like the two I linked to.  You still seem to be inclined toward rebuilding the enclosure for more space and re-aiming the subs.  At the same time you're saying you want deeper, lower bass.  But whether you know at a glance what those graphs tell you or whether you don't have a clue, I'll go over some telling points briefly here...

Open up the https://www.the12volt.com/installbay/uploads/t7512-04at1.25x4.jpg, which shows the response of THESE subs in a box with 1.25 cu. ft per sub...a total of 5 cu ft.  Look at these 'tells' that will tell you without a doubt that you will not be enjoying deep bass from these subs no matter how big the box is:

(use the 'expand' icon in the bottom right of the screen to clarify the image)

• Parameters from the manufacturer's data:  look at the Fs, which is 45 Hz.  That is the resonant frequency of this sub and it doesn't play anything lower than that freq.
• Qts = 0.846  A high Q that tells you that this sub will work the best for its design in a sealed box.  Venting is an option, but the gain is minimal at best.  Better gain is had just with the car's natural frequency (cabin gain), which is a freq range in line with what this driver does best - SPL.
• The chart:  look at the left column which reads in decibels.  The -3 point is F3, which is considered the lowest frequency this sub can play because it is at half power at that point.  You see that it is at 45 Hz, and this is with the 1.25 cu ft per sub you're aiming for.
• The distinct hump, or peak, in this response shows the range of frequencies that this sub is designed to deliver (frequencies are shown along the bottom of the graph).  L'il John likes it a bit lower than this.  You can see that this sub delivers in the range of 50 Hz up to the crossover point.

Instead of spending more time and money reconfiguring the enclosure, you should switch to a subwoofer that will provide the bass response for the type of listening and type of music that you like.  Look for parameters with a lower Fs in the 20s or 30s and a Qts between .3 to .5.  You'll find that a lot of subs will fit this category.  Go a step further and narrow it down to subs that like a .8 cu ft sealed enclosure and also have a long throw like these do, and you can keep the upfiring box as you have it.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Hi...Stevdart the part that i don't understand is that my 2 9510-44 had a lower bass and they Fs are 41 Hz, my 12" 7500 are 45.25Hz, my questions is, is it a huge difference between 41Hz and 45Hz? and i know a guy that also have 4 mtx thunder 7500 in an Eclipse and his hit lower, he has them in 1.25 Cf seal, so that part of his that can go lower is what you said about Cabin Gain, so that's why a hatcback is alway better than a car with trunk? i don't know much about car audio like you guys know, you guys are the expert and i admire that a lot, i'm just in the learning mode, and hope that someday i can be like you guys are. anyway guys thank you all for helping me.

You know, it would be nice if we could just look at a couple of parameters in a sub's spec sheet and tell how it will perform, but that's just about impossible without putting it in a box modeling program like WinISD and looking at it.  One of the best things to do is exactly what you are doing:  talking with friends who have used some different setups and personally listening to the results.  Nothing tells more than true-life results.

On the subject, though, of Fs and how it relates to how deep the bass response can go:  you can't always tell by the Fs of the driver just by looking at the number.  I picked another sub at random just to see what it looks like modeled in the program.  The Memphis M-class MC124, a single 4 ohm sub similar to what you have.

https://www.memphiscaraudio.com/products/details.asp?cat=&id=50&p=2 and https://memphiscaraudio.com/LiveImages/114/7/DocumentURL.pdf for the parameters.

You see that this sub has a low Fs of 28 Hz...but look at the response in the link here:

memphismc124-mtx7512.jpg  Open up the response I gave you in the last post to compare.

All three of these use the same 5 cu ft box for four subs.  The colored lines you're looking at are this:  yellow is the Memphis in sealed.  You see that even though it has a much lower Fs, it still gives a response very similar to what you now have with those MTX 7500s.  F3 is at about 45 Hz.  The SQ is better, though, because there is no 'hump' in the response.

The green line is the same box size but vented, and using the Memphis sub.  There is more SPL and low end extension because of the vented box that is tuned to 30 Hz.  The difference that you see in this graph between the yellow and green lines doesn't look like very much, but it is a big difference in output if you want deep bass in the popular music we listen to now.  The F3 hits lower at 39 - 40 Hz and makes a huge improvement in those deep bass hits.  (This is my way of answering your question above about comparing this sub to your 9500's).

The third line, the blue one, is your MTX 7500 in the same 1.25 per sub box but vented.  It is tuned to 40 Hz.  You see that this extends the low bass output...the F3 is at 32 Hz.  But there's a big price to pay for this low end extension.  Look at the huge peak in response that happens when you port this particular sub:  you get a peaked response of over +5 db.  What that means is that even though this sub/box combination will perform to lower bass, the benefit is outweighed by the increase in db's at the higher sub freqs.  You would have to adjust volume because of that peaked response, which would further make that F3 point seem more like a F8 point...8 decibels lower than the majority of sound that you're getting.

Getting around this overly-peaked response is just about impossible in a vehicle because of the huge box it would take.

That all has to do with the whole combination of driver parameters and how they will interact with each other.  The biggest differences between these two subs is the total Q which is given as Qts.  The MTX's very high .84 is a sign that getting any kind of smooth response will be impossible, whereas the Memhis' .46 is a middle-of-the-road number that gives you a clue that you can work with this in either sealed or vented applications.  It doesn't boil down to something that simple...like I said it would be great if we could just look at a couple of numbers and know what to expect...but if I saw these MTX parameters and it's response I would think "SPL, how loud can we make this thing get".

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

The only times i have seen a upward firing box work well is in a hatchback and that is still rare, im sure there are success stories out there but up till now i havnt seen many. For most vehicles you will see the best results facing the subs rearwards. Sometimes less is more. I would try 2 subs ported or try 3 sealed if you can get them in a box that will fit and work with your amp ohm wise

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2007 Acura TSX
SQ setup in the works

Hi...Stevdart how are you? Stevdart i was playing with the subsonic filter and it did helped alot, it was set before at 40hz when i use the 2 9500, then i set it at like 20-30hz with these 4 7500 and it did help, now i get some low bass that i didn't get before, but can the subsonic filter defect my subs? because my subs are 45Hz so can it defect it if it go below that? or what's the point on that part? anyways, tnx.

In general terms it works like this:  The box tuning frequency defines the frequency below which the driver has no damping control.  But the subsonic filter, like other filters, cuts on a slope and will start the cutoff slope above the point at which you set it.  There will always be some play in where you can set that filter point.  It doesn't have to be set at the Fb and is normally set below it.  It should be set somewhere between the Fb and a point one octave down from Fb.

It's best to use test tone freqs to set this and any other filters; this filter should be set using very low sub freqs.  You can watch the cone excursion while you adjust the ss filter and see if you are setting it too low by making sure the cone doesn't move in and out wildly at any point.  You would definitely see some out-of-control movement if you have the ss filter set too low, as long as you are inputting low enough frequencies to do a proper test.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.