how much space would you guys think i would have if i built a box out of 3/4 inch MDF and put it where the back seats are...i would be removing the seats and the box could extend into the floor as long as my seats could still lean back some. i want to built a ported box for my two kicker l7s w/ 3.25 cubic ft. per sub plus just a lil for the port.

 

no one has ever built a box where the back seats are??

 

the amount of space available totally depends on how high up you go with the box. There's a ton of room there to use.

But... I suggest you build a small enclosure for just 1 sub to use as a "test" enclosure that you can position in various places within your car. What you'll find is that your bass output is going to be significantly better with the sub all the way at the back of the car as opposed to putting it in the middle. When you put the sub(s) in the middle of the car, you get standing waves due to cancellation caused by the sound wave that's reflecting off the back of the car. I forget my calculations, but the cancellation occurs somewhere around 60-90hz depending on your specific placement. You avoid this cancellation by putting the subs as far back as possible.

 

yeah id rather keep it in the back but theres just not enough room probably only around 3 ft. built w/ mdf which is what i have now. also they call for around 3 ft per sub actually 3.25 plus the port area. they are loud now but i know they can do more. i have two l7 dual two ohms running in parralell around 1 ohm to a mtx 81000d amp gain only up around 1/4 way cause they max out. my PA2 eq is only at 0db instead of +12 which it can go to and the volume on its only up half way. the cd player is also only at subs on 3 they go to 12 and 0 is no subs. i also have a 5 farad cap 0 guage wire and a power master 160 amp alt. i just know they can do so much more cause ive heard them in ported boxes and they are impressive. the box recomended is 3.25 per sub plus port area which i belive they have tuned around 45 hz. and as far as building the wall goes i need to still see out the back window so i cant block that off although i can extend onto the hump above the tank if needed for a foot or more extra. im open to ideas fellas please help me out i have all this great stuff i know can do more.

 

the cancellation is bad enough that I'd rather put 2 smaller subs in the back than 2 big ones in the middle of the car. It'll get louder and it'll sound much better.

Tuning a box that big to 45hz is going to create a 1-note-wonder. Sure, it'll rattle your nuts more than a coin operated girlfriend, but it's going to sound terrible.

If all you're after is spl at 45-50hz, then sure, dump 2 massive subs in a large box tuned to high into the center of the car, but if you want anything listenable, reconsider your plans.

 

then what else do you recomend i just think they could be alot louder and more solid notes than they are now. and i have heard some good ported boxes i could deal w/ a smaller box if it saves some sq but i still think it needs bigger than it is now and if i leave them back there theres no way to keep that amount of space and still put the correct port in there.

 

I'm not sure that a smaller box is the answer, but a lower tuning frequency probably is.

Or, just run them sealed. Those monsters are going to be extremely bottom heavy in a ported enclosure once cabin gain is factored in.

What is the model number for the subs? I want to find their t/s parameters and see how they look in my enclosure modeling software.

 

you already have the subs? if not maybe you should be comparing 2 sealed 12's to 2 ported 10's. box for 2 10s should be doable in the back.

i can certainly vouch for sealed well boxes getting loud, i took jims advice when i did my box and put the speakers as close to the rear as i could get them, even mounted them a bit crooked to get another 1/2 inch clearance from the screws. it gets plenty loud and sounds awesome, even without deadener.

 

if your are planning to put the subs in the middle id suggest build a wall

 

yes i already have the subs and as of now they are in a sealed inclosure w/ not divider to try and squeeze every centimeter out of the existing enclosure i estimate around 3 cubic ft. right now w/ it built out of 3/4 inch mdf. as for the model number id have to look when i get home but they are the kicker solar baric l7 dual two ohm models and the amp is the mtx 81000d but if u look up the specs on it its very underated weve had it on 6 mtx 8000 12s w/ plenty of breathing room still.

 

I don't believe you've even said what size L7s they are.

 

yeah my bad they are the solar baric kicker l7 12's dual two ohm runnin about 1 ohm or so. and im open to ideas if you all have some good ones.

 

I plugged in the t/s parameters and started experimenting with box sizes & tuning frequencies. I attached the picture.

The green trace is a 3 cube box, tuned to 45hz. As you can see, it's a miserable frequency response unless your only goal in life is to make your ball bag vibrate.

The orange trace is the smallest ported enclosure I could get with a respectable frequency response. It's 5 cubes tuned to 24hz. When you combine this response with the car's cabin gain, you'll get an exaggerated bottom end, but the response will rise smoothly and will do a good job overcoming road noise at those lower frequencies. When you're parked, it'll sound boomy.

The yellow response is a sealed 1.5 cubic foot box. This is the way I'd go. When combined with your cabin gain, it'll give a smooth, slightly rising low end response that will sound more natural than the ported enclosure, but won't have quite as much bottom octave impact. But... it's small, so you can fit it into the back of the car. Once you take that into account, I think this arrangement will sound better and get as loud as the ported box in the center of your car.

 

were all those per sub or for both??

 

That's per sub. Those plots will get UGLY if you try to cram 2 subs into that airspace.

 

the more i look at that the more i dont see why the green is so bad....after around 30hz or so which is some of the lower stuff i would play the numbers look better or equal to all the other boxes what makes that type worse?? im not saying your wrong im just trying to understand the models more.

 

The green alignment is going to give you what's known as a "1 note wonder". The bass output at 50hz is so much more prominent than the output above and below that frequency, that all you're going to get is that 1 narrow band of output.

Think of this one example. Let's say you like rock music. The bass in rock music comes from 2 sources, the bass drum and the bass guitar. The bass drum is basically a fixed frequency, although it does have significant energy over a very broad range of frequencies. With that green alignment, the bass drum won't sound natural, because it'll just drone at 50hz instead of having the proper amount of output over the whole spectrum. Even worse, the bass guitar will be virtually unrecognizable. You won't know if you're hearing the bass drum or the guitar, nevermind the individual chords being played. All you'll hear is thump thump thump thump.

If you listen to rap, some songs will pound like a bastard if the majority of their bass is at 50hz. Other songs will be dead because their bass fundamentals are at a higher or lower frequency.

One of the main priorities in any speaker design, whether it's subs or tweeters, is to maintain a frequency response that's as flat and as smooth as possible, because the intent of a stereo is to reproduce the sound as accurately as possible. If your stereo has a frequency response that varies by 20 or 30dB over the audible range, it sure as hell isn't anything close to correct or accurate, and your music will sound much different (usually much worse) than it should.

Even if you're a basshead and like to crank the bass ****, you don't want that extra bass at just one narrow frequency band... you want the frequency response to be smooth even if it's not flat.

Another thing that you need to consider that isn't shown in those graphs is the effect that the car's interior is going to have. In small areas like a car interior, you get something called cabin gain. You get a boost in output at approximately 12dB/octave at lower frequencies. Basically, that curve would look like the opposite of the yellow one, so when you combine them, you get basically a straight line all the way down to below 20hz. When you combine that curve with the green one you get, well, a disaster. I wish I had software that could simulate cabin gain into the output plot to show what I mean.

 

well as i said i have a sealed box now and its around 3 cubic ft i belive not counting sub displacement and at the time has no poly fill which i will add soon. some songs are very lound and i have to turn the db on my eq down or it will max out the subs and sound horrible. other songs sound very quite compare to those and dont sound as good. also the power out put could be much more i belive in a ported box as apposed to this little sealed one. so here in lies my delima. i have all the equipment to make a pretty decent stereo but it still seems limited. what do you think my best options are. and keep in mind if i go ported i have no more space in the well to expand the box so it would have to be either moved to the back seat or the ports made to somehow go ontop of the gas tank hump and into the box?? how i would have no clue. i know im bugging you im sure but id hate to build or have built a huge ported box for it to sound about as good as me singing or something. thanks

John

 

I already told you what I think. 1.5 cubes sealed per sub. If you've got 3 cubes total, then you're right where you should be. If you've got 3 cubes for each sub, then your box is way too big, which is going to create almost as many problems as one that's too small.

The best sound quality that you're going to get from those subs is 1.5 cubes sealed per sub. If you're not satisfied with what that gives you, then you need to invest in a sub known for its sound quality instead of a sub that's made for boomers.

You should also make sure that all of your equalization & crossovers are set up properly. If you've got some bass boost or loudness filters on, it could be creating an unnatural boost in some range too.