PhLaXuS

Here's the preliminary external dimensions. I took these measurements in the dark, so I'll verify them again later. As it stands right now, the box will have a total internal volume of just about exactly 6 cubic feet not counting sub displacement, the hatch latch mechanism or loss of volume to the slot port(s). I can squeeze about another cubic foot into the box with more tweaking. This looks pretty easy to fit one 12" in, but a pair is looking a bit more difficult. I'm modeling it right now in various scenarios. Most everything I've seen so far has a peak around 50Hz which I believe is going to make things even more difficult as I believe that is the peak of the transfer for the thirdgen...

1meanGTA

3 cubic ft per sub is plenty for a ported box with almost any woofer. thing is, where are you gonna put the port? this is where i ran into problems. getting enough volume is the easy part.

Jim85IROC

iTrader: (2)

There are a few places you can fit the ports. If you spread the woofers out, you can fit the ports right between the woofers. In the one I built, I put the ports horizontal, firing out the front of the box toward the back seats. That box pounded like hell.

PhLaXuS

OK...in the aftermath of dat sucky Wilma, I still don't have power @ home (over a week now), but I do at the office so here goes. I took some measurements during daylight and here's what I came up with. Thing is, my rear well carpet is a little screwed up and I would get different measurements when they should have been the same, so if anyone can corroborate my numbers, that would be good. If not, just shrink all sides by 1/2" & there shouldn't be any problems. Now...here's the first box design. Note that I have never designed a slot-ported box, so it would be good for someone to check my logic here. I tried to go for 35 square inches or port showing for each chamber. It's gonna be hard to fit the square subs in with the hatch latch figured in, but rounds should fit without a problem. I do have questions on the left and right chambers...as they have different volumes, will this be a bit strange? I can shrink down the left chamber to match the right if need be. Another question on the slot-ports: I figured the port length as a function of volume (i.e.: the design calls for ports 8.875" x 4" x 32.5". This equals 1153.75 cubic inches. Is this the proper way to figure out the port length?). I tried to design this enclosure so that the rear well cloth cover will hide it, but if you wanted to, you could extend the ports even more utilizing the current design.

I modeled a pair of Brahma 12's and the curve did look better. They peaked ~10Hz lower than the L7's which compliments the F-body very well...

I'd like this to be an "open-source" type enclosure for our vehicles so anyone who wants, plase contribute.

9177

Here is a good page on how to figure for ports http://mobile.jlaudio.com/support_pages.php?page_id=165

and for your ports you also need to account for the material used to make the port not just the inside of the port so the ports are taking up more room than you have listed. This is the problem i have ran into. You need to snake the port around so much it becomes very difficult. The only way you can make the port shorter is to make the surface area smaller. Makeing the surface area smaller speeds up the air velocity in the port and when you have a sub that displaces alot of air such as you have you wind up with basically a sub box with a hole in it that makes tons of noise. also a lower tuning usually around 30-35 htz has a better sound than higher tuned boxes. the musically information that is below the tuning will not be heard very well and will cause the sub to unload or it would be like it was being played without a box.

PhLaXuS

I printed the article to read at home. It would be pretty easy to modify the design to make 4" x 3.9375" (if I did that math correctly-I've been sick for days) ports which would be about twice the length. The only reason I went for such a large section area is I read on here that that sounds better.

9177

The only problem with the port area you have changed to is it may add port noise. with those subs you would be best off imo using at least 20" sq of port per sub. If you very rarley listen to you subs at full power you can run a smaller port but his will also decrease the total output. Think of the port as being like another speaker, the larger it is the more output its capable of. But the more surface area there is the more port length is required to reach the desired tuning.

1meanGTA

i'd like to know jim and 9177's opinions on which would sound the best, and be the loudest, forward or upward firing ports? seeing that this is doable, im probably going to build a new box for my rl-p's, they hammer, but im getting used to it. can't really afford to buy the 15's like i was planning on right now, new box would be perfect

9177

Without the use of a meter I doubt the sound output would even be noticable. SQ probably wouldn't change much either since you can't get the port far enough away from the subs to cause problems. But if for any reason the ports would make noise it would be less noticable if they were in back father away from your ears.

1meanGTA

by the way, nice work on those plans, a person on this board (who i'll leave nameless ) and i discussed a ported box but decided that it would be more trouble than it was worth and that there wasnt enough room for properly sized ports. i've never built a ported box before, just a few sealed ones. the one i built for the well turned out awesome though, i'll get some pictures this weekend of it out of the car, it fits so tight its a real pain to take out.

9177

I still think for you RL-Ps won't fit. the amount of air those move (way more than the punch subs jim talked about in another post) they will need big ports. I think the pair will need as a minumum of 30" sq but would better off with 40" sq. At any rate good luck and post any pics.

PhLaXuS

OK...after reading the JL Port Design guide, it's obvious that I was going the wrong way in figuring the port length. Here's a better one:

PhLaXuS

And here's another that I was working on. It looked as though it was coming out pretty well, but I initially forgot to divide the chamber volume by 2 and after I did this, it turned out to be ported really high. This is probably a really bad design, but I'm placing it up here in case anyone has ideas for it...

PhLaXuS

I did just do the quick math for something running through my head just now and I could make a single 4" x 5.83" port per chamber and cram in about 58.81" of length for each sub. This would leave 23.32 square inches of port showing per chamber and would drop the tuning to ~22Hz. Sveet!

EDIT: If I shrink down the left chamber to the size of the right chamber, the total enclosure will lose ~0.22 cubic feet of volume which will raise the frequency to 23.44Hz. I'll redesign it tonight & post the new plans here.

Gummie

First off, great work. This is my first time reading through the thread and you defiantly have a lot of effort invested before you've even started construction.

I've got two comments:

- You mentioned earlier that the two chambers have different volumes because you’re running the divider in the physical middle of the box. If you move the divider over an inch or two you can even it out. There are two methods for finding the right spot: do the math or do the fireturd350 method. First build the shell of the box then fill it with half it's volume of packing peanuts and then move the divider wall around until one chamber is full.

- I realize that this is going to throw off your math, but you don't have to use a divider wall at all. This solves the problem of unequal volumes and opens up more room to route the port now that you don’t have to worry about the wall in the middle of the box.

Hopefully Jim will check up on this thread and offer some insight because he’s an accomplished box builder.

Jim85IROC

iTrader: (2)

When you build sealed boxes, having one volume be a bit off from the other isn't a big deal... you're talking about very minor differences as long as the volume difference is minor.

With ported enclosures, it effects the tuning frequency, which can have a significant impact on the sound. If you can't get them 100% equal, don't use a divider... just use a couple braces in it's place.

9177

Only problems I see are one that’s to low of a tune for the subs your using. The FS is around 31-32 htz and that’s is the usable frequency of the driver. Anything lower than that really isn't necessary as the driver probably won’t be able to do much with it.
In past experiences for me a port that has that severe of a bend at the opening will make port noise. It makes it a lot like a whistle. You should try to have the port opening walls at least as long as the widest side of you port. In this case 4” long.

PhLaXuS

OK...Here's the new design. I'm to a point now where I need either more design info or peer review. As far the Fs of the L7's, this design was based around those subs, but I was going more for a standardized box which would only require a small amount of tweaking to make work with the three or four drivers most people prefer on this forum. I can always shorten the port length by blocking out the end of the port with scrap MDF or cutting the extreme left & right side walls at an angle (maybe 60*?). I've not mentioned it yet, but all designs assume 1" MDF and for the port ducts, I was thinking about radiusing all corners with either a belt sander or wood putty (or equivalent).

Also, I hadn't thought of that final sharp bend heading up. I could make the ports exit directly forward and this shouldn't affect the length by much more than 0.58", but in order for this to work, the rear seats would have to be down for the ports to "breathe".

One question, though: When I was figuring the port length, I did not take into account any "correction" required at the start of the port. Should I add 2.789062" to the port length to correct for the fact that the divider is one wall of the port?

So...anyone have more input here or is it ready to finalize & CAD?

PhLaXuS

And here's what the S12L74's look like modeled in this design vs. the sealed box I have now. The sealed has two 0.88 ft³ chambers.

EDIT: Huh...I looked back at this and saw the resolution was total crap. I'm getting my internet access via a cell modem I nabbed from work and the Sprint servers run a tight compression on everything...

Jim85IROC

iTrader: (2)

Man, this sub's Qts is so ungodly high (presumably due to a total lack of motor control) that it's impossible to get a good curve in a reasonable box.

The only decent flat curve I could get requres 12 friggin cubic feet per sub tuned to 20hz. Go Kicker.

Anything smaller just gives you a huge bump at 50hz.

I'm not sure I'd even waste my time building a ported box for this thing.

It looks really good in a 3 cube sealed box though. It's got the same F3 as your ported design without the massive 50hz bump, plus it's got stronger output below F3. All around, a MUCH better sounding configuration.

If you just want boom, do 3 cubes ported tuned to 40hz. It'll shake your fillings loose, but all you're going to get is 50hz output.

mrray13

have u figured in port displacment with this math? if ur still getting 3.74ft^3 net after the ports, great. otherwise, u're going to lose apx .75ft^3 per side with those ports.

my suggestion? tune higher, in the 32-34hz range. the car's natural transient response is going to re-enforce the low end anyway. i'd also suggest using a 4" aeroport per sub, instead of slots. less port displacement as well as less need for port area.

i'd also suggest doing a common chamber design, and if u can find it, a shared 6" aeroport. use a simple brace in the middle to help with sub support and flexing.




wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

PhLaXuS

The box is something around 5 cubic feet sealed. Due to the long walls, bracing is required anyway so I decided why not partition it off into two chambers while I'm at it? The 3.74 cube calculation is just for the sub chambers -- this does not include port volume. I'm still open to ideas here as well. Nothing is set in stone.

Also, I tried modeling an XXX12, but when I keyed in the ts parameters --

http://www.reaudio.com/html/xxx_ts.htm

into WinISD, it kicked it back with an error. I didn't have the time to figure it out, but I'd like to know how this box would do with the following subs (assuming two per box):

13W7
XXX12
Brahma 12

I've seen preliminary data on soem of these and it looks a bit easier to work with...

PhLaXuS

I just want to get a final OK from anyone involved: does this look as though it would be a good generalized design for a ported well enclosure? I know there's more to it than this, but as it stands now, can it go to CAD or are there any more suggestions?

1meanGTA

hmm. is there any way to make it taller? you could also squeeze another half ft^3 or so by having the box wrap around the well motor piece, the way jim's and my box are. mine is basically to the max, i dont think any dimension could be any bigger other than making it taller. i'll pull it out tomorrow and take some measurements for you. i would just do the same outer dimensions as mine, just make it taller.