KU40

Well if the box can only be those dimensions regardless, then I still don't understand why the sub has to be up. If you can't fit a larger box in there because of the opening (which I agree with, that was my problem as well), it doesn't matter if the sub is up or back. Unless making the box shorter (which you could in a sub up situation) would allow you to make it deeper and give more overall box volume? But still, like I said, with those dimensions you get about 4.2-4.3 cubes gross. That's enough to fit a ported 15. A couple aeroports would eat up less volume than a slot port, and some 15s will work ported in as low as 3 cubes.

how can it stay the same if you're adding .25" onto the front baffle? The front baffle is still part of the port. His L1 would increase to 17.5" (since earlier I posted how his L1 must include the front baffle) and his L2 would decrease to 4.75" to keep the overall length the same 26.75" that I figured out earlier. So I guess yes, it would stay the same, but he'd have to realize how it will affect the port board lengths.

Really it's just about port area. You just make it as wide as you need to get the port area you want. With normal slot ported boxes, the port runs the entire height of the enclosure, so to get the port area you want you just adjust the width. If you have a 15" inside height enclosure and want 30 sq. inches of port, make it 2" wide. If you want 60 sq. inches, make it 4" wide. As long as you keep the ratio of height to width below 1:9, you're fine. As for how much port area you need, that depends on the setup. WinISD has a port velocity calculator. I believe it wants you to keep it below .14 m/s on the beta version (not sure exactly, it's been probably 5 years since I've used beta). The alpha version just has a graph that it shows you, covering the port velocity over all the frequencies. But .14 m/s still applies. Alpha is better in that you can see right away what the velocity will be at any frequency. If your ported box is tuned to 35 hz and you have a subsonic filter at 30 hz, the port velocity at, say, 20 hz doesn't really matter. And remember that usually port velocity goes up as frequency goes down. So while you may get .2 m/s of velocity at 20 hz and it seems too high, your port still may be fine if you only have .1 m/s at 30 hz, since that's closer to where you'll actually be playing. Generally 12" subs need at least 15-20 sq. inches and 15" subs need at least 35-40 sq. inches or so, with your generic slot port. At least from my limited experiences. Aero ports cut down the needed area quite a bit. A single 4" port (~12 sq. inches) for a 12 and a single 6" port (~28 sq. inches) for a 15" work fine.

In the US you get a learner's permit at 15 and you can drive to school and work. You can even get a farm permit at 14. I did.

wouldn't having 8 ga. wire directly to the coils affect the mms of the sub? The 8 gauge would be heavier than normal leads, and the sub would have to move it around with the cone.

I imagine you'll be covering it with that false floor and carpet? If so, you will need ventilation. Try putting two fans down there, one on each end of the amps, with one pushing air into the tire well and the other pulling the air out and pushing it into the trunk.

The car I had my 15 in was a W-body, just like the grand prix. I had an olds cutlass supreme. Granted his is newer so there may be some differences. If you have 16" of height, that's enough for a 15. My box was maxed out for the size of my trunk, too, and it was 3.8 cubes net tuned to 30 hz. I also faced it forwards. I tried it both forwards and back and it seemed about the same loudness, so I put it forward for easier access to my amps (mounted on back of the box). I would argue that if you face the subs forward and seal off the trunk behind the front baffle, it could/would be louder than facing them backwards. Wouldn't have to worry about the box trapping the sound in then. Seems like we've been arguing like an old married couple lately

I think 3/4" birch plywood is 13 ply. My Home Depot didn't have it, but the hometown lumber yard did (score one for the mom and pop shop!).

True is wont affect much but I like to be exact on calculating boxes. Well then we should discuss him using 1" on the front baffle, because apparently whoever designed the port didn't take that into account. The L1 length will be .25" off, and his L2 port won't be the right width. But really it just means his L1 length will be 17.5" instead of 17.25. No biggie.

beware of the sub's surround hitting the back of the seat when it's playing. don't forget to take that into account.

You can get void-free plywood (it's actually graded that way). It can be hard to find, though.

it's not really calculated. Nobody says "Oh, I know I'm going to gain 3.5 db at 32 hz and 2.4 db at 39 hz from cabin gain, so this box is ok like this......" I mean you could measure your box's frequency response curve outside of the vehicle in an environment that won't affect the SPL readings, then put it inside the vehicle and do the same thing and compare the two graphs. But I've never seen anybody actually do that. Normally it's just used as a generalization, and usually with sealed boxes. People get worried when they see that most sealed boxes have an F3 of 40 hz or so, but cabin gain usually increases the 30-40 hz zone so that the sealed box is fairly level from 30-80 hz or whatever. You'll have to divulge more on what you mean by "optimize." That could mean a flat response curve to one person, maximum SPL to another person........ In the end, you'll never be able to construct a box that will even out every peak and valley that your vehicle introduces to the response. You'll have to EQ it if you want to do that.

I assumed the 5" started from where the wood starts going that direction, just like the L1 length included the front baffle thickness. Not board cutout lengths. I guess that's something the OP would have to tell us. Either way, it's only .75 inch. Not going to affect a thing.

PE

you may as well go with the BTL. I fit a 15" sub in my trunk in the sub back, port back configuration, so it can be done. There are no guarantees that it will be louder than your Type Rs.

It'll work

It'll work. Just be easy with the amp.

Look sorta like older Cadences, but can't really tell.

One of your biggest challenges will be fitting the box through the opening to the trunk. Build a test box out of cardboard or something first to check it out. Unless you want to build the whole box in the trunk.

I just used Birch Plywood on my latest box. Excellent stuff. I'll never use MDF again as long as I can find it.

That was going to be my next question as well.

I didn't forget the .75. He mentions his first port length being 17.25" long. Well, if his box is 22.5" deep externally, that leaves only 21" internally. since his port is 4.5" wide, the first port board would have to be 4.5" from the back wall. Add 17.25 + 4.5 + the .75" for the back wall, and you get 22.5". Therefore, his L1 includes the front baffle. Then 17.25 for the first leg + 4.5" for the corner from measuring down the center, plus 5" for the second leg = 26.75". I didn't take end correction into account, I never think about it.

If those are external dimensions I get 5.25 cubes gross. Port displaces about 1 cube, let's say .3 cubes for the drivers. That leaves you with 3.95 cubes net. A port 12.5" tall, 4.5" wide and 26.75" long gives a tune of about 34 hz. You'll want to add about 6" onto the port to make it close to 32 hz. At least that's why winISD alpha is telling me.

I fell asleep at 9:00 last night, so consequently I woke up 8 hours later, at 5:15, this morning. On a sunday. Boy I'm a lamo I guess. I was going to do some early morning Christmas shopping.

Niiiiiiiiice