Removed backseats for 2 18s. I have a design would like help

[HelloImBob 10+ year member]

Ok so I finally decided to work on my project car 91 nissan maxima.

I took the back seat out and cut out the bottom of the box to start laying things out but Ive never worked with 18's as for optimal box size. I hate to say on the last 4-5 boxes I have built I was lazy and and just used the RE box calc for a good enough calculation but Id like to figure this one out right.

I would like to stay below the back window line or just barely at the bottom of the window so I can still see out my back window (for safety) I dont trust mirrors and Im not sure how well I will be able to use the side windows to see if there is a wall there.



I plan on using 2 05 XXX 18"s

I wanted to face subs forward/port forward for looks but Ive heard everybody wants to upfire and port up since I have more than a ft of space above the box to the top of the car

RE calc shows about 12.5 - 13cu ft after 8" worth of port @ 180sq in of port area. not including the displacement of subs and whatever extra bracing I will add to the box, Ive heard 18"s like around 7cubes each? I seem a little on the small side. also I need those slants on the back of the box to get it 26" deep so I figured they would work perfect as ports

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[Kangaroux 5,000+ posts]

RE calc is inaccurate //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif

 

[HelloImBob 10+ year member]

I know this, I made mention that I was lazy and used it for my older boxes for a ballpark range.

I am going to work on it today and figure out all the sq in and convet to cu ft or whatever. Ive looked up the equations and Im going to do the math today. I was just looking for some advice from somebody more experienced than I at building boxes. I didnt want to get too far into my build and have to restart.

 

[sxpimpin 10+ year member]

Yeah RE calculator is way off. A local shop used that around here, and built a box for a guy I know. Box was supposed to be 13 cuft with tuned to 27hz hz.. Unfortunately they had almost 300 inches of port. I did some quick math and the box was only 8 cuft internal for 2 18's... tuned to 46hz

 

[bhsdriller 10+ year member]

nice subs

 

[HelloImBob 10+ year member]

Yeah RE calculator is way off. A local shop used that around here, and built a box for a guy I know. Box was supposed to be 13 cuft with tuned to 27hz hz.. Unfortunately they had almost 300 inches of port. I did some quick math and the box was only 8 cuft internal for 2 18's... tuned to 46hz

hmmm that could be a problem then, Im going to have to do some math in that case. I knew the calc was off but I figured it would be within a cu ft or 2. I read the sticky about box building and the math that goes along with it. After I figure out the numbers Ill post more useful information.

EDIT:: ok so I came up with 10.9 cubes internal after double baffle and port displacement but that is still without driver displacement. Its starting to look like I will have to wall it to get enough room for 2 18s.

looks like Im going to have about 6 cubes for each 18 after all displacements if I wall it and take the box to 28" high. I was shooting for more like 7 cubes each. will I be alright with 6?

Might have to redesign the port now too and just do 1 big port, if I wall it and take it to 28" high with 2 4" ports on each side it would give me roughly 215" of port area. Time for more reading I cant remember the general guide to port area compared to box size

 

[sxpimpin 10+ year member]

I usually try to do 12-15" of port per cube. Those subs aren't spl monsters buy get really low and move alot of air. I would cut the port area down to 160" and tune in the low 30's. Cutting the port down will gain you a little bit of space too

 

[Buck 5,000+ posts]

Hit me up. I like that you took your back seats out for 18"s, so did I in my Explorer.

 

[HelloImBob 10+ year member]

Finally an update on progress!

All pieces have been cut out and all angles have been cut so boards fit together properly...wow what a task mitering those sides was.

Box is almost ready to be put together but I need a port design and I have not cut any holes in the front baffle yet for that reason. I have included a picture that I hope describes everything needed. Obviously its going to be subs forward port forward wall sitting where the backseat used to be.

Because this is a wall with 2 RE XXX18s I wanted to tune low like 26-28hz. Not looking to go higher than 28hz tuning...



FYI for anyone looking for quick updates and pictures will have to wait as I am only working on this for an hour or so here and there after work and will probably only post pictures once box is totally assembled. My goal is to have everything in place in a month or so but I wont be bummed if it takes a couple more weeks extra as long as I finish it right.

Still havnt decided on if Im going to fiberglass the inside or not. Open to opinions on if its worth it.

EDIT:: forgot to add Im happy to paypal some money to somebody like buck for a good port design and possible extra bracing where it might be needed. Not shy to spend 10-15$ for a good design closest to specs of subs with the box given. Once its in place I dont think its coming back out without getting destroyed.