Okay.. So last time I tried to design a box myself, a got the dimensions a bit wrong, there was a few things I wanted to make a bit different. Here are all the specifications Iv came up with and hopefully they are right this time.

Box Net Volume

6.75 cubic feet

Port Area

126 inches²

Port Tuning

30hz

Port Internal Dimensions

9” x 14” x 46.63”

Port Displacement (8.25” of the port will be external)(33.38” Internal Port)

9.75” x 15.5” x 14.25” (Part A of "L" Port)

=1.24625651 cubic feet

9.75” x 15.5” x 18.38” (Part B of "L" Port)

= 1.60745226 cubic feet

1.24625651 + 1.60745226

= 2.854 cubic feet + 0.18 cubic feet (Subwoofer Displacement)

= 3.034 cubic feet (Total Displacement)

Box Dimensions Needed (9.78 cubic feet)

36.75 x 15 x 37 = 9.776 cubic feet before displacement

9.776 – 3.034

= 6.742 cubic feet net

So Im off by 0.008 cubic feet.. Dont think thats a problem though. Hopefully I have it right this time. And if it is right, Im done changing my mind about this box, i must have calculated about 6 different boxes for this setup and Im sticking with this one.

Heres a picture of the design, roughly

Edited December 18, 201113 yr by MikeMartel

are you not happy with the one you have?

At the moment no, Its much smaller. 5.5 cubes if im lucky, port is pointing sideways and it was a bit leaky. It was the first box iv ever built. But i think a box thats a bit bigger with more port area will be more optimal. Along with that, ill be porting my box through the rear deck and sealing it from the trunk so i can get some more air flow throughout my cabin.

At the moment no, Its much smaller. 5.5 cubes if im lucky, port is pointing sideways and it was a bit leaky. It was the first box iv ever built. But i think a box thats a bit bigger with more port area will be more optimal. Along with that, ill be porting my box through the rear deck and sealing it from the trunk so i can get some more air flow throughout my cabin.

interesting, i have wondered the direct difference in SPL & sound between sealing the port off into the cabin VS. leaving it open to breath along with the sub & trunk pressure,

ill been tuned it.

Main reason im doing this is because of my lack of folding seats. Porting it into the cabin simply should increase SPL and how well it sounds. If you do have experience with box building id like to know if what iv calculated is right.. Im still not 100% if i even designed it correctly.

true it should, but my statment was more or less about sealing around the port and cutting off the trunk and subs off from the car, leaving only the port into the cabin.

im sorry im not a box builder of designer i wish i were.

Alright, thanks for being tuned in. Im excited for it aswell.

Main reason im doing this is because of my lack of folding seats. Porting it into the cabin simply should increase SPL and how well it sounds. If you do have experience with box building id like to know if what iv calculated is right.. Im still not 100% if i even designed it correctly.

The backseats in the Impala don't fold down?

At the moment no, Its much smaller. 5.5 cubes if im lucky, port is pointing sideways and it was a bit leaky. It was the first box iv ever built. But i think a box thats a bit bigger with more port area will be more optimal. Along with that, ill be porting my box through the rear deck and sealing it from the trunk so i can get some more air flow throughout my cabin.

So you are sealing the port opening from the trunk, what about the sub? Is the sub firing into cabin sealed off as well? In a fourth order enclosure (regular ported) the port and sub work together. They both need to be directed to the listening environment. Sealing off the trunk with the sub firing in the trunk wouldn't work well. If the sub and port are firing into the cabin then the trunk should definitely be sealed off.

I have had two different setups in my sedan. The first was a fourth order sealed from the trunk. Sub and port were facing my rear seats. It was a pain in the ass to have to fold down the seats all the time. My second setup, which is my current install, is another fourth order with the sub and port facing the back bumper. I went this route so I didnt have to fold my back seat down all the time, along with other reasons. The biggest improvement that I did to improve overall SPL was to open up the rear deck. I currently have a 12"x4" slot cut in the metal rear deck panel. The rear deck cover covers it all up. I didnt want to cut away too much a possibly affect vehicle integrity. Next year I am going to frame out the metal rear deck and open it up even more. You have to be careful not to remove too much without bracing it first. By doing this you are "kinda" turning a trunk car to a hatchback. There was a huge difference in SPL output by "venting" the rear deck. Also, the sub bass seamed to sound behind me now it sounds in front of me. I would think that this would affect resale value of the vehicle but I have no concern with that.

true it should, but my statment was more or less about sealing around the port and cutting off the trunk and subs off from the car, leaving only the port into the cabin.

im sorry im not a box builder of designer i wish i were.

^^this

I tried something very similar in my kia amanti years ago. I got alot of cancellation with this setup. a bandpass enclosure would yeild better results. IMO

that was my point.

my friend had a 2002 devile, he had 2 JL W7 12's in a box the subs faced the back seat and it had an 8 inch port that make an L thru the rear deck, and it was sealed off from the trunk...

it sounded like dog shit to me. and it moved no air unless the trunk was open. was the strangest thing.. .

i offten wondered if it would sound better if the port was not sealed off into the rear deck.

Well, This is what Iv decided to do, I'll try porting it through the rear deck and try it out for a week or two and maybe THEN I'll try sealing it off and see if it sounds any better or worse

that was my point.

my friend had a 2002 devile, he had 2 JL W7 12's in a box the subs faced the back seat and it had an 8 inch port that make an L thru the rear deck, and it was sealed off from the trunk...

it sounded like dog shit to me. and it moved no air unless the trunk was open. was the strangest thing.. .

i offten wondered if it would sound better if the port was not sealed off into the rear deck.

That's the same thing that happened in my Kia. When trunk was open it sounded great, when the trunk was closed it made the sound unbearable/ muffled/ no pressure what so ever. I ended up just sealing the box, and cutting a big hole in the rear deck lid.

Well you see that was the whole idea, lots of people say they gained SPL from cutting a hole in the rear deck lid, so i was thinking heck, i might as well just stick the port right there. . Hopefully it works well, if not, ill build a different box.

Its not gonna work dude, just try it the way it should be from start instead of waiting time on building boxes. You cant create new laws of science, cancellation is gonna happen unless both subs and port are firing through the rear deck (simple as that). Now you can cut a hole in your rear deck like edouble101 stated above to allow more pressure in the cabin, thats what I would do now and see where that gets you till you make a better design.

I dont understand why you ask us for our input on a design then when everybody is telling you otherwise you still want to do it your way. Personally since your seats dont fold down I would recone my 18" to a 15'' subwoofer, throw the sub in a 4th order bandpass enclosure that is ported through the rear deck.

Ok, so if I simply dont seal off the port then it shouldnt have cancellation? My rear deck isnt a solid piece of sheet metal to begin with, there are already some pieces cut out of it for more ventilation into the trunk space from factory, so this design isnt really much different than any other box design? Im only raising the port out of my box a couple inches. I understand the theory that cancellation would occur if the port and subwoofer are sealed in different compartments but they wont be.

Also. Why would a 4th order ported through the rear deck work but my design wont?

Edited December 19, 201113 yr by MikeMartel

Ok, so if I simply dont seal off the port then it shouldnt have cancellation? My rear deck isnt a solid piece of sheet metal to begin with, there are already some pieces cut out of it for more ventilation into the trunk space from factory, so this design isnt really much different than any other box design? Im only raising the port out of my box a couple inches. I understand the theory that cancellation would occur if the port and subwoofer are sealed in different compartments but they wont be.

Also. Why would a 4th order ported through the rear deck work but my design wont?

4th order BANDPASS

It will work because all of the air is moved through the port, the woofer is sealed inside the box.

Alright guys, Looks like ill be designing something new again, port through the rear deck isnt going to work according to basically everything iv read and that people have told me. No room for a bandpass enclosure and the BTL doesnt work so well in one anyways. Back to the drawing board.

Edited December 20, 201113 yr by MikeMartel

I think they are saying porting it through the rear deck and leaving the sub in the trunk will still cause some cancellation.

Yeah, back to the drawing board for me. Ill figure it out, ill just cut out a big slot in the rear deck, i saw a post that edouble posted yesterday talking about it. Ill try designing a new box with sub up port back and go from there.

Alright here, iv been looking stuff up and i dont understand whats going on here. IF i were to put my port through my rear deck, along with my two empty 6x9 holes and were to seal off the whole box from the trunk, shouldnt that have the exact same effect of sub foward port foward and sealing it from the trunk? Mine is just going to be sub up, port up. I really dont understand the problem. My rear deck is already fairly open, its not a solid piece of metal and wood so it should also be able to allow airflow from the subwoofer itself.

If this still wouldnt work could someone please explain why sub forward port forward would work, but sub up port up wont?