need experienced help, math involved, building a perfect box

[cebbeler7 10+ year member]

I have done my fair share of building sealed enclosures. I've always done sealed, because I've wanted sound quality more than boom boom. I'm MECP certified so I'm not necessarily an idiot, but they never exactly explained to me how to make a perfect ported box. On some subs you can get away with it by making a crappy one and it still booms, but I think this is going to be more of a challenge on getting all the lows I need to pump out of this. I attempted to build one box slot ported but my sub wouldn't hit the lows I know it can hit so this is where I need some advice. I am using 2 arc audio d2 flatlines. Here is the spec of the flatline if you don't know. Arc Audio . It's one of the only 12 in subs I know that can hit as low as a 15. I'm using an arc audio ks1000.1bx amplifier that has a bass generator and I have a line driver to boost the voltage up to 10 V, plus a power cell. I know I have enough power for these subs and I'm running the speaker wire parallel so that it's bridged down to 2 Ohms. So power is good, impedance is good, voltage is good.... now time for the box. A flatline requires about 2.5 cu feet ported. My box will be about 5 cu feet since I have two flatlines. ok simple math there. It will be 39 inches in length. 16 inches in height. 14 inches in width. So thats about 5 cubic feet right there. So plenty of air space. Now comes the issues I've been stressing over. How long do they ports need to be?? I was thinking about putting two slot 'L' ports on the ends of the box. Or the option of making just a big slot port in the middle. I need help on the port size and possibly shape. Someone please help, this has been driving me crazy.

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[RAM_Designs 5,000+ posts]

1) 39"x16"x14"(I'm assuming these are external measurements) gives you 3.93ft^3 before any displacements.

2) the 5ft^3 for the subs needs to be after all displacements(ie: bracing, subs, and port), so you'll need roughly 6.5ft^3 total, depending on your port size.

3) you just need to plug and chug with different box dimensions and port sizes to get everything to kinda come together with the right tuning/box size.

 

[cebbeler7 10+ year member]

im sorry, I messed up on the width. The width is 15 inches wide.

So thats length 39in (3.25 ft) X height 16in (1.33 ft) X width 15 in (1.25 ft) = 5.40 cubic feet. And yes that is external measurements, i'm using 3/4" mdf wood. So thats plenty for the subs (the subs have a minimum of 1.8 cubic feet I just wanted extra space and they have tested 2.5 cubic feet works best). I just need to know how to make the port(s).

 

[spltuscon 10+ year member]

Well that's only 4.25ft3 gross volume so if you go with a slot port design you end up with a 2.75" x14.5" port thats 25.7" long (32hz) and 3.26ft3 of net box volume. That's after you subtract the .24 (.12 each) sub displacement and the .75ft of the port. That's as good as you can get with a slot port and staying with enough port area (I would want more actually but sometimes you have to compromise to fit it).

 

[cebbeler7 10+ year member]

ok that makes sense. So should i make 1 port on the left or right side of the box and make it 25.7 inch long? This is what I have in my head and hard to draw on the computer. Ignore the periods, they are the only way i can create 'space'

(box facing us)

39 in length

___________________

|..|......___....___......|

|..|.....(sub)..(sub)....| 16 in height

|_|________________|

^

port

so thats what I have in my head. Usually ports are 2 inches wide so does it still need to go back 25.7 inches?

if so then the top side of the box would be:

(top)

39 in length

__________________

|...________...........|

|..|.......................| 15 in width

|..|.......................|

|..|______________|

........(sub)..(sub)

Sorry if thats hard to see but the L shaped port would be 2 inches wide and go back 25.7 feet. The slab of wood going back for the port would be 11.5 in and the slab making the rest of the port continuing the 'L' shape would be 15.25 in. So counting the 3/4 in (.75) wood of the front of the box plus 11.5 inches back

plus 15.25 in equals 25.7 in. So would this be right or am I out of my mind

 

[SpeedEuphoria 10+ year member]

try this calculator to get a good idea for slot port

RE Enclosure Calculator

just remember that you want 12-16in^2 for port area per cubic foot

 

[Wildbillpb 10+ year member]

the part where the port makes an L needs to be 6.5" so its 11.5" to the back then run 6.5" off of that for it to be tuned to 32 hz making the L part 15.25" would make it tuned to 28.8 hz and the port length would be 31.625"

 

[cebbeler7 10+ year member]

ok it all makes sense, holy crap that calculator is a life saver.

So port width of 2.75 gives me 11.5 back and 6.5 across tunes to 32.09 hz. Perfect, thank you so much guys.