2 DC Audio Lvl 5 15" shared chamber enclosure assistance

[the_garynator]

If you don't feel like reading the novel I wrote, here's the main things I'm wondering:

- Do I sacrifice after displacement volume for rear firing ports with more port area (i.e. 2x 8") vs larger box with less port area (i.e. 5x 4")

- If I run rear firing ports do I sacrifice internal volume for more room between the top back of the box and the rear window?

- for size of dual sub shared chamber box, is 1.5x the recommended a good rule? if so, does this apply to port area?

Having a tough time deciding on what compromises to make in the design. Let me start by staying that I'm no n00b, I'm not saying I know everything (if I did I wouldn't be posting this). Car audio has been a side hobby of mine off and on for a lot of years. (I remember the days before the termlab, Earthquake 40uhcs, VLX-25s, etc.)

Currently I have a single 15" lvl 5 with an audiopipe 3k. Clamped it is putting out 3011 at a little over 2ohms with box rise (sub has 2 dead voice coils out of 4 so it's wired in parallel at 1ohm). I did 151.0 @43hz at the dash with the driver's door open on my termlab, hit a 150.6 or something at the last competition after the sub sat in the sun all day and my voltage was low. Current box is a hair over 4cubes including displacement with 3x external 4" precision ports (woofer up, ports back). Box is still a little large but it doesn't matter now that i have picked up a second level 5 15" (hence the thread).

Here's my dilema, I have a rather limited amount of space and a whole lot of crap to cram in. My audio car is a 1990 240sx fastback (hatchback). I'd like to keep the box as far back as possible (right now it is inline with the front of the rear strut towers) as I have all of my amps and 8x 8" woofers where the rear seat normally is. I figure the most space forward of the strut towers I would give up is 5". I am having a hard time deciding on what compromises I am going to make to get the most out of the subs in this space.

I've spent 2 days designing 8 million different boxes and can't decide on which compromises to make. I'm hoping someone with some more experience can give me some suggestions (IE, do I sacrifice internal volume for distance from back of box to back of car so the sound from behind the box has room to come forward; etc.). I am fairly familiar with advantages/disadvantages of different design aspects, but I only recently got a termlab but unfortunately I do not have time to test 8 different boxes especially with the size that's going to be required. I have no problem making some changes, etc, but I really would like to have a good start that I won't have to completely redesign.

Here are my main constraints:

distance between rear strut towers: 32" ext

distance from front of rear strut tower to rear of trunk area is roughly 37"

Height is restricted to 17" ext at farthest point back on glass (21" from the front of the rear strut towers)

- from that point back height is restricted to something like 13"

width of opening of hatch is somewhere around 36"

I'll get better dimensions added later tonight or tomorrow.

As far as what I'm going for, my current setup can probably give you and idea. When i initially built it i had it 4.5ft3 after displacement, tuned to 33hz. since I went to 4 cubes (actually meant to go for 3.75 but made a mistake and haven't had time to fix it) and a tuning frequency of 43hz (cars resonant frequency) I gained 2-3db at 43hz, 4db at 50hz and only lost .2db at 30hz. I like to demo the system, etc. so it's sort of an sq/spl system.

oh and for power, initially i'm going to be running just the single 3k, but over the winter i'm planning on upgrading my alternators (currently 125amp and an 80amp) and replacing the 3k with 4x apsm 1500d's 2x strapped per sub.

let me know if there is any information needed that I missed.

Thanks,

Gary

[the_garynator]

here's recent pictures of my current setup:

[ChevyBoy95]

so your goal is numbers correct? if so ill stay out of this one.

[the_garynator]

I'm going for well rounded. if numbers were the only thing that mattered i'd do front firing, 2x external rear firing 8" ports and say 5.5 cubes. here's what i'm hoping for:

hair tricks (i've gotten close on 1 15" so 2 should do it)

LOUD for demos (i'm willing to sacrifice some at the dash for at the head rest, but that's more of a fine tuning thing afaik)

LOW (from what I've found in the car, due to the resonant frequency being 43hz, tuning super low doesn't make the lows much louder than tuning at 33hz, plus I am space limited so I'm thinking 43hz is a good compromize)

Can bang music cranked for at least a couple minutes at a time without overheating (not necissarily at full tilt but close, maybe 2500wrms each sub) I don't expect them to take 3k+ each for a whole song lol.

but yes, i'm a bit more focused on loud than all out sq, but it needs to sound decent at lower volumes. For example, I'm very happy with my current setup as far as the compromise between the two.

[ChevyBoy95]

well if it was music based, i would do 5.75-6.5 cubes for 2, with either 2 6in aeros or 2 8in aeros depending on what you like as far as port area. My 2 XLs in a little over 6 with 2 6in 17in long aeros, can play 24-70 pretty damn well with some peaks (to ear) at 28-35hz. I can still bass out dubstep, c&s, jazz, electro, etc. and i dont get port noise at all during full extension. but i havent metered it so it no clue on that.

[the_garynator]

well if it was music based, i would do 5.75-6.5 cubes for 2, with either 2 6in aeros or 2 8in aeros depending on what you like as far as port area. My 2 XLs in a little over 6 with 2 6in 17in long aeros, can play 24-70 pretty damn well with some peaks (to ear) at 28-35hz. I can still bass out dubstep, c&s, jazz, electro, etc. and i dont get port noise at all during full extension. but i havent metered it so it no clue on that.

That's do-able, kinda what I was thinking, but my issue is how. Do I run less port area and up fire them or do I run them rear firing and risk choking the ports because the box is too close to the back of the hatch window? or would being close on the rear top of the box be ok as long as there was room down the sides for the sound to come forward? would have to run less port area up firing to keep ports from being too long, for 4" ports I have a max length of 12" including flare to keep the inside flare far enough away from the bottom of the box.