Help with 2 15" L7 box design

[wannabang 13]

I'm helping a friend build a box. I've done a few boxes in the past, but this one is different. This one isn't a rectangular box. He wants to, or needs to, use all of his trunk space to squeeze in 2 15" Kicker L7s. The box I designed is 6.11 cubic feet after displacement tuned to 33 hz with ~78 square inches of port. It will be braced and double baffled with 3/4" MDF. My only worry is the port being cut off by the roof of the trunk, but it's got a couple inches to breathe, so it should be fine, right?

Criticism is welcome! Thanks!

Edited January 2, 2012 by wannabang

[altoncustomtech 773]

One quick note on Sketchup, if you go to the file menu, down to export, and click on 2D graphic it will create a jpg file of the drawing you've made in the current view.

It will give you a .JPG file that looks like this:

On the box, it looks okay at first glance. On any enclosure you need to make sure there's room for the port to breathe. A "couple" of inches might be a bit tight. Also, it could probably do with more port area. The minimum port area calculation calls for 110sqin for those subs.

[wannabang 13]

One quick note on Sketchup, if you go to the file menu, down to export, and click on 2D graphic it will create a jpg file of the drawing you've made in the current view.

It will give you a .JPG file that looks like this:

On the box, it looks okay at first glance. On any enclosure you need to make sure there's room for the port to breathe. A "couple" of inches might be a bit tight. Also, it could probably do with more port area. The minimum port area calculation calls for 110sqin for those subs.

Thanks for that note on Sketchup. I figured I'd be squeezing everything I could out of this. Maybe I'm not using the Torres Calculator right, but 78" is just above 12/ft. I know that's not ideal, but isn't that a standard rule/guideline (12"-16"/cubic ft)? Since the port opening is slanted slightly, I figured those 2-3" of breathing room would be alright. I'll keep playing and tweak it, though.

[altoncustomtech 773]

12-16 is a general rule of thumb that while adequate for beginners isn't, or rather shouldn't be a "rule" for all builds to go by. Ideally every build should cover the goals while staying within the budget and space restraints. That being said, audio is ALWAYS about compromise, look up Hoffman's Iron Law and you'll likely understand exactly what I'm referring to in regards to tradeoffs in general. A person will always have to give up something to get what they need out of a given setup in another, more important area. It's just the way it is. Now, the calculation that specifies 110sqin minimum port area for those subs at that tuning frequency gives you a number, sure. Will it sound like garbage if you can't get exactly 110sqin? No, not at all because of that one reason. You have a given area to work in, if you can't squeeze anymore out of it, then you can't squeeze anymore out of it and 78sqin will do just fine. More port area just means a longer port and therefore a larger enclosure, so if it won't fit in the space then don't worry about it. I simply mentioned it and gave you the number to let you know it was something to consider. Also, you'd be amazed at how many times I've gone back and looked a design over again, then again, and played with it until I found the right change to get a little closer to the size, or port area, or tuning, or whatever I was chasing. When I simply couldn't find any other way I weighed the pro's and con's of it and made a decision as to whether or not it was viable in the first place or not. You can do the same thing, it's easier than people think. Sometimes we get so caught up on what we're trying to do that we forget the big picture.

Alright, all that rambling aside now, your design is really alright. If you can possibly find the room for more port area it would be good, if not then it won't likely hurt anything especially since it's going in a trunk anyway. Any port noise will be drowned out long before it's audible in the cabin of the car in all likelihood. In any case, go for it, it looks solid enough to me.

[wannabang 13]

12-16 is a general rule of thumb that while adequate for beginners isn't, or rather shouldn't be a "rule" for all builds to go by. Ideally every build should cover the goals while staying within the budget and space restraints. That being said, audio is ALWAYS about compromise, look up Hoffman's Iron Law and you'll likely understand exactly what I'm referring to in regards to tradeoffs in general. A person will always have to give up something to get what they need out of a given setup in another, more important area. It's just the way it is. Now, the calculation that specifies 110sqin minimum port area for those subs at that tuning frequency gives you a number, sure. Will it sound like garbage if you can't get exactly 110sqin? No, not at all because of that one reason. You have a given area to work in, if you can't squeeze anymore out of it, then you can't squeeze anymore out of it and 78sqin will do just fine. More port area just means a longer port and therefore a larger enclosure, so if it won't fit in the space then don't worry about it. I simply mentioned it and gave you the number to let you know it was something to consider. Also, you'd be amazed at how many times I've gone back and looked a design over again, then again, and played with it until I found the right change to get a little closer to the size, or port area, or tuning, or whatever I was chasing. When I simply couldn't find any other way I weighed the pro's and con's of it and made a decision as to whether or not it was viable in the first place or not. You can do the same thing, it's easier than people think. Sometimes we get so caught up on what we're trying to do that we forget the big picture.

Alright, all that rambling aside now, your design is really alright. If you can possibly find the room for more port area it would be good, if not then it won't likely hurt anything especially since it's going in a trunk anyway. Any port noise will be drowned out long before it's audible in the cabin of the car in all likelihood. In any case, go for it, it looks solid enough to me.

Thanks. I'm still messing with it right now. It's actually for a Tiburon, but the port is under the hatch (toward the rear of the car) so the subs can play off the rear window.

[wannabang 13]

I guess I'll just revive this instead of starting a new topic. My buddy decided he didn't want to squeeze two 15s, so instead he's working with the one he has now. I've been configuring a new box design for his 15" Kicker L7, and this is what I have so far:

The box will be going into the hatch of a Tiburon, with the ledge underneath the trunk lid (not visible through the window). As it sits currently, the box is 4.2 cubic feet and tuned to 31 hz with 60 sq. in. of port. My only issue is the port. I can't go standard slot since I'll have air trapped under that "ledge". I have this square-ish idea rollin' around in my head, but I didn't want the sub opening going under the sub along the back wall, so I figured I'd make it loop toward the ledge, but I still think air will get trapped back there. I'm going to play around with the size of the port, to see if I can get the length allow me to use the wall supporting the ledge. I'm just looking for feedback to see if I'm on the right track.

Here's the port I was thinking about before determining I needed to alter it:

[wannabang 13]

final design. reasonable/workable?