I kind of started a post in the wrong area for BTL box questions. But I am looking at getting a 15" BTL sometime soon. I do have somewhat limited trunk space though (40x40x20). I would like maybe a little of extra room in the trunk for putting somethings (ie bags, books, backpacks, skating equipment etc). Can it be done to get the same boom / sound quality with a smaller box? I know on my other post, somebody said it was possible to make a little smaller box with biger ports to even the difference out. But how far can you take it? Like (I know you couldnt but...) making a box that only acted as a brace for the sub and maybe have some sort of diminishing cone around the sub. Like a silinder with one side a small opening and the other big enough to mount the sub into. So that way it would be able to build some pressure. Then have that silinder pointing towards the street at a 45 degree angle (sub inverted) kind of towards the driver. Then dont put on a left or right side (ports) but a bottom and top...

The main reason why I went down to the 15" from the 18" is because I believe I dont have the space for it. Maybe once I get everything upgraded in my car I will sell my 15" and go for a 18" if I am not doing the umph I want.

Thanks for all your guys help, I know I am not the best at things but thanks for working with me. I am not trying to argue with anybody but I am just throwing ideas tht pop into my mind out there. Maybe one of them is worth a shot?

Damn, how many threads are you gunna make?

Not trying to be rude but you could have gotten all the info you needed in 1 thread.

Well one was for 18 vs 15, kinda got out of hand so I tried to bring it back together. Another was about car electrical and that went elsewhere. Then another was about making strange looking boxes then it went elsewhere... I just like trying to kep the topic the same as everythign posted. Else you get to 5+, 6+, 7+ pages and the person reading the first post has no idea wtf the last post it about. I guess I could pm a op and ask them to combine everything...

Edited June 8, 200916 yr by Hell-Razor

Really, really, really simple. The specs for the box is on Fi's website, you MUST follow it otherwise you are wasting your money and should buy a smaller driver as you don't have enough space.

an external port might be able to save you some space if you do it right

Edited June 8, 200916 yr by mikee72

Whats an external port? I have been looking but I dont see a good diagram of one.

I found this http://www.subwoofer-builder.com/vent-options.htm but not sure if thats what you mean...

Edited June 8, 200916 yr by Hell-Razor

same as a regular port... except the port does not displace any internal volume so you pick your internal volume and take displacement for sub away and your done. If u know you got room to add a port later after box is built.. then that is your external port.

Alright I think I understand.

Alright I kind of half ass designed a box sitting here during work. The measurements are 30 x 38 x 18.5 (L W H). This would give me about 12 cubit feet of space inside the box if I did the external port. Would this be too big for a 15 BTL? If so how about an 18 BTL? The port area on the box (just adding a front port, not side / top at all even considered yet. Nor am I adding the Fi BTL that I am going to carve into the box for additional port) . If I were to make the ports normal they would add up to be around 6 cubic feet. Again is that too small for a 15 BTL or 18 BTL?

NOTE: I have decided my design ( no matter what size woofer I get) the magned will be mounted outside the box.

Edited June 9, 200916 yr by Hell-Razor

That is too large for even an 18", that is too much for 2 15's aswell.

That is too large for even an 18", that is too much for 2 15's aswell.

Thats awesome news! Well it means I wasted an hour and a half drawing up a design but hell thats alright. It means that I can have some of my trunk space. I need to go read up more (obviously) but whats the maximum cubic feet? I know reading the thing it says 5-8. Does that mean the max is 8 or the ideal is 8? and the ideal smaller is 5?

That is too large for even an 18", that is too much for 2 15's aswell.

Thats awesome news! Well it means I wasted an hour and a half drawing up a design but hell thats alright. It means that I can have some of my trunk space. I need to go read up more (obviously) but whats the maximum cubic feet? I know reading the thing it says 5-8. Does that mean the max is 8 or the ideal is 8? and the ideal smaller is 5?

Normally in the range of airspace larger yields more output, simply because it's more efficient.

If you have too much airspace put the port in the box to displace air, and/or add bracing.

Is it hard to tune the box if its external ports? Or even possible? I would like trunk space for things. I am kind of a clean freak and when it comes to out of sight out of mind I am completely for it.

How is something like 25x35x15 ( L W H ). Will come out to about 7.56 cubic feet. Not including bracing and everything for the sub. Should bring it down to about 6.5-7. I know this is within the range but would you guys recommend more of a "box" shape than say a triangle or a rectangle? I am leaning more towards the 18" now (I know I was talked down but my mind got the best of me). Then getting a good amp to power it decently until I can get another and bridge it.

Edited June 9, 200916 yr by Hell-Razor

Don't forget to take the volume of the wood out of your dimensions to get internal airspace. So the 25 x 35 x 15 box is actually only 6.15 cubes before sub and port displacement.

External ports are the same as internal ports to tune, you just don't have to take out port displacement. But with the box you last mentioned, you can do an internal port and be fine. It's large enough.

If you want the 18", the first box you mentioned would be ok. The internal airspace on that after wood displacement is about 10.25 cubes. The port will probably subtract another 3 cubes, so you'd be down in the range of recommended boxes for that size.