Designing a Box

[KampinKarl 0]

I took the plunge and bout a BL 12 with Cooling, Flatwind, and Internal Leads. It will be powered with a MB Quart MB Quart Q1.1500D giving it 1500w RMS @ 1ohm.

I now need to design a box that will fit in my trunk. The cutout that they have listed on the forum might work in my trunk but I would like to design one myself. I was thinking somewhere between the 2-2.5cuft (after sub and port displacement) and a slotted port tuned to 32Hz.

It seems that every online calculator gives different results or has a cuft value that is crazy high.

I was wondering what the actual formulas are for finding port length given the port area and desired port tuning? and any other formulas / equations that may be needed? I would eventually like to create an excel spreadsheet to be able to do all of the calculations needed so doing this a second time can be easier.

Also, If anyone has any tips or suggestions for designing boxes I would love to hear them.

[Quentin Jarrell 671]

Use 14 square inches of port per net cubic feet and make it 32 inches long. You will be tuned about 32-33 hertz.

[Punkeyboozter 19]

Router flares into the edges, double baffle and brace well or both.

[Punkeyboozter 19]

Whats ur max extrrnal dimensions

[KampinKarl 0]

i can fit a 34.5"x28"x17" (LxWxH) maximum but i would really prefer something 28"xWx15 or 16" (that way i can rotate the box over to one side to fit my snowboard in my car through backseat and into the trunk area). I would like to design the actual dimensions my self. I have been looking at this guide but as someone stated the equation is wrong. I know to use 12-16 sq in of port space per cubic feet but i need to know the actual equation. As i mentioned before i would like to create an excel spreadsheet that will make designing future boxes much easier.

[Punkeyboozter 19]

i can fit a 34.5"x28"x17" (LxWxH) maximum but i would really prefer something 28"xWx15 or 16" (that way i can rotate the box over to one side to fit my snowboard in my car through backseat and into the trunk area). I would like to design the actual dimensions my self. I have been looking at this guide but as someone stated the equation is wrong. I know to use 12-16 sq in of port space per cubic feet but i need to know the actual equation. As i mentioned before i would like to create an excel spreadsheet that will make designing future boxes much easier.

there are already many excel spreadsheets out there some of them are very good. most of them are based on a formula that is about 20 years old. One thing to remember many of these design tools are also based on old drivers which does not have the capabilities of these new gen high power high xmax monsters we get these days. So in many cases the graphs will appear whack and to make things even more complicated there is the aspect of cabin gain loading issue's.

Usually the results vary due to amount of decimals the program use or what aspects of box building are included such as baffle displacement bracing woofer displacement end correction etc.

If you want to take it back to the old school the formula is on the JL audio site with a lot of other useful information.

[KampinKarl 0]

I was not aware that the equations "are out of date". How would you recommend going about getting the specs for my box then. I will try to play around with Bass Box Pro 6 to see if that will have any reasonable results.

Thanks for the input.

[Punkeyboozter 19]

I was not aware that the equations "are out of date". How would you recommend going about getting the specs for my box then. I will try to play around with Bass Box Pro 6 to see if that will have any reasonable results.

Thanks for the input.

If you stick to the recommendations such as the vent size required for port for example.

In the old days you can use a 18" driver with a 4" port no problem with a few mm xmax you wont have a problem chances are now a days your 12 with 18mm will over power a 4" aero under full load.

I was actually thinking of making some 5" ports which should be good for a single 12 bl.

Slot ports are a little less efficient and need a wee bit more area.

Long story short follow the guidelines and you should be good to go.

WinISD is also a good free tool. The re tool is also not too bad if you really dont have a clue and will get you 90% where you want to be; else I find the torres box tool to be nice for some tweeking and its better then the re tool

[KampinKarl 0]

Well I think i got a possible design done with Torres' Box Tuning Calculator. Can I get your opinions?

Although the extra baffle would be added to the outside i don't see how it will take any displacement. Would you recommend bracing this box?

[Punkeyboozter 19]

Looks good,

One thing though the way you did it places the baffle in the box which will make the box bigger if you mount it on the outside and its already bordering on the large side.

apart from that it looks good and Id add some bracing as well as make the port slightly smaller as smaller ports tend to be a bit more musical unless your chasing numbers, but then again if you were chasing numbers often a smaller box with a big port gives you more of a peak that those guys are after.

As the box is now it should work for most.

didn't check the box dimensions just make sure there is some space for the rear of the sub to clear the port

[KampinKarl 0]

Would i notice a difference if the box was 2.0cuft vs 2.5cuft?

[Punkeyboozter 19]

Would i notice a difference if the box was 2.0cuft vs 2.5cuft?

you might but it also depends on other things such as your port in relation to box size and the amount of power you are planning to use.

if you use more power u can use a smaller box within reason

[KampinKarl 0]

Well I will be using 1500w RMS @ 1 ohm, I'm assuming that is considered higher power.

I have calculated another box out. Everything is in the recommended specs according to the BL Tech page. As of now the box is 2.2cuft, it gives me some room to add braces to the box.

As far as i can see this box should be perfect for me, if you had any thoughts on it let me know. I will probably start making my design with Google SketchUp tomorrow if there are no problems.

The port width is only 2.25", with a port area of 32.62 in² and port area per cuft of 14.86 in², would this create a lot of port noise?

[Punkeyboozter 19]

Looks fine to me

Now where is the build log

[KampinKarl 0]

Thanks for all of the help, I really appreciate it.

I ordered my sub on 11/28 so it will be a while before the sub comes in probably the week of the 19th, which happens to be my finals week . I will share my SketchUp design when i have it finished and will take pics during the build, which I will probably have to do before i get my sub.

One final question, Will putting a 45^o edge on the port corner mess up my tuning at all?