Port calculation question.
 

Hey guys, im planning to build a box for 2 Image Dynamics IDQ15 subs and i want to have a single chamber instead of two separate ones. I want to have a slot port running down the centre of the box but i cant seem to find any calculators to help me with the port dimensions so that the box frequency would be ~30Hz. Any ideas or tips would be greatly appreciated.

Heres a few...

RE Enclosure Calculator

PORT Size Calculations and Formulas for WOOFER and Subwoofer BOXES

Port Length Calculator

I found all these calculators but what im not sure about is if i have to divide the box volume by 2 since im using two drivers in one chamber instead of separate chambers.

You dont have to divide, Just need the proper airspace and port area for 2 subs.

Don't forget Vas
 

When you have two speakers sharing the same air volume, you need to enter Vas for two speakers. Also make sure that the speaker's physical displacement
(the amount of volume taken up by the speaker inside the box) is included, and doubled. If your design program requires it, DCR for series or parallel wiring also needs to be addressed.
The calculations in the computer can get you close, but don't forget to measure, with an RTA if you've got one, or with test tones and an SPL meter.
Then use your ears.

So lets say i have 2 subs that i want to put into one enclosure with shared airspace and a slot port in the middle. If i calculate the box and port dimensions for one sub in its own box, do i just double the values for two subs in one box?
eg. box for one sub is 1.5cuft and port is,say 3"x6"x12"
for 2 subs will it be 3 cuft and port 3"x12"x12" or 6"x6"x12" or some other variation ?

When you calculate your port dimensions, do you have a field, in which you input Vas?
If that's so, then simply input Vas x 2. So if your Vas for a single speaker is 28 liters (1 cubic foot) then you'd input 56 liters (2 cubic feet) into your calculation.

what's the volume of the box? what are the dimensions allowed for the port? Height, width, depth of the box's total outside dimensions, thickness of material (3/4", 1" etc..), and how much port area do you want. The port dimensions can vary depending on how much space you have, generally, the smaller port area (height x width), the shorter the port length....big caveat here though...the samller the port area, the greater potential for port noise (huffing). It can be quite a balancing act to design a proper port within the limited space, and tuning range.

I ran an example for you using 2 IDQ 15d4v2, and assumed a net box volume of 4 cubes total. The results with a proper port area to eliminate port noise at max output is: 14.5" height x 3.5" wide x 32.90" long, assuming a box height of 16" with 3/4" walls. Your port height and width can be any dimension combination as long as the area is 50.75 square inches in this example...so 10" x5" will work as well. As long as the total volume of the port is maintained the box will be tuned to that frequency in this example. Therefore, 50.75 x 32.90=1670 cubic inches or .97 cubic feet. SOOOOO, finally, if you want a port in the middle, just make sure your port has the total volume, and your box will be tuned to that frequency...regardless of dimensions (as long as they are reasonable...1/2" x 100" x 32.90 is not reasonable). REMEMBER THIS JUST AN EXAMPLE WITH MY ASSUMPTIONS, YOUR BOX MAY BE VERY DIFFERENT!!!

I punched in my current maximum for box dimensions, same dimensions I am currently using. I don't really know what the diameter of my existing port should be. It's just a circular hole on the side of the box, but obviously should be a correct diameter.

Using same dimensions for space, adjusted the port length/size for tuning and this is what it gives me. Wonder if I should replace what I'm currently using?

Tim

http://www.maserati.ca/stereo/box-dims.jpg

Okay so i didnt want to start a new thread just to ask this question, so im just gonna throw it in here. I started a build in my regular cab truck and im trying to squeeze 2 12" subs in a fibreglass box in there. Each sub has about 1.4cuft from guesstimation. I want to make it ported so i punched in the numbers in the calculators and got the port dimensions to be : 1" high x 2" wide x 3.5" long to tune it at 30Hz. Anybody see any issues that might arise with this port size?
Thanks.

p.s ill post pics of the build soon!!