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View Full Version : What port length should I use? Different calculators give different lengths.

RSDXzec
07-01-2012, 02:38 AM
I'm making a triple chambered box and each chamber is 2.2cf tuned to 31hz. Port dimensions are 1.57"x11.16" and when I use this calculator if I select yes or no on the slotted port option I get different results.
http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm
http://i47.tinypic.com/2qusrid.png

This box will be using a slotted port, but other calculators I have which don't have the option to choose a slotted port all say closer to 18.8" (like winISD).

Using your calculation methods or reasoning could anyone tell me what port length I'd need to get the tuning frequency I'd like.

Cheers.

edit: this website also gives me the two same options, 13 or 18
http://www.carstereo.com/help/Articles.cfm?id=31

RSDXzec
07-01-2012, 06:09 AM
any box designers here have their own equations to test against? To see if the 13" or 18" is closer to the real value I'd need?

I'm making a box with a port like this. Now to my knowledge this is a slot port
http://spe.fotolog.com/photo/46/51/51/only_sound/1256665430676_f.jpg

other calculators only give the option of slot or round port and for slot port they give 18". Except those two linked above have the options round/square and slot/non-slot port. **** this is confusing...

SMS
07-01-2012, 07:35 AM
i think you should have one of the box designers on here to help you out. also your port dimensions are way off- 1.57 wide x 11.16 is about half the port area you should have in 2.2 cubes, so if you correct the port area the length will grow maybe 10" more, that might ruin your whole design.

RSDXzec
07-01-2012, 07:43 AM
i think you should have one of the box designers on here to help you out. also your port dimensions are way off- 1.57 wide x 11.16 is about half the port area you should have in 2.2 cubes, so if you correct the port area the length will grow maybe 10" more, that might ruin your whole design.

are you sure it's too small? I've been using winisd and that port area keeps me under 25m/s so I think I'd be alright.

I've sent a PM to mobileenclosurs about it but then again I'm not paying anyone for the design so I can't expect anyone to do all the calculations for me but I would like to know which of the two port lengths I should be aiming for here.

SMS
07-01-2012, 07:59 AM
if you pay for a design the outcome will be much better, and you will only have to build one box.

RSDXzec
07-01-2012, 08:30 AM
if you pay for a design the outcome will be much better, and you will only have to build one box.

nah I much prefer to to learn for myself, that way I save a few dollars and gain some knowledge. I have designed a box before so this is my second design. I do a lot of planning before pulling the trigger which is why I'm asking here before doing anything.

I've been planning this design for the last couple of months and all I've got left to figure out is the port length.

Here's what I've got so far, it's going in a hatchback so I'm aiming for a nice horn effect for some good cabin gain.

http://i48.tinypic.com/wl88ea.png

edit: ports would be something like this

http://i48.tinypic.com/jg1j6a.png

edit 2: no worries here guys, I ended up testing a previous box I built and found its minimum excursion at 25hz which was the tuning frequency I made it for so I'll be going with 18" on this design.