double check my work

[terra 5,000+ posts]

im designing a box for 2 MJ 18's. its going to be 12 cu ft. and tuned to 31 hz.

For 192 sq in of port...i got a length of 36.457. does that mean the height of my port is 5.226 inches? also the port is going to be facing back at the bottom middle. is my work correct or if not where did i screw up

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[BassAce 10+ year member]

im designing a box for 2 MJ 18's. its going to be 12 cu ft. and tuned to 31 hz. For 192 sq in of port...i got a length of 36.457. does that mean the height of my port is 5.226 inches? also the port is going to be facing back at the bottom middle. is my work correct or if not where did i screw up

I'm having a gut feeling you took 192/36.457 to get 5.226, if so don't do that.

Also, are you going to have one chamber for each sub or just one big chamber for both? What is the height of your box?

Edit: if you want 1 port with a cross sectional area of 192 in^2 tuned to 31 Hz with 12 cubes, your port will roughly be 28-29 inches assuming that is one big chamber for both subs.

 

[terra 5,000+ posts]

ur gut feeling is right..this is my first slot port. i usually go round port. its going to be a common chamber..height is 23 inches.

so for 192sq in....what kind of port length am i looking at? and also..can i change the height of the port? i was planning on doing a port maybe...5 inches tall and in the middle but im kinda thinkin of a wider port thats not so tall

 

[BassAce 10+ year member]

ur gut feeling is right..this is my first slot port. i usually go round port. its going to be a common chamber..height is 23 inches.

So I'm guessing you want the port to be the height of the enclosure, so the height of the vent is going to be 21.5 inches. I'm going to use this calculator to give an estimate of the length of the port: http://www.carstereo.com/help2/Articles.cfm?id=31

I place 21.5 for the length and 9 for the width. It would be wise to make the width to a number that would be easily measured on a measuring tape. And I got 29.24 inches for the length of the port. With the calculator I just used and showed you, I'm not sure if they calculate the end correction.

I would recommend you plugging in 29.24 into this formula and see if you get 31Hz as an answer:

http://mobile.jlaudio.com/support_pages.php?page_id=165

 

[BassAce 10+ year member]

I double checked the formula and the calculator calculated the physical length of the port(29.24in) and the sub needs to see 33.74in. So that calculator did factor in end correction. So you need to build you box to have a port that has a physical length of 29.24 in. I guess you can get away with making it 29.25in since .01 inches bigger will not audibly effect the tuning.

 

[terra 5,000+ posts]

ya i want subs up port back...so the port is going to face the back hatch and go 32 inches wide along the bottom of the side facing the hatch. for a height of 4 inches and 32 inches wide i got a depth of 4.57 inches....correct?

 

[terra 5,000+ posts]

someone?