help me with my port calculations

[THEMERQ]

this is all using the torres box calculator.

my outside dimensions are LxWxH 40.5 x 24.5 x 19.5 it comes out to 9.7 gross cubes. bracing displacement is .11 cubes, driver displacement is .28 cubes. that leaves me with 9.31 net cubes before port displacement.

my problem is i cant seem to tune the box to 30 Hz without volume dropping drastically AND maintaining 12-16 square inches of port area AND a 1:6 port ratio.

i tried the port at 18" high X 6" wide X 30" length and that drops me down to 6.82 NET cubes, 108 square inches of port area, and 1:3 port ratio.

i tried 18" high X 3" wide X 11" length and that drops me 8.68 NET cubes, 54 square inches of port area, and a 1:6 port ratio.

this is for 2 15s and im trying to maintain at least 4 cubes per sub. what am i doing wrong?

[iKidwell]

you don't NEED 4 cubes per subs unless you're not gonna give them enough power..and your box dimensions seem weird, you have 40.5 depth and only 24.5 width? give me your max dimensions and i'll work a box out for you

[THEMERQ]

i do my dimensions differently than the calculator, those are my max inner dimension.

max outer dimensions are 42"wide x 24.5" depth X 17.5" high tuned @30 Hz. port with 3 common walls

[Sanitarium]

just do that. 3.5 cubes per 15 is fine, and is actually optimal if you're gonna overpower them.

[THEMERQ]

ok i came up with another one, i think this one is perfect. sanitarium thanks for your design but i have to shorthen the heigth as little bit.

new external dimensions are 42" wide X 24.5" deep x 17.5" high. that gives me 8.63 cubes gross. minus .28 cubes of sub displacement, minus .07 cubes of bracing. 8.28 cubes NET before port displacement.

port inner dimensions are 16" high x 5.5" wide x 32" long with 3 common walls. that will tune the box to 30.02 Hz and 88 square inches of port area.

for this box the port must bend at 18.25"(this includes the baffle) and run another 13.75" to complete the 32" of length corect?. so my two port pieces will be 17.5"x 16", and 13.75"x 16"?

all this yields 6.19 NET cubes @ 30.02 Hz.

[Torres]

any reason as to why you use inner dimensions for the box? if you build the box to fit in those dimensions you'll be ok. but if you use 40.5" of width to design, then build to 42", then everything will be off.

just curious...i think i'm just confused

[THEMERQ]

on paper i did inner to figure out my volume. i didnt mean to post them the first time, i intened to post the outer dimensions.

is the new one correct?

[Torres]

ah ok i gotcha.

as far as the box, looks good. except you want the port length of the wood to add up to the 'physical port' length. so making it so the wood measures out to be 25.75" long, this will make your effective port length 32". 32" - 5.5" (for the port height) - .75" (for the thickness of the box wall/baffle) = 25.75". measure down the middle of the port and you get 32"

if it were me tho, i'd change the port to 16" x 6", and make it anywhere from 15" - 20" long. i like to tune my boxes a little bit higher tho. sounds better for daily imo. plus gives you a little more volume for the subs

[THEMERQ]

ah ok i gotcha.

as far as the box, looks good. except you want the port length of the wood to add up to the 'physical port' length. so making it so the wood measures out to be 25.75" long, this will make your effective port length 32". 32" - 5.5" (for the port height) - .75" (for the thickness of the box wall/baffle) = 25.75". measure down the middle of the port and you get 32"if it were me tho, i'd change the port to 16" x 6", and make it anywhere from 15" - 20" long. i like to tune my boxes a little bit higher tho. sounds better for daily imo. plus gives you a little more volume for the subs

i still dont understand what this means. i saw a correlation with the numbers before i posted the box but i could not get it. basically what your saying is even though i chose the port to be 32" long. it only has to be 25.75" physically? and just to make sure, if the port will bend then the port must stay the same width all the way through right?

i also tried making the port 6" wide but it was coming out to some crazy long length.

Edited December 26, 2010 by THEMERQ

[Torres]

look at this picture. if the port stayed 32" long, your actual port would be longer. you measure down the middle of the port giving you your effective port length. notice the physical port length is 10" in red. if you keep that 10" and bend the port, it increases the effective port length.

so if your port is 32" long, and you bend it the same way you're going to be adding 5.5" of port length to the effective port length

and i'd only change the port area to tune higher. if you're still going to tune around 30 hz then yeah i'd assume it'd still be pretty long and leave it the way you had it