port displacement?

[thegr8cody]

my box demensions are 44x20x20 which is 8.5 cubic feet and my port is 18.5x6.5 which is 120 square inches but my port has to twenty nine inches long so i had to elbow it,so does the box that that shape makes equal a new box volume or is it still 8.5 cubic feet?

[Derrick824]

You rbox will be 8.5cu ft. minus port displacement.

[thegr8cody]

welll the port is thirteen inches back and 16 inches for the elbow but do i just count the wood for displacement or the 6.5" x 18.5" thats what i dont know how to calculate for port displacement

[Derrick824]

I'm figuring that the 44x20x20 are external box dimensions.  So using 3/4" mdf your internal dimensions would be 42.5x18.5x18.5 which equals 8.41cu ft.  Your port dimensions of 18.5 x 6.5 are internal so again figuring you made this out of 3/4" mdf your external dimensions would be 19.25 x 7.25 x 29 which equals 2.34cu ft. of displacement.  8.41 - 2.34 = 6.07cu ft. after port displacement.  Don't forget to account for sub displacement as well.  With 6.07ft of usable space and 120" of port 29" long = about a 39hz tune.

Somebody please check behind me on this.

[thegr8cody]

if i do 44x24x20 i want 7.5 cubic feet after port displacement and i wanna keep the port at 18.5 x 6.5 but how do i get a tune to 32hz,i built my box according to winsid beta specs,and it was supposed to be at 32hz but it picks up around 35hz

[Derrick824]

For 7.5cu ft. with a 18.5 x 6.5 port it'll need to be 36.34" long to be tuned to 32hz.

[thegr8cody]

so after port displacement with tht bif of a port that'll be 6 cubic feet but if i build a new box thats 44x26x20 external and after port displacement with the same 36.34" port it'll be 8.5 which is what i want,how'd you come up with 36"s,winsid told me 29

[David]

numbers will vary from programs to program, thats why i like my calculator.

to find port displacement calc it the same way as a box, if it bends split it in two and than add those numbers together, dont forget to include the thickness of your port material.

[thegr8cody]

thanks i'll let you know how it goes this weekend,ealier i was tuning my stereo and i been playin it on 27 -30 of 40 since its so loud i was scared to turn it up so i went to my old house and turned it on 30 and watched to see how much it moved and i seen i could turn it up all the way so i did and i watched it and it seemed safe, so after playin music and watchin it at full volume i decided to sit in it and here it,well after listening to it for about 10 seconds of a song i decided to put in my usaci cd and i played a 39hz track and got to enjoy it for about 2 seconds before hearin the sub drop and beat out the baffle,so i'm gonna double baffle the next one : )

[Derrick824]

44x24x20 external gives you 10.23ft gross volume.  The port will be 18.5x7.25x36.34 external which gives you a port displacement of 2.82ft.  10.23-2.82=7.41ft of volume.  WinISD tells me that a 7.41cu ft box with one 18.5x6.5 port 36.34" long = a 32.19hz tune.

How did you figure 6cu ft of volume?