Math check please- PSP ported
11-02-2010, 10:13 AM
#1
Math check please- PSP ported
We'll be starting our first box build in years this weekend. 
Trying to figure the cubes and tuning from a slot port box, in the space we have, proved too tough for me.
Sooo to PSP flared ports we go, to gain the few cubes. I need to order them still, but we'll build the box anyhow
Building for 3 12" - one chamber
1.75 cubes each sub
34hz tuning
3-4" PSP flared ports
Thats 5.25 cubes plus port and sub displacment
The 3 subs displace .51
the box needs to be 5.76 cubes now
To the PSP flared port calculator
5.25 at 34hz with 3-4" flared ports
1 flared port- 14.8142" long
3.14 x 4 x 4 x 14.8142 / 1728 = .43
3 ports displacement = 1.29 ...
5.76 + 1.29= 7.05 cubes
So
a box that fits behind the 3rd row of seat while the seats are up ..
48.5" width x 18" height x 17.25" width with .75" MDF =
7.06 cubes
For port velocity, 3-4 " flared ports are about 40 cuin of port area for 5.25cubes - thats about 7-8 per cube. Good enough The 3 subs will be on 1500-2500 watts for the time being.
Is it close enough to give it a try with these specs?
Trying to figure the cubes and tuning from a slot port box, in the space we have, proved too tough for me.
Sooo to PSP flared ports we go, to gain the few cubes. I need to order them still, but we'll build the box anyhow
Building for 3 12" - one chamber
1.75 cubes each sub
34hz tuning
3-4" PSP flared ports
Thats 5.25 cubes plus port and sub displacment
The 3 subs displace .51
the box needs to be 5.76 cubes now
To the PSP flared port calculator
5.25 at 34hz with 3-4" flared ports
1 flared port- 14.8142" long
3.14 x 4 x 4 x 14.8142 / 1728 = .43
3 ports displacement = 1.29 ...
5.76 + 1.29= 7.05 cubes
So
a box that fits behind the 3rd row of seat while the seats are up ..
48.5" width x 18" height x 17.25" width with .75" MDF =
7.06 cubes
For port velocity, 3-4 " flared ports are about 40 cuin of port area for 5.25cubes - thats about 7-8 per cube. Good enough
The 3 subs will be on 1500-2500 watts for the time being.Is it close enough to give it a try with these specs?
11-02-2010, 05:49 PM
#3
--SPECIAL ED--
Join Date: Aug 2010
Posts: 138
i dont think that will be enough port.
how do you gain airspace by using ports? dont you subtract port displacement from the gross volume?
heres my calculations
( assuming your measurements are outside of the box )
47 x 16.5 x 16.75 = 7.5 cubes
port displacement = 3.14 x 2 x 2 = 12.5 12.5x 14.8 = 185
185 x 3 = 555 555 / 1728 = .32
port displacement is .32 for all the ports
sub displacement you said was .51
SO...
7.5 - .32 = 7.18 7.18 - .51 = 6.67
so, by my calculations you have 6.67 cubes after sub and port displacement
port area per cube 12.5x3 = 37.5"
37.5/ 6.6 = 5.6
so! your box is 6.6 cubes with 5.6 square inchs of port per cube
thats if i did that correct
how do you gain airspace by using ports? dont you subtract port displacement from the gross volume?
heres my calculations
( assuming your measurements are outside of the box )
47 x 16.5 x 16.75 = 7.5 cubes
port displacement = 3.14 x 2 x 2 = 12.5 12.5x 14.8 = 185
185 x 3 = 555 555 / 1728 = .32
port displacement is .32 for all the ports
sub displacement you said was .51
SO...
7.5 - .32 = 7.18 7.18 - .51 = 6.67
so, by my calculations you have 6.67 cubes after sub and port displacement
port area per cube 12.5x3 = 37.5"
37.5/ 6.6 = 5.6
so! your box is 6.6 cubes with 5.6 square inchs of port per cube
thats if i did that correct
11-02-2010, 06:04 PM
#5
To the PSP flared port calculator
5.25 at 34hz with 3-4" flared ports
1 flared port- 14.8142" long
3.14 x 4 x 4 x 14.8142 / 1728 = .43
3 ports displacement = 1.29 ...
Your math is off, JDN has it right, but here's my reasoning which won't make a big difference, but at least you can see it:
volume of pipe= area of circle (Pi x radius squared) x length= 3.14 x (2x2)= 12.56 ( I like to use 15 cubic inches to compensate for the wall thickness of the tube as well, as most tubes are about 4.3-4.5" in diameter...you can always measure.) x 14.8=186 cubic inches (or 225 using 15) x 3= 558 or 675 cubic inches /1728= 0.32 0r 0.39 cubic feet (a lot less than 1.29
)So, your box just needs to be 6.15 cubes gross (5.25 + .51 + .39 (i'd use this number or the one derived after measuring the port outside diameter).
5.25 at 34hz with 3-4" flared ports
1 flared port- 14.8142" long
3.14 x 4 x 4 x 14.8142 / 1728 = .43
3 ports displacement = 1.29 ...
Your math is off, JDN has it right, but here's my reasoning which won't make a big difference, but at least you can see it:
volume of pipe= area of circle (Pi x radius squared) x length= 3.14 x (2x2)= 12.56 ( I like to use 15 cubic inches to compensate for the wall thickness of the tube as well, as most tubes are about 4.3-4.5" in diameter...you can always measure.) x 14.8=186 cubic inches (or 225 using 15) x 3= 558 or 675 cubic inches /1728= 0.32 0r 0.39 cubic feet (a lot less than 1.29
)So, your box just needs to be 6.15 cubes gross (5.25 + .51 + .39 (i'd use this number or the one derived after measuring the port outside diameter).
Last edited by veeman; 11-02-2010 at 09:24 PM.
11-02-2010, 08:15 PM
#6
You know I don't see the math as of yet,
but I'll certainly believe you all..lolDid I mention these port are going IN the box, not outside.
I may just have to trust the PSP calculator like Yuli suggested..
That bit of less size is great, but it's crappy that I have to reread for the 10th time and I still don't get it...
Ms. brewster!! I gotta go bathroom
11-02-2010, 08:57 PM
#7
i dont think that will be enough port.
how do you gain airspace by using ports? dont you subtract port displacement from the gross volume?
heres my calculations
( assuming your measurements are outside of the box )
47 x 16.5 x 16.75 = 7.5 cubes
port displacement = 3.14 x 2 x 2 = 12.5 12.5x 14.8 = 185
185 x 3 = 555 555 / 1728 = .32
port displacement is .32 for all the ports
sub displacement you said was .51
SO...
7.5 - .32 = 7.18 7.18 - .51 = 6.67
so, by my calculations you have 6.67 cubes after sub and port displacement
port area per cube 12.5x3 = 37.5"
37.5/ 6.6 = 5.6
so! your box is 6.6 cubes with 5.6 square inchs of port per cube
thats if i did that correct
how do you gain airspace by using ports? dont you subtract port displacement from the gross volume?
heres my calculations
( assuming your measurements are outside of the box )
47 x 16.5 x 16.75 = 7.5 cubes
port displacement = 3.14 x 2 x 2 = 12.5 12.5x 14.8 = 185
185 x 3 = 555 555 / 1728 = .32
port displacement is .32 for all the ports
sub displacement you said was .51
SO...
7.5 - .32 = 7.18 7.18 - .51 = 6.67
so, by my calculations you have 6.67 cubes after sub and port displacement
port area per cube 12.5x3 = 37.5"
37.5/ 6.6 = 5.6
so! your box is 6.6 cubes with 5.6 square inchs of port per cube
thats if i did that correct
ding ding ding.
we have a winner.
to the o/p, if you have the space, add an extra port. port area is your friend
