PDA

View Full Version : help on gross...



tapout383
03-20-2009, 01:52 AM
it says my box has a gross of 7.48 Cubic Feet. What can i expect my net to be if i have two 6'' aeros with a 18'' Fi BTL old style with triple stack motor?

HlorridiXplorer
03-20-2009, 02:00 AM
ports external? add the volume of the ports to the gross.

ports internal? subtract the volume of the ports from the gross.

cylinder area = (pi*r^2)*Length

find the displacement of the subs on fi's website and subtract them from volume of the box.

davescomptips
03-20-2009, 02:20 AM
ports external? add the volume of the ports to the gross.
ports internal? subtract the volume of the ports from the gross.
cylinder area = (pi*r^2)*Length


If I remember correctly you never ADD the volume of the ports. Think of the port as a closed cylinder - they can not add to the volume of the box. Now, they can subtract from the volume. The amount they take from the gross volume depends on how many inches of the port is inside the box.

EuphoricBass247
03-20-2009, 02:26 AM
right around 6.8-7.0cu/ft net depending on tuning

tapout383
03-20-2009, 02:31 AM
ill say the ports are 6x15...radius would be 3 there internal woofer displacment is .25

tapout383
03-20-2009, 02:32 AM
holy hell this was only supposed to be a 6.0 box lol dang o well more doesnt hurt i guess

tapout383
03-20-2009, 02:33 AM
12.3 is what it says if its 6.8 cubes

HlorridiXplorer
03-20-2009, 02:37 AM
If I remember correctly you never ADD the volume of the ports. Think of the port as a closed cylinder - they can not add to the volume of the box. Now, they can subtract from the volume. The amount they take from the gross volume depends on how many inches of the port is inside the box.

some people think that when you run external ports you have to add their volume because it is more air that the sub with my using along with the volume of the box.

I don't calculate port volume into any of my boxes because I tune my ports off a Termlab to where the system is the loudest and i'm constantly changing them so their length is constantly changing so for me to add in the volume of the ports would be stupid because their volume is constantly changing.

davescomptips
03-20-2009, 02:45 AM
some people think that when you run external ports you have to add their volume because it is more air that the sub with my using along with the volume of the box.


It's more volume for the sub only because the port isn't in the box.

Look at it this way...
Fill your bathtub with water. Hold two bricks above the water. Did the water rise? No, there was no change in the total volume.

Drop the two bricks into the water. Did the water rise? Yes. The bricks add to the total volume.

Then explain to your Mom, wife, or girlfriend why you are washing bricks in the bathtub! :)

9BlackN*Black6
03-20-2009, 03:03 AM
It's more volume for the sub only because the port isn't in the box.

Look at it this way...
Fill your bathtub with water. Hold two bricks above the water. Did the water rise? No, there was no change in the total volume.

Drop the two bricks into the water. Did the water rise? Yes. The bricks add to the total volume.

Then explain to your Mom, wife, or girlfriend why you are washing bricks in the bathtub! :)

:hilariou:

tapout383
04-04-2009, 05:32 PM
ok so im getting ready to tune my box for my btl 7.4838 is what i have before aero and sub displacment...psp cacultor ask for box volume and im not sure what to put in as the volume of the box will change when sub and aero is factored in

iamamp3pimp
04-04-2009, 06:31 PM
you designed it backwards.

now i will help you

well say that the sub is .25 cuft and the ports all together equal about .73 cuft

take your gross and subtract 1 cuft, put in your port info 3 6" ports 15" long

and see what it tells you.

iamamp3pimp
04-04-2009, 06:32 PM
thats if ports are internal.

if they are external, they dont factor into anything at all.

so in your case, gross - 1 cuft = net

iamamp3pimp
04-04-2009, 06:34 PM
did you build it already?

tapout383
04-06-2009, 02:25 PM
um i built it already but havent cut the ports....

tapout383
04-06-2009, 02:26 PM
i only have 2 6'' ports btw

bjfish11
04-06-2009, 03:37 PM
It's more volume for the sub only because the port isn't in the box.

Look at it this way...
Fill your bathtub with water. Hold two bricks above the water. Did the water rise? No, there was no change in the total volume.

Drop the two bricks into the water. Did the water rise? Yes. The bricks add to the total volume.

Then explain to your Mom, wife, or girlfriend why you are washing bricks in the bathtub! :)

Thats not how it works.

You have your gross volume... if the ports are internal, you subtract the displacement for the net. If they are external, you simply dont do anything, because they are not displacing any volume inside the box. However, you dont add anything either, because the volume of the ports, are not "usable" airspace by the driver.

tapout383
04-06-2009, 03:41 PM
Thats not how it works.

You have your gross volume... if the ports are internal, you subtract the displacement for the net. If they are external, you simply dont do anything, because they are not displacing any volume inside the box. However, you dont add anything either, because the volume of the ports, are not "usable" airspace by the driver.

lol ok but there not external...my box dems are 17.5'' tall 32'' wide and 28'' depth i have to 6'' aeros and a Fi BTL 18'' i just need someone to help me :( geez i think i would have 6.4 cubes after sub and aeros but someone needs to chime in that knows before i cut

BobbyDD
04-06-2009, 03:45 PM
Thats not how it works.

You have your gross volume... if the ports are internal, you subtract the displacement for the net. If they are external, you simply dont do anything, because they are not displacing any volume inside the box. However, you dont add anything either, because the volume of the ports, are not "usable" airspace by the driver.

He said pretty much the same thing you did BJ.

tapout383
04-06-2009, 03:52 PM
can someone just help ME please?

bjfish11
04-06-2009, 04:16 PM
He said pretty much the same thing you did BJ.

Reading ) me. I apologize.

OP... people have given you the numbers. Run them through the psp-inc.com calc nd you should get what you need.