Simple Question i hope

[Bwcad1]

particle board comes in 4x8 sheets

[Evanjl]

o alright when i went to lowes all i saw was foot wide boards
probably just wasnt looking in the right place

also when it comes to buying ports all i can find are ones 4'' long i need a 7'' one........should i use PVC pipe or do they make ports that long


sorry i have lots of questions but i guess thats the only way you learn

[geolemon]

Calculating the displacement of ANYTHING is simple math.

Round port? Measure the outside of the port (a 4" diameter PVC port has 0.25" walls, so you'd measure 4.5" diameter. Remember Pi * R^2? Then multiply that by the length of the port, and you have your total area in cu.in. Divide that by 1728 (12"x12"x12") and you have your total area in cu.ft.

Square port? Length times width times depth. Divided by 1728 if you want cu.ft.

Sub displacement is listed on the spec sheet - or estimate it at about 0.1 cu.ft. for a normal 12" sub.

not rocket science - make sure when you are calculating your box volume, that you are calculating the airspace INSIDE the box, which doesn't use any EXTERNAL dimensions, of course (rather, external dimensions minus two walls worth of material - if 0.75" thick MDF, then external dimensions minus 1.5" for each of those).

Hope that helps.

[Evanjl]

yes you were a good help thank you
so the air inside the port doesnt not count for box volume

all together including the subs and ports i need about a 3.94 cu ft box(would it matter if i bumped that up to 4 cu ft)
haha good bye trunk space

and yea when drawing up plans i made sure i was calculating the airspace inside the box

[geolemon]

yes you were a good help thank you
so the air inside the port doesnt not count for box volume

No - think of the port as a speaker!
There's air inside that tube that ends up being set into resonance - moving air outside and inside the box just like your speaker cone. ]all together including the subs and ports i need about a 3.94 cu ft box(would it matter if i bumped that up to 4 cu ft)
haha good bye trunk space
and yea when drawing up plans i made sure i was calculating the airspace inside the box[/QUOTE]
That's pretty normal for a pair of 12's. There's no "including port and subs", because the air inside the box is a dynamic element that affects efficiency and frequency response, where anything else (are you using any bracing to make the box more rigid? ...for example ) is non-air, taking up space inside that box. Heck, you could mount the subs inverted (magnets out), and have the ports external outside the box if you want. You could design the box any way you want, and as long as your interior air volume, and port dimensions are correct, it'll perform as it is supposed to.

[Rovin]

i normally use this

http://www.the12volt.com/caraudio/boxcalcs.asp

&

http://www.carstereo.com/help/Articles.cfm?id=31 ........

[geolemon]

i normally use this

http://www.the12volt.com/caraudio/boxcalcs.asp

&

http://www.carstereo.com/help/Articles.cfm?id=31 ........

That volume calculator doesn't provide any means of accounting for the displacement of your subs, displacement of your ports, or displacment of any interior bracing that eat up volume inside the box.

Be sure you always calculate those volumes, and then subtract them from the air available inside the box (or add them to the total volume you need inside the box before you begin calculating - but at that point, it's as simple as dividing by the desired width and depth to find your resulting height)!

[cargodz]

And Don't use particle board... use MDF (costs a lil more but much more solid for box building) either that or 3/4 inch plywood will still work better than partical board too.
Partical board and OSB have their place, but wouldn't suggest building a box with it... great for amp racks and trim work though

[Rovin]

yes Geolemon i was fully aware of that & what u write is exactly what i have always done

but thats a good heads up for ppl who were not sure before ....