PDA

View Full Version : Quick Help with Math

terra
08-11-2007, 08:16 PM
OK im building my box at 12 cu ft tuned to 31 hz. 41x20x30 roughly 192 sq in of port area...port back subs up. port going along the bottom width 39 inches wide and 5 inches tall with a kerfed port. i get a port length of 14.54 inches. correct or i done screwed up?

terra
08-12-2007, 09:12 PM
help ?

ngsm13
08-12-2007, 09:17 PM
Are those external dimensions?

How big is the flare on the port?

nG

terra
08-12-2007, 09:52 PM
those are external..and the flare on the port..i havent decided yet. how will that affect port length? i thought it was measured from where the flair ended and became port..

ngsm13
08-12-2007, 10:29 PM
With the dimensions you gave, you'll have a total internal volume of 12cubic feet.

This does NOT account for port displacement, driver displacement, or anything.

This means if you built that exact box, sealed. It would give the drivers 12cubic feet minus their actual displacement.

Using the specs you gave me. Your NET internal volume (the volume the subwoofers will actually "see") is 9.7cubic feet.

With you port dimensions and length, NOT counting the flare, it will be tuned between 45-46hz.

So, your enclosure would actually be 9.7 cubes tuned to ~46hz... even higher with the flare.

nG

ngsm13
08-12-2007, 10:30 PM
Just an :fyi:

nG

terra
08-13-2007, 03:56 AM
ok sorry i made the mistake in the dimensions. its 41x32x22 which gave me 12.9 cu ft. minus 3 cu ft for subs and bracing and port to get 9.9 net cu ft. port 5 inches tall and 39.5 in wide..i get a depth of 11.58 inches. how do i account for the flare on the port?

ngsm13
08-13-2007, 09:23 AM
ok sorry i made the mistake in the dimensions. its 41x32x22 which gave me 12.9 cu ft. minus 3 cu ft for subs and bracing and port to get 9.9 net cu ft. port 5 inches tall and 39.5 in wide..i get a depth of 11.58 inches. how do i account for the flare on the port?

How the **** are you doing your calculations? And what program are you using to give you port length?

This gives you a total volume of 14.3cubes.

Subtract port, driver, and bracing displacement and you are down to 12.3 cubes NET volume. With 39.5 x 5 x 11.75 port, you are tuned to ~40hz.

nG

terra
08-13-2007, 03:30 PM
haha i totally forgot to change the dimensions there my bad...its been a long couple days. i made the calculation off old dimensions again. so with those dims i got 14.3 cu ft. so ok 12.3 net cu ft and a port length of 13.68 inches. i hope i didnt forget anything this time

ngsm13
08-13-2007, 03:47 PM
Still 12.3cubes NET @ ~41-42hz

nG

terra
08-13-2007, 05:53 PM
ok just tell me this as apparantly im missing something. how long does the port have to be if 12.3 net and port of 39.5x5 tuned to 31 hz....?

ngsm13
08-13-2007, 07:42 PM
ok just tell me this as apparantly im missing something. how long does the port have to be if 12.3 net and port of 39.5x5 tuned to 31 hz....?

That will change your dimensions.

You need to pick a NET volume, TWO of the Three Dimensions of your box, and a Port size...

Then you solve for the third side by adding NET Volume + Sub/port/brace displacement.