How? Port Displacement....and Box Design...

[eliassami5]

Why all the guessing and approximations?

The easy way -

You know what you want your net volume to be.

You should know the driver displacement.

You know how much port area you need.

Calculate the port length based on area (you should know approximate H x W too for a slot port).

You now know port displacement.

Gross volume = net volume + driver displacement + port displacement.

the problem is that he wants 4 cubic feet (minus the port and sub disp.) but when he designs his box and subtracts out the port and sub displacement it dosent come out right. Its a game of guess and check, its not like hes building a wall which dosent involve all of this designing and re-designing to fit in a particular tight space.

[bkolfo4]

I don't get your calculations above. I know this is off:

"port displacement is 1.67 cubic feet for all 4 ports combined" ??

Even with an OD of 3.5", that is (1.75^2 x pi) x 8" long x 4 ports = 308 / 1728 = .18 ft^3 displacement.

He needs 4 ft net

driver displacement is 0.2 ft

He wants (4) 3" ports. they need to be 13.36" long for a 35 Hz tune (not 8.6" long). We will call it 13", since up to 40 Hz is acceptable to him.

Assume they are made of PVC, so the displacement (subtract .75" where they go through the wood) will be about 0.27 ft for the ports

Gross volume needs to be 4.47 ft^3 or 7730 in^3.

We know max dimensions are 23"long X 37"wide X 15"tall. Assume 15" tall, that is 13.5 internal. 7730 / 13.5 = 572.5

Need a length x width that equals 572.5. (4) 10's won't fit across 37", so go with 23" deep (21.5" internal). 572.5 / 21.5 ~ 26.75

Box can be 15" tall x 28.25" wide x 23" deep.

(4) 3" ports 13" long.

That is 4 ft^3 tuned to 35 Hz.

Brian

[Rogers]

save the money on ur system and buy a better ride man...just IMOO

what does it matter.... its a car with a big trunk and a decently strong electrical system.... the car was given to me=free... and i have all the equipment... i just need a box... and thats all i asked for... im not even sure you know what kind of car it is.... i would prefer this to NOT be a usless post thread.....thank you!

[Rogers]

I don't get your calculations above. I know this is off:

"port displacement is 1.67 cubic feet for all 4 ports combined" ??

Even with an OD of 3.5", that is (1.75^2 x pi) x 8" long x 4 ports = 308 / 1728 = .18 ft^3 displacement.

He needs 4 ft net

driver displacement is 0.2 ft

He wants (4) 3" ports. they need to be 13.36" long for a 35 Hz tune (not 8.6" long). We will call it 13", since up to 40 Hz is acceptable to him.

Assume they are made of PVC, so the displacement (subtract .75" where they go through the wood) will be about 0.27 ft for the ports

Gross volume needs to be 4.47 ft^3 or 7730 in^3.

We know max dimensions are 23"long X 37"wide X 15"tall. Assume 15" tall, that is 13.5 internal. 7730 / 13.5 = 572.5

Need a length x width that equals 572.5. (4) 10's won't fit across 37", so go with 23" deep (21.5" internal). 572.5 / 21.5 ~ 26.75

Box can be 15" tall x 28.25" wide x 23" deep.

(4) 3" ports 13" long.

That is 4 ft^3 tuned to 35 Hz.

Brian

wow confusion...lol.... lets just clear up some stuff... the ports are 3"id and 3.25" od...... im going to go get a fresh sheet of mdf today so i hope we can get this cleared up....

[Nightshade]

Someone said that you need 14-16 sqin per cuft for a box and that's true when you are using a slot port. Since you are using aero ports you can get away with much less port area. You'd be fine to do around 9-12 sqin per cuft when using an aero instead of trying to get 14-16 with them. Unless you aren't using aeros and just some round pvc, then I would do a little more port area per cuft since the ports won't have the flares on them.

[bkolfo4]

(3) 4" ports would be more port area. If you bought aero ports from PE, it would work even better.

http://www.parts-express.com/pe/showdetl.c...tnumber=268-352

I would also double the top baffle.

Need 4.2 ft^3 + port displacement.

(3) 4" ports need to be 17" long (that is how long aeros come - tunes around 36-37 Hz in this case)

Port displacement is around 0.4 ft^3, so you need 4.6 ft^3 gross. That is 7948.8 in^3

With 23 deep x 15 tall external, 7948.8 / (21.5 x 12.75) = 29 internal width.

Box will be 15" tall x 23 deep x 30.5 wide. 1.5" top baffle, 3/4" sides and bottom.

4 ft^3 NET volume, (3) 4" ports tuned to 36-37 Hz.

If you are not going to buy aeros, it can be adjusted to lower the tuning to 35 Hz if you want.

Brian

[Rogers]

(3) 4" ports would be more port area. If you bought aero ports from PE, it would work even better.

http://www.parts-express.com/pe/showdetl.c...tnumber=268-352

I would also double the top baffle.

Need 4.2 ft^3 + port displacement.

(3) 4" ports need to be 17" long (that is how long aeros come - tunes around 36-37 Hz in this case)

Port displacement is around 0.4 ft^3, so you need 4.6 ft^3 gross. That is 7948.8 in^3

With 23 deep x 15 tall external, 7948.8 / (21.5 x 12.75) = 29 internal width.

Box will be 15" tall x 23 deep x 30.5 wide. 1.5" top baffle, 3/4" sides and bottom.

4 ft^3 NET volume, (3) 4" ports tuned to 36-37 Hz.

If you are not going to buy aeros, it can be adjusted to lower the tuning to 35 Hz if you want.

Brian

ok so i bought a sheet of mdf today i doubt its enough but i can always get more... id rather not buy aeros... i just bought 5 feet of 3"schedule40 pvc today... ok so let me get this understood....

15"tall x 23"deep x 30.5"wide.... double baffle..... ok i got that....

so for the ports really i could go anywhere from 9.71 to 13.36.... according to the port calcs that 40 and 35hz so anywhere inbetween would be a good correct????

since im doubleing up the baffle is it necessary to do anymore bracing???? im thinkin i proble wont.....

man i hope i dont fuck this up......lol.... so for board placement... should i just cut the bottom piece and put the walls on top of it... and then put the baffles ontop of them or should the top of the baffle be flush with the walls? ive seen it done both ways.... i just didnt know if you adjusted the enclosure for flush baffle displacement..... let me know man!

[Rogers]

mabe you just need to draw it out with crayons for me.... or sketchup, whatever your best with....lol

[bkolfo4]

I cut my bottom and and top baffles full size and sandwich the walls between them.

Port lengths are correct for (4) 3" ports.

(4) 3" ports are less volume than (3) 4" ports, so you can make the box 29.25" wide if you want. Not going to make much difference.

Sounds good, and I am sure it will turn out GREAT.

Brian

[Rogers]

I cut my bottom and and top baffles full size and sandwich the walls between them.

Port lengths are correct for (4) 3" ports.

(4) 3" ports are less volume than (3) 4" ports, so you can make the box 29.25" wide if you want. Not going to make much difference.

Sounds good, and I am sure it will turn out GREAT.

Brian

so then i could just even it out and do 30 wide just to make it easier.... as long as i keep the ports between say 9.5 and 13.5 inches.... not going to make much difference... right... it sounds like it will be in the tuning range of what i want it to be....

i appreciat your time man....... that goes to everyone, thanks..... except the asshat that told me to get a different car...