HEy.. I'm about to build my own Ported Box.. and I need someone to help me out with the Calculations.

My Box is going to be 22 x 13.5 x 15 inches.. I'm looking to tune to 36hz. Unless someone recommends another frequency.

Any help would be awesome!

BTW.. I'm using a JBL 600.1 and I have a 2 ohm DVC Type R running on it.. I'll be running it at 4 ohms.. so only 300 watts going into it.

Thanks in advance!

Internal dimensions? If so, that is 2.58 cuft gross volume, so try a 4" diameter port 7.75" long.

External dimensions with 3/4" wood? If so, that is 1.92 cuft gross volume, so try a 4" diameter port 11.5" long.

Hey! Thanks

Do you mind me asking you what program you used to do that? BTW.. it's the outer dimensions.

Would you recommend a bigger enclosure? Because my trunk certainly has room for it.

Also.. when you said gross volume.. does that include displacement for the sub and port?

[ August 01, 2003, 03:01 PM: Message edited by: Gabe ]

Hrm, I'm building a sealed box (Ext. 16" x 13" x 10.75") which is 0.8ft^3 (recommended).

I'm running same setup except I've an Alpine
amp (MRP-M350) pushing 350W @ 2ohm.

Will find out how it sounds in a couple days
when evertyhing gets put together

Right now I have it in a 0.9 cubic foot sealed box.. well.. not really sealed. It's just a spare box my friend had laying around.. it leaks.. so I decided it's time to build my own.

Might as well try ported.. I'm starting to think my box is too big? 1.75 was the recommended max for ported boxes.. any suggestions? [img]graemlins/dunno.gif[/img]

Thickness - 0.75" MDF
Dimensions - 22 x 13.5 x 15 inches
Gross volume - (22-1.5)(13.5-1.5)(15-1.5)/1728 = 1.921875 ft^3
Driver displacement - 0.128 ft^3
Port diameter - 4"
Port length - 12" (11.25" internal)
Port displacement - (3.14159*2^2*11.25)/1728 = 0.0818123 ft^3
Net volume - 1.921875 - 0.128 - 0.0818123 = 1.712062691 ft^3

Tuning - (Using diysubwoofers.org formula)

(k*Dv)+Lv = (23562.5*Dv^2*Np)/(Fb^2*Vb)
Dv = 4*2.54 = 10.16
Vb = 1.712062691*28.319 = 48.4839
Np = 1
Lv = 12*2.54 = 30.48
k = 0.614, 0.732, 0.85 (See http://www.diysubwoofers.org/portcal.htm)

For k = 0.614 (i.e. PVC piping), Fb = ...
(0.614*10.16)+30.48 = (23562.5*10.16^2*1)/(Fb^2*48.4839)
36.71824 = (2432253.2)/(Fb^2*48.4839)
36.71824 = (50166.20363)/(Fb^2)
Fb^2 = (50166.20363)/(36.71824)
Fb = Sqrt(1366.247501)
Fb = 36.963 Hz

For k = 0.732, Fb =
(0.732*10.16)+30.48 = (50166.20363)/(Fb^2)
37.91712 = (50166.20363)/(Fb^2)
Fb^2 = (50166.20363)/(37.91712)
Fb = Sqrt(1323.048893)
Fb = 36.374 Hz

For k = 0.85 (i.e. Aeroport), Fb =
(0.85*10.16)+30.48 = (50166.20363)/(Fb^2)
39.116 = (50166.20363)/(Fb^2)
Fb^2 = (50166.20363)/(39.116)
Fb = Sqrt(1282.498303)
Fb = 35.812 Hz

If you build the box correctly (no leaks), it should be fine ...

[ August 01, 2003, 06:08 PM: Message edited by: Jmac ]

Gabe, why would you build the box bigger then the
recommended spec for sealed?

Anywho, mine is just over 0.8ft^3 (0.80061429 to
be exact) and I already had my wood cut and paid
so I'm not turning back.

Crossing my fingers this sounds good [img]smile.gif[/img]

I'm impressed that diysubwoofers actually uses the end correction factor. Nobody ever thinks of that. ;) BUT then you can see the minimal difference in length it makes and you can see why it is often ignored. Real world - you'll never hear it.

When at work or not wanting to open a full box designer at home I like to use http://tools.autoaudio.com/ventcalc/ for a quick port length number.

I used a calculator for the volumes as shown above and I used an allowance for driver displacement based on similar drivers I am more familiar with.

Wait wait... let's all come to a consensus here.. what should my overall port length be to tune to 36hz..?

Well I said 11.5" and Jmac did his calculations on 12" so right in that range. You wouldn't hear the differnece of 1/2".