single ported sub, or dual port
 

I have my JBL gto 12" sub, right now its is a box thats way to small, i thought it was good, after being built instead of the 1.75, it came out to 1.54, then taking out the slot port and driver, it went to (my calculated) 1.2, and apperently after imputting port specs into a ca;culator its tuned around 50hz!... not good. and i heard using a box wall as a port wall wasent good either, idk

i want to build a new box. ive been using winisd to model one, and i think im going to try a round port, i have tons of long 3" PVC availiable, so possibly a port out of that, but i can get anything.

anyways i have a few questions about if i wanted to do a dual port, or even where i start on winisd to get a box design.... if i wanted to put it in my trunk, driver facing my tailights, could i put a port on either side of the driver? how the heck do you calculate 2 ports in a box?

1. You have to read all the winisd information on how to use it, otherwise you won't know what you're doing or how to do it.
2. You have to enter the t/s parameters of the sub into the winisd chart, then you can calculate using that sub.
3. Most important factors to look for are: Cone excursion with rms power , port velocity with rms power, group delay, and obviously the most important the response curve and spl with rms power.
4. Winisd can calculate using multiple ports, round, square or rectangular ports, and a whole lot of other stuff which is impossible to go through on here.
5. Jbl usually specifies their boxes volume with port and speaker displacement included...so 1.75 cubes is the gross internal volume including port and speaker.

NET volume after driver and port are calculated??

Did they offer why? Assuming the wall is still properly braced, this is fine.

1.75 is the gross internal volume including port and speaker displacement (as per jbl's literature), ergo, net would be around 1.65 cubes given a 4"x10" round port and that sub should use up about 0.10 cubes.

hmm, i see, well i bought some 3/4 MDF and im gonna try a new box with a round port this time, or even 2, one on each side of the driver,

or should i stick with slot? although round sounds easier... also which way should the round port opening be facing in the box? if the speaker is facing the front is a staight port a few inches off the back wall ok, or if i need to put in a PVC elbow can i make the port opening face up inside the box? can it go any way as long as it is IN the box or what?

the car audio guy locally wants 175 to build one, with sheets at 35$ a peice i can again i guess, really dont want to put thet much into it, most of its labour anyways

Round ports are actually better flowing all things considered, and they're easy to add as long as you design the box with the placement in mind. Try to keep them straight, but an elbow is fine, and use a calculator to determine the right size or go with the jbl recommendation (4" x10"). Try to keep the port on the same face as the sub, but generally anywhere on the box will work fine if you can't. Build it yourself if you have the tools and some skills...main things for a box to work (assuming correct volume etc...) is to build it strong and seal it properly...it can look like crap and still perform (just look at spl boxes!!)