Is there a difference where the port is?

[carshateme]

I'm going to be purchasing 2 lvl 3 12" dc subs soon and 12" don't fit in my trunk sideways wise due to the fact that my trunk is only 13.5" high. So I decided to put the subs on the top.

But the main question is...do I want a box with a single port on the side like this box 1

Or would a port in the center be better off like box 2.

or would box 3 be the ideal for a sit up box...where the ports run on the bottom of the box.



Appreciate the comments. and the boxes aren't going to look exactly like in the pictures. like box 3 is not going to have a divider in the middle but the port will run in the middle of the box.

[m4ick]

I don't have confidence that there is enough room for box 3's port to actually wrap all the way around the box and reach the listening area without it being completely mis-tuned.

Box 1 is the easier to construct and allows for a longer port if need be (you can turn the corner); more power takes a wider port, and a wider port takes a longer port. The center port is going to be more math intense to design if it hits the back of the box (standard programs for box design don't split the port part way through).

Keep the box as short as possible to allow airflow and use box 1.

[m4ick]

And be sure to account for your sub woofer's "mounting depth" + at least the width of the pole vent (the little hole on the bottom of the sub). So if you turn the corner at the back of the box, make sure you don't get too close to the back of the sub.

[AKHeathen]

Well, box 2 used to be one of my more preferred designs, when you have the room to fire it rearward, and box1 is a pretty common box i have seen from builder/designers, especially with smaller drivers, like 8's, though it is something i never seem to choose with my designs...... Now, i would say box3 would be the best bet, if you have the necessary space to do so. Aside from mounting depth, you need to have clearance past the vent, more than 2x the port width(smallest dimension) and, i would say, 2x the port sq-in passage past the box, or you will end up with extra un-tuned porting in the trunk. Not sure how prepared you are to build, but one option is the use of sonotubes built into the box to mount the subs and fire them rearward.... Just an idea to kick around....

[m4ick]

Originally Posted by AKHeathen

box1 is a pretty common box i have seen from builder/designers, especially with smaller drivers, like 8's, though it is something i never seem to choose with my designs......

That design DOES cause one driver to have more excursion than the other (don't know the math but have seen it consistently) but if the port is too long then box 1 does the trick. If you can keep the port slim enough not to hit the back of the box (within twice the port width you MUST cut short or turn a corner), then box 2 is great and will keep both subs working evenly. But at a higher power levels you need a wider/longer port.

[AKHeathen]

I've done both shared, and separated centerfire vents, and only a few deeper enclosures did not wrap the rear wall. The shared center did seem to have better output/sound at higher levels

[AKHeathen]

Oh, and i would use a devider if you use box3.

[carshateme]

In box 3 there is a divider, but someone put a thought in my head. What about triangular ports..I don't know how to calculate them though, but it seems like a good idea...although I'd still have to put them on the bottom due to the fact that my subs have to go upwards and my port is preferred to be pointed towards the trunk opening

[AKHeathen]

I'VE seen many triNgle ports in action, but i have not, and never will use them. The angles are just too bad. You would calculate them like a square port, just the same way they teach you in school for finding area....