Building my first ported

[TPABlazer]

I ran my dumax TS parameters from ED thru winisd, and came up with a 1.724 cu/ft box, tuned for 26.8hz, with a 2 inch diameter port, thats 5.19 inches long.

which will fit into my limits for construction, assuming pvc pipe is a valid port material.

does this sound right? Should I tune higher or lower?

From the Spec sheet wth my 12a:

fs: 27.34 hz
qe: .45
qm: 4.71
qts: .41
vas: 46.27 ltr
sd: 0.0465 m^2
re: 3.61 ohm

mmd: 216.80 g
cms: 0.0002 m/n .152339 mm/n
rms: 8.12 ohmm
sd: 0.0465 m^2 effective radius
bl: 17.49 n/a
re: 3.61 ohm

xmag: 29.5 mm
Xsus 26.00
Xmax 25.4
mag center -2.2mm
sus center 2.6mm

Also its going in my blazer, firing toward the tailgate if it wont sound better firing up?

[helotaxi]

You will have serious issues with port noise. You need a much larger port to keep the velocity of the air moving through it down. It will require a longer port, but the 2" port will sound terrible.

[dbornotdb]

2.11 cuft after dispacement. Tuned to 26.8 hz. 4" port, 19.5" long. Nice and flat. Face the sub up with the port firing back to the tailgate.

[Fitz]

i've seen it on several seperate occasions... does it matter what way the port faces/which way the port entrance is in the box.. and how does it affect SQ/SPL?

[TPABlazer]

2.11 cuft after dispacement. Tuned to 26.8 hz. 4" port, 19.5" long. Nice and flat. Face the sub up with the port firing back to the tailgate.

can the 4 inch diameter pipe have a bend in it? since I cant fit that much back..or should I just use a slot port and get it to equal the same port volume?

[dbornotdb]

i've seen it on several seperate occasions... does it matter what way the port faces/which way the port entrance is in the box.. and how does it affect SQ/SPL?

What you don't want is for the port to exit on the opposite side of the subs mounting surface. The backwave would just go straight through and out the port. Not really allowing for a wave to develope. I might not have explained it exact, put you get the idea.

[dbornotdb]

can the 4 inch diameter pipe have a bend in it? since I cant fit that much back..or should I just use a slot port and get it to equal the same port volume?

The PVC can definatly have a bend in it. Just remember to subtract for the length of the bend when added.

And if you choose to slot port it, the opening of the slot has to equal the opening of the round in square inches. Once you have that, the length of the port is the same. The length is what tunes the box.

[dbornotdb]

I also wanted to add this so it might help you understand how to change the ports.


Round To Square Port Conversions

Pie x R squared

For example::Say you have a 6" port that is 13" long, take half of the port size (Radius), in this case 3". Now multiply 3x3, (R squared). This is 9. Now do 9xPie, which is 9x3.14. Now you just got the square inch of your port. In this case 28.26.

Now you can design a square, rectangle, triangle or a port that is the sub logo. As long as you match the square inch.

For example::28.26 could be made into a 3"x9 3/8" opening, 13" long.

The lenghth of the port will stay the same. It determins the tuning frequency and is not effected by the conversion.

[helotaxi]

What you don't want is for the port to exit on the opposite side of the subs mounting surface. The backwave would just go straight through and out the port. Not really allowing for a wave to develope. I might not have explained it exact, put you get the idea.

This depends entirely on how everything is facing. You don't need "a wave to develop" we are not building a TL enclosure based on 1/4 wave theory, we are building a bass reflex enclosure based on a Helmholtz resonator. Basically the way the standard ported enclosure works is it vents the pressure created by the inward stroke of the sub and the resistance created by the length and area of the port slow the pulse so that it is in phase with the pressure wave created by the outward stroke of the sub. The pressure coming from the port will be perfectly in phase with the direct pressure from the sub at the tuning frequency. As you move away from tuning the phasing becomes less and less perfect and the reinforcement becomes less and less. Any time the port opening is not on the same face and on the same plane as the sub itself, the phasing will be other than optimal. You can negate some of this by corner loading the port or the sub and allowing the pressure coming from one or the other to reflect off a trunk wall. It will not be perfectly in phase but it will be better than nothing.

[helotaxi]

[COLOR=Blue]The PVC can definatly have a bend in it. Just remember to subtract for the length of the bend when added.

You don't use the whole length of the bend. The bend is equivelent to a length of the pipe as long as the elbow section measured down the center.

[dbornotdb]

You don't use the whole length of the bend. The bend is equivelent to a length of the pipe as long as the elbow section measured down the center.

Correct. You do not measure the "bell" end of the bends. You measure the actual usable pipe there. You measure from end to end using the center as a guide to get correct measurments.

[TPABlazer]

eh?i dont get this measuering across the bell but not the elbow and then carry the niner...