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View Full Version : porting an interveted sub



evo2k3
12-21-2002, 12:25 PM
I have been building boxes for a few year now, But i have never ported one. I have currely got a 12w7 inverted, my question is this:
I would assume I can still port it the same way as any other box right? I know nothing about the number of ports, diameter or length (i think shape is a question as well). Someone refer me to an FAQ or tutorial on porting? Includeing somewhere to get the parts (flaired ends, pip extension....ect).

evo2k3
12-22-2002, 12:32 AM
unfortunatley....i haven't the slightest clue what the "normal" way is, more specific quetsions:

round ports....right?
what diameter ports?
how many (i assume 2?)
how to calculate port length (JL recomeds tuning the box to something like 32hz?
tricks of the trade to prevent things like wistling and other unwanted noise?

anything else I need to know?
its amazing, i have build 14 or 15 sealed boxes, but never learned a **** thing about porting. Thanks experts!! :)

evo2k3
12-22-2002, 12:44 AM
http://www.jlaudio.com/subwoofers/pdfs/W7_DS.pdf

i was reading a bit on JL's website and they suggest the use of slot ports...what are the advatages/disadvatages of this....is there a 'general' consesus on which to use, whats best for my application?

F150Matt
12-22-2002, 02:55 AM
Well, slot ports are generally easier because there is less chance of port noise(whistling etc.) JL probably recommends a certain size port and length. Usually the manufacturer recommendations are for daily drivers with decent sound quality, and they usually offer 2 or 3 different sized boxes. If you are planning on competing in SPL comps, you'll want a bigger box than recommended and a bigger port. I recommend you call JL and tell them exactly what you want out of the sub and then let them tell you how big the box should be, tuning, and port size. Good luck.

evo2k3
12-28-2002, 11:15 PM
so i was calulating the port length....originally for 4 x 3" ports and they get way to long for my box, so i found using 2 x2" ports creates a port length around 7 inches (perfect in my setup) i could prob just do one 3 or 4" port as well, what are the advatages to having more or less cross sectional area, or fewer ports? is there a rule of thumb that says one way is better? last question, how acurately do i need to cut the ports, am i going to have to cut and that file down the end untill i get it perfect (then file to round the ends) or if my port is 7.75" inches can i just cut it with in 1/16th or so?

evo2k3
12-28-2002, 11:27 PM
i am leaning more twords a slot port now, and jl suggest it for the w7.....does a slot port always need to take on the "L" shape? it seams a bit simpler to make this type of port....but if i wrap the carpet around the edge, does that change the size of the port enough to change the tunning?

evo2k3
12-28-2002, 11:31 PM
can you refer me to a website to read up on slot porting...i dont quite understand it yet?

evo2k3
12-29-2002, 12:40 AM
ok....screw slots...im going back to round......how do i calulate the speed the air is coming out at? these are the specs encase they help:

2x2" pr 1x3" port(s) ?!?!?!?!!? someone decide for me!
volume: 1.77 ft^3
tune freq: 32hz

someone had a website with a port length calulater on it....lost the link though?

evo2k3
12-29-2002, 12:52 AM
1 jl 12w7.....with a max of 700 watts going to it.

btw....i really apreciate the help man!!

evo2k3
12-29-2002, 12:56 AM
void this post

evo2k3
12-29-2002, 01:01 AM
Originally posted by Jmac
You're going to need a lot more port than that ;)

5" diameter looks about right ... I doubt you could get away with a 4" ...

could i do something will like 2x 3" ports? 1 5" port doesn't fit asteticly in my system, but i want spl/sq over looks....if i had to i could make it work.

mwess
01-02-2003, 06:01 PM
Are you sure you have a W7 inverted? From what i have seen of those if you invert it you will smash the surround. and to mount it you would actaully have to drill a screw through the surround. So pick another sub to tell storeys about.

evo2k3
01-04-2003, 01:32 PM
Originally posted by mwess
Are you sure you have a W7 inverted? From what i have seen of those if you invert it you will smash the surround. and to mount it you would actaully have to drill a screw through the surround. So pick another sub to tell storeys about.

ok *******, first off you obviously know less than me about this. yeah i do have a w7 inverted, i will go ahead and enlighten you as to how JL tells you to do it. you build your stanard box, whne cuuting the hole for the circle you make it the diameter of the outer most mountig ring on the sub, so the whole sub clears it (if you left it like this is would just drop right through). now you make you 1" baffel for the sub, mount the sub to it and then glue, silicon and screw the baffle to the box so the speaker suround moves in and out of the larger cutout in the orginal box. so pick another ******* to try to call on there bluff.

evo2k3
01-04-2003, 01:36 PM
ok jmac you gave me these ssuggestions :\
Area of two 3" ports = 2(Pi)(1.5)(1.5) = 14.137 square inches
Area of four 2.5" ports = 4(Pi)(1.25)(1.25) = 17 square inches
Area of five 2" ports = 4(Pi)(1)(1) = 15.708 square inches
Area of one 5"port = (Pi)(2.5)(2.5) = 19.635 square inches

but said i would want at least 16" of port area, would the 2x3" ports (14in) create a noticable diference in port noise? secondly, how do i calulate the length they need to be, im pretty sure that they are going to need to bend around and ****, so what do i use for all of those bends, i was thinking just use 3" pvc all the way, but i dont know what i would put on the surface of the box to finish it? please include the equations for calulating port length (btw im woking with about 1.95 ft^3 before port displacment.)

mwess
01-04-2003, 02:14 PM
I was being an *******, and i really thought you coulndt invert that speaker, ive seen them a few times but never inverted, and i looked at the mounting thing on their website. What you said to do to invert it makes sense and i will think twice before i question someones setup...

evo2k3
01-04-2003, 02:26 PM
first off sorry mwess....i snapped i was in a bad mood :( anyways back to the topic....i just got this winisd pro to do some calcs for me, and do people leave all the defaults for air pressure, humidity, should i put in the actuall peak power the sub is getting? i ask because it its showing me a air vel. of 1200 ft/s which is like 390m/s, well over the 30m/s recomendation....somehow i think i did something wrong....btw its a 12w7 in a 1.95cu ft box. tuned to 32hz...in that program, is the crossectional area, the same as what you refer to as port area? i would assume soooo.

evo2k3
01-04-2003, 02:39 PM
ok i was looking at the wrong thing...i went to the rear chamber port air velocity, now i want the peak of that graph under 30 m/s (98.4 ft/s) right? if it gets really close to that, or a little above, is it going to make a huge diference? or might i get port noise every now and then? for example, 2 3" ports keeps the lengths to resonable sizes, but puts the vel. at 38 m/s...this just simplifies everything for me, how much port noise is going to be seen in that scenario?

evo2k3
01-04-2003, 06:51 PM
im not sure how i have to take that in acount....are you familar with winis pro? i just entered the volume before ports displacment and played with the port diamter and number of ports.....is the program taking it in acount, or do i need to do something else? also i want to just use pvc (3") so i have access to right angles and such, but how or what do i use for a flange on the surface? with quite length ports i am afraid they are going to rattle against the box, is this a legit conern, should i ankor them inside somehow? remmeber...this is my first shot at porting.

evo2k3
01-04-2003, 07:15 PM
well im not changing the tunning freq ever....its going to be 32hz....are you saying the total displacment for the ports (no matter what combination of size and length i use) is always going to be the same in the same volume box? if so what is it? also i can i take that in acount, as the volume changes, the port length change, which then changes the volume again....seems cirular, what am i missing?

evo2k3
01-04-2003, 07:57 PM
ok...so the program is useless for port length basicly right? how do i calulated the length needed then?

evo2k3
01-04-2003, 08:38 PM
Originally posted by Jmac
I can do it for you ;) I don't have an equation for it, unfortunately, but I do have a professional program that does it accurately :)

All I need are the exterior dimensions of the box, width of wood, and port size (2 x 3" ports, right ?) :)

box is in construction so ill give them to you tommorow...whats the proessional program? how much it cost you, i might be intrested. you dont actully need to dimmensions, wont the volume be sufficeient? i ask because its a rather odd shape...ill post a diagram tommorow.