What frequency should I tune my ported box for a S12L5???


I just built two boxes for my S12L5....one is a sealed box about 1.1 cu ft (15"x15"x12") and thw other is a box i wanna port, or vent, its about 2 cu ft (20"x20"x12.5").....both are made of 3/4 in MDF and the one i wanna port is not put together....just cut out.

i wanna know what a good frequency to tune the port, or vent, to would be??? (somewhere between 28hz-40hz) my amp has a 15hz-40hz subsonic filter on it. but i dont wanna put a 90degree turn in the port....i dont know how to calculate for that...but if i need to, how do i???

i wanna put the sub in the sealed box or the ported one....which ever i like better when i get the ported one done
thanks for any help

New member
Username: Yhammack

Post Number: 10
Registered: 01-2004
Best program to help you out is WinISD

New member
Username: Glasswolf

Post Number: 944
Registered: 12-2003
a: box is too small to port.
b: do you want max SPL or do you want the box to hit deeply?
deep, tune to 28Hz.
max SPL, tune the box to the resonant freq of the vehicle.

glasswolf...Kicker says i can have a vented box that is 1.75 cu ft for the solobaric....

that would mean that to port in a 2 cu ft box could be .25 cu ft and still have the needed airspace for the solo.....

i used this calculator to try and build a box

it says that if i tune the 20x20x12.5 box to 30hz then to port needs to be 15.929in with a 4 inch port and the box will still have 1.988 cu ft volume left....will this work????is the calculator right???


Silver Member
Username: Glasswolf

Post Number: 962
Registered: 12-2003
you said earlier the box was 1.1cu ft.
that was too small to port.

remember to figure for driver and port displacement.
subtract both from the box volume when figuring the net and gross volumes.

Bronze Member
Username: Its_bacon12

Post Number: 85
Registered: 12-2003
he said that he has 2 boxes he wanted to port one being 1.1 cubic feet and the other being 2 cubic feet so.....hehe

oh btw glasswolf, my box that i made is dont, u wanna see some pics of it? its 2.75 cubic feet tuned to 34Hz

Silver Member
Username: Glasswolf

Post Number: 976
Registered: 12-2003


I keep hearing people say they tuned their port to about 34hz....would that be a good frequency for my S12L5 or not???? also i know that the biger the opening of the port, the longer it has to be, but can you tell a difference in the sound if the port has a larger opening??? is the port noise lowered???or what???

also..I was gonna use the same box i wrote about above (2 cu ft one)and put a vent in it that was tuned to 34hz....will there be much of an increase in SPL compared to the 1.1 cu ft sealed one its in now???and is 34 hz a good frequency to tune the solo to.....
and one more thing...i heard that if i tune a box to the frequency that is best for the truck it will be loudest....how do i find this frequency???

thanks for any help

Silver Member
Username: Glasswolf

Post Number: 980
Registered: 12-2003
larger diameter ports cause less noise, yes.
This is often called "port whistle" which is very annoying when it happens.
34Hz is a good spot for tuning.. you don't want to use a frequency below that of the Fs of the sub.
remember when you calculate box volume for calculating ports, you need to subtract teh driver displacement and port volume from the interior volume of the box.

I'm gonna tune the box to 34hz but i heard that if i tune it to the resonance frequency of the truck, then it will be that loudest it can be...(i think you said it, glasswolf) but how do i find the resonance frequency of my truck????

Silver Member
Username: Glasswolf

Post Number: 991
Registered: 12-2003
yeah that is true, but that frequency is usually around 60Hz, and the box will sound like crap.
loud yes, good no.
Are you after SQ or SPL here?

glass, im going for a little more SPL than i have now (with the L5 in a sealed box).
I dont want it to be real sloppy. I want the extra spl that a vented box gives....will it give really give me a full +3 dB compared to my sealed one??? I am putting it in a 98 chevy ext cab truck.

also i have seen you recommend the JBL BP600.1 but it doesnt have a subsonic filter so i couldnt use it for a vented sub...right?? or can i put one on it some how???
all i have for the sub is a Boss r1400d (it says 500x1 @ 4 ohms and i'm running it in 1 ohm and the amp is not that efficient its rated 700 @ 1 ohm so i'm guessin its given me bout 600 @ 1 ohm)

it does pretty good in the sealed box its in now but that box is 3/4 plywood (1.1 cu ft).....lol
will i be able to notice a difference in the sound it i put it in an 3/4 inch MDF sealed one(1.1 cu ft)???just had to ask that....

glass, by the way, these are the exact messurments i am going to use for the vented box:

Height: 20"
Width: 20"
Depth: 12.5"
Wood Thickness: .75"
Speaker Displacment: 0.07586 cu ft
Port Frequency: 34hz
Round Port Diameter: 4.5 in
Rectangle Vent Opening: (Height)1.994" (Width)7.976"
Gross Box Volume: 2.103 cu ft
Port Volume: 0.143 cu ft
Port Length: 15.544 in

do you have any way to check these numbers??? will they work???
I used this calculator to create the box (ported box calculator):

thnks for the help youve given me so far...

Gold Member
Username: Glasswolf

Post Number: 1009
Registered: 12-2003
good calculator to use.
you can get an add-on subsonic filter for the JBL amp. they're cheap.
you also want to run two Y-splitters for the RCA inputs so all four inputs get audio signal.
that'll make the JBL perform at it's peak.
tune the box low, to 34Hz if you want a little more SPL over sealed, and you want it to sound good.
Use a bandpass box and tune it to the vehicle's resonant freq if you want the most SPL you can get, with no SQ in mind at all. (think SPL competitions)
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