I am building my first sub, and after all my research and finally getting a volume, etc. I am having trouble with the port. Does anyone know a sure way to figure out what the dimensions of the port should be? I have tried a calculation in a book, and a few programs and spreadsheets. Everyone comes up with a different answer.

Any help is apreciated. Thanks

[micb3rd]

Port dimentions are determined by what speaker you are using (Thiele and small paramaters) enclosure size, vent mouth area and vent tuning point.

It is normally useful to use WINISD or simular software to model your driver and enclosure to have a good play to find a good responce.

What subwoofer driver are you using?

I may be able to surgest a few designs for you.

I have posted my other t/s parameters on other postings and got all the information I needed as far as box size, etc, etc, but I am just stuck on the port. Like I said just keep getting different port sizes depending on prog, book, etc.

These are my paramters

Driver coustic ht-812
Vas 130.000 litres
Qts 0.320
Qes 0.450
fs 26.0 Hz
Xmax 7.62 mm
Dia. 30.48 cm
PEMax 250 watts

Constants
Ro 1.18 kg/m^3
c 345.00 m/s



Enclosure Specifications
Desired Qtc 0.60
Qr 1.88
Vr 2.52
Vb 51.68 litres
Fb 34.66 Hz
F3 39.1 Hz

Sd 7.30E-02 m^2
Vd 5.56E-04 m^3
n0 0.005
SPL 88.9 dB/1W/1m
K1 0.741
K2 110.696
Amax 1.000
Par 0.741
Per 151 watts
PeakSPL 113 dB

okay so this is why i am so confused...

for port sizes these are the calcs i get

winisd - 3" wide 5 " long
4 " wide 10 " long

formula from book - 3" wide 10" wide

website spreadsheet - 6" wide 5" long

see why I am so confused, any suggestions anyone?

thanks

[micb3rd]

I modeled subwoofer driver, the default WinISD box looked ok, it comes up with a enclosure of 60.5 Liters, a vent tune 32.95 hz which gives a port 4.02 inch diamater by 11.51 inchs depth.

The subwoofer will not drop to the deepest of low bass but it looks like it will have ok performance above 30 hz.

Its is a 4 ohm driver so what are you going to use for amplification?