Home » Sponsored » Pi Speakers » port size
port size [message #52071] Fri, 25 April 2008 08:09 Go to next message
David Morehouse is currently offline  David Morehouse
Messages: 22
Registered: May 2009
my delta 12lf's are in 3.5 cu.ft. boxes,with 2-4in. ports 6.25 in. each in length. 40-45 hz. These are no where near the port size Wayne uses. Why such a large difference? Should I retune?

Helmholtz formula [message #52073 is a reply to message #52071] Fri, 25 April 2008 11:36 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18272
Registered: January 2001
Illuminati (33rd Degree)

Check out the Helmholtz formula below. You can tune to the same frequency using different port sizes. As port area is increased, port length also has to be increased to tune to the same frequency. When in doubt, measure impedance and look for the minimum between the peaks.
Here's a little BASIC program that will calculate the formulas for you:

10 INPUT"Enclosure Volume";VE
20 INPUT"Diameter of Port";PD
30 INPUT"Length of Port";PL
40 VB=VE*1728:PI=3.1415926535:AP=PI*((PD/2)^2):LC=PL+((8*PD)/(3*PI))
50 FR=(13548/(2*PI))*(AP/(VB*LC))^.5
60 PRINT"Fr =";FR;"Hz."
70 GOTO 10

Previous Topic: 2Pi Towers cabinet question
Next Topic: Rear port
Goto Forum:

Current Time: Sat May 28 18:26:00 CDT 2022

Sponsoring Organizations

DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps

Lone Star Audiofest