|
Minimum Vent
Diameter |
The first two formulas shown
here represent the minimum usable port diameter for subwoofer
speaker enclosures - they are set up to avoid power compression and
vent noise. The first one is the one I use for bandpass
designs (from "The Loudspeaker Design Cookbook" by Vance Dickason -
I divide the tuning frequency by two before I use it in this formula
though), and the second is a more conservative formula from the
works of Richard Small, which is useful for vented
speaker designs. |
dv - is the required
diameter of the port in inches. |
Fb - is the tuning
frequency of your enclosure in Hertz. |
|
|
Vd - is the volume
displaced by the driver (in cubic meters) traveling through it's
full excursion (peak-to-peak). To figure out Vd for a speaker,
find the Sd value for your driver in the table below, and multiply
that number times the Xmax (in meters) of your
speaker. |
Driver
Diameter |
Sd
(M2) |
18" |
0.1300 |
15" |
0.0890 |
12" |
0.0530 |
10" |
0.0330 |
8" |
0.0220 |
6.5" |
0.0165 |
6" |
0.0125 |
5.25" |
0.0089 |
|
|
Vent
Length |
This formula is also from "The Loudspeaker Design Cookbook". It tells you
how long you need to make the vent. |
Fb - is the tuning
frequency of your enclosure in Hertz. |
Lv - is the length of your
port in inches. |
R - is the inside radius
of your vent tube. |
Vb - is the internal
volume of your enclosure in cubic inches. To convert cubic feet
to cubic inches, multiply by 1728.
If you want to use
multiple ports, divide your enclosure volume by the number of ports
you want to use, then use the result of this calculation as your Vb
in the formula below to find out how long each port should be (a tip
from JL Audio™). |
|
If you want to calculate square
vents, the formula below will give you the value of R to
use in the formula above. |
|
In the formula above, a is
the area of your square vent (height x width), and (Pi) is approximately
3.141592. |