Index Page  

Vent Conversions

Rectangular ports act basically the same way a round port does. Because of it's shape, a rectangular port is less likley to produce port noise. For example, when you blow across a top of a soda bottle, you can get it to whistle. If it was a square or rectangualr shape, it would be much more difficult to produce a note. Sometimes it's easier to build a rectangular equivalent of a round port when a large diameter is required. It's also less of a task integrating it into an enclosure when a longer port length is needed. To calculate the area of a port, this formula - (Diameter/2) x (Diameter/2) x 3.14 is used. Below you'll find the areas for some commonly used ports.

 
Areas for Round Ports
Diameter in Inches
Area in Square Inches
2 inch
3.14
2 x 2 inch
6.28
3 inch
7.07
2 x 3 inch
14.14
4 inch
12.57
2 x 4 inch
25.14
5 inch
19.63
2 x 5 inch
39.26
6 inch
28.27
2 x 6 inch
56.54

 

Once you have the area, it's relatively easy to figure your rectangle dimensions. Take the area and divide it by the width you want to work with for your rectangular vent. Let's say your enclosure and woofer call for a 6 inch round port (area = 28.27 square inches) and you want to use a 6 inch wide port. Here's how you arrive at the height - 28.27 / 6 = 4.71 inches. Generally, it's best to keep the Height to Width ratio no greater than 1 to 5. Below is a table with the rectangular equivalents to common port diameters in various Height to Width ratios.

Rectangular Equivalent of Round Port (in Inches)
Inside Diameter
Surface Area
1:1
1:2
1:3
1:4
1:5
1
.079
.089 X .089
.063 X 1.25
.051 X 1.53
.044 X 1.77
.040 X 1.98
2
3.14
1.77 X 1.77
1.25 X 2.51
1.02 X 3.07
.089 X 3.54
.079 X 3.96
3
7.07
2.66 X 2.66
1.88 X 3.76
1.53 X 4.60
1.33 X 5.32
1.19 X 5.94
4
12.57
3.54 X 3.54
2.51 X 5.01
2.05 X 6.14
1.77 X 7.09
1.59 X 7.93
5
19.63
4.43 X 4.43
3.13 X 6.27
2.56 X 7.67
2.22 X 8.86
1.98 X 9.91
6
28.27
5.32 X 5.32
3.76 X 7.52
3.07 X 9.21
2.66 X 10.63
2.38 X 11.89
8
50.27
7.09 X 7.09
5.01 X 10.03
4.09 X 12.28
3.54 X 14.18
3.17 X 15.85
10
78.54
8.86 X 8.86
6.27 X 12.53
5.12 X 15.35
4.43 X 17.72
3.96 X 19.82
12
113.10
10.63 X 10.63
7.52 X 15.04
6.14 X 18.42
5.32 X 21.27
4.76 X 23.78
14
153.94
12.41 X 12.41
8.77 X 17.55
7.16 X 21.49
6.20 X 24.81
5.55 X 27.74
16
201.06
14.18 X 14.18
10.03 X 20.05
8.19 X 24.56
7.09 X 28.36
6.34 X 31.71
18
254.47
15.95 X 15.95
11.28 X 22.56
9.21 X 27.63
7.98 X 31.90
7.13 X 35.67
20
314.16
17.72 X 17.72
12.53 X 25.07
10.23 X 30.70
8.86 X 35.45
7.93 X 39.63

Go to Vent Length Charts (SIngle and Dual Port)
2 inch Vents    3 inch Vents    4 inch Vents    5 inch Vents     6 inch Vents

1

Tech Center Index       Car-Fi.com (Low Speed)       Car-Fi.com (High Speed)