How to Port a Speaker Box
Porting a speaker box is an easy procedure, requiring only that you cut the appropriately sized hole and drop a pre-sized porting tube in place. The work involved in porting a box properly isn't physical in nature -- it involves doing your homework beforehand to determine the exact port dimensions and port tube length that you'll need with a given box, speaker and frequency requirements. Ported speaker boxes are generally much larger than sealed boxes, so you'll need to tread a fine line when retrofitting a formerly sealed box to a more powerful, ported enclosure.
Other People Are Reading
Things You'll Need
- Tape Measure
- Calculator
- Hacksaw
- Drill and bits
- Hole Saw
- Port Tube
- Adhesive
Instructions
-
-
1
Determine your speaker's low-end frequency range, and the bass range that you'd like to enhance. This is the most critical aspect to port tuning, since the port will act as a tuned resonator to enhance soundwaves only within a certain range. For this example, you'll deduce the proper port size and tubing length for a 12-inch speaker in a 16-inch-square box, and shoot for a frequency range of 40 hertz.
-
2
Do some math to determine the inside area of your box in cubic feet. Most speaker boxes are made of 3/4-inch medium-density fiberboard, so you'll subtract 1.5 inches from the speaker's external measurements and calculate the area from that number. To calculate for the 16-inch square box, you'll multiply 14.5 x 14.5 x 14.5, which equals 3,048 cubic inches. Then, you'll multiply that number by 0.000578 to convert it to cubic feet (equals 1.76 cubic feet). You can do this calculation manually, or you can do a browser search for "sub box volume calculator" to find a calculator to do it for you.
-
-
3
Determine the desired diameter of your port (2 inches in this case); divide that by two (equals 1), then multiply that figure by itself (equals 1). Multiply that by 14,630,000 (equals 14,630,000) -- call this figure "the numerator." Now, multiply desired frequency (40) by itself, then by the box volume in cubic feet (1.76) and then by 1,728 (equals 4,866,048). Divide the port diameter by 2 (equals 1), multiply that by 1,463 (equals 1,463) and subtract this figure from the large, millions-range, number you just got (4,866,048 - 1,463 = 4,864,585) and call this "the divisor." Finally, divide the Numerator by the Divisor (14,630,000 / 4,864,585 = 3.00), and divide that by two to get the final port length. This box will need a port of 2 inches in diameter and 1.50 inches in depth to tune for 40 hertz.
-
4
Take a massive dose of Tylenol, do a browser search for "sub port length calculator" and let it do all of this for you. The actual formula is Port Length = ((14630000*(D/2)*(D/2) /((Fb*Fb*Vb*1728)-(1463*(D/2))))/2 , where D is the diameter of the port, Vb is the volume of the box and Fb is the desired frequency. Whether you did this algebra manually or with a calculator, you'll find that you can play with the variables to determine the port size that best suits your needs. Once you know that, you need only order the appropriate-diameter plastic port tube and cut it to length with a hacksaw.
-
5
Cut a hole somewhere in the front of your speaker box -- where you cut it isn't really important, as long as it's on the front -- using a hole-saw, pop your resonator tube in place and hold it there with screws or adhesive inside the wooden tube-hole.
-
1
References
- "Foundations of engineering Accoustics"; Frank J. Fahy
