I have a new project coming up (ported line array) and was wondering if volume of a port was the only thing that effects the tuning? I was thinking of having a curved back on my cabinet where i will port out to (Aprox. 45degree cut on port) will this effect sound quality? I'm shooting for a very similar port to the klipsch palladium's.
(example: say my cylindrical port had a volume of 30 cubic inches, if i changed my port shape in anyway as long as its 30 cubic inch volume it should give the same tuning correct?)
(example: say my cylindrical port had a volume of 30 cubic inches, if i changed my port shape in anyway as long as its 30 cubic inch volume it should give the same tuning correct?)
Actually, the volume of air in the port is involved – although the vent length and diameter together define that volume.
The vent is modeled as a spring-mass system, and as such, it has its own natural frequency. The mass is found by multiplying the volume of air by the density of air. This mass of air can be thought of as vibrating back and forth in the tube, against the “springiness” of the volume of air in the enclosure behind it. (Think of a piston against a compression chamber.) The force from the spring depends on the cross-section area of the port, found from the diameter.
Of course, someone (Benade, if I recall correctly) determined some “end correction factors” for the moving mass of air. The resulting formula has a "1.463” term in it which accounts for one free end, and one flanged end, which is typical.
Happily, the formula for finding Fb reduces to the familiar form involving only the port length, diameter, and box volume. The physicists did the rest for us.
+1
To better answer the original question . . .
In general, if you change the diameter and length of a port to maintain the same port volume, the tuning frequency will change. This is because the spring constant depends on the diameter of the port.
Recommend using the formula to calculate port dimensions for a given tuning frequency. Here is a link to one form of the equation.
The Subwoofer DIY Page - Port Calculations
Note that Vb in the formula is the box volume, not the port volume.
Dave
In general, if you change the diameter and length of a port to maintain the same port volume, the tuning frequency will change. This is because the spring constant depends on the diameter of the port.
Recommend using the formula to calculate port dimensions for a given tuning frequency. Here is a link to one form of the equation.
The Subwoofer DIY Page - Port Calculations
Note that Vb in the formula is the box volume, not the port volume.
Dave
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