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Re: Dual 18" Separate Chambers ??If you have 2 drivers in a box where both drivers share the same volume of air you calculate the port using both woofers' parameters (Volume of displacement or Vd). If you divide the box volume in half, you not only would need 2 ports (one for each side), which changes the size of each port (smaller diameter ports can be used because each is only carrying half the load as before) but you are also using only one woofer to drive that port which changes the size again (half the driver Vd). Therefor the math is different, even though the end result needs to be the same.The ports themselves don't care what size the box is (within reason anyway, the woofer will dictate box size way more than the port will). They are simply a tuned pipe that resonates at a frequency. The biggest challenge is getting a port that is big enough to not "whistle" when a lot of air is moving through it, yet is still small enough to actually fit inside the cabinet. A 1" diameter port can be tuned pretty low and be very short but it will not pass enough air to be useful. For subs you need large diameter ports and the larger the port diameter, the longer it needs to be for a given frequency.
Re: Dual 18" Separate Chambers ??
If you have 2 drivers in a box where both drivers share the same volume of air you calculate the port using both woofers' parameters (Volume of displacement or Vd). If you divide the box volume in half, you not only would need 2 ports (one for each side), which changes the size of each port (smaller diameter ports can be used because each is only carrying half the load as before) but you are also using only one woofer to drive that port which changes the size again (half the driver Vd). Therefor the math is different, even though the end result needs to be the same.
The ports themselves don't care what size the box is (within reason anyway, the woofer will dictate box size way more than the port will). They are simply a tuned pipe that resonates at a frequency. The biggest challenge is getting a port that is big enough to not "whistle" when a lot of air is moving through it, yet is still small enough to actually fit inside the cabinet. A 1" diameter port can be tuned pretty low and be very short but it will not pass enough air to be useful. For subs you need large diameter ports and the larger the port diameter, the longer it needs to be for a given frequency.
