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Ported Enclosures: The enclosure’s port should be tuned to a certain frequency so that the enclosure is capable of playing all frequencies above that tuning. The enclosure can play below
that frequency, but only half and octave before the cone starts to over-extend. Hence, set the Subsonic HPF to 1/2 an octave below the tuned frequency.
Here is a simple formula to help you gure out the proper Subsonic HPF setting for your particular ported enclosure. Keep in mind that one octave up is double the frequency and one
octave down is half the frequency:
1. Divide the tuning frequency of your port by two. This is one octave lower than your tuning frequency.
2. Divide the quotient (answer) of step 1 by two: This is half an octave lower.
3. Now subtract the quotient (answer) of step 2 from the port’s tuning frequency.
Example:
Port tuning frequency is 46Hz
1. 46Hz ÷ 2 = 23Hz (one octave lower)
2. 23Hz ÷ 2 = 11.5Hz (half an octave lower)
3. 46 - 11.5 = 34.5Hz (round up to 35Hz)
So, you would set your Subsonic HPF to 35Hz.
Please note: The subsonic lter is NOT a cut-off. It has a roll-off slope that will attenuate the frequency it is set to. Attenuation will increase as the frequencies get lower, meaning the
power to the woofer decreases at the ltered frequencies which reduces excursion and the potential for damage.
Subsonic lters have steep slopes such as 3rd or 4th order (18 or 24dB/Oct) so it can be set as close to your ½ octave frequency as possible, or 25 – 35Hz sealed, without losing power
in the surrounding frequencies.
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