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Sealed Enclosures
Sealed boxes are tuned by enclosure volume: larger enclosures tune lower; smaller enclosures tune higher. Subsonic frequencies can cause damage to your woofer as they cause it to
play below the enclosure’s tuning, forcing it to the limits of its excursion and making it expend a lot of energy. To avoid damage to your woofer, set the Subsonic HPF to 25Hz – 35Hz.
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 an octave before the cone starts to overextend. Hence, set the Subsonic HPF to half 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 4.
2. Now subtract the quotient (answer) of Step1 from the port’s tuning frequency. This is half an octave lower than your tuning frequency.
Example:
Port tuning frequency is 46Hz:
1. 46Hz ÷ 4 = 11.5Hz (half an octave lower)
2. 46Hz – 11.5Hz = 34.5Hz (Round up to 35Hz.) This is half an octave lower than 46Hz.
Please note: The subsonic lter is NOT a cutoff. 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 they can be set as close to your half-octave frequency as possible, or 25Hz – 35Hz sealed, without losing
power in the surrounding frequencies.
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