i dont know what your referring to when you save F's...and im pretty sure about the frequency...im pretty retarded lol...but im pretty sure its when you port a box to a certain frequncy...like i have an elclipse Ti and if i was going to build a ported box for it i would make the slot port in it tuned to 27hz giving it the best boom i could...its the measurement of how big the slot would be
Fs- The frequency at which a speaker naturally resonates in free air. (measured in Hz)
When you have a speaker in a ported enclosure, the port is tuned to a specific frequency at which the sub becomes most efficient, giving the greatest output. The tuned frequency is based on the enclosure volume, and cross-sectional area of the port (length and diameter for round ports.) Generally, ports tuned in the 25-35Hz range are best suited to deep bass and sound quality response. Tuning to the 40-70Hz range is generally used for greater SPL (louder) systems but at teh loss of sound quality as the box will tend to sound more boomy and overly warm at those frequencies. Tuning only applies to enclosures that utilize ports or radiators such as bandpass, vented, transmission line, folded horn, passove radiator, and so forth. Sealed and aperiodic enclosures have no ports and thus, aren't tuned to any specific band of frequencies.