Dig deeper into enclosure design- you'll need to understand other parameters on the way to the end results. There's a lot of info that creates 'deer in the headlights' reactions, at first.
Lower resonant fequency requires a very large enclosure or a very long port- think of the port as if it were a soda bottle and you're blowing across the opening and it wants to produce one note. Add water (make it shorter) and the pitch goes up, remove water (add length) and the pitch goes down- a low note requires the length and it's the same principle used in pipe organ design but there's no room in a house for a 32' or 64' pipe. The woofer in a sealed enclosure produces low frequencies if it's very large but the port is used to extend the low frequency response by tuning it (selecting the length that allows the one note to blend well with the response from the sealed enclosure).
Vas describes the compliance the resistance to movement when some force is exerted of the speaker in a specific enclosure volume- air can be compressed and a very large volume of air is very soft, a smaller volume of air offers more resistance to being compressed. In order to produce low frequencies, a speaker driver needs to move air- if it can't move much when the signal reaches it, the sound level won't be sufficient to hear it well, if at all, so the cone will need to move in & out farther (think of it as a piston). Since the cone's diameter won't increase, the only way to move more air is to increase the distance (excursion) it moves in & out.
Excursion is used in enclosure design, too.
Everything resonates at its own frequency- a speaker driver that has a high Fs isn't really suitable for low frequencies because it
Discover the meaning of Thiele-Small parameters (Fs, Vas, Qts, Qes, Qms, Cms, Sd, Re, Mms, Bl, Rms, impedance, power ratings). Learn their role in speaker design, the difference between T-S and electro-mechanical specs, and how to simulate boxes with Speaker Box Lite.
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