What is a subwoofer with a general formula?

The belt-like box design usually consists of two separate box chambers, one hidden inside and one connected to the outside with a bass reflex hole. The box hidden inside is sealed, the woofer is mounted on the box, and the single diaphragm faces the outside of the box. The woofer is not visible from the appearance of the box. When the woofer moves, the air that drives the outer box passes through the bass reflex hole to form an Acoustic Filter, which produces a fourth-order (24dB attenuation per octave, also designed as a sixth-order) filter for a certain frequency band. . Its advantage is that the power can be the best of all the different types of cabinets, and the transient response is probably only inferior to the closed box. The ultra-low bass with a general formula is relatively rare on the market due to the high manufacturing cost of the cabinet.