Bottom bass reflex acoustic systems
Bottom
— acoustic systems in which there is a phase inverter (FI; see "Acoustic design"), displayed on the underside of the speaker cabinet. It can be either the only FI or an addition to the front or rear air duct (see the relevant paragraphs).For normal operation of the phase inverter, it is necessary that there is a certain free space in front of the duct outlet; it cannot be placed close to obstacles. Therefore, this variant is found in two specific varieties of AS. The first are floor and shelf models with specially designed stands that provide an optimal distance from the bass reflex output to the solid base of the stand (or to the surface on which the speaker is installed). The second is wall-mounted (suspended) models, designed for a large amount of free space under the column. But from an acoustic point of view, it cannot be unequivocally said that this option is better or worse than others — a lot depends on other design features, as well as on the personal preferences of listeners.
As for the combination with other types of FI, in such cases the lower air duct performs mainly an auxiliary function, further improving the sound quality at low frequencies.