bass reflex speaker cabinet
The reproduction of low tones is significantly influenced by the design of the resonance body of the speaker boxes.
Principle of the bass reflex box
Such a resonance body is formed in the air volume of a loudspeaker box and can be influenced by design features so that the natural resonance frequency of the loudspeaker box is as low as possible. Technically, the air volume behind the speaker cone, which acts like an air cushion, is used. This air cushion acts like a spring system on the diaphragm and is conducted through air ducts to the outside, outside the speaker box.
The prerequisite for reproducing the lowest possible audio frequencies is a loudspeaker with a large diameter and a sufficiently large air volume. In the bass reflex box, an air tube is added to the resonating body. The diaphragm movement causes the air in the air tube to move back and forth over the air cushion, forming a Helmholtz resonator within itself whose natural frequency depends on the tube size. If this natural frequency is tuned with the natural frequency of the loudspeaker chassis, the low frequency range can be extended to lower frequencies
The airflow is compressed in the exit port and has a phase rotation of 180°. It increases the efficiency of the bass reflex box and at the same time provides a directional effect of the radiated low frequencies.
Principle of the bandpass box
A somewhat different mode of operation of a bass reflex box has the bandpass box. This construction works with a closed chamber, which is located behind the speaker. The sound is emitted from the front through the opening channel to the outside. The closed chamber has an inherent resonance that favors the radiated sound level in this frequency range. This raises the sound level in the frequency range of the resonance frequency. Since the radiated sound does not enter the closed chamber, there are also no acoustic short circuits. The bandpass concept is mainly used in subwoofers.