Helmhotz resonator
Bass reflex boxes use Helmholtz resonators for bass reproduction. Such an acoustic resonator is a hollow body with an opening. The air in the opening bounces on the air cushion of the resonator.
In this context, one also speaks of the spring stiffness, which depends on the body volume. This spring stiffness is used in loudspeaker technology to tune the bass reflex box so that the low frequencies are preferentially radiated. In practice, a tube is used as the resonant body and the resonant frequency is selected so that it enhances the low-frequency reproduction.
The Helmholtz resonator is found in many musical instruments. It is the body of the instrument, for example the violin body. It is not the cavity resonators like those of organ pipes or those of a flute.
Helmholtz resonators can be used to raise frequencies, but equally to absorb them. Such resonators are used in room acoustics as absorbers, for example, as insulating panels with holes, each of which forms a Helmholtz resonator.
The Helmholtz resonator is named after its inventor, the German physicist Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who in 1847 formulated the law for the conversion of energy forms.