pressure chamber loudspeaker
When a sound is radiated from a loudspeaker diaphragm, the sound wave is adapted to the sound characteristic impedance of the air. This is an impedance match, which occurs with lower efficiency for higher tones than for lower tones.
For impedance matching to occur with better efficiency, a larger diaphragm builds up sound pressure in a chamber that is forced through a narrower opening. The flow velocity in the exit opening is greater than that of the diaphragm.
In order for the sound to be emitted to the air behind the narrowed exit port, there is a funnel-shaped hollow body behind the exit port, usually in an exponential shape. Thanks to this shape, the sound waves equipped with higher sound pressure can detach from the funnel and are radiated into the air.
A representative of these pressure chamber loudspeakers is the funnel loudspeaker.