What is the baffle

HiFi lexicon: acoustic short circuit

The acoustic short circuit is responsible for the fact that loudspeakers need housings: If the membrane of a loudspeaker swings forwards, the air is compressed on the front (higher pressure), while it becomes “thinner” (lower pressure) on the back of the loudspeaker. The pressure conditions in front of and behind the loudspeaker are exactly opposite: there is a phase difference of 180 degrees (see also interference). In such a framework - especially with low-frequency vibrations - the air finds sufficient time to flow back and forth between the front and back in a pressure-equalizing manner. The Eliminate opposing waves accordingly, the desired degree of sound radiation does not come about.

In order to acoustically isolate the front and rear of the loudspeaker, a simple open baffle (a plate in which the individual loudspeakers are installed) is theoretically sufficient. However, in order to effectively avoid cancellation, the edge of the speaker would have to be at a distance from the center of the membrane of the built-in loudspeakers that is ¼ of the wavelength of the frequency that is still to be clearly radiated. At 80 Hz, for example, a distance of more than 1 m from the edge would be required. Accordingly, the baffle would have overall dimensions of over 2m.

The latter is the reason why housings are (mostly) used: They prevent air from flowing between the front and rear of the loudspeaker in a pressure-equalizing manner, without the need for oversized loudspeakers to be built (see bass reflex loudspeakers, transmission line loudspeakers).