Professional Definition

A measurement method based on the reciprocity theorem, which states that in a linear, stationary acoustic system, swapping the positions of the sound source (excitation) and the point of reception (response) does not change the transmission value of that system, provided the appropriate boundary conditions are maintained.

In engineering practice, especially when examining acoustic insulation of partitions or machine enclosures, this means that the sound attenuation on the path from point A to point B is the same as from point B to point A. This allows for the determination of enclosure parameters by placing an omnidirectional sound source inside the object being tested and measuring the sound intensity outside, which is often technically easier to realize than simulating an external acoustic field (e.g., aircraft noise).

Acoustics in Simple Words

Imagine two people talking to each other through a long, thick ventilation pipe. If person A shouts into one end, and person B hears it with some loudness, the reciprocity principle states that if they switch roles and person B shouts with the same intensity, person A will hear it just as loudly. The pipe does not