In-field measurements of sound-energy distribution in classrooms

David Lubman's interest in classroom acoustics contributed to the development of the ANSI S12.60 standard. Classroom standards, either explicitly or implicitly, aim to ensure an adequate signal-to-noise ratio (SNR) for all students in normally occupied positions. This objective is achieved through strategies adhering to well-known room criteria, such as reverberation time (T). Assuming a uniform distribution of background noise, SNR then depends on the spatial distribution of sound energy. This latter aspect depends on T and the arrangement of absorbing materials. This is why standards, in some cases, provide informative recommendations on the placement of absorbing materials, as exemplified in Annex C of ANSI S12.60-1. The study experimentally verifies the slope of the spatial distribution of sound energy within classrooms of different types, comparing ANSI S12.60 with two European standards: the Italian UNI 11532-2 and the British BB 93. The distributions of G and G50 from in-field measurements were analyzed at mid-range frequencies (500–1000 Hz) and in the 250 Hz octave band. Measurements show greater spatial decays than those generally reported in the literature. The recommendations regarding the distribution of absorbent material suggested by the three standards are discussed.