Acoustic Characteristics of Four Subway Stations in Naples, Italy

Due to the presence of a large number of travelers and the high traffic of trains, subway stations are noisy environments. This noise prevents listening to safety messages, as well as affects people's conversations and health. Subway stations are also the performance spaces selected by street musicians, who perform in poor acoustic conditions. This study evaluates the acoustic characteristics of four new subway stations in Naples, Italy. Using the impulse response method, monaural parameters were measured. Results indicate average reverberation times longer than three seconds at middle frequency, and values of clarity (both C80 and D50) and sound transmission index (STI) far from optimal for listening perception. As expected, the train tunnels of the subway lines resulted in a high absorption at low frequencies, making subway stations particularly frequency-selective. Acoustic corrections for reducing the noise levels and improving the acoustic characteristics are studied. In particular, this paper investigates the effect of adopting a sound-absorbing and fire-resistant plaster on the ceiling of the subway tunnel.