Urban impulse responses measured via the synchronous addition of fireworks to access speech intelligibility in evacuation broadcast

Although an evacuation broadcast via an outdoor public address at the time of disaster is an important source of information, the long-path echoes from buildings and mountains reduce speech intelligibility. In assessing speech intelligibility, it is proposed to use firework explosions to simulate urban impulse responses and calculate speech transmission indices (STIs). In this study, investigators were stationed across cities during firework festivals to record explosions, and the individual events were synchronously combined to improve signal-to-noise ratios, yielding urban impulse responses. The urban impulse responses had distinct echo-time patterns originating from buildings and surrounding mountains, and the estimated source power of the fireworks had a nearly flat energy spectrum. The sound exposure level (LE) of the impulse responses was consistent with values calculated using outdoor sound propagation models (ISO 9613-2). In addition, the STIs of the impulse responses had a highly accurate linear relationship with sound exposure levels, LE's. Therefore, it is important to estimate LE more precisely using geometrical data of cities in assessing the speech intelligibility of evacuation broadcasts.