Development of a metric utilizing outdoor sonic boom for correlating indoor human annoyance responses

In 2015, the CAEP (Committee for Aviation Environmental Protection) SSTG (SuperSonic Task Group) assessed over 70 metrics for resolving acceptability of sonic booms. A ground rule was metric application to the outdoor sonic boom signature. Studies indicate people spend 90% of time indoors and sonic boom is expected to be the same or more annoying indoors. NASA developed an IER (Indoor Environment Room) facility to simulate indoor sonic booms and collected 30 humans’ responses to 140 representative booms. Because all other metrics were based on human perception of loudness without indoor effects, a new metric was developed. Previous work suggested indoor annoyance from sonic booms was predominantly based upon indoor loudness, building response and associated rattle. This new metric combines one metric for indoor loudness and one metric for building response and rattle. Indoor loudness [PL(i)] is based upon the highest correlated outdoor metric, PL, but calculated after adjusting 1/3 octave levels for transmission loss. Building response (BR) averages of 1/3 octave levels in the 10-40 Hz range. The combined metric correlated the NASA indoor data with an R2 of 0.939, higher than the next best metrics: ISBAP 0.921, PL(i) 0.910 and PL 0.881.