Relational anomalies in A weighted and linear scale sound level measurements associated with jet aircraft departures

Noise levels from jet aircraft operations at major airports are often perceived by nearby residents as being louder and more intrusive than claimed by airport proprietors. This can cause heated opposition by citizens to airport development and expansion plans. To further clarify the issue, a noise study was conducted using four noise meters; two Type 1 and two Type 2. Simultaneous sound level measurements were taken on the A-weighted and linear scales in airport and nonairport noise environments; and included octave band analyses. In both noise environments the average differential between full spectrum A-weighted and linear scale measurements is approximately 15 dB, except when influenced by jet aircraft departures. During jet aircraft departures, this A/linear differential was as small as 4 dB; and the smaller the difference between simultaneous measurements the louder the perceived noise from the departing plane. This measurement anomaly was unique to departing jet aircraft. Propeller driven aircraft operations, or jet aircraft landings, showed little or no change in the A/linear noise differential. The measurements suggest that a significant amount of noise is not being measured by the sound level meters during jet aircraft departures: either deducted by weighting filters or due to instrument limitations. However, by conducting simultaneous measurements of A weighted and linear scale sound levels, this relational anomaly can provide a simple, realistic indicator of jet aircraft loudness in the airport noise environment.