Queuing for quiet–The natural soundscape microstructure from a visitor perspective

The passage of PL100-91 The National Parks Overflights Act of 1987 and PL106-181 The National Parks Air Tour Management Act chartered the National Park Service (NPS) and Federal Aviation Administration (FAA) to restore natural quiet to park settings, especially those with lengthy occurrences of nonindigenous sounds. Dose–response studies sponsored by NPS and FAA showed that among several dependent variables tested, nonindigenous time audible was the best predictor of visitor-reported annoyance and interference with natural quiet. Other than for Grand Canyon NP, PL100-91 lacked specificity for depicting nonindigenous times audible. Since 1991, several field investigations have produced over 400 h of source identification logs maintained by audiometrically screened observers. At over 25 sites in 7 parks, the data acquisition protocol used a forced-choice, hierarchical menu structure with audible source state changes timed to the nearest second. The identical protocol across all studies provided the basis for examining the amount of time a visitor would have to wait (T) to experience a contiguous block of indigenous-only sounds of duration (D), given a random arrival time. The paper reports means and distributions in T for various values of D, observed data clusterings across site groups, and the effects of mitigating variables.