Grand Canyon National Park: Acoustic monitoring report 2017

Job, Jacob

This report presents the summary results of acoustical data gathered at two backcountry locations within Grand Canyon National Park. Data were collected at these sites during the summer and fall of 2017. Data collected at a third site (GRCA007) contained corrupt audio files, so a full acoustical analysis was not performed for this site. In this deployment, sound pressure level (SPL) was measured continuously every second by a calibrated sound level meter. Other equipment included an anemometer to collect wind speed and direction and a digital audio recorder collecting continuous recordings to document sound sources. In this document, “sound pressure level” refers to broadband (12.5 Hz - 20 kHz), A-weighted, 1-second time averaged sound level (LAeq, 1s), and hereafter referred to as “sound level.” Sound levels are measured on a logarithmic scale relative to the reference sound pressure for atmospheric sources, 20 µPa. The logarithmic scale is a useful way to express the wide range of sound pressures perceived by the human ear. Sound levels are reported in decibels (dB). A-weighting is applied to sound levels in order to account for the response of the human ear (Harris, 1998). To approximate human hearing sensitivity, A-weighting discounts sounds below 1 kHz and above 6 kHz. For reference, Table 1 provides examples of sound levels measured in parks compared to sound levels of common sound sources. Overall, measured existing ambient sound levels (LA50) at the park at site GRCA031 during the summer were 38.9 and 21.8 dB during the day and night respectively and fall season levels were 30.6 and 15.3 dB during the day and night. At site GRCA032 during the summer, measured levels were 28.5 and 38.4 dB during the day and night respectively and fall season levels were 26.4 and 18.6 dB during the day and night. Table 2 reports the percent of time that measured levels at the monitoring locations were above four key sound level values. The first value, 35 dB (LAeq, 1s), addresses the health effects of sleep interruption. Recent studies suggest that sound events as low as 35 dB can have adverse effects on blood pressure in sleeping humans (Haralabidis et al. 2008). This level, 35 dB, is also the desired background sound level in classrooms (ANSI S12.60-2002). The second value addresses the World Health Organization’s recommendations that noise levels inside bedrooms remain below 45 dB (LAeq, 1s) (Berglund et al. 1999). The third value, 52 dB (LAeq, 1s), is based on the EPA’s speech interference level for speaking in a raised voice to an audience at 10 meters (EPA 1974). This value addresses the effects of sound on interpretive presentations in parks. The final value, 60 dB (LAeq, 1s), provides a basis for estimating speech interference on normal voice communications at 1 meter. Visitors viewing scenic areas in the park would likely be conducting such conversations. Sound levels are often measured over narrow frequency bands...

Grand Canyon National Park: Acoustic monitoring report 2017

Series

Other versions

Collections