Page 17 - Fall2020

FEATURED ARTICLE
Public Exposure to Airborne Ultrasound and Very High Frequency Sound
Timothy G. Leighton, Ben Lineton, Craig Dolder, and Mark D. Fletcher
Over the last decade, members of the public have com- plained of “high-pitched” sounds in public places causing adverse effects (e.g., headaches). Their reports were dis- missed by colleagues, family, and friends, who could hear nothing, and by health care professionals and experts for a range of reasons, including assertions that airborne ultra- sound could not affect humans because it mostly reflects off the skin and because the ultrasonic intensities in air are low. Those complaining were told that even if such sounds existed, the sounds could not be ultrasonic because
“humans cannot hear above 20 kHz.” Faced with universal dismissals, in 2015, the concerned individuals consulted one of the authors, Professor Leighton. He published evi- dence that such tones existed (Leighton, 2016a), provided methods for the public to detect them (Leighton, 2016a,b), identified a range of commercially available sources and others in development, outlined why the regulatory framework needed revisiting (Leighton, 2016a), and cast doubt on assertions that these high-frequency sources cannot cause adverse effects (Leighton 2017). Fletcher et al. (2018a,b) conducted human trials and interest grew around the world, including in a special issue in The Jour- nal of the Acoustical Society of America (Leighton, 2018). International interest in this topic further increased with claims of ultrasonic attacks on the Cuban embassy (Leigh- ton, 2018). A scheme by which the public can distinguish such tones from, say, tinnitus was provided, as illustrated in the following case study.
A Case Study
On September 14, 2019, Jill Zawatski, a teacher from the Seattle (WA) area, wrote to Leighton because her students aged 14-18 claimed that a “high-pitched” sound in the classroom gave them headaches. School administration, teachers, and maintenance workers could hear nothing, but Mrs. Zawatski had come across Leighton’s work and
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https://doi.org/10.1121/AT.2020.16.3.17
understood from it that there was a huge variation in the sensitivity of human hearing to high frequencies and, prob- ably, to being adversely affected by high-frequency sound.
On receiving her e-mail, Leighton explained that the first step is to distinguish the perceived sound from tinnitus by (1) testing whether the sound is reduced when wearing ear protection or when moving to another location; and (2) attempting to detect the sound using a smartphone once the settings have been appropriately adjusted (the upper frequency limitation, 24 kHz, is determined by the data acquisition and not the microphone; Leighton, 2016a,b).
Mrs. Zawatski promptly recorded an audio file showing a tone at 18 kHz (see Figure 1). This frequency is covered by ultrasonic regulations because the dozens of national and international bodies (Leighton, 2016a) setting guide- lines for ultrasonic exposure have, by using third-octave
Figure 1. Time-frequency analysis of the recorded audio file showing a steady tone at just over 18 kHz in the classroom. SPL, sound pressure level.
Volume 16, issue 3 | Fall 2020 • Acoustics Today 17