Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
Perception of infrasound the right source loudspeakers when they were positioned at different angles from the elephant’s head. The elephant could localize sounds best at a frequency below 1 kHz, with perfect identification of the left or right speaker at angles of 20 degrees or more, and chance level discriminations below 2 degrees. Sound localization ability was measured to be best at 125 Hz and 250 Hz, intermediate at 500 Hz, 1 kHz, and 2 kHz, and very poor at frequencies at 4 kHz and above. A possible reason for this is that elephants are very good at using interaural phase differences which