A/B Ultrasound is concerned with sound waves that occur above human perception. The normal“audible” environment in which the human ear is capable of sensing is 20 Hertz to 20 kHz (1,000 Hertzis 1 kiloHertz or 1 kHz). The average threshold of human perception is 16,500 Hertz or 16.5 kiloHertz. audible wavelengths range in size from as small as 3/4 inch (1.9 cm) to as large as 56 feet (17m). The frequencies sensed by airborne ultrasound instruments such as the UE UCA586 are above 20kHz to 100 kHz. The wavelengths are magnitudes smaller than the audible, ranging from 1/8 inch (0.3cm) to 5.8 inch (1.6 cm).