Subsonic hearing and speech should be changed to Infrasonic hearing and speech.
Subsonic, Transonic, Supersonic and Hypersonic refer to velocity relative to the speed of sound.
Ultra and Infra refer to frequencies above and below the normal range of hearing (just as ultraviolet and infrared are above and below the visible spectrum).
Subsonic, Transonic, Supersonic and Hypersonic refer to velocity relative to the speed of sound.
Ultra and Infra refer to frequencies above and below the normal range of hearing (just as ultraviolet and infrared are above and below the visible spectrum).
Subsonic
