Dolphins can detect frequencies as high as 200 000 Hz. Bats can detect frequencies as high as 120 000 Hz. Bats, being nocturnal creature, must rely on sound echolocation for navigation and hunting. Cats can detect frequencies as low as approximately 45 Hz and as high as 85 000 Hz. Dogs can detect frequencies as low as approximately 50 Hz and as high as 45 000 Hz. Humans are not alone in their ability to detect a wide range of frequencies. Any sound with a frequency below the audible range of hearing (i.e., less than 20 Hz) is known as an infrasound and any sound with a frequency above the audible range of hearing (i.e., more than 20 000 Hz) is known as an ultrasound. For now, it is sufficient to say that the human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz. The mechanics of the ear's detection ability will be discussed later in this lesson. The ears of a human (and other animals) are sensitive detectors capable of detecting the fluctuations in air pressure that impinge upon the eardrum. Subsequently, a guitar string vibrating at 500 Hz will set the air particles in the room vibrating at the same frequency of 500 Hz, which carries a sound signal to the ear of a listener, which is detected as a 500 Hz sound wave. And of course the frequency at which each particle vibrates is the same as the frequency of the original source of the sound wave. The process continues throughout the medium each particle vibrates at the same frequency. The second particle begins vibrating at 500 Hz and thus sets the third particle of the medium into vibrational motion at 500 Hz. The first particle of the medium begins vibrating, at say 500 Hz, and begins to set the second particle into vibrational motion at the same frequency of 500 Hz. This is sensible since each particle vibrates due to the motion of its nearest neighbor. A commonly used unit for frequency is the Hertz (abbreviated Hz), where 1 Hertz = 1 vibration/secondĪs a sound wave moves through a medium, each particle of the medium vibrates at the same frequency. If a particle of air undergoes 1000 longitudinal vibrations in 2 seconds, then the frequency of the wave would be 500 vibrations per second.
The frequency of a wave is measured as the number of complete back-and-forth vibrations of a particle of the medium per unit of time. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. Regardless of what vibrating object is creating the sound wave, the particles of the medium through which the sound moves is vibrating in a back and forth motion at a given frequency. The vibrating object that creates the disturbance could be the vocal cords of a person, the vibrating string and sound board of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. The vibrating object is the source of the disturbance that moves through the medium. A sound wave, like any other wave, is introduced into a medium by a vibrating object.