The ear is an amazing body part because it enables humans and animals to hear what goes on around them. Hearing is one of the five senses of the body. The ears help the body to pick up sound waves and vibrations. Sound travels in waves through the air, the ground, and various other substances. Sound cannot be seen, but it can be felt by vibrations.
The number of vibrations that are produced per second is called frequency. Frequency varies for each sound and is measured in hertz. One hertz is equal to one vibration per second. A sound with a low frequency will have a low pitch, such as a human's heartbeat. A sound with a high frequency will have a high pitch, such as a dog whistle. Humans cannot hear sounds of every frequency. The range of hearing for a healthy young person is 20 to 20,000 hertz. The hearing range of humans gets worse with age. People lose the ability to hear sounds of high frequency as they get older. The highest frequency that a normal middle-aged adult can hear is only 12-14 kilohertz. Also, the hearing range for men worsens more quickly than the hearing range for women. This means that women will have the ability to hear notes of higher pitch than men of the same age do.
What is sound and frequency? Sound is a longitudinal mechanical wave of any frequency. Frequency is the number of cycles, or complete vibration experienced at each point per unit. Frequency is measured in hertz. The hertz, Hz, is the derived SI unit of frequency. The frequency of a sound wave determines its tone and pitch. The frequency range of a young person is about 20 to 20,000 hertz.
The human ear is capable of hearing many of the sounds produced in nature, but certainly not all. Some low frequencies like a heart beat of 1 or 2 Hz can not be heard, just like sonar sounds produced by dolphins which are too high. Any frequency that is below the human range is known as infrasound. It is so low that it may be detected by a creature with big ears, such as an Elephant. In fact, recent research indicates that elephants also communicate with infrasound. Ultrasound, on the other hand, is above the range of the human ear. Bats, whales, porpoises, and dolphins use ultrasound for navigation. Most bats can detect frequencies as high as 100,000 Hz!
Proposed in the 1970s as a possible explanation for ghosts. The Stone Tape Theory speculates that inanimate materials can absorb energy from living beings. In other words a ‘recording’ or track is laid down during moments of high tension, such as murder. This stored energy can consequently be released, resulting in a display of the recorded activity. The replay can take the form of a full manifestation or partial sounds such as voices or footsteps. Paranormal investigators commonly refer to such phenomena as residual hauntings. Ghosts are not spirits but non-interactive recordings similar to the registration capacities of an audiotape machine that can playback previously recorded events. While the theory may explain some ghostly sightings, no one knows what the recorded energy actually is. However, the possibility that it could be composed by our natural electric and magnetic fields is one of the explanations that the Stone Tape Theory advances.