During the last few years, the trend of listening to music from portable stereo earphones/mobile phones has become very popular especially in younger people. The rate of deafness in teenagers is increasing at an alarming rate due to direct louder-sound exposure into the ear through earphones or headphones. The sound from most portable stereo music system lies in the range of 95 to 108 dB. According to a medical survey report, 1 in 5 American teenagers suffers from hearing impairment. Moreover, scientists at the University of Leicester have proved, through their published results, that the high volume on the headphones destructs the coating of nerve cells which ultimately cause deafness.
Sound is one of the types of energy which travels in the form of waves. The branch of science which deals with sound is called Acoustic. For the perception of sound, we require a vibrating body, a medium and a receiver. For example, the vocal chord in our body vibrates to produce a sound which travels through air and finally it is perceived by our ear(s). There are two types of waves namely electromagnetic waves and mechanical waves regarding propagation through a medium. The electromagnetic waves such as light waves, microwaves, infrared waves etc. do not need any medium for propagation. However, sound waves are mechanical waves and require a medium to travel from one place to another. Although sound waves pass through solids, liquids and gases, each with a different speed, they cannot travel through a vacuum.
In everyday life, we hear different sounds with our ear(s).

A human ear comprises three parts: external (pinna), middle, and the inner portion. In the middle part of the ear, there are the eardrum and tiny bones attached to it. In the inner ear, there is a spiral-shaped cochlea. The pinna collects sound and directs it, acting as a funnel, to the external auditory canal that ends at the eardrum. The sound vibrates the eardrum and the tiny bones. The vibrations thus produced are conducted to the cochlea which converts sound into nerve impulses that ultimately travel to the brain.

There are some attributes of sound such as pitch, ‘quality’ and loudness (volume) etc. The pitch of the sound determines its shrillness and a shrill sound has a high pitch. We distinguish sounds of various musical instruments due to its ‘quality’. The sounds of two musical instruments are different because their qualities are different. The loudness of the sound tells us how high or low is the sound. The loudness of the sound is measured in decibels (dB). Loud noise is very harmful to hearing. Sounds louder than 85 dB, for a prolonged exposure, can cause permanent hearing loss. Experts suggest that sound of loudness 85 dB or lower is safe for our ears. Sound can be grouped roughly into five main categories with respect to loudness. These are: Faint sound (up to 30 dB), Moderate sound (from 30 to 70 dB), Very loud sound (from 70 to 90 dB), Extremely loud sound (from 90 to 110 dB) and Painful sound (above 110 dB).
Last but not least, parents must discourage their children from listening to audio through earphones/headphones. The reason is that once your hearing is gone, it can never come back.

(The writer is Punjab University Physics Department Chairman and Member Syndicate on Associate Professor’s seat. He can be reached at: [email protected])