The noise problem in the USA

According to the Levels Document, the day-night sound level of residential areas should not exceed 55 dB to protect against activity interference and annoyance. It is estimated that well over 100 million people, live in areas where the noise exceeds this level. Besides, indoor levels are often comparable to or higher than levels measured outside.

HEARING LOSS
To understand hearing loss it is important to understand how normal hearing takes place. There are 2 different pathways by which sound waves produce the sensation of hearing: air conduction and bone conduction.
• In air conduction, sound waves move through the air in the exte
al auditory canal (the "ear canal" between the outside air and your eardrum). The sound waves hit the tympanic membrane (eardrum) and cause the tympanic membrane to move.
• The bones in the middle ear are connected to the tympanic membrane. When the tympanic membrane moves, this movement is transmitted to the bones. These 3 bones are called the malleus, the incus, and the stapes. Movement of the stapes causes pressure waves in the fluid-filled inner ear.
• The cochlea is an inner ear structure surrounded by fluid. It contains multiple small hairs. Pressure waves in the fluid cause the hairs to move. This movement stimulates the auditory nerve. Different frequencies of noises stimulate different hairs on the cochlea, which translate to the sensation of sounds of different pitch.
• Hearing by bone conduction occurs when a sound wave or other source of vibration causes the bones of the skull to vibrate. These vibrations are transmitted to the fluid surrounding the cochlea and hearing results.
There are 2 basic types of hearing loss, which are called conductive and sensorineural.
• Conductive causes: Conductive hearing losses result from physical problems with the movement of the sound wave through the ear. A simple example is blockage of the ear canal.
o Obstructed exte
al ear canal - Cerumen (wax) build-up, hematoma (blood...