There is not a limited list of noise sources that can cause hearing loss; rather, exposure to excessively high levels from any sound source over time can cause hearing loss. Signs and symptoms
The first symptom of NIHL may be difficulty hearing a conversation against a noisy background. The effect of hearing loss on speech perception has two components. The first component is the loss of audibility, which may be perceived as an overall decrease in volume. Modern hearing aids compensate this loss with amplification. The second component is known as "distortion" or "clarity loss" due to selective frequency loss. Consonants, due to their higher frequency, are typically affected first. For example, the sounds "s" and "t" are often difficult to hear for those with hearing loss, affecting clarity of speech. NIHL can affect either one or both ears. Unilateral hearing loss causes problems with directional hearing, affecting the ability to localize sound. Temporary and permanent hearing changes
PTS (Permanent Threshold Shift) is a permanent change of the hearing threshold (the intensity necessary for one to detect a sound) following an event, which will never recover. PTS is measured in decibels. TTS (Temporary Threshold Shift) is a temporary change of the hearing threshold the hearing loss that will be recovered after a few hours to couple of days. Also called auditory fatigue.
An acoustic signal from a sound source, such as a radio, enters into the external auditory canal (ear canal), and is funneled through to the tympanic membrane (eardrum), causing it to vibrate. The vibration of the tympanic membrane drives the middle ear ossicles, the malleus, incus, and stapes to vibrate in sync with the eardrum. The middle ear ossicles transfer mechanical energy to the cochlea by way of the stapes footplate hammering against the oval window of the cochlea, effectively amplifying the sound signal. This hammering causes the fluid within the cochlea (perilymph and endolymph) to be displaced. Displacement of the fluid causes movement of the hair cells (sensory cells in the cochlea) and an electrochemical signal to be sent from the auditory nerve (CN VIII) to the central auditory system within the brain. This is where sound is perceived. Different groups of hair cells are responsive to different frequencies. Hair cells at or near the base of the cochlea are most sensitive to higher frequency sounds while those at the apex are most sensitive to lower frequency sounds. There are two known biological mechanisms of NIHL from excessive sound intensity: damage to the structures called stereocilia that sit atop hair cells and respond to sound, and damage to the synapses that the auditory nerve makes with hair cells, also termed "hidden hearing loss". Physiological response
The symptoms mentioned above are the external signs of the physiological response to cochlear overstimulation.