Being close to an explosion can leave you deaf instantly. Other acoustical damage, however, leads to hearing loss that comes on more slowly.We live in an age when acoustical trauma injury from sound abounds, and we often dont even realize the potential for harm. It begins early in life. Studies have shown that as many as 60 percent of entering college freshmen already display some hearing loss. Much of that may be due to whats come to be commonly called noise pollution.Loud noise can harm hearing by damaging the sensitive, tiny hair cells in the inner ear. Certain onditions can make these hair cells even more sensitive than usual. During aerobic exercise our blood diverts from our ears to our legs, arms, and heart. This altered blood flow makes the hair cells more vulnerable to noise. Thus, many fitness experts warn that you double your risk of permanent hearing loss when you jog while wearing headphones. Likewise, dancing to a blaring stereo boosts the already high potential for hearing damage. Recent studies have confirmed that many people have damaged hearing as a result of listening to loud music, either from frequent attendance at rock concerts or through the pervasive use of portable music players. Damage from noise is related to two factors: loudness and duration. Loudness is measured in decibels. One point to remember about decibel scales is that an increase of only three decibels results in a doubling of sound pressure. So a jackhammer at 120 decibels is emitting much, much more than twice as much sound pressure as a normal conversation of 60 decibels.When is enough, enough? Here are a couple simple tests to determine if you are submitting yourself to dangerous levels of sound.