Listening to amplified music for less than 1.5 hours produces measurable changes in hearing ability that may place listeners at risk of noise-induced hearing loss, new research shows. While further research is needed to firmly establish this risk, the investigation is significant because it provides the first acoustical data for a new method to assess the potential harm from a widespread cultural behavior: "leisure listening" to amplified music, whether in live environments or through headphones.
A team of Danish acoustics researchers present the results of their preliminary study at the Acoustics 2012 meeting in Hong Kong, May 13-18, a joint meeting of the Acoustical Society of America (ASA), Acoustical Society of China, Western Pacific Acoustics Conference, and the Hong Kong Institute of Acoustics. Their goal is to help develop recommendations for how sound engineers, musicians, event organizers, and the general public should safely enjoy amplified music so they are protected from hearing loss -- just as workers are now protected by occupational health standards.
Explains Rodrigo Ordonez, Ph.D., lead scientist of the Danish team from Aalborg University's Department of Electronic Systems: "Modern low-distortion, high-power loudspeaker systems and headphones make it easy for people to be exposed to potentially harmful sound levels at discotheques, concerts, or while using portable music players."
He adds that in the realm of industrial noise and work-related sound exposures, decades of experience and personal tragedy -- many workers lost hearing from factory conditions -- has produced the hearing-damage risk criteria currently used. Based on well-documented acoustical parameters, these criteria outline measurement procedures and expected impact on hearing.
"Yet when it comes to musical sound exposure -- and in particular, amplified music -- it is not known if the same measures used for industrial noise will accurately describe the effects on hearing and the risk these behaviors pose," Dr. Ordonez says.
To investigate the potential health risk from amplified music, the team measured sounds known as "otoacoustic emissions" as an index of auditory function. These are sounds generated within the inner ear in response to sound stimuli, and they can be measured in the ear canals of people who have healthy hearing. Research shows that otoacoustic emissions disappear when the inner ear is damaged. In this study, the researchers measured otoacoustic emissions to gauge changes in hearing ability before and after exposure to amplified music, testing this method in a live concert environment. Comparing how these two sets of measures change after a sound exposure with the acoustical parameters of the amplified music can lead to a better understanding of how our hearing is affected.
Results revealed two main findings: One is that it is possible to measure changes in hearing after exposures of relatively short duration, less than 1.5 hours. The second is that there are noticeable individual differences in sound exposure levels, as well as in the changes on otoacoustic emissions produced by similar exposure conditions.
Next steps in the team's work include refining their measurement methods and describing the biophysical effects and mechanics that music sound levels have on individuals. Ultimately they hope to provide data and a scientific rationale on which to establish damage risk criteria for music sound exposure.
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