The Impact of Portable Digital Music Players on Hearing in High School and Middle School Students

In previous decades, teenagers’ music permeated the house from stereo speakers and radios. Although disruptive, the audible sound enabled parents to regulate the noise level, thereby preventing noise-induced hearing loss. Since the advent of portable music players (PMP), teens routinely use earphones to listen to music in privacy. Parents are less aware of the noise level to which their children are exposed. Devices sold in the U.S. have recorded noise levels as high as 115 dB, leading us to initiate research to determine the impact of portable media players on the hearing of children in the U.S. It is known that acute exposure to loud noise may result in a temporary threshold shift, heralding permanent hearing loss with continued exposure. To determine whether listening to a PMP may result in exposure to noise levels loud enough to result in permanent hearing loss over time, we assessed whether a measurable temporary change in hearing occurred in middle and high school students. Thirty students completed a questionnaire. A preliminary audiogram, after avoiding noise for a 14-hour period, was performed to assess each student’s baseline hearing. Students then listened to their PMP, in accordance with their usual practice, for up to 60 minutes, and hearing was retested. A significant number of subjects, 22 of 30 (Relative Risk of 1.47 with a Confidence Interval of 1.15 to 1.78 ) were found to have a temporary worsening of their hearing, leading to concern that current student practices may lead to permanent damage to their hearing. To determine the level of awareness of noise exposure and available volume limits (10) to protect hearing, thirty middle school and high school students completed a questionnaire. Of 30 subjects, 27 reported listening to an iPod for the study. Fifteen of the 27 with iPods reported that they were unaware that volume limits may be set on iPods; 22 of the 27 thought that their parents were unaware that volume limits may be set; and only 4 subjects actually set a volume limit on their iPod. Five subjects reported sometimes noticing a temporary hearing loss after listening to their PMP, seven reported rarely noticing such a loss, and the remaining 18 subjects reported never noticing a temporary hearing loss after listening to their PMP. Eight subjects reported listening to their PMP at less than half volume with the remaining twenty-two subjects setting the volume to greater than half volume. There was no correlation between reported volume setting and worsening of audiogram results. To determine whether listening to a PMP may result in exposure to noise levels loud enough to result in hearing loss, we assessed whether a measurable temporary change in hearing occurred in the students. Of the 30 subjects, 22 were found to have a temporary worsening of their hearing (figure 1) which was significant at the 95% level with a relative risk of 1.47 (CI 1.15 to 1.78). The difference in the mean before and after listening to the PMP totaled 10.67 dB over the 14 tested ranges. A paired t-test revealed that the average increase of 10.67 dB has a 95% confidence interval of 2.35 to 18.98 dB. Analysis of the results indicates that exposure to a PMP causes a statistically significant temporary noise-induced hearing loss. The results are also significant when we look at the magnitude of the hearing decline. The mean decline of 10.67 dB over all fourteen frequencies represents a less than 1 dB change average per frequency, a slight but measurable and statistically significant difference. This study was conducted in an office setting with a relatively low level of background noise to avoid background noise as a confounding variable on study results. Students, however, were asked to listen to their iPods in accordance with their usual volume settings. Some of the students stated that they vary their volumes in accordance with background noise. One student asked if she should set the volume as if her mother were vacuuming. Another student indicated that she typically listens to her iPod on a train and was surprised at how loud it seemed in the office. It is possible that results would have been different had students been listening to their PMPs in the presence of background noise. There was concern that there may be subject bias, though the direction of such bias was unclear. On one hand, some students may have assumed that the study anticipates worsened hearing after listening to their PMP, and consequently experienced more uncertainty on the second test. On the other hand, other students may have actively wanted to prove that PMPs had no effect upon their hearing, and consequently striven harder to respond on the second test. Additionally, upon review of audiogram results with subjects, one student whose hearing had improved expressed that listening to music made him more alert. The effect that music may have on alertness and thus on measurement of hearing had not previously been considered by the researchers.