Jun 182009
 

by Brian Fligor and Deanna Meinke, The ASHA Leader 5/26/09

While the media continue to spotlight the risk of noise-induced hearing loss (NIHL) from personal music players (PMPs), a number of myths have surfaced in the public arena. It’s important for professionals to stay informed and provide contemporary perspectives and accurate information to those for whom we care.

MYTH 1: Personal music players are a primary reason for NIHL in children.

PMPs are the most commonly reported “noise” source for children 6-19 years old who have their hearing tested as part of a research project at the Dangerous Decibels exhibit at the Oregon Museum of Science and Industry (OMSI). Hearing tests and noise history data is available online at Dangerous Decibels; data accessed on April 15, 2009, reveals that 65% (n=2,266) of youth use stereo headphones and 20% report using firearms. Sixteen percent (n=25,651) of youth in this age bracket have thresholds worse than 20 dB HL at 4 kHz.

Although PMP use may be implicated in NIHL, it is unlikely that PMPs are the primary reason for the occurrence of notched high-frequency hearing loss configurations at young ages.

NIHL develops gradually over long periods of exposure to a variety of noise sources. NIHL will take years to develop in the small percentage (~5%-10%) of individuals who listen at hazardous sound levels for extended periods of time. Immediate acoustic trauma from fireworks and/or firearms is a much more likely culprit for the notched high-frequency hearing loss evident in young children (Gupta &Vishwakarma, 1989).

MYTH 2: PMP manufacturers have eliminated the risk of NIHL by providing a means of locking the PMP’s volume control setting.

Efforts to reduce hearing loss risk by limiting volume level fail to take into account that NIHL risk is due to the combination of time and sound level, not just the listening level. If the level were to be limited to the maximum level known to not increase risk for NIHL, then no headphone would transduce sound above 78 dBA (Melnik, 1991). In many circumstances a person might want or need to turn the sound up higher than 78 dBA, so this solution would not survive in the marketplace. Legislation passed in France in 2005 limited PMP sound output to a maximum 100 dBA and voltage output to to a maximum 150 mV (Legifrance, 2005). However, 100 dBA is not “safe” by any stretch of the imagination; listening for longer than 15 minutes at this “limited” level exceeds the National Institute for Occupational Safety and Health (NIOSH) recommended exposure level (NIOSH, 1998).

Some headphone manufacturers claim to limit output to 85 dBA, but this approach neglects to consider the risks of listening duration and inappropriately polices chosen listening level when listening duration is less than several hours per day. Software that can be set by parents to provide a maximum output on the PMP has merit because it can help parents feel confident that at least their child isn’t listening at maximum volume. Without expert guidance to assign an appropriate maximum limit, however, parents operate with a false sense of security and potentially put their children at risk.

MYTH 3: Insert earphones are worse than other styles of earphones for your ears.

The media picked up on a detail from a study by Fligor and Cox (2004) that sound levels produced by earbud headphones were several decibels higher than over-the-ear headphones at the same volume control. The intent was not to malign earbuds, but rather to demonstrate the caveats of trying to apply general “rules of thumb” about maximum recommended listening duration and listening level. Data presented at the NIHL in Children at Work and Play meeting in October 2006 and forthcoming in a peer-reviewed journal document that regardless of the output capacity of an earphone (earbud vs. over-the-ear), people use headphones at the same listening level and that this chosen listening level is, in part, determined by the background noise in the listening environment. Some in-the-canal earphones that isolate the ear from background noise are actually used at lower listening levels than over-the-ear earphones that have lower maximum output because the users don’t have to ramp up the volume to hear over the ambient sound.

Read the full article, including the story on these other myths at:

http://www.asha.org/Publications/leader/2009/090526/090526e/

– MYTH 4: The music is too loud if you can hear it from your child’s headphones.

– MYTH 5: 85 dBA time-weighted average is a safe noise exposure reference for children when applied to PMPs

– MYTH 6: Sound levels measured at the eardrum can be directly compared to damage risk criteria.

– MYTH 7: PMPs should never be played at hazardous sound levels.

– MYTH 8: Noise cancellation earphones provide safe listening because they cancel the hazardous noise.

– MYTH 9: A recommended maximum volume control setting and listening duration for adults is appropriate for children and babies.

– MYTH 10: Today’s PMP technology puts listeners at greater risk.

– Thanks to bhNEWS and NVRC, Fairfax