The latest issue of the Journal of Speech and Language Hearing Research has an article on the loudness of on-stage loudspeakers (monitors) used by musicians to hear themselves. Jeremy Federman and Todd Ricketts had professional singers adjust two types of monitors to two loudness levels. The two types of monitors were floor speakers and in-ear buds, the two levels were minimum acceptable listening level (MALL) and preferred listening levels (PLL). You can imagine this, having your stereo at the softest possible level that you can still hear, but won't disturb your spouse, that is a MALL. But when you crank it up so you can really hear it, that is a PLL. PLLs and MALLs were set by each musician listening to their own voice. Other musical sources and crowd noise simulations were set at different levels by the scientists.
The graph at top shows that in-ear buds were set consistently at lower levels than floor monitors, about .6 dB, except the left-most condition The different sets of bars show different ratios of Overall Music Level (OML) and Crowd Noise (CN), so the outlier is when the overall music level was lowest (92 dB) and there was no crowd noise. But ANOVAs revealed a significant difference between monitor types overall, with no significant effect of the overall loudness or trial condition.
The authors have a good caution though:
Although a statistically significant result was observed between the two monitor types for PLL, the actual mean difference of 0.6 dB (see mean data in Figure 2) could be regarded as nonsignificant in a real-world consideration of noise exposure recommendations. For this study, a 3 dB or greater difference in listening levels between monitor types (i.e., NIOSH time-weighted average) would have been considered functionally significant (as opposed to statistically significant) because such a result would potentially double allowable real-world exposure time based on NIOSH recommendations. The statistical significance of the findings is related to the large number of samples involved in statistical analysis.
It is refreshing to see a study that admits the different between statistical significance and actionable significance. A serious result from this study is the average dB of MALLs: 109.0 dB for floor monitors and 103.2 dB for in-ear buds. OSHA safety regulations would allow exposure to 105 dB for 1 hour each day before serious damage might occur to hearing. Most amplified shows last considerably longer than one hour, especially when pre-show soundchecks are included. So to you amplified musicians out there, invest in a good pair of sound-attenuating in-ear monitors and work with a hearing expert to get them fitted well. That can double or quadruple the amount of time you can safely listen to yourself play!
Update: Daniel Wolf shows that classical musicians are also in danger. I had a trumpet teacher who always carried sets of ear plugs in his case, which he would hand out to the violists or 2nd violinists sitting in front of him.
J. Federman and T. Ricketts, "Preferred and Minimum Acceptable Listening Levels for Musicians While Using Floor and In-Ear Monitors," Journal of Speech, Language, and Hearing Research, Vol 51 (Feb. 2008), 147-159.