Critical Levels of Music and Noise

How can I ensure that the music will not damage my ears?

I get this question often, either on my blog, personal email, or from my musician clients whom I see clinically.  My answer is “If the music is less than 85 decibels you are not at risk, and even if you are in a musical environment above 85 decibels, you can still be safely exposed as long as it is for not too long a time”.  I then go on to talk about a sound level meter and tell people they can even download one as an app on their smart phone- and that they should use the “A-weighting scale to get dBA measurements”.  And if their eyes have not glazed over by this point, I mention that every 3-decibel increase over 85 dBA doubles their damage… 85 dBA is safe for 40 hours a week; 88 dBA is safe for only 20 hours a week; 91 dBA is safe for only 10 hours a week… It’s not just the sound level in decibels, but also how long one is exposed- it is the “dose”.

By this time, they are fighting to get out of my office and usually screaming “NO MORE MATH!!!!!!!”  I never dreamed that mathematics would be so useful in getting rid of clients who have overstayed their welcome in my office.  If they still haven’t left my office, I launch into a wonderful discussion about critical levels- this usually does the job.

Music and noise have many similarities (and differences).  One similarity is that many types of music and noise have quiet and loud periods.  In music, it may be the percussion and horn section that contributes most of the music energy or, conversely, it may be the woodwind section that provides the quieter, more mellow aspects to music.  In noise, there may be percussive elements such as in a stamping plant or a rivet gun that provide the peaks to the noise level, and then perhaps there is a more “steady state” lower level din that permeates the work space when the riveters take a break.

This caused researchers – mostly in the 1970s and early 1980s – to look at the highest level in any particular frequency region that would just begin to cause some temporary threshold shift (TTS).  Specifically the “critical level” is the level at any one frequency that would cause 5 dB of TTS.  A closely related concept is “effective quiet,” which is the level that causes no TTS.

We have all experienced TTS and lived to tell the tale.  After we’ve attended a rock concert or sometimes even after cutting our lawn, our ears appear to be numb or perhaps we have some tinnitus.  If I were to measure your hearing at that point, and compare it with your hearing just before you went to the concert, that difference would be the TTS.  As the name suggests, TTS is temporary.  And as discussed in previous blogs, there is no correlation between TTS and eventual permanent hearing loss- at most one can say that before having some permanent noise- or music-induced hearing, one has had to have experienced some TTS, but other than that, there is no relationship.  Nevertheless, short of doing an experiment where researchers knowingly ruin someone’s hearing (for the benefit of science), they are limited by doing TTS studies where the effect is temporary.

The estimation of “critical level” or “effective quiet” is an attempt to get a handle on how safe any given environment is, on a frequency-by-frequency basis.  This would have ramifications for the use of hearing protection devices- one can simply subtract the attenuation at any desired frequency from the measured environmental spectrum of the noise or music, and determine whether it is below the critical or effective quiet level. In most cases, when you do the math, less is typically better than more, especially when it comes to music.  Indeed, Mead Killion and his colleagues at  Etymotic Research came out with a uniform earplug called the ER-15  in 1988 which was then (and 25 years later still is) ideal for many forms of music.  It provided exactly 15 dB of attenuation, and only 15 dB of attenuation.  Hearing protection devices that provide attenuations of 30 dB are simply unnecessary when it comes to music.

I cannot look into the mind of Mead Killion, but I am sure that he and his colleagues at Etymotic (and Elmer Carlson from Knowles Electronics who invented the idea) knew a lot about critical levels and a lot about music when they came out with the ER-15 musicians’ earplug.

The table below shows four sets of data- one is the average data from Mills, Gilbert, and Adkins (1979) across the frequency region for “Effective Quiet” Levels- sound levels that would just be on the verge of creating TTS.  The other three curves are the actual measured average sound levels for three musical instruments- the clarinet, violin, and the trumpet.

The average frequency-by-frequency sound levels (dB SPL) measured for three instruments in a classical domain as compared with estimates of Effective Quiet (in bold) and italics- levels that would create 5 dB of TTS.  Except for the trumpet in the lower frequency region, the average playing levels were below the Effective Quiet levels.  The ranges of the musical instruments were not shown, but some instruments did exceed the Effective Quiet levels by 8-10 dB, implying that hearing protection of 8-10 dB would be useful.

Several things are apparent in this chart.  Other than the trumpet in the lower frequency region, the average playing levels of the instruments do not exceed the Effective Quiet level.  Of course, these are average playing levels and there were some violins and trumpet players who did indeed exceed these levels.  The other thing is that if you examine the slope of the Effective Quiet data, it falls off in the 2000-4000 Hz region.  That is, it seems that it takes less sound energy to create TTS in the higher frequency region.  However- and this almost seems too good to be true- the sound emanating from these musical instruments is inherently of a lower level in these higher frequency regions- the spectra of these musical instruments seem to parallel the Effective Quiet data, as if our auditory systems were innately designed to accept music with minimal auditory damage.  This, however, would not be the case with all musical instruments, such as the drums that generate significant mid- and high-frequency energy that far exceeds the Effective Quiet levels at 2000 and 4000 Hz.