Traditionally, occupational noise exposure has been the “diagnosis of choice” for the hearing loss division of the various Worker’s Compensation Boards. In Canada, Worker’s Compensation Boards have provincial jurisdictions and not federal. In the European Union and many other countries, a federal or international standard is adhered to. Regardless of which jurisdiction holds hegemony over hearing loss prevention and compensation, the vast majority of cases are concerned with industrial or military noise sources.
The debate about whether long-term music exposure should be viewed in the same way as long-term noise exposure is almost as controversial as the debate about the veracity of climate change or the effects of acid rain on our environment.
When it comes to music exposure, the debate is not really a debate-which makes it identical to the issue of control of acid rain. A lake is considered dead (or in danger) when the PH falls below a critical level. In Canada it is 7.4 on this scale; marine life ceases to exist below this point. In other countries the level is set even lower- this is a political decision and not based on science. The percentage of lakes that are affected by acid rain will be large if the 7.4 fence is considered and not a problem at all if a fence of 7.2 is considered.
Similarly with music exposure (or noise exposure). Many jurisdictions will accept a claim of noise exposure only if the exposure is for 5 years or longer (based on a 40-hour work week) and also greater than 85 dBA. Yet many “workers” have significant hearing losses after only 4 years of exposure and from levels that are barely in excess of 80 dBA. These “susceptible” workers are usually accepted for compensation, but not until there is significant investigation.
The 85-dBA “fence” is a political decision and not based on science. Depending on the model used (e.g. ISO R-1999), exposure to 85 dBA will result in a permanent 6 dB of hearing loss at 4000 Hz after a period of time- that is, even 85 dBA is not completely safe. There is a recommendation from the World Health Organization (WHO) that all “noise” levels should be kept below 80 dBA, and from a purely protective perspective, the WHO is correct. (I guess that it would be called the WHOM in Canada, eh?).
Now let’s add the issue of music into the equation. Music can have sound levels around 50 dBA and a moment later the levels can increase to over 120 dBA. Music can be intermittent and silent periods are much more common in music than they are in a metal factory. There are ways of calculating this on-off time fraction of noise exposure, but the initial calculations are based on long periods of “on” and long periods of “off.” In music, the on-off periods can be only seconds or even milliseconds and not minutes or hours.
In short, when it comes to music exposure we are not exactly sure what is going on. Our industrial noise exposure models are fairly accurate up to 115 dBA and for longer periods of “on” and “off” than found with music, but we don’t have good models (yet) for music exposure.
And, unlike noise exposure, music exposure does not end when a musician or music teacher leaves the venue or classroom. Many professional musicians practice for several hours a day and teach for several more. And many musicians, like everyone else, use MP3 players and occasionally go hunting.
So, it is not really surprising that regulatory bodies that seek to compensate musicians for long-term music exposure are dragging their feet. If I were a regulator I might have the same concerns.
But musicians do develop hearing loss, even if “noise surveys” indicate that they are not at risk. This negative finding should be viewed as the inability of noise surveys to be performed properly for music rather than that there is a lack of potential damage. Musicians’ hearing loss is coming from some place and the most likely etiology is from their music.
Unlike many sources of occupational noise exposure that have significant low- and mid-frequency energy, music tends to have very significant mid- and high-frequency content. In many treble and percussive instruments the higher frequency harmonic structure can be more intense than the lower frequency fundamental energy. A quick and dirty trick to verify this is to use a sound level meter in an orchestra; toggle between the dBA and the dBC settings on the sound level meter. If there is minimal difference between the two scales, then there is minimal lower frequency sound energy. Recall that the dBA scale filters out some of the sound below 1000 Hz whereas the dBC scale is a non-filtered (or linear) scale. If there is minimal difference, then there is minimal energy below 1000 Hz.
This has implications for noise exposure as well as audiometric asymmetries. Most noise exposure criteria in various jurisdictions state that industrial exposure has an equal effect on both ears. This makes sense only if the noise exposure is lower frequency emphasis (below 1000 Hz). The long wavelengths of the lower frequency sounds do not “see” the head as an acoustic shadow such that the sound levels at both ears are roughly the same, regardless of where the offending machines are. This is not the same as for music. Because of the shorter high level wavelengths found with music (i.e., higher frequency harmonics), the head creates an acoustic shadow- the head shadow effect, such that a violinist who holds the violin near the left ear has a sound level that can be about 4 dB lower at the right ear than the left ear, resulting in audiometric asymmetries. In addition, factory floors tend to be highly reverberant such that a machine on the left of a worker may generate noise levels that are just as high to the right of the worker. In contrast, most forms of music are played and listened to in relatively low-reverberation environments. A music source at the left ear (e.g., a violinst or rock drummer) is of lower level when measured at the right ear because of the relative lack of reflected sounds.
And to make matters even more complicated, where should we be measuring the sound level? At the ear level? One meter in front of the musician? In the ear canal near the tympanic membrane?
Occupational noise exposure from industry is measured near the worker, but I don’t know of any jurisdictions that require that it be measured in the ear canal (using a probe-tube microphone). This makes sense since most of the occupational noise is lower frequency- far below the ear canal resonance around 2700 Hz. But what about music exposure that has significant energy in the 2700-3000 Hz region- the G just below the top note on the piano keyboard? This sound energy (of a harmonic) can be enhanced by 17-20 dB greater than that created in the playing environment. There will be a significant difference in noise measured with many forms of music depending on where it is measured, as opposed to occupational noise exposure.
These are just some of the various measurement issues that may arise when measuring the exposure that a musician receives.
Currently in Canada only British Columbia and Ontario have a policy that covers music exposure in musicians. The tide is slowly changing as more and more regulators come to grips with the interesting differences between long-term music and long-term noise exposure. “Numbers” that need to be achieved prior to the granting of hearing loss due to noise are continually being re-examined. Musicians do have hearing loss and it comes from their lifelong music exposure. Hopefully the gap between reality and recognition will go the way of the 8-track cassettes.
