Control methods in assessing musicians’ earplugs Part 2.

Last week we talked about using a higher stimulus level to assess the benefit of a musicians’ earplug.  Actually it was for all hearing protectors, but since this is a blog about music, this applies equally to musicians’ earplugs.  In that blog we talked about using a real ear measurement system and using the normal stimulus that comes with such a system.  This can be a pure tone sweep (using a bank of filters such as with Audioscan products) or an FFT (used frequently with Frye products).  But what about using a musician’s own instrument to assess hearing protectors?

In some sense (actually in most senses) this may be preferable, despite the lack of a well-controlled and repeatable input to the hearing protector.  The clarinet may be played at 87 dB SPL one time and another clarinet player may play it at 89 dB SPL or even 93 dB SPL.  The use of the more calibrated and controlled stimuli discussed in last week’s blog certainly has its place.

If one’s goal is to assess the reliability and repeatability of a hearing protector on an individual, then one must use calibrated and well controlled stimuli and test methods.  If however, you want to get a sense of what sounds and at what levels actually reach a person’s temporal lobe (i.e., which sounds are audible) then either method would work well.

in the first, one just needs to “add” this negative gain to the audiogram similarly to how we can add insertion gain to the audiogram.  In the second approach where an individual’s own instrument is used, we may be able to pick up something that would not show up on a single pure tone sweep.  For example, it is possible that a hearing protector is “level dependent” and like hearing aids, this simply means that the hearing protector would have different characteristics depending on the level  of the input to the hearing protector.

In the realm of modern hearing aids, it is common place to use several different stimulus levels to assess “quiet” speech, “medium” speech, and “loud” speech.   There are some level-dependent hearing protectors that would provide a different amount of attenuation depending on the input level.  Personally I cannot see how that would benefit a musician and I haven’t really used this with my musician population, but to be fair, they do exist and other audiologists may have different protection fitting philosophies.

Similar to the method mentioned in the last blog, one needs to calibrate the real ear measurement system correctly according to the manufacturer’s specifications. And this time, similar to checking the noise floor technique mentioned last week, set the stimulus level to 0 dB (for Audioscan products) and “off” (for Frye products).  This has the effect of turning off the real ear measurement loudspeaker and also disabling the reference microphone.  Therefore care should be taken to ensure that the musician doesn’t move during the test.  You are now ready to use the musician’s own instrument to assess the real ear attenuation of their personal hearing protection.

I typically have the musician play 9 notes on their instrument and do a “run” of the real ear measurement system each time.  For a low pitched note, a middle pitched note, and a high pitched note, play each one at a quiet (piano), a medium (mezzo forte), and a loud (fortissimo) level (3 notes x 3 playing levels).  This is actually done 18 times and not 9 times–once with no hearing protection and then immediately after with hearing protection and the difference is of importance.

Understandably I do not do this on every musician I see. I did for the first 10 years I worked with musicians, but have now developed a pretty good sense of what instruments can and cannot do.  And I would suggest to any new hearing health care professional who wants to do this, that you do it as much as you can in order to feel comfortable.  One can argue (and indeed I do argue) that this is as much for the training of the hearing health care professional as it is for assessing the musician.

With these data one can see whether an individual, using their own instrument, reed, bow, or mouthpiece can generate levels that are potentially damaging or whether you just need to watch out for the guy sitting or standing beside you.  It is quite possible that a musician when practicing alone may not require hearing protection and this approach will be quite useful to help answer that question.

And oh yes- the question that is always asked… what about percussion instruments such as the drum or a plucked string instrument such as the guitar or harp?  Clearly the sound levels assessed are a function of when you measure them- at the beginning, just after the pluck or during the fading off of the note.  This is where a swept bank of filters (such as that used with the Audioscan products) would have some limitation and the use of an FFT (Fast Fourier Transform, such as that used with the Frye products) would be better.  I wouldn’t base any of my purchasing decisions of one real ear measurement over another on this issue, but it is a difference and there are products on the market place that actually use both.

Even if you wanted to short cut this approach and ask the musician to play and sustain a single mid-frequency note at a fortissimo (loud) level, this one measure can provide information on whether musician should be wearing their personal hearing protection all of the time they play music, or perhaps only when performing.  In other words, is it the “other guy” who is the culprit?