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Fitting Amplification to Musicians with Hearing Loss: Interview with Marshall Chasin, Aud

Fitting Amplification to Musicians with Hearing Loss: Interview with Marshall Chasin, Aud

October 22, 2013 Interviews

Douglas L. Beck, AuD, spoke with Dr. Chasin about hearing aids and musicians, music-induced hearing loss, and how to wearing hearing aids in loud environments.

Academy: Hi, Marshall. Always a pleasure to chat with you!

Chasin: Thanks, Doug, good to be with you, too. I suspect we'll be addressing musicians and hearing loss?

Academy: Absolutely. And so let's start at the beginning. I suspect you would agree that in general music is louder than speech? Further, music is more or less a low frequency event (some 71 percent of musical tones on a piano are below 1000 Hz) and speech is more or less a high frequency event (approximately 71 percent of speech sounds are above 1000 Hz). Given that, what should the musician with normal hearing do while listening to music, and what should the musician who wears hearing aids do while listening to music? And to make it more interesting, what should a musician (with normal hearing and a musician with hearing aids) do while performing?

Chasin: Okay, well that's quite a substantial question! Let's start with the fact that indeed, music is more intense than speech (generally speaking). And, as a consequence, there are different strategies to be considered, based on the listening situation, the person listening, their needs and their hearing status.

The most important thing for the musician with normal hearing is to protect his/her hearing. Most often this can be readily accomplished using a number of commercially available and custom made hearing protection ear plugs. In fact, if the musician with normal hearing is practicing an hour or two hours a day, it's a good idea to have custom-made ear plugs made to provide appropriate hearing protection via attenuation of sound, and to maximize physical comfort.

Academy: And, so again, for the musician with normal hearing, the key is protecting his or her hearing. I might add that my favorite custom-made ear plug is the Etymotic ER-15. Can you tell me your thoughts on those, and perhaps other options?

Chasin: I like the ER-15, too, and Etymotic offers it the same model with multiple attenuation filters, so the customization process is the same, but for some musicians, such as percussionists, they may need more attenuation, and so they may consider the ER-25, but those are decisions best made one-on-one, with guidance from a knowledgeable professional.

Academy: Yes, good point. I agree. Marshall, what are typical loudness levels for speech and music?

Chasin: Well, it varies quite a bit. When we think of quiet speech, it might be 55 dBSPL, medium speech might be 65 dBSPL, and loud speech might be 75 or 80 dB SPL. But for music, you have to shift it all much higher. Specifically, quiet music is around 80 to 85 dBSPL, medium music might be 95 or so and loud music is easily in excess of 100 dB. And so for someone with a mild-moderate sensorineural hearing loss (SNHL), who may need 20 to 25 dB of gain for certain speech sounds, it's important to realize he or she may not actually need any amplification at all for most music situations. Quite often for performing musicians, I recommend they remove their hearing aids and instead, and/or use hearing protection devices (HPDs) like the ER-15s we spoke about earlier.

Academy: When I perform around town, I check the sound pressure level (SPL) using the free downloadable app on my smart phone. On stage, the SPL is often 100 to 105 dBA, and 10 feet in front of the PA speakers, the sounds can easily be 110 to 120 dBA.

As best I can tell, these numbers are not unusual for a local band, and if anything, they're low! And with regard to downloadable free SPL meter apps, Joseph Smaldino, PhD, showed a few years ago, the downloadable SPL meter apps are more than accurate enough to base these decisions on.

Chasin: I agree. The sounds musicians are exposed to while performing are very intense. As you know, Doug, humans are very good at discerning spectral changes, but they're very bad at judging loudness. I think most people would be shocked to find out that when they're at their favorite restaurant on a Saturday night, and when there are lots of people around, the sound level is often above 90 or 95 dBA SPL—and that's very loud!

Academy: I agree. I've seen that quite often in the last year, and I'll take it the next step, again using my free downloadable SPL meter app. When I fly, I have often noticed the background cabin noise is easily 80 to 85 dBA even while cruising at a steady altitude—which is why so many of us cannot hear the announcements! They're totally masked by the cabin noise.

I'll bet they set the PA loudness levels on the ground with the engines off, and while the background noise is perhaps 65 to 70 dBA, and so the announcements sound great on the ground with a signal to noise ratio (SNR) of 15 dB and a broadcast level of 85 dB. But in the air, the SNR is often likely near zero, rendering the announcements (often) unintelligible.

Chasin: Good observation. I'll have to start measuring that when I fly.

Academy: So back to the topic at hand, for musicians with normal hearing, hearing protection is your primary thought. However, for musicians with hearing loss who wear hearing aids, what do you suggest?

 Chasin: In general, the best thing to do is remove the hearing aids. The hearing loss from music is very similar to hearing loss from factory noise, even though the musician is probably not exposed to loud music for 40 hours per week, as the factory worker likely is. Of course, if you're in a rock band, you might gig one or two times a week and you may be exposed to 110 to 115 dBA, which clearly is an injurious level, but the exposure might be only two or three hours.

Conversely, classical musicians may practice two or three hours daily and might perform five or six times a week, and so they may have less intensity exposure than rockers, but classical musicians have greater exposure times. And so again, the bottom line is for musicians with hearing loss who wear hearing aids, it's wise to remove the hearing aids for practice and for performance, and it's wise to think about protecting your remaining hearing!

Another very important issue is that hearing aids are not really designed to amplify sounds that are 90 dB or louder. As we said earlier, hearing aids are designed to amplify quiet, medium, and arguably some loud speech sounds…but they're not made to amplify loud music or other loud sounds. Further, when sounds louder than 90 to 95 dB are amplified they distort like crazy as they saturate the analog to digital converter which causes the hearing aids to sound awful!

Academy: I agree. So back to basics—if you have normal hearing or hearing loss, you need to protect your (remaining) hearing, and if you wear hearing aids, they are not to be worn in loud environments such as loud music, the shooting range, or loud military/industrial noise environments.

Chasin: That's absolutely correct. People usually don't need to wear hearing aids to amplify sounds presented above 90 dB. Unfortunately, some hearing aid manufacturers don't seem to understand the differences in speech and music and the best protocols to maximally listen to each. Some manufacturers specify frequency changes, others address compression changes, but few offer proof that what they suggest is correct.

In fact, in the summer of 2013, in I wrote something along the lines of "Some manufacturers suggest a wider frequency response for a music program than for a speech program; others suggest an enhanced mid-frequency and others suggest an enhanced low-frequency end. These suggestions are silly and for the most part should be ignored..." and further "…if a wider frequency response is at all possible…it should be equally applied to speech and music…."

Academy: And, so I suspect you're advocating that while listening to live music, the hearing aid should be set very similar to how one would listen to speech?

Chasin: Absolutely. In general, both require maximal auditory cues (with respect to spectral content, loudness and dynamic range and spatial cues) for maximal perception.

Academy: And so what do you recommend for musicians (and others) who actually have a more severe hearing loss, and they want, or need, to wear their hearing aids in these very loud environments?

Chasin: They may want to try to one of the strategies I've previously written about. First, while listening to a loud radio or other loud sound source, if possible, it's best to turn the volume of the sound source down, and then crank up the volume of the hearing aid, so the input to the hearing aid is lower, allowing the hearing aid circuit to do what it was designed to do.

The second strategy is to place three or four layers of scotch tape (cellophane tape) over the hearing aid microphone to reduce the sound pressure before it enters the hearing aid, this works very well. However, I certainly recommend experimenting with the scotch tape beforehand to know how many layers and exactly where and how to place it!

Academy: And what happens to the fidelity of the hearing aid when applying scotch tape to the mic?

Chasin: That's a good question! I've listened to hearing aids with the scotch tape in place and the sound quality appears to be fine. I have measured it, and it does sound pretty much like it's supposed to through the speech frequencies and the low and mid-tones of music.

Academy: Okay, that's interesting. What else do you suggest?

Chasin: Sometimes, the audiologist or dispenser might order a hearing aid that has a "minus 6 dB per octave" microphone. As you know, Doug, in typical hearing aids we use a broad-band or flat microphone response to amplify all sounds maximally, but, if the manufacturer incorporates these readily available "minus 6 dB per octave" microphones we decrease the input to the analog to digital converter in the lows, perhaps by some 6 dB at 500 Hz and by 12 dB at 250 Hz. We get 6 to 12 dB less SPL at the analog to digital convertor (which typically saturates at about 95 to 96 dB input) and so it's less likely to cause the circuit to saturate.

Lastly, another option is to have an analog compressor placed at the front end of the circuit, before the analog to digital convertor, to compress sounds so as to not allow the analog to digital convertor to ever saturate, and then the sound can be digitally expanded inside the digital circuit. There are some available technologies currently in the marketplace that do exactly that.

Academy: And I know you also spoke about an "auto-range" solution. How does that work?

Chasin: When we talk about the 96 dB limited range of the analog to digital convertor, it doesn't mean it has to start at 0 dB SPL as the bottom and use 96 dB SPL as the top end. What if you were to shift it to start at 10 dB SPL or 20 dB SPL, then you could use a 96 dB dynamic range and you might be able to go up to 106 dB SPL or 116 dB SPL before saturating the front end. Like some of the above technical suggestions, there are some examples of this is the marketplace already. There are many solutions for how to wear hearing aids in very loud environments- some are very low tech and some are very high tech.

Academy: Thanks Marshall…as always, I've enjoyed our discussion and you've given me some really important things to think about!

Chasin: Thanks, Doug, it was entirely my pleasure!

Marshall Chasin, AuD, is a recipient of the 2012 Queen Elizabeth II Diamond Jubilee Medal and a recipient of the 2013 Jos Millar Shield (British Society of Audiology).

Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology.

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