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La Scena Musicale - Vol. 12, No. 8 May 2007

Music & Hearing Aids

by Dr. Marshall Chasin / May 30, 2007

I must have seen John in my clinic about five times now. Each time, this music-lover and audiophile has asked me to adjust his hearing aid for him. Eventually, we concluded that his aid worked fine for helping him hear speech, but was inadequate for music listening. One solution would have been to install a hearing aid with a “music program,” but many such programs merely altered the balance of sound. John and I realized that there was no simple way for music-lovers with hearing aids to satisfy their need for musical sound quality.

Finding the “best” hearing aid for music enjoyment and playing is challenging. Part of the problem is that hearing aid design engineers are mainly concerned with optimizing hearing for speech. In some cases, speech-optimized hearing aids can also prove useful for music (this is especially true for vocal, in particular folk, music). Nevertheless, when musical instruments are added to the mix the resulting input to a hearing aid becomes more complex.

One option is to purchase a second set of hearing aids specifically tuned for music but this solution is like using a jackhammer to drive in a nail. Many hearing aids have more than one “program” that allow them to adjust for speech, and then for music. Costs may vary widely depending on the type of hearing aid and on where it is bought. In Canada, a hearing aid may cost $1,000 whereas the same model may be priced double or triple this amount in the United States. Depending on the circuitry used, the cost can range from $500 to $3,000, but beware – a higher price does not necessarily mean better quality.

What is the difference between a hearing aid for speech and one for music? There are two main physical differences: 1.) the long-term spectrum of music versus speech; 2.) differing overall intensities.

Human speech, on average, depends on a 17-cm long vocal tract, a tongue that can narrow the pathways in the mouth, and a highly dampened nasal cavity. The long-term spectrum of speech is well-defined and typically language-independent. In all languages, most of the intensity comes from the lower pitched vowels such as the “a” in “father,” whereas most of the intelligibility or clarity comes from the higher-pitched consonant sounds.

Hearing aid engineers generally try to achieve a balance between the loudness of the vowels and the clarity of the consonants. In contrast, music can be produced by many vocal and instrumental sources. Unlike speech, music is highly variable in terms of amplification, intensity and frequency making it impossible to establish the equivalent of a “long-term music spectrum.” There is simply no music “target” as there is for amplified speech. A hearing aid that is designed to balance the loudness of the vowels and the clarity of the consonants may have limited value for music. The most that can be said is that the amplification in a hearing aid for music should be approximately 6 decibels quieter than that for speech.

From a distance of one metre, speech averages 65 decibels. Because speech is created by the human vocal tract, and most human lungs are similar in the subglottal pressures used to drive the vocal chords, the potential intensity range is well-defined but limited - only 30 to 35 decibels separate the softest sound (“th”) from the loudest sound (“a”). In contrast, depending on the music being heard, various instruments can generate very soft sounds (20 to 30 decibels, like the brushes of a jazz drummer) to the very loud sounds of an amplified guitar or the brass of Wagner’s Ring Cycle (both in excess of 120 decibels). The dynamic range of music as input to a hearing aid is on the order of 100 decibels compared to the 30-35 decibels resulting from speech.

What does all this mean for hearing aid mechanics? Typically, sound enters a hearing aid like any sound amplification system – it is picked up by the hearing aid microphone, and then amplified electrically. In modern hearing aids musical sounds can be altered in subtle ways. The amplified sound is sent to a small loudspeaker (the “receiver”) in the ear. Since music tends to be more intense than speech, the part of the hearing aid amplification just after the microphone (the “front end”) can be overloaded. Poorly designed “front ends” can easily cause distortion. Audio files demonstrating how a poorly configured “front end” in a hearing aid can distort loud music are found in the links section of the Musicians’ Clinics of Canada website (www.musiciansclinics.com under “Marshall Chasin’s PowerPoint lectures”). Hearing aids that can handle these more intense inputs have been available since the late 1980s and are more effective for music listening.

For clients like John who already have a hearing aid that is good for speech but poorly-configured for music, there are strategies that can be used to maximize musical enjoyment. One strategy is to turn down the input (such as the volume of a home stereo system) and turn up the volume of the hearing aid. This will reduce the input to the “front end” making it less likely to cause distortion.

Another technique, often used by live music enthusiasts, is to place a cover (like a band-aid) over the hearing aid microphone to dampen the sound (the volume can be increased later to compensate for the attenuation of the cover). For people who have behind-the-ear hearing aids, a helpful “trick” is to twist the aid around by 180 degrees so that the front faces backwards thus suppressing sound from the front. Directional microphones found in almost all behind-the-ear hearing aids are designed to suppress noise if it is coming from the rear.

It is advisable to consult with an audiologist to find a hearing aid model that can be set to different “programs” so as to optimize speech and music listening. If, like John, you already own a hearing aid, you can minimize the “front end” distortion by reducing the music volume or by “tricking” the aid into thinking it has been lowered. Then, sit back and bask in the joy of music! n

(c) La Scena Musicale