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 |