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What We Know AND What We Don’t
Moving Forward with a Hybrid Approach
Real World Gear: In Ear Monitors
Enrolling in “IEM 101”
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Both in print and in casual conversation among musicians and sound
professionals, several claims are regularly made regarding the potential
benefits in-ear personal monitoring systems (IEM) provide in terms of
hearing conservation, and often, this is contrasted to the approach
of using conventional wedge monitors. While studies by both manufacturers
as well as third parties have tried to identify and/or quantify the
benefits, to date no studies have been published, often because proprietary
information about a device is necessarily withheld by the group performing
the study.
So... What do we really know about what happens when we couple an IEM
system to a healthy hearing mechanism? Let’s review what we currently
know about the hearing mechanism (better known as the human ear), IEM,
and the interaction between the two, then compare this information to
questions that have not yet been addressed but need to be answered before
making an educated decision about any benefits and limitations of IEM.
Professional musicians and sound people face a common dilemma. The accuracy
and emotional nature of performance is (to some degree) dependent upon
the acoustic feedback they receive. However, overexposure to these (too
often) loud sounds can put the end-user at risk of losing the ability
to hear accurately.
Regardless of musical genre, we know that loudness levels at concerts
regularly exceed safe levels of exposure, at least as defined by several
government agencies like OSHA and NIOSH. When levels are excessive,
functional and physiological hearing problems are almost certain to
follow.
THE BIG THREE
In the broadest sense, there are three types of hearing loss people
can inherit or acquire over their lifetime.
Conductive loss refers to damage in the ear before the cochlea. Examples
of conductive losses are an object in the ear canal (such as too much
earwax or a cyst), a perforation or plaque growth on or around the eardrum,
a growth onto, or disarticulation of the middle ear “hearing bones”
and etc. Typically, this type of loss can be fixed with either pharmaceutical
or surgical therapy.
Central auditory processing disorder indicates damage or faulty processing
in the neural pathways and/or hearing centers of the brain.
And sensorineural loss refers to damage to (or after) the cochlea. This
may or not include neural damage from the auditory nerve to the early
auditory processing centers in the brain. A sensorineural loss is permanent,
often progressive (it becomes worse over time), and cannot be completely
or perfectly restored to normal hearing by medical or surgical intervention.
Damage from overexposure to loud sound can affect the hearing mechanism
(the cochlea in particular) as well as the body. Our ears were designed
to hear over a 100 dB range of acoustic sounds, but not to tolerate
sounds over 130 dB SPL or greater.
The human cochlea is a real-time frequency analyzer, capable of bioelectric
transduction of signals ranging from about 20 Hz to 20 kHz, as well
as recognizing streams of acoustic information, while at the same time
being able to discriminate as little as 1 Hz differences in the mid-frequency
bands. The healthy hearing mechanism can focus on a sound source in
order to extract information in noise, and can localize these sound
sources in space.
The typical “noise induced” hearing loss (NIHL) results
in a sensorineural loss with a characteristic drop in hearing sensitivity
at or near 4 kHz. Ultimately (and sometimes prior to seeing a reduction
in thresholds at 4 kHz), there is an accompanying high frequency hearing
loss above 8 kHz. Loss of high-frequency hearing impedes our ability
to localize sounds (the high-frequency cues we use for this task are
no longer available to the listener with a high-frequency hearing loss)
and also effectively causes a subtle “smearing” effect across
different frequency regions of the cochlea.
In addition, loss of hearing due to overexposure to loud sounds may
affect the way a sound is referenced or perceived (loudness) in relationship
to its actual sound pressure level. Historically, audiologists call
this “loudness recruitment”, but recently, work by Dr. Mary
Florentine at Northeastern University in Boston has demonstrated that
what is really occurring is a loss of sensitivity to soft sounds, rather
than an abnormal growth of loudness. Loudness in fact, is not “growing
abnormally”, rather, NIHL results in a loss of the lower portion
of the listeners dynamic range.
It should also be noted (Mueller and Hall, 1998) that hearing loss from
overexposure to loud sounds could also result in non-auditory problems.
Examples include: illness, neuroticism, colitis, headache, endocrine
disorders, fatigue, hypertension, biochemical disorders, insomnia, cardiac
disease, ulcers, and irritability.
IEM ENTERS THE PICTURE
There are two broad classes of IEM earpieces: custom-made, one-piece;
and modular, where the output transducer is coupled to the earpiece.
Custom-made units are created from ear-mold impressions of the user’s
ear, and typically, have greater bandwidth, which is perceived as superior
in terms of overall sound quality.
Modular earpieces, on the other hand, can have a custom-made earmold
or can use foam or silicone to create “one-size-fits-all”
earpieces. Their bandwidth is typically more limited and may provide
a poorer signal to noise ratio across the bandwidth.
Since the development of IEM, many manufacturers have recommended it
as a method of improving fidelity for performers while decreasing overall
stage volumes. While it’s true that IEM offers the advantages
of being tiny, light weight and providing significant improvement over
stage wedges in terms of overall fidelity (due to the proximity of the
amplifier to the eardrum), it has yet to be demonstrated whether IEM
can be successfully used as a method of hearing conservation.
In hearing literature, as well as in some consumer-based audio magazines,
many authors regularly cite the superior acoustic isolation provided
by custom-made earpieces versus modular models. However, no actual data
has been published to date to substantiate most – if any –
of these claims.
At the same time, IEM does provide several obvious benefits including
increased mobility on stage, individualized mixes with individual volume
controls on the performers belt-pack, and differing amounts of acoustic
isolation from amplifiers.
Hearing Note 1 Using an IEM system does not guarantee hearing protection!
Some IEM rigs are capable of producing levels in excess of 130 dB SPL.
Prolonged exposure to these kinds of levels will likely cause hearing
loss. It is up to each user to be responsible for protecting his/her
hearing.
Of course, acoustic isolation can also present a problem for the performer.
Most commercially available IEM systems don’t allow easy communication
between performers, since they don’t include microphones or transmitters.
The earpiece needs to be taken out and re-inserted in order to talk
onstage. This can be an inconvenience.
Another complaint often mentioned is that the acoustic isolation gives
the listener the sensation of isolation from the audience. This is usually
remedied by mixing an ambient mic into each performer’s mix.
Hearing Note 2 Tinnitus (head noise) is a common occurrence and occurs
in many forms. It can be intermittent or constant, mild or severe, and
vary from a low roar to a high-pitched type of sound. It also may be
subjective (audible only to the patient) or objective (audible to others).
Further, it may or may not be associated with hearing impairment. Tinnitus
must always be thought of as a symptom and not a disease. Because the
function of the auditory (hearing) nerve is to carry sound, when it
is irritated from any cause, the brain can interpret the impulse as
noise. (Courtesy of House Ear Institute)
LIABILITY ISSUES
While most professional touring sound companies do not report statistics
regarding hearing loss of employees, given the increasing incidence
of litigation from audience members at concerts where sound levels have
been extremely high, it may become important for such companies to pay
increased attention to the requirements of other industries where reporting
audiometric data is commonplace.
According to a recent report in the November/December 2003 Access Audiology
newsletter, published by the American Speech Language Hearing Association,
effective January 2004, OSHA will put into effect a new rule applicable
to employers who record and report hearing loss of their employees.
New requirements include use of a “two-step criterion for determining
when to report recordability of hearing losses”. Work-related
hearing losses must be reported to OSHA when:
There has been a “standard threshold shift”, defined as
an average shift in hearing threshold of 10 dB or greater at 2 kHz,
3 kHz, and 4 kHz, relative to the audiometric baseline (formerly 25
dB); The average hearing level in the same ear is 25 dB or greater at
2 kHz, 3 kHz and 4 kHz.
OSHA hopes that implementation of these new rules will cause employers
to become more aware of noise exposure as an occupational hazard, and
therefore more motivated to provide improved hearing conservation and
noise control programs. Audio professionals might consider incorporating
these guidelines into their own private record keeping of employee audiometric
data.
OSHA will also begin recording and tracking hearing loss on the “OSHA
300 Log of Workplace Injuries and Illnesses”. This means that
accurate statistics regarding hearing loss will now be monitored by
a central agency, and employers will be able to quantify work-related
hearing loss in addition to other injuries acquired on the job.
According to author Claire Bernstein: “For audiologists, this
represents a dramatic advance and is expected to have a major impact
on tracking the real incidence of work-related hearing loss. Driven
by financial considerations, most employers rely on hearing protection
in lieu of noise control. With these statistics OSHA will now have more
thorough tracking information so it can better direct research, training,
and enforcement activities.”
Since listening is our life’s work, and exposure to loud sound
is part of the job, it’s important to take preventative steps,
rather than attempt to eradicate loud sound altogether, in an effort
to care for our ears. There are several easy things you can do to improve
your hearing health.
• Monitor both the intensity level and duration of exposure. If
the duration of exposure will be long, try to limit the intensity level.
Conversely, louder levels may be acceptable, but for a shorter duration
of exposure.
• Pay attention to your physical relationship to other sound sources.
Standing directly in the path of the sound source can cause greater
levels of exposure, compared to enclosing or baffling a sound source
or standing at an angle from the source.
• After exposure, give your ears a rest. Take at least an hour
to sit somewhere quiet. If your session runs long, take frequent breaks.
• Be aware of exposure to nonmusical, “recreational”
noises like loud television or driving with the windows open at high
speeds. If possible, use hearing protective devices when environmental
noises seem excessive.
Limiting Your Exposure |
TAKING CARE
If a musician chooses to purchase IEM, an experienced audiologist should
“shoot” the earmolds for the end-user. Responsible audiologists
should make themselves available to attend either a rehearsal and/or
a soundcheck where they can take “probe microphone measurements”.
By placing a small microphone in the ear canal, an audiologist can take
a measure of how loud (in dB SPL) the user “wears” their
IEM. This information makes it possible for the audiologist to counsel
the user on a preferred range of loudness to monitor at during performances,
which should help minimize the risk of hearing loss.
In addition to careful fitting and the measuring of loudness levels,
music and audio professional should have their hearing professionally
tested at least once a year. If possible, it would be ideal to find
an audiologist who can perform “high-frequency audiometry”.
By industry standards, audiologists typically test up to only 8 kHz,
but some audiologists have the specialized equipment necessary to test
up to 18 kHz or 20 kHz. Although there are no established “normal”
criterion for high frequency audiometry, serial test results may be
compared over time, which may be a useful clinical indicator of early
hearing loss in the long run.
Regular recordings of “otoacoustic emissions” may also provide
evidence of sub-clinical hearing loss (damage to the cochlea that is
seen before it effects you to the point where there is an audiometric
decrease in hearing thresholds).
When used cautiously, IEM may offer a dramatic range of improvements
for the professional audio engineer or touring musician. Appropriate
use may also serve to protect your most valuable and irreplaceable instrument;
your ears.
Moving Forward with a Hybrid Approach
Real World Gear: In Ear Monitors
An expert view on IEM and hearing
Rachel Cruz holds a Bachelors degree in Music Production and Engineering
from Berklee College of Music and a Masters degree in Audiology and
Hearing Sciences from Northwestern University. She is a research associate
at the House Ear Institute in Los Angeles, in the Department of Auditory
Implants and Perception, and works as a private contractor providing
musicians’ hearing services (fitting IEM) with Sensaphonics Hearing
Conservation. She can be contacted at rcruz@hei.org.
