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Personal Monitors: What You Should Know
Michael Santucci, MS, CCC-A
Affordable wireless and hard-wired systems are making personal in ear monitoring systems, until now used mainly by top touring acts, available to a broader range of musicians and engineers. Improved and consistent sound quality, reduced feedback and freedom of mobility are just a few of the many advantages emphasized by manufactures, and most claim that their products provide high-quality audio, with hearing safety built in. However, hearing safety is often minimized or misunderstood. Before committing to this emerging technology, product safety and quality should be carefully evaluated.
It is no secret that exposure to high sound levels from conventional stage monitors may cause irreversible damage to the inner ear, resulting in permanent hearing loss and tinnitus, or ringing in the ears. Personal monitoring devices, though miniature in size compared to stage monitors, are still capable of producing harmful levels of up to 120dBA at the eardrum. However, with proper use and the guidance of a well-informed audiologists, they can allow a performer to hear the full dynamic range of music, while protecting the ear from permanent hearing damage.
After intensive training in the science of hearing and hearing loss, the majority of audiologists hold a master's degree, and some go on to complete a doctorate. Unfortunately, most audiologists have little or no experience in dealing with the special circumstances and individual needs of musicians, let alone sound reinforcement technology, Current college curricula do not educate the audiologist in hearing protection strategies for rock musicians. A well-informed audiologist who specializes in working with musicians has probably invested extra time to understand both the applications of personal monitoring devices and the integration of hearing protection strategies.
Make the effort to locate an audiologists with expertise in the safe use of personal monitors. Ask specific questions: "What are the qualifications of the professional taking the ear impression? How can a personal monitor protect hearing? What is the maximum SPL of the transducer? Can the volume of this device be measured during rehearsal? How long can this personal monitor be worn and at what volume, before there is a risk of damage?"
An effective strategy for protecting professional ears should include a case history, a hearing test, the use of peak limiters, the measurement of sound levels in the ear, plus an understanding of the use of personal monitors as protective devices. A confidential interview with the audiologist provides them with important information about the specifics of past stage monitoring, individual hearing problems and possible medical conditions that may restrict the use of monitor placement in the ear. This information assists in the selection of the appropriate personal monitor.
A hearing screening test is essential and highly recommended. An initial hearing test serves as a baseline for future tests and takes only a few minutes. Regular testing is the only means to measure the effectiveness of the personal monitor as hearing protection. A new test, otoacoustic emissions (OAE), may provide early indication of outer hair cell damage, even before conventional tests show any significant decrease in hearing.
Some audiologists are equipped with miniature probe microphone technology, which can measure sound levels at the eardrum. Used during live rehearsals this procedure establishes personal guidelines (OSHA or ISO) to eliminate damage caused by improper use. The technology enables the audiologist to direct the performer to the appropriate sound level for the daily number of hours the monitors will be used. This is the only method able to demonstrate and document the loudness of the personal monitor in the ear during actual use.
The use of brick-wall peak limiters only protects the ear from trauma caused by transient spikes and pops. Although peak limiters are an important part of the safety equation, they cannot be relied on to regulate the volume of user-controlled headphone amplifiers. Long-term exposure to moderate levels over many hours is as dangerous as occasional short bursts. Although professional engineers should be able to reduce accidental exposure to brief transients, the greater risk to hearing comes from everyday use at unsafe levels.
As protective devices, customer-molded transducers offer greater acoustic isolation than generic ones. For proper protection, the personal monitor must be able to isolate the ear from ambient sound of the backline and P.A. This higher signal-to-noise ratio inside the ear canal allows the performer to listen clearly at lower levels. Wearing a consumer "ear bud" while listening to a Walkman on "five" in a quiet room may be sufficiently clear, but on a noisy street, the same program material may need to be on "ten" for the listener to perceive the same loudness, as ambient noise masks the signal. Unless the device fits inside the second bend of the ear and seals the canal, outside sounds will mask the signal and force louder monitoring. Any product with open sound ports and surface placement of the transducers will have a reduced ability to isolate from background noise. Ear canals come in all shapes and sizes. A custom mold of the ear extends beyond the second bend of the ear canal and should be taken by an audiologist. First the audiologist otoscopically inspects the ear canal for wax, debris or disease. A cotton or foam block is carefully placed near the eardrum, and silicone material is injected into the canal to find the shape of the ear. It is a painless but unusual experience. The ear impression is sent to the manufacturer where the shell is cast and the electronics installed.
Manufacturing techniques, transducer types, construction materials and service vary among manufacturers. Personal monitors can be made of soft material, hard acrylic or a combination of both. The following features are recommended:
- The canal portion should be soft to maximize comfort and deep to provide acoustic isolation.
- Testing in a 2cc coupler (the average volume of an ear canal) should be provided to document the product's consistency.
- A minimum 90-day warranty for manufacturing defects should be standard.
- Ear impressions should be retained for remakes.
- Choices from a variety of transducers, styles, materials and isolation capabilities should be offered to satisfy personal sound quality preferences and address individual hearing protection concerns.
It's safe to say that personal monitoring is here to stay. Audiologists now have adequate tools to direct musicians and engineers in the safe use of these devices and to implement effective strategies for prevention of hearing loss. Take time to investigate before committing to a product. They're the only ears you'll ever have.
Reprinted from Mix, May 1996
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