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In a previous blog, a brief history was provided concerning the 30-year effort by hearing conservation professionals to obtain approval from OSHA in 2013 for the use of insert earphones rather than supra-aural headphones. For audiometric testing, Audiologists have used insert earphones in clinical practice for decades.
Why should your clinic switch to using insert earphones?
Background Noise Reduction. As mentioned in the prior blog, supra-aural headphones provide little in the way of noise reduction. A common complaint among those being tested is the distracting presence of background noise. Indeed, it has been shown that industrial sound booths in mobile vans and fixed clinics routinely fail to comply with OSHA’s allowable noise limits. One of the reasons why insert earphones are so popular among Audiologists in clinical settings is also the primary reason why industrial clinics should adopt them…the use of insert earphones is essentially equivalent to placing a sound booth in a person’s ear canals! The foam eartips block out huge amounts of noise lessening the likelihood of distraction and typically resulting in lower, more accurate audiometric thresholds.
Comfort. No tight headband, no pressure on the outer ears. And because the eartips come in three sizes…small, regular and jumbo…most will find them comfortable to wear. It has been this Audiologist’s experience that around 85-90% will use the regular size, nearly all the rest use the small size, with only a handful needing the jumbo size.
Improved Hygiene. In order to minimize the potential for spreading infectious disease, supra-aural earphones should be cleaned in between patients, or a new set of earphone covers used for each patient. Realistically, this often does not take place. Insert earphone eartips, however, are designed for single usage. The eartips are inexpensive and easily replaced between patients without the messiness of chemical agents. This also reduces the likelihood of damaging the speaker elements…a wet chemical leaking into a speaker element can quickly ruin it. This risk is eliminated with insert earphones.
Better Interaural Attenuation. Those who have attended a CAOHC-approved audiometric technician training course are familiar with the term “pure-tone air-conduction audiometry.” This simply means that the pure tone signal (1000 Hz, for instance) used during the hearing test reaches the eardrum via the air in the ear canal. Supra-aural headphones are designed for air conduction testing. However, when the pure tone signal is delivered at a high decibel level, the headphone itself can vibrate the bones of the skull carrying the pure tone signal directly to the cochlea of the opposite ear…the ear you don’t want to test. This is called bone conduction and can lead to inaccurate hearing tests. It typically occurs when a person has one fairly normal-hearing cochlea while the other cochlea has significant hearing loss, typically when there is a 40 dB or more difference between ears at a given test frequency. Testing such persons with supra-aural headphones is challenging and obtaining accurate thresholds often not possible in an industrial clinic. Fortunately, insert earphones provide far greater interaural attenuation. That is, the decibel level of the test signal has to be greatly increased before insert earphones cause bone conduction. A 70-dB difference between ears is a conservative estimate. Thus, it allows persons with more-or-less normal hearing in one ear and a severe loss in the opposite ear to be accurately tested in an industrial setting rather than having to send those persons to a local Audiologist for testing.
Collapsing Ear Canals. Most persons have somewhat round, open ear canals and those persons can be appropriately tested with supra-aural headphones. However, some persons have narrow ear canals, almost slit-like (see picture at right). The pressure applied by supra-aural headphones to the outer ear can cause the ear canal to close in these persons. When this happens, audiometric thresholds will be artificially raised making him appear to have more hearing loss than he actually has. Fortunately, insert earphone eartips will prevent the ear canal from closing so that the person’s hearing can be accurately measured without having to send this person to a local Audiologist for testing.
Making the Switch to Inserts
How exactly would this switch take place? First, contact the provider of your annual audiometer calibration as they can probably obtain these earphones. Alternatively, they can be ordered directly from Etymotic Research for about $400 (https://www.etymotic.com/auditory-research/insert-earphones-for-audiometry.html) along with a supply of eartips (mostly regular, some small, one pack of jumbos).
Second, the audiometer must be recalibrated for insert earphones. Once recalibrated, do not switch back and forth between inserts and supra-aurals unless your audiometer is specifically designed to accommodate both headphone types. Having said this, there will be little reason to use supra-aurals once inserts are in place even if the audiometer will accommodate both.
Third, remember that daily audiometer calibration checks are still required. If using a bioacoustic ear, check with the manufacturer to see if adaptors are available to connect the insert earphones to the bioacoustic ear. The Monitor Instruments MI-300 bioacoustic ear is compatible with insert earphones with adaptors available directly from them.
OSHA’s allowance of insert earphones represents a significant step forward in the technology used for industrial audiometric testing.