Of the 360 million people worldwide with disabling hearing loss (WHO, 2014), many do not have access to adequate audiologic examinations or treatment. To meet the hearing health care needs of these populations, more audiologists will be needed to provide hearing services through teleaudiology. In addition, audiologists frequently travel to remote locations to attend to rural communities or to those who may live in urban areas but lack readily-available access to audiological care. Such services may be provided in community clinics, educational settings, retirement or nursing homes, or within home-health settings. While audiologic test equipment is often available in the delivery of such services, the luxury of an audiometric sound-treated booth is frequently not.
Neither supra-aural earphones nor insert earphones are made to sufficiently attenuate background acoustic interference when testing outside of a sound-treated enclosure. However, a recent study by Clark, et. al., looked to see if the use of noise-canceling earphones can, within controlled environments, create audiometric testing conditions consistent with the permissible ambient noise level standards for audiometric test rooms set by the American Standards Institute (Int J Audiol. 2017;56:989). Further more, the study assessed if there were any adverse effects on bone-conduction testing through any potential increase in the occlusion effect when noise-canceling earphones are placed over an insert earphone used for contralateral masking.
The study was conducted using the Bose QuietComfort 15 circumaural earphones designed to passively reduce unwanted noise through the earphone itself along with an electronically-generated signal that is 180 degrees out of phase relative to incoming sounds. An Audioscan Verifit (model VF-1) probe-microphone system was used to measure the sound pressure level in the ear canal close to the tympanic membrane with and without noise-canceling earphones in place. One-third octave band sound pressure level measures were then obtained within a typical clinic office room with no acoustic treatment. Sound reduction levels of the noise-canceling earphones were subtracted from room noise levels and compared with ANSI-allowable ambient noise levels (ANSI, 1999).
Twenty participants, recruited in accordance with methods approved by the University of Cincinnati Institutional Review Board, were tested to determine the influence of noise-cancelation earphones on the occlusion effect during bone-conduction testing. Forehead placement was necessary in bone-conduction testing to ensure that the placement of the noise-canceling earphones do not dampen the vibrations of the bone-conduction oscillator. It should be noted that when testing with a forehead placement, a greater intensity is required to stimulate the cochlea, thereby necessitating proper calibration for forehead placement or judicious use of correction factors.
The sound levels in dB SPL near the tympanic membrane as determined through probe-microphone measures without and with noise-canceling earphones are shown in Table 1, along with a comparison of these levels to ANSI one-third octave permissible ambient noise sound pressure levels for audiometric testing (ANSI, 1999). Comparisons of row C with rows D and E reveal that sound levels at the ear with noise-canceling earphones are below the maximum permissible ambient noise SPL for all frequencies when testing for air-conduction thresholds with insert earphones and for frequencies above 1,000 Hz with ears uncovered as in bone-conduction testing.
When assessing the potential effects of adding noise-canceling earphones over an insert receiver during clinical masking for bone-conduction testing, it was found that noted occlusion effects resulted primarily from the insert earphone. No additional clinically significant occlusion effect from noise-canceling earphones was found during routine bone-conduction audiometry.
When assessing rooms as potential audiometric test sites, particularly for patients with known hearing loss, it is not necessary to have a test environment that allows for testing down to audiometric zero. The ANSI standard for maximum permissible ambient noise levels for audiometric test rooms clearly notes that these maximum levels “should be adjusted appropriately when hearing thresholds for pure tones are measured above and below 0 dB HL” (ANSI, 1999). As Margolis and Madsen pointed out, if testing hearing thresholds down to 20 dB HL is deemed acceptable to the examiner, then 20 dB can be added to the ANSI maximum permissible levels (J Am Acad Audiol. 2015;26:784). Given this caveat, audiometric testing with noise-canceling earphones by either air conduction or bone conduction can be completed on most clinical patients, making the use of noise-canceling earphones a feasible alternate testing arrangement when sound-treated enclosures are not available.
Certainly, not all rooms have equal acoustic qualities and not all testing situations in out-of-office locations or during teleaudiology service delivery can be deemed the same. Therefore, it is important that a testing or supervising audiologist ascertain the average room noise SPL across the frequency spectrum to determine the room's validity as a sufficiently quiet location for testing with noise-canceling earphones. Similarly, not all noise-canceling earphones have the same attenuation properties as those in this study. As such, audiologists must be familiar with the properties of the noise-canceling device being used. The acceptable room noise levels for air- and bone-conduction testing with noise-canceling earphones that Clark, et al., used are shown in Figure 1.
The findings of the study is consistent with those of Bromwich and colleagues, suggesting that noise-canceling earphones can be used for both teleaudiology and remote audiologic air-conduction testing when a sound-treated booth is not available (Laryngoscope. 2008;118:104). The noise-canceling earphones provided sufficient reduction of the room noise to create a sound pressure level below the ANSI standards at all frequencies when testing air-conduction thresholds with insert earphones, as well as for frequencies greater than 1,000 Hz when testing without inserts during bone-conduction tests. For the lower frequencies, it should be noted that the sound pressure level under the noise-canceling earphones was never greater than 4 dB higher than allowable levels for conditions with ears uncovered (i.e., bone-conduction testing). The study findings support the utility of noise-canceling earphones for offsite audiometric testing for most clinical patients when a sound booth is not available.
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