Ambient noise in the test environment will impact signal detection during hearing threshold measurements due to psychoacoustic masking effects. Technical standards specify the maximum permissible ambient noise levels (MPANLs) for use during audiometric testing. MPANLs are dependent on several factors, including transducer characteristics (supra-aural, circumaural, type of ear cushions or earphone enclosures, and insert earphones), the nature of the hearing test being performed (air conduction vs bone conduction and threshold test vs screen at a suprathreshold level), and measurement instrumentation. The nature of the ambient noise (spectrum and constant vs variable) at the test site must be determined and continually accounted for during the boothless hearing test procedure. Ambient noise monitoring procedures are reviewed and examples of ambient noise characteristics in real-world settings, where hearing testing might be performed outside of a sound-treated environment, are provided. Practical considerations are presented, including examples of available tools for ambient noise monitoring, selection of test locations, and transducer attenuation. These are discussed in the context of calculating MPANLs and how best to ensure that ambient noise levels are not negatively impacting the validity of hearing thresholds.

Audiometric testing is important for diagnostic evaluations, hearing screening, and monitoring of potential hearing loss due to medical conditions and treatments. Historically, hearing testing, especially the measurement of hearing thresholds, has been limited to the confines of sound-treated booths. Recent interest in developing technology and protocols for boothless audiometry warrants an understanding of several critical factors that must be considered to ensure test results are valid. Test validity will be compromised if environmental noise masks the test signal.

Fletcher (1940) suggested that the human auditory system behaves like a bank of overlapping bandpass filters termed “auditory filters.” The signal detection threshold (the ability to detect a pure-tone stimulus during a hearing test) increases with the presence of wider masking noise bandwidth up to a point after which the signal threshold becomes independent of the masker bandwidth. Only sounds that fall within the critical bandpass filter can mask the pure-tone stimulus. In the context of performing pure-tone audiometry, only the background noise that falls within the critical bandpass filter of the pure-tone stimuli can mask the tone. Consequently, the ANSI/ASA S3.1-1999 (R2018) (ANSI/ASA, 2018a) specifies the maximum permissible ambient noise levels (MPANLs) that will prevent threshold shifts >2 dB for most listeners (∼50%) when pure tones are presented at reference equivalent hearing threshold levels and thresholds are obtained in the presence of background noise levels permitted within the standard.

Failure to sufficiently control ambient noise levels will artificially elevate a hearing threshold due to simultaneous energetic masking of the test signal by the background noise. Masking occurs when the pure-tone hearing threshold at a given test frequency is raised by the presence of another (masking) sound in the test environment. Simultaneous masking refers to reducing or eliminating the perception of a test stimulus due to the simultaneous presence of a second masking stimulus. In our context, background ambient noise in the room is the masking stimulus that occurs at the same time as the test stimulus (pure-tone presentation).

In the cochlea, the process of masking occurs when one sound cannot be encoded by the eighth cranial nerve neurons because a competing stimulus is triggering the firing of these same neurons. Sounds having relatively low frequency energy can mask sounds having higher frequency energy, providing the low frequency sounds have adequate amplitude. This is referred to as an “upward spread of masking.” Ambient noise with low frequency components will cause masking of higher frequency pure-tone stimuli. For this reason, noise levels at frequencies at and below the test stimulus frequency must be carefully monitored to prevent masking of the test tone, resulting in an artificially elevated hearing threshold. For a detailed explanation of the upward spread of masking phenomenon, see Allen and Sen (2006) and Allen (2008).

Air and bone conduction audiometry are performed using standardized test procedures (ANSI/ASA S3.21-2004 [R2019]) (ANSI/ASA, 2019) and calibration standards (ANSI/ASA S3.6-2018) (ANSI/ASA, 2018b) to ensure consistency of hearing threshold measurements when testing is administered by different examiners in different locations and environments. Two of the relevant standards are the American National Standards Institute (ANSI) Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms (ANSI/ASA S3.1-1999 (R2018) and the International Organization for Standardization (ISO) 8253-1:2010(en) (ISO, 2010) Acoustics—Audiometric test methods—Part 1: Pure-tone air and bone conduction audiometry. Both standards specify the maximum sound pressure levels of ambient noise that can be present in the test environment. ISO 8253-1:2010 uses the term “maximum permissible ambient sound pressure levels” (MPASPLs) rather than MPANLs. U.S. occupational noise exposure regulations and guidelines also specify MPANLs for pure-tone air conduction audiometry, conducted as part of a hearing conservation program (OSHA, 1983; NIOSH, 1998; FRA, 2006; Department of Defense, 2019). In these contexts, maximum means that these decibel levels should never be exceeded. Control or monitoring of ambient noise levels is necessary for assuring that pure-tone hearing thresholds reflect the softest tone that a listener can detect 50% of the time in quiet (ANSI/ASA S3.21-2004 [R2019]; ASHA, 2005). This consideration becomes especially critical when conducting boothless audiometry outside of a sound-treated booth or room designed to minimize ambient noise levels.

The ANSI/ASA S3.1-1999 (2018) MPANLs are expressed in decibels (re: 20 μPa) for each octave band or one-third octave band and based on psychophysical data designed to account for the “individual variations in the ability of listeners to detect pure-tone signals in the presence of noise.” MPANLs for air conduction audiometry also take into consideration the differences in the stimulus signal at the tympanic membrane due to resonance and presence of standing waves in the ear canal (Souza , 2014) and differences in the amount of attenuation provided by the earphones being used. MPANLs are specified for testing to 0 decibels hearing level (dB HL) with ears covered when referencing supra-aural and insert earphone transducers and for ears uncovered as when performing bone conduction or sound field testing. The ANSI/ASA S3.1-1999 (2018) MPANLs differ as a function of the range of pure-tone test frequencies being tested (125–8000 Hz, 250–8000 Hz, and 500–8000 Hz) to prevent masking of the lowest frequency pure-tone stimulus within the test range due to the upward spread of masking from noise at lower frequencies. If the lowest frequency pure-tone stimulus being presented is higher than 500 Hz, the range of MPANLs from 500 to 8000 Hz should be referenced. The ANSI/ASA S3.1 standard assumes that the slope of the upward spread of masking is 14 dB per octave, based upon the work of Berry (1973). For convenience, these values have been summarized for octave bands in Tables I–III for ears not covered, supra-aural earphones, and insert earphones test conditions.

TABLE I.

ANSI S3.1-1999 (R2018) MPANLs in dB sound pressure level (SPL) per octave band for bone conduction audiometry when testing to 0 dB hearing level (HL) (ears not covered).

Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  29  21  16  13  14  11  14 
250–8000  35  21  16  13  14  11  14 
500–8000  44  30  16  13  14  11  14 
Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  29  21  16  13  14  11  14 
250–8000  35  21  16  13  14  11  14 
500–8000  44  30  16  13  14  11  14 
a

See ANSI/ASA S3.1-1999 (R2018) for one-third octave band levels.

TABLE II.

ANSI S3.1-1999 (R2018) MPANLs in dB SPL per octave band for air conduction audiometry when testing to 0 dB HL (ears covered) with TDH-type supra-aural earphones.

Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  35  25  21  26  34  37  37 
250–8000  39  25  21  26  34  37  37 
500–8000  49  35  21  26  34  37  37 
Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  35  25  21  26  34  37  37 
250–8000  39  25  21  26  34  37  37 
500–8000  49  35  21  26  34  37  37 
a

See ANSI/ASA S3.1-1999 (R2018) for one-third octave band levels.

TABLE III.

ANSI S3.1-1999 (R2018) MPANLs in dB SPL per octave band for air conduction audiometry when testing to 0 dB HL (ears covered) using Etymotic ER-3A or E-A-RToneTM 3A insert earphones with a 0–3 mm insertion depth.

Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  59  53  50  47  49  50  56 
250–8000  67  53  50  47  49  50  56 
500–8000  78  64  50  47  49  50  56 
Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
125–8000  59  53  50  47  49  50  56 
250–8000  67  53  50  47  49  50  56 
500–8000  78  64  50  47  49  50  56 
a

See ANSI/ASA S3.1-1999 (R2018) for one-third octave band levels.

ANSI/ASA S3.1-1999 (2018) does not explicitly provide MPANLs for circumaural earphones or other contemporary transducers, rather these must be precisely calculated using earphone-specific mean attenuation and optional standard deviation (SD) values as specified in Annex A of the standard. ANSI S3.1-1999 (R2018) allows for subtraction of one SD from the mean attenuation to more conservatively account for the actual attenuation achieved by 84% of the laboratory subjects.

1. Adjustments for minimum test level

The ANSI/ASA S3.1-1999 (R2018) standard also provides instructions for establishing alternative MPANLs when minimum test levels are different than 0 dB HL. Screening at higher stimulus levels (>0 dB HL) provides an allowance for higher MPANLs because the screening level in (dB) is arithmetically added to the MPANL values for testing to 0 dB HL. For instance, if the screening is being performed at 25 dB HL, then 25 dB can be added to the ANSI/ASA S3.1 MPANL values for testing to 0 dB HL. The same approach can be taken if the minimum testable threshold level is known in advance. If testing to −10 dB HL, 10 dB is subtracted from the ANSI/ASA S3.1 MPANLs for testing to 0 dB HL. This results in MPANLS that are more lenient for supra-threshold screenings and more restrictive if measuring hearing thresholds below 0 dB HL.

ISO 8253-1:2010 specifies MPASPLs for testing bone conduction with ears uncovered and when testing ears covered with “typical current supra-aural earphones” for three test ranges (125–8000 Hz, 250–8000 Hz, and 500–8000 Hz). The MPASPLs allow for hearing threshold measurement down to 0 dB HL with a maximum uncertainty of +2 dB due to ambient noise. However, the standard does allow for an adjustment of +8 dB to the MPASPLs if a maximum of +5 uncertainty for ambient noise is permitted. No guidance is given regarding how or when this adjustment should be considered. Additionally, the ISO 8253-1:2010 does not reference a specific upward slope of masking correction for testing different frequency ranges. There are no explicit MPASPLs specified within ISO 8253-1:2010 for testing with insert or circumaural earphones. Within the standard, MPASPLs for Etymotic (Lucid Hearing Holding Company, LLC, Elk Grove, IL) ER-3A (insert style) and Sennheiser (Wennebostel, Germany) HDA 200 (circumaural style) must be derived from the “average sound attenuation” values, in decibels, from the typical current supra-aural earphone, Table III (ISO 8253-1:2010). The ISO standard states that if other types of earphones are used, the difference in the sound attenuation of those earphones and the supra-aural attenuation values in Table III of ISO 8253-1:2010 shall be “added” to the MPASPL values specified for supra-aural earphones in Table II (ISO 8253-1:2010). For example, if the average attenuation for the Etymotic ER-3A earphone is 37 dB at 1000 Hz, and the average attenuation for the typical current supra-aural earphone is 15 dB, then the difference in attenuation is 22 dB, which can then be added to the MPASPL of 23 dB SPL specified for “typical” supra-aural earphones at 1000 Hz, allowing for a derived MPASPL of 45 dB SPL for the ER-3A insert earphone when testing to 0 dB HL at 1000 Hz. The ISO adjusted MPASPLs may over- or underestimate permissible noise levels because they reference the attenuation achieved by 50% of the laboratory subjects and do not incorporate the SDs of the transducer attenuation measurements in the MPASPL calculations to better predict actual attenuation for the majority (84%) of wearers. For this reason, we recommend using Appendix A of the ANSI/ASA S3.1-1999 (2018) standard and method of computing MPANLs using the mean attenuation and one SD values rather than the ISO8253-1:2010 standard. See Sec. III A 5 for additional comments on calculating MPANLs.

As mentioned previously, several government regulations or publications specify MPANLs to be met when testing the hearing of workers as part of a hearing conservation program, none of which are consistent with each other. The MPANLs provided by the Occupational Safety and Health Administration (OSHA) 29 CFR 1910-95 Table D–1 (OSHA,1983) are those originally specified in ANSI S3.1-1960 (ANSI, 1960), which are outdated and shown to be inadequate for threshold testing down to 0 dB HL with supra-aural earphones (Berger and Killion, 1989; Williams , 1992; Wright and Frank, 1992; Frank , 1993; Franks , 1992; Frank and Williams,1994; NIOSH, 1998; Lankford , 1999). Berger and Killion (1989) found that referencing OSHA MPANLs with TDH-type (Telephonics®, Farmingdale, NY) supra-aural earphones leads to elevated hearing thresholds by 10 dB or more at most test frequencies in those with normal hearing. OSHA MPANLs should not be used for boothless audiometry purposes when using supra-aural earphones. Insert earphones were developed in 1984 after the OSHA (1983) regulation was promulgated. A more recent OSHA letter of interpretation permits the use of insert earphones and allows the use of ANSI MPANLs (unspecified ANSI version) when insert earphones are used for audiometric testing (OSHA, 2017). A recent OSHA (2022) letter of interpretation states that OSHA will allow the use of ANSI MPANLs in lieu of the MPANLs in the occupational noise exposure standard when insert earphones or other types of earphones are used (e.g., supra-aural and circumaural). This is important as the current ANSI/ASA S3.1-1999 (2018) standard provides methods to account for the attenuation of any transducer.

The Federal Railroad Administration (FRA) references the same MPANLs as OSHA (1983) in Table D–1 for supra-aural earphones and, therefore, these values are also too lenient for threshold testing as low as 0 dB HL (FRA, 2006). Interestingly, FRA (2006) does specify MPANLs when testing with insert earphones that are consistent with ANSI/ASA S3.1-1999 (R2018). The Mine Safety and Health Administration (MSHA) avoided the issue of specifically defining MPANLs for testing mine workers by stating that the audiometric testing should be conducted using “scientifically validated procedures” and the physician, audiologist, and technician should be capable of making these professional judgments (MSHA, 1999). Last, the Department of Defense (DoD) Instruction 6055.12 Ambient Noise Section states that hearing testing (500–8000 Hz) “is conducted in a testing environment with background octave band SPLs, in accordance with ANSI/ASA Standard S3.1, and not greater than (a) 500 Hz, 27 dB; (b) 1000 Hz, 29 dB; (c) 2000 Hz, 34 dB; (d) 4000 Hz, 39 dB; (e) 8000 Hz, 41 dB” (Department of Defense, 2019). These levels are different than the MPANLs specified by the current ANSI/ASA S3.1-1999 (R2018) standard for testing 500–8000 Hz and incomplete in terms of referencing specific transducers or test frequency ranges.

The National Institute for Occupational Safety and Health (NIOSH) recommended that audiometric hearing tests be conducted in a room where noise levels conform to ANSI S3.1-1991 (ANSI, 1991), which was the current MPANL standard at the time (NIOSH, 1998). NIOSH also recommended that ambient noise levels be recorded on each audiogram. Tables VIII–X in the  Appendix provide summaries of the MPANLs recommended by the ANSI and ISO standards organizations and those specified by government organizations in the U.S. for use when testing workers as part of a hearing conservation program.

The MPANLs for specific transducers that are not included in ANSI/ASA or ISO standards are often reported by manufacturers (e.g., Grason-Stadler, Eden Prairie, MN; Edare LLC, Lebanon, NH; eMoyo, Johannesburg, South Africa; and RadioEar, Middlefart, Denmark) and/or published in the research literature by scientists or developers (e.g., Fisher and Williams, 2013; Swanepoel , 2015; Clark , 2017; Meinke , 2017; Folkeard , 2019; Smull , 2019). On occasion, it is unclear as to what standard was followed (if any) when determining MPANL values that are being reported to end-users. Novel methods are often introduced, such as probe microphone measurements underneath the transducer. It then becomes the product user's responsibility to determine if the reported MPANLs followed ANSI S3.1-1999 (R2018) or if the reported MPASPLs followed ISO 8253-1:2010 methods. If not, then the end-user must critically evaluate the appropriateness of the MPANL determination process and question the ability to use the device for valid hearing sensitivity measurements, especially when testing outside of a sound-treated booth. The variety of attenuation measurement methods and independent reporting of transducer-specific attenuation characteristics justifies the need for standardized laboratory attenuation measurements for audiometric transducers when determining MPANLs.

The attenuation characteristics of different earphones are critical factors when establishing MPANLs. Each type of earphone attenuates ambient sound by a specific amount at each test frequency. The calculation of MPANLs specified in ANSI/ASA S3.1-1999 (2018) includes the mean transducer attenuation minus one SD at each frequency to provide the sound reduction value for each earphone type. This calculation provides MPANLs that should protect 84% of all listeners from ambient noise masking effects. Attenuation values of the transducers were measured using the laboratory real-ear attenuation at threshold (REAT) methods specified in ANSI S12.6-1984 (R1990) (ANSI, 1990) for hearing protectors, which has since been updated to ANSI/ASA S12.6-2016 (ANSI, 2020). There are no ANSI/ASA or ISO standards specific to measuring the attenuation of audiometric earphones, however, the application of REAT testing has been adapted for this purpose in ANSI/ASA S3.1-1999 (R2018) (Berger and Killion, 1989; Frank and Wright, 1990; Wright and Frank, 1992).

The amount of attenuation obtained with audiometric earphones is related to the fit and seal that the earphone makes with the ear or head and varies by type of transducer (supra-aural, circumaural, and insert). Force of the headband must also be considered for supra-aural and circumaural styles. Just like hearing protectors, the earphone design, materials, and individual fitting impact the amount of attenuation. The American Speech-Language Hearing Association (ASHA) notes that the tester should ensure that hats, headbands, eyeglasses, earrings, or anything that may interfere with the proper positioning of the earphone on or in the ears be removed at the time of testing (ASHA, 2005). It is also important to consider the actual fit of the transducer on each person to assure that the headband height is correctly adjusted and beards, wigs, or other head coverings do not interfere with the seal of the transducer. If accommodations are made that compromise the fit of the transducer, then this should be noted on the audiogram, and reference MPANLs would no longer be an accurate reference for that situation when testing outside of a sound-treated booth.

1. Supra-aural earphones

The measured attenuation for supra-aural earphones using MX41/AR or Type 51 ear cushions has been reported in several studies using the procedures outlined in ANSI S12.6-1984 (R1990) and three were incorporated into ANSI/ASA S3.1-1999 (R2018) (Arlinger, 1986; Berger and Killion, 1989; Frank and Wright (1990) (see Table IV). These studies were selected for inclusion because the earphone attenuation used to derive the ears covered MPANLs were obtained using experimenter fitting and measurement methods as specified in ANSI S12.6-1984 (R1990). Supra-aural earphones using MX41/AR or Type 51 ear cushions provide relatively low levels of ambient noise attenuation, particularly in the low frequencies (2.8 dB at 250 Hz), as reflected in the ANSI/ASA S3.1-1999 (2018) standard. This precludes them from being used for threshold testing down to 0 dB HL or screening at 25 dB HL outside of an appropriately insulated sound booth (Table IV). The exception for screening might be if the hearing screening was performed at relatively high frequencies in quiet environments while monitoring ambient noise levels.

TABLE IV.

Attenuation values averaged in ANSI/ASA S3.1-1999 (R2018) MPANLs for calculation of MPANLs for supra-aural earphones in adult subjects.

Study Supra-aural earphone: Cushion Mean attenuation (dB SPL) ±SD
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 3000/3150 Hz 4000 Hz 6000/6300 Hz 8000 Hz
Arlinger (1986)   TDH-39: MX41/AR  5.1 ± 6.8  2.8 ± 4.6  6.1 ± 5.5  12.9 ± 4.8  22.4 ± 4.6  27.9 ± 5.3  28.3 ± 5.2  24.5 ± 8.6  24.5 ± 7.5 
Berger and Killion (1989)   TDH-50: MX41/AR  6.5 ± 4.8  5.4 ± 5  6 ± 5.3  11.7 ± 4.8  17 ± 5.6  —  22.2 ± 5.4  —  22.7 ± 6.3 
Frank and Wright (1990)   TDH-49P: MX41/AR  5.9 ± 5.0  4.1 ± 5.3  3.5 ± 6.4  12.3 ± 5.4  18.7 ± 6.2  23.5 ± 6.2  26.0 ± 7.3  25.6 ± 7.5  24.2 ± 7.6 
Frank and Wright (1990)   TDH-49P: P/N 51  6.4 ± 6.1  3.2 ± 5.3  4.2 ± 6.6  12.5 ± 6.6  19.0 ± 5.6  23.7 ± 5.1  26.4 ± 5.9  22.1 ± 7.4  21.5 ± 6.9 
Study Supra-aural earphone: Cushion Mean attenuation (dB SPL) ±SD
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 3000/3150 Hz 4000 Hz 6000/6300 Hz 8000 Hz
Arlinger (1986)   TDH-39: MX41/AR  5.1 ± 6.8  2.8 ± 4.6  6.1 ± 5.5  12.9 ± 4.8  22.4 ± 4.6  27.9 ± 5.3  28.3 ± 5.2  24.5 ± 8.6  24.5 ± 7.5 
Berger and Killion (1989)   TDH-50: MX41/AR  6.5 ± 4.8  5.4 ± 5  6 ± 5.3  11.7 ± 4.8  17 ± 5.6  —  22.2 ± 5.4  —  22.7 ± 6.3 
Frank and Wright (1990)   TDH-49P: MX41/AR  5.9 ± 5.0  4.1 ± 5.3  3.5 ± 6.4  12.3 ± 5.4  18.7 ± 6.2  23.5 ± 6.2  26.0 ± 7.3  25.6 ± 7.5  24.2 ± 7.6 
Frank and Wright (1990)   TDH-49P: P/N 51  6.4 ± 6.1  3.2 ± 5.3  4.2 ± 6.6  12.5 ± 6.6  19.0 ± 5.6  23.7 ± 5.1  26.4 ± 5.9  22.1 ± 7.4  21.5 ± 6.9 

2. Passive noise reduction earphone enclosures

The poor attenuation of supra-aural earphones has led to attempts to mount the transducer within a passive noise-reducing enclosure [e.g., Audiocups (Amplivox Ltd., Eden Prairie, MN) and Auraldome]. The attenuation provided by passive noise-reducing earphone enclosures for hearing testing has been reported in several studies (Roeser and Glorig, 1975; Murray and Waugh, 1988; Berger and Killion, 1989; Frank and Wright, 1990; Franks , 1992; Frank , 1997). Presently, neither ANSI nor ISO have recognized the use of sound excluding earphone enclosures for audiometry due to discrepancies in the attenuation reported for low frequency sound (ANSI/ASA S3.1-1999 (R2018), Appendix F) and potential problems with output calibration and elevated pure-tone threshold variability (Roeser and Glorig, 1975; Morrill, 1986; Frank and Wright, 1990). Murray and Waugh (1988) noted that some fittings resulted in the separation of the pinna from the earphone located inside the transducer. For these reasons, we support the recommendation by Frank and Sinclair (2002) against using passive noise reduction earphone enclosures.

3. Insert earphones

Insert earphones provide greater attenuation than supra-aural earphones, but attenuation varies as a function of eartip insertion depth into the ear canal. ANSI/ASA S3.1-1999 (R2018) defines insertion depth as the “position of the outer edge of a foam eartip of an insert earphone relative to the opening of the ear canal after the eartip has been inserted and allowed to expand in the ear canal.” According to this specification, an insertion depth of 0 mm would mean that the outer edge of the foam eartip is flush with the opening of the ear canal. A positive insertion depth value of 3 mm would mean that the outer edge of the foam eartip is 3 mm inside the opening of the ear canal, whereas a negative depth value would mean the outer edge of the foam eartip extends outside of the opening of the ear canal and indicates a shallower fit. The length of the foam section of an eartip is 13 mm for the standard 8–13 mm diameter (ER3–14A), small 6–9 mm diameter (ER3–14B), and large 10–14 mm diameter (ER3–14 C) eartips (per manufacturer's specifications). Three studies were used for characterizing the attenuation characteristics of insert earphones (Berger and Killion, 1989; Frank and Wright, 1990; Wright and Frank, 1992) and are summarized in Table V. These studies used insertion depths ranging from 0–3 mm and attenuation was measured using procedures defined in ANSI S12.6-1984 (R1990).

TABLE V.

Attenuation values averaged in ANSI/ASA S3.1-1999 (R2018) MPANLs for calculation of MPANLs for insert earphones in adult subjects.

Study Insert earphone, eartip, and insertion depth Mean attenuation (dB SPL) ±SD
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 3000/3150 Hz 4000 Hz 6000/6300 Hz 8000 Hz
Berger and Killion (1989)   ER-3A, ER-14 eartips 2–3 mm depth  32 ± 6.4  35.8 ± 6.3  37.6 ± 5.4  36.6 ± 3.5  33.1 ± 3.2  —  39.4 ± 3.6  —  42.5 ± 3.4 
Frank and Wright (1990)   ER-3A, ER-14 eartips 0 mm depth  29.3 ± 5.4  28.5 ± 5.7  29.8 ± 5.2  29.8 ± 4.5  34.4 ± 3.5  39.1 ± 2.8  38.9 ± 3.4  42.0 ± 3.3  42.4 ± 4.3 
Wright and Frank (1992)   E-A-RToneTM 3A, E-A-Rlink™ tips 3B 0–1 mm depth  28.2 ± 6.6  30.0 ± 6.6  33.8 ± 6.0  35.7 ± 5.0  34.8 ± 3.8  38.2 ± 3.4  37.6 ± 4.3  39.1 ± 4.2  42.4 ± 3.3 
Study Insert earphone, eartip, and insertion depth Mean attenuation (dB SPL) ±SD
125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 3000/3150 Hz 4000 Hz 6000/6300 Hz 8000 Hz
Berger and Killion (1989)   ER-3A, ER-14 eartips 2–3 mm depth  32 ± 6.4  35.8 ± 6.3  37.6 ± 5.4  36.6 ± 3.5  33.1 ± 3.2  —  39.4 ± 3.6  —  42.5 ± 3.4 
Frank and Wright (1990)   ER-3A, ER-14 eartips 0 mm depth  29.3 ± 5.4  28.5 ± 5.7  29.8 ± 5.2  29.8 ± 4.5  34.4 ± 3.5  39.1 ± 2.8  38.9 ± 3.4  42.0 ± 3.3  42.4 ± 4.3 
Wright and Frank (1992)   E-A-RToneTM 3A, E-A-Rlink™ tips 3B 0–1 mm depth  28.2 ± 6.6  30.0 ± 6.6  33.8 ± 6.0  35.7 ± 5.0  34.8 ± 3.8  38.2 ± 3.4  37.6 ± 4.3  39.1 ± 4.2  42.4 ± 3.3 
a. Comments on anatomical reference for determining ear tip insertion depth.

It should be noted that using the “opening of the ear canal” as a reference point for eartip insertion depth (ANSI/ASA, 2018a) is somewhat ambiguous as the ear canal is a hole rather than an anatomical structure. Lindgren and Berger (1989), Frank and Wright (1990), and Wright and Frank (1992) (verified by Frank, 2022) all used the outer margin of the eartip being flush with the floor of the concha cavum as the reference point for 0 mm insertion depth. We recommend using the floor of the concha cavum as the reference point for determining insertion depth as it provides a relatively consistent and easily identified anatomical landmark across subjects as shown in Fig. 1.

FIG. 1.

Foam eartip placed in the right ear with the outer margin of the eartip flush with the floor of the concha cavum. This is the recommended anatomical reference for 0 mm insertion depth for insert earphones.

FIG. 1.

Foam eartip placed in the right ear with the outer margin of the eartip flush with the floor of the concha cavum. This is the recommended anatomical reference for 0 mm insertion depth for insert earphones.

Close modal
b. Comments on insert earphone eartip insertion.

Several studies demonstrated that attenuation is significantly changed as a function of eartip insertion depth with deep insertion depth resulting in greater attenuation than shallow insertion depth (Clark and Roeser, 1988; Berger and Killion, 1989; Lindgren and Berger, 1989; Frank and Wright, 1990; Wright and Frank, 1992). A consideration when following the ANSI/ASA S3.1-1999 (R2018) standard is that the MPANLs are based on an average of eartip attenuations from studies that were conducted using insertion depths from 0 to 3 mm. The difference in attenuation between 0 and 3 mm insertion depths exceeds 5 dB at 250, 500, and 1000 Hz (Table V), making the differences potentially clinically significant in terms of threshold measures in the presence of ambient noise. Eartip insertion depth is a critical consideration for determining accurate MPANLs, but it is also important for determining the occlusion effect if one is performing boothless bone conduction audiometry, which requires both ears to be occluded during testing (Neave-DiToro , 2018).

Occluding or restricting the volume of the ear canal or space just outside of the ear canal causes a perceived increase in loudness in low frequency sound when the stimulation is presented through a bone conduction transducer. Occlusion devices, ear plugs placed very deep in the ear canal, produce minimal perceived occlusion effects. The same is true when the opening of the ear canal is covered by something with a relatively large volume, such as large volume circumaural earmuffs. However, any degree of occlusion between these extremes will alter bone conduction hearing thresholds and can result in misleading test results, such as increasing an air conduction-bone conduction difference (air-bone gap), giving a false indication of the presence of a conductive hearing loss. Bone conductor placement (mastoid vs forehead) calibration factors must also be considered when doing bilaterally occluded diagnostic testing (e.g., Studebaker, 1962; Frank, 1982; Rao , 2020).

Subject or patient comfort has been reported to be a limiting factor in terms of actual eartip insertion depth in clinical practice. Clark and Roeser (1988) noted that some subjects could not tolerate a deep insertion depth due to ear discomfort during the fitting, and Frank and Wright (1990) reported that the common practice of everyday users of insert earphones was to use an insertion depth of 0–1 mm. ASHA (2005) states “insert earphones are to be placed ‘comfortably deep’ in the ear canal and in accordance with manufacturer recommendations.” This statement is an oxymoron because comfort is compromised by the deep insertion depth (2–3 mm) recommended by the earphone manufacturer (Etymotic Research Inc., 2022). Consequently, the MPANLs for insert earphones in ANSI/ASA S3.1-1999 (R2018) likely represent the ideal maximum attenuation condition and the MPANLs would need to be lowered if insert earphones are not always inserted deeply. This factor can be mistakenly overlooked when reporting MPANLs as acceptable to test to 0 dB HL when using insert earphones, especially if failing to report the actual fitting depth obtained during the test. Martin (2020) conducted a study designed to identify the eartip insertion depth that was widely tolerated by the listeners and corresponded to an easily identifiable anatomical landmark (as indicated in Fig. 1). Outcomes indicated that an insertion depth of 0 mm was well tolerated in 97% of 308 ears.

In practice, there appears to be a wide range of eartip insertion depths used by clinicians and technicians. Bell-Lehmkuhler , (2009) measured the eartip insertion depth used by an experienced audiologist and certified audiometric technicians trained to place the eartips at the manufacturer's recommended depth of 2–3 mm beyond the floor of the concha cavum (Etymotic Research Inc.). The actual insertion depths ranged from −11 to +9 mm (Fig. 2). The shallowest insertions were barely inserted into the ear canal (−11 mm) and the deepest insertions (+9 mm) were obtained in very large ear canals. This degree of variability would make it impossible to attain consistent, adequate attenuation of ambient noise levels for boothless threshold testing and introduce errors in bone conduction thresholds due to variations in the occlusion effect. The results of this study indicate that one cannot assume that, in practice, eartips will be inserted either consistently or according to manufacturer's specifications or any other specified depth. It is imperative that clinicians performing boothless audiometry use the specific eartip insertion depths that take comfort into consideration and were used when the MPANLs and bone conduction adjustment factors for occlusion were determined.

FIG. 2.

(Color online) Comparison of eartip insertion placement depths in adult ears (adapted from Bell-Lehmkuhler , 2009, Fig. 4). Each of 6 certified technicians fitted the insert earphones on and tested 5 listener test subjects for a total of 30 listener subjects. The experienced audiologist, using his or her own separate insert earphone fitting technique, tested the same 30 listeners (n = 60 ears). The audiometric technicians were trained to follow the manufacturers' insertion depth specification of having the outer margin of the ear tip inserted 2–3 mm deep to the floor of the concha cavum. Note that less than 3% of the total placements were at the insertion depth specified by the manufacturer (2–3 mm). Also, note that 73% of placements were shallower than the well tolerated insertion depth of 0 mm recommended by Martin (2020) and the authors of this paper. Variability in insertion depth will result in variability in the amount of environmental noise that is attenuated, thereby affecting MPANLs for air and bone conduction testing, which ultimately cause errors in threshold measurement. Variability in insertion depth will also create variability in occlusion effects, causing errors in bone conduction threshold testing.

FIG. 2.

(Color online) Comparison of eartip insertion placement depths in adult ears (adapted from Bell-Lehmkuhler , 2009, Fig. 4). Each of 6 certified technicians fitted the insert earphones on and tested 5 listener test subjects for a total of 30 listener subjects. The experienced audiologist, using his or her own separate insert earphone fitting technique, tested the same 30 listeners (n = 60 ears). The audiometric technicians were trained to follow the manufacturers' insertion depth specification of having the outer margin of the ear tip inserted 2–3 mm deep to the floor of the concha cavum. Note that less than 3% of the total placements were at the insertion depth specified by the manufacturer (2–3 mm). Also, note that 73% of placements were shallower than the well tolerated insertion depth of 0 mm recommended by Martin (2020) and the authors of this paper. Variability in insertion depth will result in variability in the amount of environmental noise that is attenuated, thereby affecting MPANLs for air and bone conduction testing, which ultimately cause errors in threshold measurement. Variability in insertion depth will also create variability in occlusion effects, causing errors in bone conduction threshold testing.

Close modal

Efforts to further increase the attenuation of insert earphones incorporated the use of a hearing protector “earmuff” positioned over an ear already fitted with insert earphones (Berger and Killion, 1989; Fisher and Williams, 2013). Both studies indicated ambient noise attenuation advantages when combining earmuffs and foam eartips. Berger and Killion (1989) reported that adding earmuffs to deeply placed Etymotic ER-3A insert earphones (2–3 mm insertion depth) provided additional attenuation ranging from 2.8 dB at 2000 Hz to 14.9 dB at 500 Hz. This is an excellent way to increase passive noise attenuation and reduce ambient noise that can influence threshold testing; however, there are no MPANL standards for this combination within ANSI/ASA S3.1-1999 (R2018) or ISO 8253-1:2010. Measuring the attenuation of combined earmuffs and eartips to calculate MPANLs should be performed using the insertion depth of the eartips that will be consistently used in practice. It should be noted that the maximum limits of passive attenuation using ear plugs and/or earmuffs is determined by the amount of sound energy passing directly to the ear structures by radiating through the bony and soft tissues of the head. This attenuation limit ranges from a maximum of approximately 55 dB at 500 Hz to a minimum of approximately 45 dB at 2000 Hz. Achieving attenuation of ambient noise levels greater than this requires insulating the entire head from sound vibration using earplugs in combination with a helmet attenuator. The properties of bone and soft tissue conduction of energy to the cochlea places a ceiling on the amount of passive attenuation possible using insert earphones, even combined with earmuffs, and limits the sound levels acceptable during boothless audiometry testing. For a discussion of the combined attenuation and bone conduction limits of ear plugs and earmuffs, see Berger (2003).

4. Circumaural headphones

As early as 1968, in a report from the Naval Submarine Medical Center in Groton, CT, Harris (1968) suggested that a change from supra-aural to circumaural headphones would provide an opportunity to test in noisy environments because of their relatively good attenuation, however, opportunities were limited at that time by the lack of a calibration method and performance standards for this type of headphone. The calibration challenges for circumaural headphones can be resolved using device-specific reference equivalent threshold sound pressure levels (RETSPLs; e.g., Clavier , 2022; Ordoñez , 2022; Han and Poulsen, 1998). However, MPANLs are still not explicitly specified in the ANSI/ASA S3.1-1999 (2018) standard for circumaural headphones. This is unfortunate as the use of circumaural headphones has grown in the context of performing testing outside of a sound booth due to the higher attenuation values as compared to supra-aural earphones and ease of fitting. The lack of explicitly stated and standardized MPANLs is further compounded by the changing landscape of commercially available circumaural headphones, which is constantly making previously used products, such as the Koss HV/1A and Sennheiser HDA 200, no longer available. This has created the need for researchers to evaluate the attenuation and performance specifications for other commercially available headphones for use in audiometric testing. Examples include the Bose® (Framingham, MA) Aviation X active noise reduction headphones (Bromwich , 2008), Sennheiser 280 CL (Folkeard , 2019), RadioEar DD450, and Sennheiser HD 280 Pro (Smull , 2019). Fortunately, Appendix A of ANSI/ASA S3.1-1999 (2018) provides a detailed description regarding how to derive MPANLs (octave band or one-third octave band) for a specific transducer (of any style) that is not referenced explicitly within the standard, providing that attenuation measurements can be obtained. The complexity of Table A.1 in ANSI/ASA S3.1-1999 (2018) and the lack of accessing ANSI standards has likely limited the application of this approach, which is unfortunate in the context of rapidly changing technologies being developed to test hearing.

5. Calculating MPANLs

An Excel (Microsoft Corp., Redmond, WA) spreadsheet, entitled “Audiometric Testing, Permissible-Noise Calculator,” that will enable you to compute octave band or one-third octave band MPANLs for any transducer is available courtesy of Elliott Berger and can be found at the National Hearing Conservation Association website.1 The spreadsheet is adapted from Appendix A in ANSI/ASA S3.1-1999 (R2018).

It is important to realize that ANSI S3.1-1999 (2018) assumes that the slope for the upward spread of masking function is 14 dB per octave below the lowest test frequency being tested (Berry, 1973). Therefore, the MPANL values for testing 125–8000 Hz must be corrected for the upward spread of masking by adding +14 dB to the 250 Hz MPANL to determine the MPANL at 125 Hz when testing the range of 250–8000 Hz. The correction for testing the range of 500–8000 Hz is +14 dB added to the 500 Hz MPANL to calculate the 250 Hz MPANL, and +28 dB is added to the 500 Hz MPANL to calculate the 125 Hz MPANL. These corrections are incorporated as separate tabs in the “Audiometric Testing, Permissible-Noise Calculator” spreadsheet.1 All of the frequencies (125–8000 Hz) should be monitored regardless of the frequencies being tested.

As mentioned previously, the ANSI S3.1-1999 (R2018) MPANLs for supra-aural earphones (Table I) and insert earphones (Table II) were calculated using mean attenuation values and rounded (adjusted) to the nearest dB. The standard suggests that more conservative MPANLs are necessary to decrease the chance that individual listeners will experience a threshold shift greater than 2 dB because they are fitted with less than average attenuation. Approximately 84% of the listeners will experience less than a 2 dB threshold shift when the mean attenuation of the transducer is reduced by one SD. It may be especially critical to apply these stricter criteria when testing to evaluate small changes in hearing over time as when monitoring ototoxicity, noise exposure, or the effects of pharmaceutical treatments. Standard deviations (SDs) for making adjustments for supra-aural and insert earphones are provided in Table A.2 of ANSI/ASA S3.1-1999 (R2018). Adjusted outcomes are provided in Table VI for supra-aural earphones and Table VII for insert earphones as calculated using the “Audiometric Testing, Permissible-Noise Calculator” spreadsheet1 and presented without rounding to the nearest dB.

TABLE VI.

Attenuation adjusted ANSI S3.1-1999 (R2018) MPANLs in dB SPL per octave band for air conduction audiometry when testing to 0 dB HL (ears covered). These values limit threshold shifts to <2 dB for approximately 84% of the listeners tested using TDH-type supra-aural earphones.

Test frequency range (Hz) Octave bands (Hz)
125 250 500 1000 2000 4000 8000
125–8000  29.5  20.3  15.2  20.4  28.4  30.7  29.5 
250–8000  34.3  20.3  15.2  20.4  28.4  30.7  29.5 
500–8000  43.2  29.2  15.2  20.4  28.4  30.7  29.5 
Test frequency range (Hz) Octave bands (Hz)
125 250 500 1000 2000 4000 8000
125–8000  29.5  20.3  15.2  20.4  28.4  30.7  29.5 
250–8000  34.3  20.3  15.2  20.4  28.4  30.7  29.5 
500–8000  43.2  29.2  15.2  20.4  28.4  30.7  29.5 
TABLE VII.

Attenuation adjusted ANSI S3.1-1999 (R2018) MPANLs in dB SPL per octave band for air conduction audiometry when testing to 0 dB HL (ears covered). These values limit threshold shifts to <2 dB for approximately 84% of the listeners tested using Etymotic ER-3A or E-A-RToneTM 3A insert earphones inserted 0–3 mm deep.

Test frequency range (Hz) Octave bands (Hz)
125 250 500 1000 2000 4000 8000
125–8000  52.6  46.6  44.3  42.8  45.0  45.8  52.4 
250–8000  60.6  46.6  44.3  42.8  45.0  45.8  52.4 
500–8000  72.3  68.3  44.3  42.8  45.0  45.8  52.4 
Test frequency range (Hz) Octave bands (Hz)
125 250 500 1000 2000 4000 8000
125–8000  52.6  46.6  44.3  42.8  45.0  45.8  52.4 
250–8000  60.6  46.6  44.3  42.8  45.0  45.8  52.4 
500–8000  72.3  68.3  44.3  42.8  45.0  45.8  52.4 

6. Comments on determination of transducer attenuation

The attenuation of the transducer is a critical element when deriving MPANLs and, therefore, the measurement of transducer attenuation deserves the same critical scrutiny and standardization afforded to hearing protection attenuation measurements. The attenuation measurements used in the current ambient noise standard, ANSI/ASA S3.1-1999 (R2018), were obtained while referencing an earlier version of ANSI/ASA S12.6-1984 (R1990). This standard has recently been updated and revised as ANSI/ASA S12.6-2016 (R2020), “Methods for Measuring the Real-Ear Attenuation of Hearing Protectors,” which describes the procedures for measuring, analyzing, and reporting the passive noise-reducing capabilities of hearing protectors. Hence, we recommend that each transducer be tested in accordance with the current ANSI/ASA S12.6 standard using 20 normal adult hearing listeners and, ideally, be performed by accredited National Voluntary Laboratory Accreditation Program (NVLAP) laboratories, such as those used for hearing protector attenuation labelling requirements (NIST, 2001). The NVLAP operates as an unbiased, confidential third party to accredit testing and calibration laboratories as originally specified in 15 CFR Part 285 (NVL, 1976). This approach would make comparison of attenuation measurements across transducers transparent and eliminate any potential bias that a manufacturer may have when claiming that testing can be performed in environments with higher ambient noise levels.

There is a need for research to inform future MPANL/MPASPL standards regarding attenuation characteristics for each type of transducer when fit to children of different ages. Wright and Frank (1992) found differences in attenuation measured on youth (6–14 years old) for TDH-49/Model 51 cushion and insert earphones (E-A-RToneTM 3A, St. Paul, MN) as compared to adults. The attenuation values for supra-aural earphones were similar or slightly higher than adult values, whereas attenuation values were slightly lower for insert earphones. Wright and Frank (1992) suggested that attenuation measurements on children should be used to further inform ANSI/ASA standards.

The shelter of the sound-treated booth has minimized the need for monitoring ambient noise levels during hearing threshold testing. Once we leave the booth, control over noise levels becomes extremely challenging. The nature of boothless settings is that ambient sounds are often variable in frequency and amplitude and beyond the control of the test operator. It becomes imperative that ambient noise levels at each test frequency be continually monitored throughout the hearing threshold testing or screening procedure. Boothless audiometry or hearing screening may be conducted in a wide variety of settings. Examples of ambient noise levels measured in several settings where boothless audiometry may be performed are presented in Fig. 3 in relation to the ears uncovered MPANL levels specified in ANSI/ASA S3.1-1999 (R2018). In these examples, the highest and lowest sound pressure levels vary by 20–28 dB within each octave band and are highest in the low frequencies (125–250 Hz) as compared to high frequencies (4000–8000 Hz). Note that Fig. 3 provides a static representation of ambient sound levels while, in reality, ambient noise levels outside of a sound-treated booth (and sometimes within the booth) often fluctuate over time. The key to valid testing is to understand the overall noise environment where hearing testing will be performed (whether in or out of a booth) in terms of both levels and variability over time and, then, establish an appropriate monitoring plan.

FIG. 3.

Examples of ambient noise levels (dB SPL) at octave band frequencies recorded from several locations that could serve as testing sites for boothless audiometry evaluations. Sound levels were measured using calibrated type I or type 2 sound level meters equipped with an octave band analyzer. MPANL values for ears uncovered (for testing from 125 to 8000 Hz) as specified in ANSI/ASA S3.1-1999 (R2018), which would be applicable when doing bone conduction threshold testing with unoccluded ears, are presented for reference. The sound levels presented are intended to demonstrate the range of noise levels that one might encounter when seeking locations to conduct boothless audiometry and not necessarily representative of levels at these locations at all times during the day. Noise levels may fluctuate, and one cannot assume that measurements taken at one point in time will be valid during the entire testing session. Therefore, it remains imperative that continuous ambient noise level monitoring be performed during the entire test session. Sites where recordings were made include (A) ear, nose, and throat (ENT) exam room, (B) community clinic exam room, (C) hospital ward, (D) community health center exam room, (E) school classroom (unoccupied), (F) chemotherapy treatment room, (G) nursing home patient room, (H) physician's consult room, (I) factory conference room, (J) school classroom (occupied), and (K) audiology consult room.

FIG. 3.

Examples of ambient noise levels (dB SPL) at octave band frequencies recorded from several locations that could serve as testing sites for boothless audiometry evaluations. Sound levels were measured using calibrated type I or type 2 sound level meters equipped with an octave band analyzer. MPANL values for ears uncovered (for testing from 125 to 8000 Hz) as specified in ANSI/ASA S3.1-1999 (R2018), which would be applicable when doing bone conduction threshold testing with unoccluded ears, are presented for reference. The sound levels presented are intended to demonstrate the range of noise levels that one might encounter when seeking locations to conduct boothless audiometry and not necessarily representative of levels at these locations at all times during the day. Noise levels may fluctuate, and one cannot assume that measurements taken at one point in time will be valid during the entire testing session. Therefore, it remains imperative that continuous ambient noise level monitoring be performed during the entire test session. Sites where recordings were made include (A) ear, nose, and throat (ENT) exam room, (B) community clinic exam room, (C) hospital ward, (D) community health center exam room, (E) school classroom (unoccupied), (F) chemotherapy treatment room, (G) nursing home patient room, (H) physician's consult room, (I) factory conference room, (J) school classroom (occupied), and (K) audiology consult room.

Close modal

Ambient noise level monitoring should be performed at and below the frequencies which are being evaluated by hearing threshold testing or screening. Monitoring of noise levels using A-weighted decibel measurements will usually be inadequate, especially below 1000 Hz due to underestimation of the effects of low frequency noise, resulting in the upward spread of masking (Killion and Studebaker, 1978). ANSI/ASA S3.1-1999 (R2018) gives the operator the choice of monitoring octave or one-third octave bands of energy during testing. Monitoring of octave bands should be sufficient in most instances and equipment with this capability is more readily available than systems with the capacity to measure one-third octave bands. It is adequate to use the next highest octave band as the reference MPANL value when it is not possible to monitor one-third octave band noise levels. The exception to this logic would be when there is an audible concentration of sound energy in a particular frequency region, such as a whistle, screech, hum, or tonal noise, in which case, one-third octave bands would be the appropriate choice (Killion and Studebaker, 1978).

A common misunderstanding of the report by Killion and Studebaker (1978) is that normal hearing can be tested in an environment having an ambient noise level of 40 dBA. Careful reading of the study indicates that testing in a 40 dBA environment is adequate for testing down to 25 dB HL in the soundfield with ears uncovered and not down to 0 dB HL. A background noise level of 47 dBA was recommended as the limit for testing under a supra-aural earphone mounted in an MX-41/AR cushion for testing down to 25 dB HL. They indicated that testing down to 0 dB HL with this transducer requires an ambient noise level of no greater than 22 dBA. Killion and Studebaker (1978) also emphasized that these A-weighted values assume that the background noise has a reasonably smooth spectrum and it falls within a range of typical noises as illustrated in Fig. 1 of Botsford (1973). The determination of accessible A-weighted noise limits requires the consideration of multiple factors, including the attenuation of a specific transducer, variability in fit, and the spectral characteristics of the environmental noise. Generalization of an acceptable A-weighted ambient noise reference level for boothless audiometry is fraught with potential error.

Clause 4.3 in ANSI/ASA S3.1-1999 (R2018) states that ambient noise measurements in the audiometric test room should be made during the “worst possible conditions under which hearing tests might be conducted.” For boothless audiometry, it is likely impossible to predict the noisiest conditions in any environment that might arise during testing. Therefore, instrumentation and techniques for real-time monitoring of noise levels have been developed.

Ambient noise should be monitored using octave or one-third octave bands that correspond to the test frequency of the stimulus. This can be performed using a sound level meter with octave or one-third octave band filters. The challenge is that noise levels are continually changing in uncontrolled settings outside of the sound-insulated booth, and it is difficult to perform the test while watching the octave band levels fluctuate on a sound level meter. The TSI BA-202-25 and BA-202-27 bio-acoustic simulators (Shoreview, MN) provide a portable option for monitoring ambient noise levels according to OSHA (1983) or ANSI S3.1-1999 (R2018), respectively, when testing with supra-aural earphones. Levels can also be custom set (by the manufacturer) to any requested ambient noise limits within the range of the associated microphone for any transducer. These units are typically mounted on a wall or positioned near the person being tested, and the examiner must monitor the flashing lights on the front panel of the device to manually pause the testing when levels are exceeded. Some computerized automated audiometers have built in real-time, in-line sound level meters with octave band capabilities for monitoring ambient noise. An example is the CCA-200mini audiometer coupled to a bioacoustics simulator BAS 200 sound level meter (Benson Medical Instruments, Eden Prairie, MN). The system monitors ambient noise at the test frequency, pauses stimulus presentation, and alerts the tester if noise levels exceed MPANLs at that frequency for supra-aural earphones. The Affinity Compact (Interacoustics) is another example of a commercially available audiometer with ambient noise monitoring capabilities. It has an external microphone for noise monitoring, and the MPANL values for the specific transducer in use can be programmed into the system. The operator must monitor the ambient noise levels indicated on the computer screen.

A flexible, stand-alone system for ambient noise level monitoring is the Max Levels Meter on some of the sound measurement apps for iPhone Operating System (iOS; Apple, Cupertino, CA) systems available from Faber Acoustical LLC (Lehi, UT).2 The Max Levels Meter has two traffic light (green, yellow, red) displays that can be assigned to two user-defined frequency ranges of interest. We recommend setting one range to monitor low frequency octave bands of 250, 500, and 1000 Hz and one high frequency range to monitor octave bands at 2000, 4000, and 8000 Hz. A formative evaluation of the Max Level Meter conducted at the National University of Singapore found that audiologists preferred having one or two frequency ranges to monitor rather than all of the octave bands individually. Max Level Meter monitors each octave band that is selected by the user in dB SPL. Transducer-specific MPANL values can be inserted into a table that specifies at what sound levels the warning lights turn from green to yellow or red, indicating that the current sound levels are exceeding the MPANL values (see Fig. 4). A red light is displayed if any octave band noise level exceeds the MPANLs for testing. This provides the operator with an easy way to monitor when noise levels are too high to provide valid testing down to 0 dB HL (or at higher values if hearing screening is being performed). The app uses the internal iPad or iPhone (Apple, Cupertino, CA) microphone, which has a noise floor of approximately 20 dB SPL, well below the MPANLs for boothless audiometry using insert earphones. The system must be calibrated using a Type 1 or 2 sound level meter for comparison. External Type 1 or Type 2 microphones can also be used with the system if desired. In practice, the iOS device with the app must be placed near the person being tested with the screen easily visible to the operator as shown in Fig. 4. Any blockage or barrier to the microphone will result in underrepresenting ambient noise levels.

FIG. 4.

An example of ambient noise monitoring during pure-tone air and bone conduction threshold testing in a classroom setting using the Faber Acoustical Max Levels Meter. The iPad microphone (Apple, Cupertino, CA) is located near the subject and the screen is within clear view of the audiologist conducting the test. For this protocol, the left column indicators are set up to monitor octave band sound pressure levels (dB SPL) for octave band frequencies from 250 to 1000 Hz and the right column indicators are set up to monitor octave band sound pressure levels (dB SPL) for octave band frequencies from 2000 to 8000 Hz. The red in the left column indicates that at that moment, the ambient noise level at one of the octave bands from 250 to 1000 Hz has exceeded the MPANL value for the transducers being used for this application [RadioEar IP30 insert earphones with Peltor (3M, St. Paul, MN) X2A earmuffs]. The green light indicates that the noise levels for the octave bands from 2000 to 8000 Hz are not exceeded at this moment, therefore, testing of those frequencies can be performed. In practice, testing at frequencies corresponding to the red light is paused until the noise level returns to acceptable levels or testing is relocated to a different environment with lower levels of ambient noise.

FIG. 4.

An example of ambient noise monitoring during pure-tone air and bone conduction threshold testing in a classroom setting using the Faber Acoustical Max Levels Meter. The iPad microphone (Apple, Cupertino, CA) is located near the subject and the screen is within clear view of the audiologist conducting the test. For this protocol, the left column indicators are set up to monitor octave band sound pressure levels (dB SPL) for octave band frequencies from 250 to 1000 Hz and the right column indicators are set up to monitor octave band sound pressure levels (dB SPL) for octave band frequencies from 2000 to 8000 Hz. The red in the left column indicates that at that moment, the ambient noise level at one of the octave bands from 250 to 1000 Hz has exceeded the MPANL value for the transducers being used for this application [RadioEar IP30 insert earphones with Peltor (3M, St. Paul, MN) X2A earmuffs]. The green light indicates that the noise levels for the octave bands from 2000 to 8000 Hz are not exceeded at this moment, therefore, testing of those frequencies can be performed. In practice, testing at frequencies corresponding to the red light is paused until the noise level returns to acceptable levels or testing is relocated to a different environment with lower levels of ambient noise.

Close modal

Several reports refer to testing in a quiet room, but what makes a room quiet? These are some helpful suggestions to assist the practitioner of boothless audiometry when seeking a test location:

  • Before setting up the testing station, do a walkthrough survey of the space, ideally, during the same time of day as the testing will occur;

  • rooms that are carpeted and have sound absorbent tile ceilings can be helpful;

  • try to place the testing station away from room or hall entrances and exits and any obvious noise source (speakers for public address system or music, registration areas, waiting areas, or vending machines);

  • minimize foot traffic through the testing area;

  • if possible, test in a room with a door that can be closed;

  • close windows;

  • monitor sounds of HVAC system (considerable cause of low frequency noise) and location of HVAC vent openings. The test station may have to be moved away from them.; and

  • anticipate potential outdoor noise sources adjacent to the test site. There may be noisy activities (playground, school, parking lot, trains, roadway, or delivery traffic) that are not noisy now but will be when you are testing. Schedule testing around noisy periods (e.g., school recess/lunch or high traffic volume) or move the test station as far away from the windows as possible.

An increasing number of manufacturers are marketing boothless audiometers. It is important to know that boothless audiometry is a protocol and not a device. It can be performed with any audiometer, and the limitations are the MPANLs for the specific transducer and the necessity of having a continuous noise level monitoring system. It is the user's responsibility to determine if commercially available boothless audiometers meet the principles presented in this document.

Audiometric threshold testing and screening can be conducted outside of a sound-insulated booth using any commercially available, calibrated audiometer provided that three conditions are met:

  • The MPANLs for the specific transducer configuration were determined using (a) ANSI/ASA S12.6-2016 (R2020) to determine transducer attenuation and (b) Appendix A in ANSI/ASA S3.1-1999 (2018), as described in Sec. III A 5 in this paper, to determine the MPANLs;

  • the transducers are fit in the manner with which the MPANLs were determined (e.g., specified insertion depth for eartips); and

  • the ambient noise levels in the test environment are continually monitored for acceptability during measurement of hearing threshold at each test frequency and remain below MPANLs during testing.

  1. Specific transducer (i.e., make and model) attenuation should be determined by an NVLAP laboratory or published in a peer-reviewed paper and include the mean and SD of attenuation values for each test frequency. Apply these measures to determine the MPANLs for the transducer being used;

  2. the attenuation should be measured in the specific way that the transducer will be worn by the listener. This is critical for insert earphones as insertion depth significantly influences transducer attenuation and occlusion;

  3. an insert earphone eartip insertion depth of 0 mm relative to the floor of the concha cavum is recommended for standard practice as it provides adequate attenuation and is well tolerated by the majority of individuals being tested;

  4. ambient noise levels should be continually monitored for each audiometric test frequency using calibrated equipment during testing. If noise levels exceed MPANLs, testing should be temporarily stopped until noise levels return to below MPANL levels;

  5. if ambient noise levels in the test environment cannot be reduced to below MPANL values, threshold testing to 0 dB HL (or screening to another higher level) cannot be accurately performed in that environment; and

  6. the audiogram or other test result documentation should note that the testing was performed under boothless conditions, ambient noise monitoring was performed during testing, and thresholds were determined when ambient noise levels were below MPANLs for each test frequency; and

  7. boothless audiometry protocols, including the monitoring of ambient noise levels, should be included as part of standard training courses for audiologists and others providing hearing tests and screenings within their scope of practice.

We would like to thank Odile Clavier and Jennifer Martin for their proofreading and editorial suggestions and Elliott Berger for creating the user friendly MPANL calculator tool and making it available to the public.1

See Tables VIII–X for a comparison of MPANLs and MPASPLs for air and bone conduction audiometry.

TABLE VIII.

MPANLs and MPASPLs in dB SPL for bone conduction audiometry when testing to 0 dB HL for ears uncovered as specified in ANSI S3.1-1999 (R2018) and ISO 8253-1:2010.

Octave bandsa (Hz)
Criteria Test frequency range (Hz) 125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  125–8000  29  21  16  13  14  11  14 
ISO 8253-1:2010 MPASPLs (dB SPL)  125–8000  20  13  15 
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  250–8000  35  21  16  13  14  11  14 
ISO 8253-1:2010 MPASPLs (dB SPL)  250–8000  28  13  15 
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  500–8000  44  30  16  13  14  11  14 
ISO 8253-1:2010 MPASPL (dB SPL)  500–8000  Not specified 
Octave bandsa (Hz)
Criteria Test frequency range (Hz) 125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  125–8000  29  21  16  13  14  11  14 
ISO 8253-1:2010 MPASPLs (dB SPL)  125–8000  20  13  15 
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  250–8000  35  21  16  13  14  11  14 
ISO 8253-1:2010 MPASPLs (dB SPL)  250–8000  28  13  15 
ANSI S3.1-1999 (R2018) MPANLs (dB SPL)  500–8000  44  30  16  13  14  11  14 
ISO 8253-1:2010 MPASPL (dB SPL)  500–8000  Not specified 
a

See ANSI/ASA S3.1-1999 (R2018) or ISO 8253-1:2010 for one-third octave band levels.

TABLE IX.

MPANLs and MPASPLs in dB SPL for air conduction audiometry when testing to 0 dB HL (ears covered) with supra-aural earphones as specified in ANSI S3.1-1999 (R2018), ISO 8253-1:2010, OSHA (1983), NIOSH (1998), and FRA (2006). Note: The Department of Defense (2019) values are provided for comparison, but they do not apply to a specific transducer and are generic for “audiometric testing.”

Octave bandsa (Hz)
Criteria Test frequency range (Hz) 125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  125–8000  35  25  21  26  34  37  37 
ISO 8253-1:2010 MPASPLs (dB SPL)  125–8000  28  19  18  23  30  36  33 
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  250–8000  39  25  21  26  34  37  37 
ISO 8253-1:2010E MPASPLs (dB SPL)  250–8000  39  19  18  23  30  36  33 
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  500–8000  49  35  21  26  34  37  37 
ISO 8253-1:2010 MPASPLs (dB SPL)  500–8000  51  37  18  23  30  36  33 
OSHA (1983) and FRA (2006) MPANLs (dB SPL)  500–8000  NA  NA  40  40  47  57  62 
Department of Defense (2019) MPANLsc  500–8000  NA  NA  27  29  34  39  41 
Octave bandsa (Hz)
Criteria Test frequency range (Hz) 125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  125–8000  35  25  21  26  34  37  37 
ISO 8253-1:2010 MPASPLs (dB SPL)  125–8000  28  19  18  23  30  36  33 
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  250–8000  39  25  21  26  34  37  37 
ISO 8253-1:2010E MPASPLs (dB SPL)  250–8000  39  19  18  23  30  36  33 
ANSI S3.1-1999 (R2018)b,c MPANLs (dB SPL)  500–8000  49  35  21  26  34  37  37 
ISO 8253-1:2010 MPASPLs (dB SPL)  500–8000  51  37  18  23  30  36  33 
OSHA (1983) and FRA (2006) MPANLs (dB SPL)  500–8000  NA  NA  40  40  47  57  62 
Department of Defense (2019) MPANLsc  500–8000  NA  NA  27  29  34  39  41 
a

See ANSI/ASA S3.1-1999 (R2018) or ISO 8253-1:2010 for one-third octave band levels.

b

Referenced by NIOSH (1998).

c

The U.S. DoD does not specify supra-aural earphones or any other transducer.

TABLE X.

MPANLs in dB SPL for air conduction audiometry when testing to 0 dB HL (ears covered) using insert earphones as specified in ANSI S3.1-1999 (R2018), NIOSH (1998), and FRA (2006). Note: ISO 8253-1: 2010 does not provide MPASPLs for insert earphones, and OSHA (1983) does not provide MPANLs for insert earphones.

Criteria Earphone (insertion depth) Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  125–8000  59  53  50  47  49  50  56 
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  250–8000  67  53  50  47  49  50  56 
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  500–8000  78  64  50  47  49  50  56 
FRA (2006)d MPANLs (dB SPL)  Generic insert earphones  500–8000  NA  NA  50  47  49  50  56 
Criteria Earphone (insertion depth) Test frequency range (Hz) Octave bandsa (Hz)
125 250 500 1000 2000 4000 8000
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  125–8000  59  53  50  47  49  50  56 
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  250–8000  67  53  50  47  49  50  56 
ANSI S3.1-1999 (R2018)b MPANLs (dB SPL)  ER-3Ac or E-A-RToneTM 3A (inserted 0–3 mm deep)  500–8000  78  64  50  47  49  50  56 
FRA (2006)d MPANLs (dB SPL)  Generic insert earphones  500–8000  NA  NA  50  47  49  50  56 
a

See ANSI/ASA S3.1-1999 (R2018) or ISO 8253-1:2010 for one-third octave band levels.

b

Referenced by NIOSH (1998).

c

Etymotic Research.

d

In Appendix E.I.C of FRA (2006), it states “Insert earphones shall not be used for audiometric testing of employees with ear canal sizes that prevent achievement of an acceptable insertion depth (fit).”

2

See www.faberacoustical.com (Last viewed December 14, 2022).

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