Threshold Sound Pressure Levels Research Articles

The Critical Thing about the Ear's Sensory Hair Cells.

The capabilities of the human ear are remarkable. We can normally detect acoustic stimuli down to a threshold sound-pressure level of 0 dB (decibels) at the entrance to the external ear, which elicits eardrum vibrations in the picometer range. From this threshold up to the onset of pain, 120 dB, our ears can encompass sounds that differ in power by a trillionfold. The comprehension of speech and enjoyment of music result from our ability to distinguish between tones that differ in frequency by only 0.2%. All these capabilities vanish upon damage to the ear's receptors, the mechanoreceptive sensory hair cells. Each cochlea, the auditory organ of the inner ear, contains some 16,000 such cells that are frequency-tuned between ∼20 Hz (cycles per second) and 20,000 Hz. Remarkably enough, hair cells do not simply capture sound energy: they can also exhibit an active process whereby sound signals are amplified, tuned, and scaled. This article describes the active process in detail and offers evidence that its striking features emerge from the operation of hair cells on the brink of an oscillatory instability-one example of the critical phenomena that are widespread in physics.

Vocal count responses of narwhals to bulk carrier noise in Milne Inlet, Nunavut, Canada

AbstractConcerns were raised about possible behavioral disturbance to narwhals (Monodon monoceros) when exposed to shipping noise in Milne Inlet, Baffin Island, Canada. We deployed passive acoustic recorders in August and September 2018 and 2019, along and adjacent to the nominal shipping corridor. We measured broadband (0.01–25 kHz) sound pressure levels (SPL) after correcting for the auditory weighting function of high frequency cetaceans. Received SPLs and counts of Whistles, Buzzes, and Knocks were compared in a before‐during‐after study of individual bulk carrier transits, relative to periods with no ships. Narwhal call counts were generally lower once bulk carriers were within line‐of‐sight, including when ship noise levels were just above ambient noise levels. Call counts varied both “before” and “after” individual bulk carriers passed by the recorders. There was no evidence of a behavioral threshold SPL below which a response did not occur. We did not observe call count reductions to the same extent in 2019 compared to 2018 as higher ambient noise levels in 2019 likely masked some individual ship noise. There was no evidence of habituation or sensitization to the bulk carrier noise within or between years. Continued acoustic monitoring is recommended, especially if bulk carrier transits increase.

The equivalent threshold sound pressure levels and test-retest threshold variability of a consumer-grade insert earphone fitted with stock, foam, and otoacoustic emission probe ear tips

Objective Consumer-grade insert earphones (IEs) can be utilised for audiometry, but their calibration values and threshold reliability may differ from the audiometric IE. This study measured the equivalent threshold sound pressure levels (ETSPLs), and the test-retest threshold variation when a consumer IE (Sennheiser CX100) was fitted with: (1) silicone stock ear tips that came along with the earphone, (2) replacement foam ear tips (KZ acoustics) and (3) silicone otoacoustic emission (OAE) probe ear tips. Design and study sample Study 1 determined ETSPL values in 25 normal-hearing subjects aged 18–25 years at seven test frequencies (500–8000 Hz). Study 2 assessed the intra- and inter-session test-retest threshold reliability in a separate group of 50 adult subjects. Results The ETSPL values for the consumer IE deviated from the reference values for audiometric IEs, with the largest differences (7–9 dB) observed at 500 Hz across ear tips. This is likely related to shallow tip insertions. However, test-retest threshold variations were comparable to those reported for audiometric transducers. Conclusions Ear tip-specific corrections to the reference thresholds in the standards are required for calibration of consumer IEs used in low-cost audiometry when their ear tips only allow superficial insertion into the ear canal.

Effect of individual attributes on allowable level of household sounds inside a residential space

The threshold sound pressure level of noise annoyance generated by various household sounds in a quiet residential space was investigated through psychophysical experiments. An audiovisual environment was simulated assuming a situation in which eight types of household sounds are heard in a residential space, and the lower threshold sound pressure level of annoyance at which household sounds are perceived as annoying was measured using the method of adjustment. The measured results were analyzed in relation to the noise sensitivity of subjects and the extent of sound insulation of their own houses. The results showed that individual factors related to the noise sensitivity and sound insulation score, as well as the audiovisual environmental factors related to the background noise and day-night condition, have significant influences on the lower threshold sound pressure level of annoyance.

Reference equivalent threshold sound pressure levels for the Wireless Automated Hearing Test System.

This paper presents reference equivalent threshold sound pressure levels (RETSPLs) for the Wireless Automated Hearing Test System (WAHTS), a recently commercialized device developed for use as a boothless audiometer. Two initial studies were conducted following the ISO 389-9 standard [ISO 389-9 (2009). "Acoustics-Reference zero for the calibration of audiometric equipment. Part 9: Preferred test conditions for the determinations of reference hearing threshold levels" (International Organization for Standardization, Geneva)]. Although the standard recruitment criteria are intended to yield otologically normal test subjects, the recruited populations appeared to have slightly elevated thresholds [5-10 dB hearing level (HL)]. Comparison of WAHTS thresholds to other clinical audiometric equipment revealed bias errors that were consistent with the elevated thresholds of the RETSPL populations. As the objective of RETSPLs is to ensure consistent thresholds regardless of the equipment, this paper presents the RETSPLs initially obtained following ISO 389-9:2009 and suggested correction to account for the elevated HLs of the originally recruited populations. Two additional independent studies demonstrate the validity of these corrected thresholds.

Evaluation of Remote Check: A Clinical Tool for Asynchronous Monitoring and Triage of Cochlear Implant Recipients.

Background:A new Remote Check App permits remote self-testing of hearing function for Nucleus cochlear implant (CI) recipients and enables asynchronous review by their clinician to support patient-management decisions.Objectives:To evaluate the Remote Check App for: (1) ease of use; (2) overall acceptance of the test battery by CI recipient or their carer in the home setting; (3) test–retest reliability of audiological threshold and speech recognition measures via wireless streaming; and (4) to compare outcomes from patient-driven measures with conventional clinician-driven measurements of aided-hearing function.Design:Single-site, prospective, repeated-measures cohort study with 32 experienced CI users (28 adults and 4 children).Methods:Participants completed self-testing using the Remote Check app at home and in the clinic. Measures include audiological, objective and subjective tests. Self-administered speech recognition in noise, via the digit triplets test (DTT) and aided thresholds, via the aided threshold test (ATT) were reassessed in free-field and by clinicians following conventional clinical protocols. Results of ATT and DTT were compared across test conditions. Completion time and perceived ease of self-driven assessments were documented. Insights from subsequent real-world experience with Remote Check are summarized and compared to the study findings.Results:Remote Check was rated as easy to use by the majority (87%) of subjects. Mean group test–retest score differences for self-administered testing within the clinic versus at-home environments were nonsignificant (p > 0.05): 1.4 dB (SD = 1.97) for ATT and 1.6 dB (SD = 1.54) for DTT. Mean group test–retest score difference for patient-driven DTT in streamed versus the free-field condition was 1.8 dB (SD = 2.02). Self-administered, streamed, ATT via Remote Check, resulted in significantly lower thresholds compared to clinician-driven warble-tone thresholds in the free-field by 6.7 dB (SD = 6.8) (p < 0.001). ATT thresholds via Remote Check were not significantly different from predicted thresholds based on the Threshold Sound Pressure Level of the sound processor.Conclusion:Remote Check is the first CI telehealth assessment tool that uses wireless streaming to enable comprehensive, easy and reliable self-testing of hearing function by the CI recipient or their carer, in the comfort of their home. Asynchronous access to test results can assist clinicians in monitoring and triaging individuals for appropriate patient-management based on their needs. Use of remote monitoring may also help to reduce the burden of unnecessary clinic visits on clinic resources, patient travel time and associated costs. Remote Check is an important step toward addressing the current growing need for asynchronous audiological telepractice to support long-term care of CI recipients.

Interaction between strong sound waves and cloud droplets: Cloud chamber experiment

Acoustic agglomeration refers to the group effect of micro-particle groups in a strong sound field, which promotes relative motion among the particles, leading to the rapid agglomeration of the particle groups. The existing theoretical and experimental research on acoustic agglomeration is focused on solid particles such as soot particles and aerosols, and the acoustic agglomeration of micron-scale cloud droplets has not been intensively investigated. In this study, a cloud with an average particle size of ~10 μm is generated in a cloud chamber at room temperature, and a series of acoustic agglomeration experiments of cloud droplets under the action of sound waves with a frequency and sound pressure level (SPL) of 35–100 Hz and 112–122 dB, respectively, are conducted to examine the impact law of the sound waves with different frequencies and SPLs on the cloud droplet size spectrum. At a constant sound frequency, the agglomeration effect of the cloud droplets is more pronounced under the action of sound waves with a higher SPL. Under a constant SPL, the agglomeration effect is the most notable when the sound frequency ranges from 50 to 65 Hz. The threshold SPL for the effective agglomeration ranges from 114 to 121 dB when the sound frequency is 35–100 Hz, and the threshold SPL gradually increases with the sound frequency. The findings can clarify the effect of the sound waves in promoting cloud condensation and provide guidance to develop atmospheric intervention technologies based on strong sound waves.

Utilizing True Wireless Stereo Earbuds in Automated Pure-Tone Audiometry.

True wireless stereo (TWS) earbuds have become popular and widespread in recent years, and numerous automated pure-tone audiometer applications have been developed for portable devices. However, most of these applications require specifically designed earphones to which the public may not have access. Therefore, the present study investigates the accuracy of automated pure-tone audiometry based on TWS earbuds (Honor FlyPods). The procedure for developing an automated pure-tone audiometer is reported. Calibration of the TWS earbuds was accomplished by electroacoustic measurements and establishing corrected reference equivalent threshold sound pressure levels. The developed audiometer was then compared with a clinical audiometer using 20 hearing-impaired participants. The average signed and absolute deviations between hearing thresholds measured using the two audiometers were 3.1 dB and 6.7 dB, respectively. The overall accuracy rate in determining the presence/absence of hearing loss was 81%. The results show that the proposed procedure for an automated air-conduction audiometer based on TWS earbuds is feasible, and the system gives accurate hearing level estimation using the reported calibration framework.

A Modeling Comparison of the Potential Effects on Marine Mammals from Sounds Produced by Marine Vibroseis and Air Gun Seismic Sources

Concerns about the potential environmental impacts of geophysical surveys using air gun sources, coupled with advances in geophysical surveying technology and data processing, are driving research and development of commercially viable alternative technologies such as marine vibroseis (MV). MV systems produce controllable acoustic signals through volume displacement of water using a vibrating plate or shell. MV sources generally produce lower acoustic pressure and reduced bandwidth (spectral content) compared to air gun sources, but to be effective sources for geophysical surveys they typically produce longer duration signals with short inter-signal periods. Few studies have evaluated the potential effects of MV system use on marine fauna. In this desktop study, potential acoustic exposure of marine mammals was estimated for MV and air gun arrays by modeling the source signal, sound propagation, and animal movement in representative survey scenarios. In the scenarios, few marine mammals could be expected to be exposed to potentially injurious sound levels for either source type, but fewer were predicted for MV arrays than air gun arrays. The estimated number of marine mammals exposed to sound levels associated with behavioral disturbance depended on the selection of evaluation criteria. More behavioral disturbance was predicted for MV arrays compared to air gun arrays using a single threshold sound pressure level (SPL), while the opposite result was found when using frequency-weighted sound fields and a multiple-step, probabilistic, threshold function.

An evaluation of the Sennheiser HDA 280-CL circumaural headphone for use in audiometric testing

Objective: Evaluation of the Sennheiser HDA 280-CL circumaural headphone for the determination of (1) equivalent threshold sound pressure levels (ETSPL) for 125–18,000 Hz.; (2) real ear attenuation (250–8000 Hz); (3) insertion loss (63–18,000 Hz); (4) frequency response (125–18,000 Hz); (5) total harmonic distortion (THD) (125–10,000 Hz); and, (6) linearity (11,200–18,000 Hz).Study Sample: Twenty-five normal hearing adults aged 18–25 participated in (1) and (2).Design: (1) Hearing thresholds were measured using the Sennheiser HDA 280-CL. Frequency specific ETSPL values were calculated in an artificial ear. (2) Sound field thresholds were measured with the ears open and covered with the headphone to obtain the real ear attenuation thresholds (REAT). These values were used to determine the maximum permissible ambient noise levels (MPANL). (3) A B&K HATS mannequin recorded the output levels of a broadband pink noise with the ears open and covered with the headphones. (4, 5) The frequency response, THD and linearity were measured in an artificial ear.Results: Values for ETSPL, REAT, MPANL, insertion loss, as well as measures of frequency response, THD and linearity are presented.Conclusions: The Sennheiser HDA 280-CL meets the requirements for audiometric testing and the values presented can be used for calibration.

Northern bottlenose whales in a pristine environment respond strongly to close and distant navy sonar signals.

Impact assessments for sonar operations typically use received sound levels to predict behavioural disturbance in marine mammals. However, there are indications that cetaceans may learn to associate exposures from distant sound sources with lower perceived risk. To investigate the roles of source distance and received level in an area without frequent sonar activity, we conducted multi-scale controlled exposure experiments (n = 3) with 12 northern bottlenose whales near Jan Mayen, Norway. Animals were tagged with high-resolution archival tags (n = 1 per experiment) or medium-resolution satellite tags (n = 9 in total) and subsequently exposed to sonar. We also deployed bottom-moored recorders to acoustically monitor for whales in the exposed area. Tagged whales initiated avoidance of the sound source over a wide range of distances (0.8–28 km), with responses characteristic of beaked whales. Both onset and intensity of response were better predicted by received sound pressure level (SPL) than by source distance. Avoidance threshold SPLs estimated for each whale ranged from 117–126 dB re 1 µPa, comparable to those of other tagged beaked whales. In this pristine underwater acoustic environment, we found no indication that the source distances tested in our experiments modulated the behavioural effects of sonar, as has been suggested for locations where whales are frequently exposed to sonar.

Dynamics of liquid sheet breakup in the presence of acoustic excitation

We present the results of experimental investigations on the effect of acoustic excitation on the breakup of the liquid sheet formed by oblique impingement of two liquid jets for varying Weber number over a wide range of excitation frequencies (100–2000 Hz) and sound pressure levels (50–120 dB). Visualization studies reveal violent sheet flapping, reduction in the sheet breakup length and width, impact wave amplification and rise in droplet density shed from the sheet. Overall, increase in excitation frequency increases the threshold sound pressure level at which the sheet responds. Reduction in the sheet breakup length and width with frequency is observed at some selected frequencies, which rules out the possibility of resonance. For smooth sheet regime, visual observations show that the dominant sheet breakup mechanism shifts from Rayleigh–Plateau (R–P) to Kelvin–Helmholtz (K–H) instability. It is shown using temporal analysis that the reduction in the sheet breakup length may be attributed to periodic sheet collapse and reformation. Drop shedding frequencies in flapping liquid sheet are seen to synchronize with those excitation frequencies which are lower than or nearly equal to the fundamental frequency without excitation. Acoustic excitation reduces the mean droplet size significantly without altering the drop size distribution pattern that follows a universal Gamma distribution.

Reference equivalent threshold sound pressure levels for Apple EarPods.

Reference equivalent threshold sound pressure levels (RETSPLs) are used when calibrating audiometric equipment to a hearing threshold level of zero at various frequencies. To the best of the authors' knowledge, the RETSPLs for Apple EarPods (MB770G) have not been reported, and so this study aimed to measure them. The hearing thresholds of 36 normal-hearing subjects (72 ears) were measured at 250, 500, 1000, 2000, 4000, and 8000 Hz, with the measurements being performed twice in 33 subjects (66 ears) for evaluating the test-retest reliability. This study provides Apple EarPod RETSPLs and shows significant Pearson's correlations (p < 0.001) with no significant Wilcoxon signed-rank test differences (p > 0.01), which confirm the test reliability.

Calibration of brief stimuli for the recording of evoked responses from the human auditory pathway.

The relationship between the calibration RETSPL-values (reference equivalent threshold sound pressure level) in dB p-p.e.SPL and the corresponding sound pressure levels in dB SPL for brief stimuli is formulated mathematically. The formula is applied on ten brief stimuli consisting of a click, four tone-bursts, a chirp, and four octave-band chirps presented at a stimulus rate of 20 stimuli per second, and using the average acoustical parameter-values from a sample of 20 ER-3A insert earphones in the occluded-ear simulator. The reference calibration values in dB SPL for the ten stimuli are then established. These theoretical values are verified by direct measurements using two different sound-level-meters. It is concluded that the calibration values in dB SPL can be applied in the practical calibration of common brief stimuli. Calibration with these reference values involves only a sound-level meter, and the need for including an oscilloscope in the calibration setup is therefore eliminated.

Affordable headphones for accessible screening audiometry: An evaluation of the Sennheiser HD202 II supra-aural headphone

Objective: Evaluation of the Sennheiser HD 202 II supra-aural headphones as an alternative headphone to enable more affordable hearing screening. Design: Study 1 measured the equivalent threshold sound pressure levels (ETSPL) of the Sennheiser HD 202 II. Study 2 evaluated the attenuation of the headphones. Study 3 determined headphone characteristics by analyzing the total harmonic distortion (THD), frequency response and force of the headband. Study sample: Twenty-five participants were included in study 1 and 15 in study 2 with ages ranging between 18 and 25. No participants were involved in study 3. Results: The Sennheiser HD 202 II ETSPLs (250–16000 Hz) showed no significant effects on ETSPL for ear laterality, gender or age. Attenuation was not significantly different (p > 0.01) to TDH 39 except at 8000 Hz (p < 0.01). Maximum permissible ambient noise levels (MPANL) were specified accordingly. The force of the headband was 3.1N. THD measurements showed that between 500 and 8000 Hz intensities of 90 dB HL and higher can be reached without THD >3%. Conclusion: Sennheiser HD 202 II supra-aural headphones can be used as an affordable headphone for screening audiometry provided reported MPANLs, maximum intensities and ETSPL values are employed.

Distribution characteristics of normal pure-tone thresholds

Objective: This study examined the statistical properties of normal air-conduction thresholds obtained with automated and manual audiometry to test the hypothesis that thresholds are normally distributed and to examine the distributions for evidence of bias in manual testing. Design: Four databases were mined for normal thresholds. One contained audiograms obtained with an automated method. The other three were obtained with manual audiometry. Frequency distributions were examined for four test frequencies (250, 500, 1000, and 2000 Hz). Study sample: The analysis is based on 317 569 threshold determinations of 80 547 subjects from four clinical databases. Results: Frequency distributions of thresholds obtained with automated audiometry are normal in form. Corrected for age, the mean thresholds are within 1.5 dB of reference equivalent threshold sound pressure levels. Frequency distributions of thresholds obtained by manual audiometry are shifted toward higher thresholds. Two of the three datasets obtained by manual audiometry are positively skewed. Conclusions: The positive shift and skew of the manual audiometry data may result from tester bias. The striking scarcity of thresholds below 0 dB HL suggests that audiologists place less importance on identifying low thresholds than they do for higher-level thresholds. We refer to this as the Good enough bias and suggest that it may be responsible for differences in distributions of thresholds obtained by automated and manual audiometry.

Hearing thresholds of harbor seals (Phoca vitulina) for playbacks of seal scarer signals, and effects of the signals on behavior

Acoustic mitigation devices (AMDs) are used to deter marine mammals from construction sites to prevent hearing injury by offshore pile-driving noise. In order to quantify the distance at which AMDs designed as ‘seal scarers’ are detected by seals, the 50% hearing thresholds for playbacks of their sounds were determined. The broadband hearing threshold sound pressure levels (SPLs) of two harbor seals for signals from two AMDs were similar (63–69 dB re 1 μPa, rms). Effects of the AMDs on the seals’ behavior were quantified at three SPLs: one which just did not cause behavioral changes, one which caused one of the seals to haul out occasionally, and one which caused one of the seals to haul out more than 10% of the time. The corresponding mean received SPLs were, respectively, Ace Aquatec: 109, 124, and 134 dB re 1 μPa, rms; Lofitech: 128, 133, and 138 dB re 1 μPa, rms. Thus at similar received levels, the Ace Aquatec seems more effective than the Lofitech in deterring harbor seals. Detection and behavioral response distances of the AMD sounds for harbor seals at sea can be estimated by combining the results from the present study with data on AMD source levels, propagation conditions, and background noise levels near construction sites.

Earphones in extended high-frequency audiometry and ISO 389-5

Objective: To determine common reference equivalent threshold sound pressure levels (RETSPL) for the earphones used in the extended high-frequency (EHF) range, as different earphones are commercially available, but there are not RETSPLs for each model. Design: Hearing threshold sound pressure levels were measured up to 20 kHz for the Sennheiser HDA 200 audiometric earphone, and were compared to the ISO 389-5 (2006) norm and other investigations using that earphone and different ones. Study sample: A total of 223 otologically-normal subjects (aged 5–25 years old) participated in the hearing determination. Results: The results are in good agreement with previous studies of hearing thresholds using the same and other earphones. Conclusions: The results of the present investigation are relevant for the international standard for the calibration of audiometric equipment in the 8 to 16 kHz frequency range, ISO 389-5. The data may be used for a future update of the RETSPL for circumaural and insert audiometric earphones.

Reference hearing threshold levels for chirp signals delivered by an ER-3A insert earphone

Objective: To establish reference hearing threshold levels for chirps and frequency-specific chirps. Design: Hearing thresholds were determined monaurally for broad-band chirps and octave-band chirps using the Etymotic Research, ER-3A insert earphone. The chirps were presented using two repetition rates, 20 and 90 stimuli/s, and with alternating polarity in blocks of one second duration. The test procedure and test conditions were in accordance with the recommendations given in . The ascending method () was applied using a step size of 5 dB. The chirps were played back from a Tucker Davies Technologies System II, and a Matlab program controlled the test setup. The results are specified in dB peak-to-peak equivalent threshold sound pressure levels (dB peETSPL). Study sample: The test group consisted of 25 otologically-normal young adults (age 18–25 years). Results: The results are in good agreement with the results from another investigation of hearing thresholds using the same chirp stimuli, and the values for the octave-band chirps are in line with the standardized reference values for corresponding tone bursts (). Conclusions: The results of the present investigation are relevant for the international standard on short duration signals, .

Equivalent hearing threshold levels for the Etymotic Research ER-10C otoacoustic emission probe

Objective: To determine the equivalent threshold sound pressure levels (ETSPL) for a commercially available distortion product otoacoustic emission (DPOAE) probe, and to study the impact of probe fitting and eartip size on the calibration. Design: Twenty-eight otologically normal test subjects participated in the ETSPL determination for the Etymotic Research ER-10C probe. Study sample: ETSPLs were determined up to 16 kHz and were compared to the reference hearing thresholds associated with the ER-3A insert earphone. Both ‘regular’ and ‘baby’ foam eartips were used. Results: At most frequencies, no significant threshold differences were observed between the insert earphone and the DPOAE probe. However, at 1 kHz and 4 kHz, the mean thresholds for the insert earphone were generally lower than those for the DPOAE probe, suggesting systematic differences at those frequencies. Repeated calibration runs resulted in deviations of about 0.6 dB. Similar deviations were noticed when using foam eartips of different sizes up to 10 kHz. Conclusions: Knowing the reference thresholds for DPOAE probes enables measurements of (subjective) hearing thresholds and (objective) otoacoustic emissions using the same probe. Probe fitting and eartip size had negligible effect on the determination of ETSPLs. The obtained data may be proposed for inclusion in future audiometry standards.