Real-ear-to-coupler Difference Research Articles

Does the Receiver Type Used in Receiver-in-Canal Hearing Aids Have an Effect on Real-Ear-to-Coupler Difference and Coupler Response for Flat Insertion Gain Values?

Background and Aim: Real-Ear-to-Coupler Difference (RECD) is affected by the type of transducer and its coupling method. This study aimed to investigate the effect of receiver type used in Receiver-in-Canal (RIC) hearing aids on RECD and Coupler Response for Flat Insertion Gain (CORFIG) obtained by the same coupling method. Methods: In this study, the right ears of 30 normal-hearing adults (25 men and 5 women, with a mean age of 28.13±5.62 years) were studied. We used the RIC hearing aids with two standard and power receivers. The foam of the ER-3A insert earphone was used as a coupling system in both receivers. By using the Audiogram Direct test within Phonak’s fitting software, 70 dB HL intensity was produced at different frequencies, once in the real- ear and again in the HA-1 coupler. By assessing the difference between real-ear and HA-1 coupler measurements, the RECD was first obtained. Then, the CORFIG was obtained at different frequencies by subtracting the Microphone Location Effect (MLE) and RECD from Real-Ear Unaided Gain (REUG). Results: The RECD and CORFIG values obtained from the standard receiver at all frequencies were significantly different from those from the power receiver (p<0.05), where the use of the power receiver resulted in lower RECD and higher CORFIG. With the increase in frequency, the RECD increased. A small frequency changes of 50 Hz had a significant effect on RECD and CORFIG. Conclusion: The type of receiver used in RIC hearing aids has a significant effect on the RECD and CORFIG values. Keywords: Real-ear measurement; real-ear-to-coupler difference; insertion gain; hearing aid

The Complexity of Hearing Aid Fitting: Children with Congenital Hearing Loss and Middle Ear Dysfunction.

The early diagnosis of hearing loss (HL) and hearing rehabilitation facilitate language and communication development. Some children exhibit mixed HL due to middle ear effusion (MEE) or acute otitis media (AOM). Mixed HL can affect HL evaluation and hearing aid (HA) fitting. The present study retrospectively evaluated the prevalence of MEE/AOM among children with congenital sensorineural HL (SNHL) who were fitted with HAs and its effect on the HA fitting. Thirty-six HA fittings carried out between 2017 and 2020 at one rehabilitation center were examined. Medical and audiological information was retrieved for children between 6 and 32 months old. The number of appointments and HA fitting times were recorded. Twenty-eight children were included in the study. Eighteen children, in addition to SNHL, had a conductive component resulting from MEE/AOM. The children with these pathologies required significantly more HA fitting sessions and hearing tests, fewer real ear to coupler difference (RECD) measurements and longer HA fitting periods. The findings indicate that a large number of children fitted with HAs have an additional conductive component that makes the fitting process longer. Since early rehabilitation is necessary for language development, otolaryngologists should be aware of the adverse effects of MEE/AOE on the HA fitting process. It is important to inform parents that when there is a conductive component, the HA fitting process may take longer and that treatment by an otolaryngologist is vital. This study stresses the importance of multidisciplinary cooperation for optimal HA fitting.

Predicting wideband real-ear-to-coupler differences in children using wideband acoustic immittance.

Individual differences in ear-canal acoustics introduce variability into hearing aid output that can affect speech audibility. Measuring ear-canal acoustics in young children can be challenging, and relying on normative real-ear-to-coupler difference (RECD) transforms can lead to large fitting errors. Acoustic immittance measures characterize the impedance of the ear and are more easily measured than RECD. Using 226 Hz tympanometry to predict the RECD is more accurate than using age-based average RECD values. The current study sought to determine whether wideband acoustic immittance measurements could improve predictions of wideband real-ear-to-coupler difference (wRECD). 150 children ages 2-10 years with intact tympanic membranes underwent wRECD and wideband acoustic immittance measures in each ear. Three models were constructed to predict each child's measured wRECD: the age-based average wRECD, 226 Hz admittance wRECD, and wideband absorbance wRECD. The average age-based wRECD model predicted the child's measured wRECD within 3 dB in 62% of cases, but both the 226 Hz admittance and wideband absorbance wRECD were within 3 dB in 90% of cases. Using individual 226 Hz or wideband absorbance to predict wRECD improved the accuracy and precision of transforms used for pediatric hearing aid fitting.

Predicting children’s real-ear-to-coupler differences based on tympanometric data

Objective Paediatric hearing-aid verification relies on measures of output obtained from the ear canal or in a coupler with the child’s real-ear-to-coupler difference (RECD). Measured RECD cannot always be completed in children, leading to fitting inaccuracies. Audiologists often have tympanometry data that characterises the child’s ear-canal acoustics. The goal of this study was to determine if tympanometry can be used to improve predictions of measured RECD. Design A retrospective analysis of RECD and admittance, tympanometric peak pressure, and equivalent ear-canal volume from 226 Hz tympanometry collected as part of a longitudinal study of children with hearing loss were modelled with Bayesian hierarchical regression. Study sample Two-hundred sixty-six children with mild-to-severe hearing loss contributed data. Results Age-based average RECD models were within 3 dB of measured RECD values in 54% of cases with normal middle ear status and 50.6% of cases with abnormal middle ear status. Immittance-predicted RECD were within 3 dB in 69.6% of cases with normal middle ear status and 74.4% of cases with abnormal middle ear status. Conclusion Immittance-predicted RECD was more accurate than age-based average RECD, particularly in children with abnormal middle ear status. The findings suggest that 226 Hz tympanometry could be used clinically to improve predictions of measured RECD when it cannot be measured.

Effect of Real-Ear Adjusted Stimuli on Vestibular Evoked Myogenic Potential Variability in Children and Young Adults.

There is large variability in cervical and ocular vestibular evoked myogenic potential (c- and oVEMP) amplitudes. One potential source of variability is differences in ear canal shape and size. Real ear-to-coupler difference (RECD) values are used to measure the acoustic environment of an individual's ear canal. RECD may be a useful measure to calibrate air conducted VEMP stimuli, which are elicited at high intensities and may put patients at risk of unsafe sound exposure. A recommendation for avoiding unsafe exposure is to use a 125 dB SPL stimulus for individuals with an equivalent ear canal volume (ECV) ≥ 0.9 mL and a 120 dB SPL stimulus for individuals with a smaller ECV. The purpose of this project was to determine if using a stimulus calibrated in the ear using RECD values significantly reduces intra-subject and inter-subject VEMP amplitude variability. We hypothesized that using a RECD-calibrated stimulus would significantly reduce inter-subject amplitude variability but not significantly reduce intra-subject variability. We further hypothesized that an RECD-adjusted VEMP stimulus would better protect against delivering unsafe sound exposure compared to the method of using ECV alone. Eleven children (4 to 9 years), 10 adolescents (10 to 18 years), and 10 young adults (20 to 40 years) with normal hearing, tympanometry, vestibular and neurological function participated. On all subjects, RECD was measured twice per ear to account for test-retest reliability. cVEMP and oVEMP were then recorded bilaterally with a 500 Hz tone burst at a traditional and an adjusted VEMP intensity level. The traditional intensity level was 125 dB SPL for individuals with ≥ 0.9 mL ECV and 120 dB SPL for individuals with ≤ 0.8 mL ECV. The adjusted intensity level was calculated by subtracting the average 500 Hz RECD measured values from the 500 Hz normative RECD value. This value was applied as a correction factor to a 125 dB SPL stimulus. Peak to peak amplitudes were recorded and used to calculate asymmetry ratios. Young children had significantly smaller ECVs compared to adolescents and young adults. Young children had larger RECDs; however, this was not significant in post hoc analyses. The method of calibration had no significant effect on intra-subject variability for cVEMP [ F (1, 27)= 0.996, p = 0.327] or oVEMP [ F (1, 25)= 1.679, p = 0.206]. The method of calibration also had no significant effect on inter-subject amplitude variability for cVEMP [ F (1, 120)= 0.721, p = 0.397] or oVEMP [ F (1, 120)= 0.447, p = 0.505]. Both methods of calibration adequately protected against unsafe exposure levels. However, there were subjects with ECVs ≥ 0.9 mL who approached unsafe exposure levels from the ECV-calibrated stimulus, suggesting there may be rare cases in which a 125 dB SPL stimulus is unsafe, even for patients with larger ECVs. The calibration method made no significant difference in intra- or inter-subject variability, indicating that the acoustic environment of the outer ear is not significantly contributing to VEMP amplitude variability. The RECD-adjusted stimulus is effective in protecting against unsafe exposure levels for two trials of both c- and oVEMPs. There may be instances where more than two trials of each test are required, which increases the effective stimulation level. Clinicians should be cautious when delivering VEMPs and not unnecessarily expose patients to unsafe levels of sound.

Habituation of changed acoustics properties after canal wall down mastoidectomy

PurposeOur objective is to evaluate the effect of habituation on the altered ear canal acoustics after canal wall down mastoidectomy.MethodsA total of 11 participants with single sided dry cavities and normal contralateral ear canals with normal hearing thresholds were included in the study. Filtered sound fragments were created that simulate the different acoustic properties based on the participants Real Ear to Coupler Difference (RECD) of the cavity ear and the contralateral normal ear canal. These filtered sound fragments are presented to the cavity ear canal and the contralateral normal ear canal using inserts earphones. Participants performed a subjective quality assessment of the sound fragments using paired comparison with a seven-point scale (− 3 till + 3).ResultsMean assessment of sound quality revealed the following results; naturalness of sounds of the cavity ear canal is 0.29 (± 1.41; ns) in favour of the filtered sound fragment of the normal ear canal. Mean assessment of sharpness of sounds in the cavity ear canal is 1.55 (± 1.21, p = 0.55) in favour of the filtered sound fragment of the normal ear canal. Overall preference in the cavity ear canal was in favour of the normal ear canal acoustics 0.72 (SD ± 1.54 p = 0.224).ConclusionsPatients with cavity ear canals seem to habituate to their altered ear canal acoustics. Transforming the ear canal acoustics of the cavity ear to normal ear canal acoustics seem to sharpen the incoming sounds. Overall assessment of quality of sound of the normal ear canal acoustics is better than the cavity acoustics.

Real-Ear-to-Coupler Difference: Physical and Perceptual Differences.

The real-ear-to-coupler difference (RECD) is a recommended measure for accurate hearing aid fittings, especially for pediatric populations. However, for adults, many clinicians question whether it is necessary. Hearing aids were fit on two groups of 85 older adults seen at a Veterans Administration audiology clinic. One group was fit using RECD measurements, whereas the second group was fit with population-based average RECD values. The two groups had similar pure-tone hearing thresholds. Like previous studies, there was little difference between the measured RECD for the right and left ears among the participants. Although the majority of the measured RECDs were within 1 SD of the mean, approximately 20% of those measured were outside of the normal range. It also was found that all participants produced lower (improved) Hearing Handicap Inventory for Elderly-Screening (HHIE-S) scores from pre- to postfitting, thus suggesting a reduction in self-perceived hearing handicap. Despite having similar prefitting HHIE-S scores, those participants who had their hearing aids fit using measured RECD values had lower postfitting scores than the group that was fit with average RECD values. Furthermore, there was a significant difference between the groups on several questions of the International Outcome Inventory-Hearing Aids, suggesting that there was higher satisfaction with the fittings based on the custom RECD rather than the fittings based on the average RECD. This study demonstrated that, in addition to performing verification using real-ear measurements, accurate conversion of dB HL to dB SPL using personalized RECD likely improved hearing aid satisfaction.

Modeling individual noise-induced hearing loss risk with proxy measurements of external-ear amplification.

Significant variability in noise-induced hearing loss (NIHL) susceptibility suggests there are factors beyond sound level and duration of exposure that contribute to individual susceptibility. External-ear amplification (EEA) from external-ear structures varies significantly due to ear size and shape, potentially influencing NIHL susceptibility. This study tested the hypothesis that EEA can be predicted using non-technical proxy measurements including pinna height (cm), body height (m), and earcanal volume (cm3). 158 participants (4-78 years) completed otoscopy, tympanometry, pinna measurements, body height measurements, and two EEA measurements: (1) total real-ear unaided gain (REUG) of the open ear and (2) real-ear to coupler difference (RECD), representing unaided gain from the earcanal. Participants' individual noise doses were compared in hypothetical exposures. REUG ranged from 5 to 19 dBA and was correlated with pinna height. High-REUG participants were estimated to accrue noise doses at least 5 times higher than low-REUG participants. RECD ranged from 7 to 24 dBA and was correlated with earcanal volume and body height. The results support the hypothesis that EEA measurement could significantly improve estimation of an individual's position along the NIHL risk spectrum. Non-technical proxy measurements of EEA (pinna height, body height, earcanal volume) were statistically significant but yielded high variability in individual EEA prediction.

The accuracy of standard audiometric hearing level thresholds in pediatric patients

ObjectivesStandard audiograms provide decibels Hearing Level (dB HL) thresholds, which are referenced to normative values specified in decibels Sound Pressure Level in an acoustic coupler. Due to variability in external ear acoustics, the actual sound levels reaching the eardrum can vary across individuals. The real-ear to coupler difference (RECD) is a frequency-specific measurement of the difference between sound levels measured at the eardrum and in a coupler. Here, we compare the standard audiogram dB HL levels to RECD corrected hearing thresholds (dB RECHL) in children. MethodsChildren who underwent standard audiometric and RECD testing were included. The dB RECHL was established and the differences between dB HL and dB RECHL (threshold error) was calculated. A threshold error >5 dB was considered significant. ResultsA total of 166 children were included (mean age 12 years). Overall, 14% had normal hearing, 52% had conductive hearing loss and 27% had sensorineural hearing loss. Hearing threshold levels were overestimated by the standard audiogram compared to dB RECHL, at all frequencies (250–6000 Hz). In the lower frequencies and at 6000 Hz, 33–59% of patients were overestimated, with a threshold error up to 25 dB. In the mid frequencies, 33% were overestimated with a similar threshold error. ConclusionStandard audiogram thresholds overestimated hearing levels in children which may have clinical implications. This problem can be addressed by correcting thresholds with RECD. More studies are needed to assess the effect of correcting thresholds on hearing outcomes in children.

Relationship of Head Circumference and Age in the Prediction of the Real-Ear-to-Coupler Difference (RECD).

Pediatric hearing instrument fitting is optimally performed with individually obtained real-ear-to-coupler difference (RECD) measurements. If these measurements cannot be obtained, predicted values based on age are used. Recent evidence obtained from children aged 3-11 years suggests that head circumference (HC) may be a viable alternative or addition to age for use in RECD prediction. The purpose of the present study was to determine if HC can be used to predict RECDs in infants, children, and adults. A correlational design was used. HC and RECD values were measured in all participants. Participants were 278 North American infants and children (136 males and 142 females) aged 1.6 months to 11 years and 109 adults (42 males and 67 females) aged 18 years to 83 years. After otoscopic inspection and immittance measurements were performed to assess candidacy for inclusion in the study, HC was measured twice for all participants and a single RECD measure was obtained for each participant at twelve frequencies (250 through 12500 Hz). The reliability of HC measurements was assessed with an intraclass correlation analysis. Linear regression analyses were performed with age and HC as predictor variables and RECDs as the dependent variable. Analysis indicated good reliability of the HC measurement. The relationships between RECD and HC were comparable with the relationships between RECD and age. Combining HC and age did not improve predictive accuracy. HC can be used in children and adults as an alternative metric in the prediction of RECDs when individual RECDs cannot be obtained.

Relationship of Head Circumference and Age in the Prediction of the Real-Ear-to-Coupler Difference (RECD)

Background: Pediatric hearing instrument fitting is optimally performed with individually obtained realear-to-coupler difference (RECD) measurements. If these measurements cannot be obtained, predictedvalues based on age are used. Recent evidence obtained from children aged 3–11 years suggests thathead circumference (HC) may be a viable alternative or addition to age for use in RECD prediction.Purpose: The purpose of the present study was to determine if HC can be used to predict RECDs ininfants, children, and adults.Research Design: A correlational design was used. HC and RECD values were measured in allparticipants.Study Sample: Participants were 278 North American infants and children (136 males and 142 females)aged 1.6 months to 11 years and 109 adults (42 males and 67 females) aged 18 years to 83 years.Data Collection and Analysis: After otoscopic inspection and immittance measurements were performedto assess candidacy for inclusion in the study, HC was measured twice for all participantsand a single RECD measure was obtained for each participant at twelve frequencies (250 through12500 Hz). The reliability of HC measurements was assessed with an intraclass correlation analysis.Linear regression analyses were performed with age and HC as predictor variables and RECDs asthe dependent variable.Results: Analysis indicated good reliability of the HC measurement. The relationships between RECDand HC were comparable with the relationships between RECD and age. Combining HC and age did notimprove predictive accuracy.Conclusions: HC can be used in children and adults as an alternative metric in the prediction of RECDswhen individual RECDs cannot be obtained.

Skill Transference of a Probe-Tube Placement Training Simulator.

Probe-tube placement is a necessary step in hearing aid verification which needs ample hands-on experience and confidence before performing in clinic. To improve the methods of training in probe-tube placement, a manikin-based training simulator was developed consisting of a 3D-printed head, a flexible silicone ear, and a mounted optical tracking system. The system is designed to provide feedback to the user on the depth and orientation of the probe tube, and the time required to finish the task. Although a previous validation study was performed to determine its realism and teachability with experts, further validation is required before implementation into educational settings. This study aimed to examine the skill transference of a newly updated probe-tube placement training simulator to determine if skills learned on this simulator successfully translate to clinical scenarios. All participants underwent a pretest in which they were evaluated while performing a probe-tube placement and real-ear-to-coupler difference (RECD) measurement on a volunteer. Participants were randomized into one of two groups: the simulator group or the control group. During a two-week training period, all participants practiced their probe-tube placement according to their randomly assigned group. After two weeks, each participant completed a probe-tube placement on the same volunteer as a posttest scenario. Twenty-five novice graduate-level student clinicians. Participants completed a self-efficacy questionnaire and an expert observer completed a questionnaire evaluating each participant's performance during the pre- and posttest sessions. RECD measurements were taken after placing the probe tube and foam tip in the volunteer's ear. Questionnaire results were analyzed through nonparametric t-tests and analysis of variance, whereas RECD results were analyzed using a nonlinear mixed model method. Results suggested students in the simulator group were less likely to contact the tympanic membrane when placing a probe tube, appeared more confident, and had better use of the occluding foam tip, resulting in more improved RECD measurements. The improved outcomes for trainees in the simulator group suggest that supplementing traditional training with the simulator provides useful benefits for the trainees, thereby encouraging its usage and implementation in educational settings.

Evaluation of the Repeatability and Accuracy of the Wideband Real-Ear-to-Coupler Difference.

The real-ear-to-coupler difference (RECD) is an ANSI standardized method for estimating ear canal sound pressure level (SPL) thresholds and assisting in the prediction of real-ear aided responses. It measures the difference in dB between the SPL produced in the ear canal and the SPL produced in an HA-1 2-cc coupler by the same sound source. Recent evidence demonstrates that extended high-frequency bandwidth, beyond the hearing aid bandwidth typically measured, is capable of providing additional clinical benefit. The industry has, in turn, moved toward developing hearing aids and verification equipment capable of producing and measuring extended high-frequency audible output. As a result, a revised RECD procedure conducted using a smaller, 0.4-cc coupler, known as the wideband-RECD (wRECD), has been introduced to facilitate extended high-frequency coupler-based measurements up to 12.5 kHz. This study aimed to (1) compare test-retest repeatability between the RECD and wRECD and (2) measure absolute agreement between the RECD and wRECD when both are referenced to a common coupler. RECDs and wRECDs were measured bilaterally in adult ears by calculating the dB difference in SPL between the ear canal and coupler responses. Real-ear probe microphone measures were completed twice per ear per participant for both foam-tip and customized earmold couplings using the Audioscan Verifit 1 and Verifit 2 fitting systems, followed by measurements in the respective couplers. Twenty-one adults (mean age = 67 yr, range = 19-78) with typical aural anatomy (as determined by measures of impedance and otoscopy) participated in this study, leading to a sample size of 42 ears. Repeatability within RECD and wRECD was assessed for each coupling configuration using a repeated-measures analysis of variance (ANOVA) with test-retest and frequency as within-participants factors. Repeatability between the RECD and wRECD was assessed within each configuration using a repeated-measures ANOVA with test-retest, frequency, and coupler type as within-participants factors. Agreement between the RECD and wRECD was assessed for each coupling configuration using a repeated-measures ANOVA with RECD value, coupler type, and frequency as within-participants factors. Post hoc comparisons with Bonferroni corrections were used when appropriate to locate the frequencies at which differences occurred. A 3-dB criterion was defined to locate differences of clinical significance. Average absolute test-retest differences were within ±3 dB within each coupler and coupling configuration, and between the RECD and wRECD. The RECD and wRECD were in absolute agreement following HA-1-referenced transforms, with most frequencies agreeing within ±1 dB, except at 0.2 kHz for the earmold, and 0.2-0.25 kHz for the foam tip, where the average RECD exceeded the average wRECD by slightly >3 dB. Test-retest repeatability of the RECD (up to 8 kHz) and wRECD (up to 12.5 kHz) is acceptable and similar to previously reported data. The RECD and wRECD are referenced to different couplers, but can be rendered comparable with a simple transform, producing values that are in accordance with the ANSI S3.46-2013 standard.

Using the Real-Ear-to-Coupler Difference within the American Academy of Audiology Pediatric Amplification Guideline: Protocols for Applying and Predicting Earmold RECDs.

Real-ear-to-coupler difference (RECD) measurements are used for the purposes of estimating degree and configuration of hearing loss (in dB SPL ear canal) and predicting hearing aid output from coupler-based measures. Accurate measurements of hearing threshold, derivation of hearing aid fitting targets, and predictions of hearing aid output in the ear canal assume consistent matching of RECD coupling procedure (i.e., foam tip or earmold) with that used during assessment and in verification of the hearing aid fitting. When there is a mismatch between these coupling procedures, errors are introduced. The goal of this study was to quantify the systematic difference in measured RECD values obtained when using a foam tip versus an earmold with various tube lengths. Assuming that systematic errors exist, the second goal was to investigate the use of a foam tip to earmold correction for the purposes of improving fitting accuracy when mismatched RECD coupling conditions occur (e.g., foam tip at assessment, earmold at verification). Eighteen adults and 17 children (age range: 3-127 mo) participated in this study. Data were obtained using simulated ears of various volumes and earmold tubing lengths and from patients using their own earmolds. Derived RECD values based on simulated ear measurements were compared with RECD values obtained for adult and pediatric ears for foam tip and earmold coupling. Results indicate that differences between foam tip and earmold RECDs are consistent across test ears for adults and children which support the development of a correction between foam tip and earmold couplings for RECDs that can be applied across individuals. The foam tip to earmold correction values developed in this study can be used to provide improved estimations of earmold RECDs. This may support better accuracy in acoustic transforms related to transforming thresholds and/or hearing aid coupler responses to ear canal sound pressure level for the purposes of fitting behind-the-ear hearing aids.

Alternative metrics for real-ear-to-coupler difference average values in children.

Ideally, individual real-ear-to-coupler difference (RECD) measurements are obtained for pediatric hearing instrument-fitting purposes. When RECD measurements cannot be obtained, age-related average RECDs based on typically developing North American children are used. Evidence suggests that these values may not be appropriate for populations of children with retarded growth patterns. The purpose of this study was to determine if another metric, such as head circumference, height, or weight, can be used for prediction of RECDs in children. Design was a correlational study. For all participants, RECD values in both ears, head circumference, height, and weight were measured. The sample consisted of 68 North American children (ages 3-11 yr). Height, weight, head circumference, and RECDs were measured and were analyzed for both ears at 500, 750, 1000, 1500, 2000, 3000, 4000, and 6000 Hz. A backward elimination multiple-regression analysis was used to determine if age, height, weight, and/or head circumference are significant predictors of RECDs. For the left ear, head circumference was retained as the only statistically significant variable in the final model. For the right ear, head circumference was retained as the only statistically significant independent variable at all frequencies except at 2000 and 4000 Hz. At these latter frequencies, weight was retained as the only statistically significant independent variable after all other variables were eliminated. Head circumference can be considered as a metric for RECD prediction in children when individual measurements cannot be obtained. In developing countries where equipment is often unavailable and stunted growth can reduce the value of using age as a metric, head circumference can be considered as an alternative metric in the prediction of RECDs.

Effects of Tubing Length and Coupling Method on Hearing Threshold and Real-Ear to Coupler Difference Measures

This tutorial demonstrates the effects of tubing length and coupling type (i.e., foam tip or personal earmold) on hearing threshold and real-ear-to-coupler difference (RECD) measures. Hearing thresholds from 0.25 kHz through 8 kHz are reported at various tubing lengths for 28 normal-hearing adults between the ages of 22 and 31 years. RECD values are reported for 14 of the adults. All measures were made with an insert earphone coupled to a standard foam tip and with an insert earphone coupled to each participant's personal earmold. Threshold and RECD measures obtained with a personal earmold were significantly different from those obtained with a foam tip on repeated measures analyses of variance. One-sample t tests showed these differences to vary systematically with increasing tubing length, with the largest average differences (7-8 dB) occurring at 4 kHz. This systematic examination demonstrates the equal and opposite effects of tubing length on threshold and acoustic measures. Specifically, as tubing length increased, sound pressure level in the ear canal decreased, affecting both hearing thresholds and the real-ear portion of the RECDs. This demonstration shows that when the same coupling method is used to obtain the hearing thresholds and RECD, equal and accurate estimates of real-ear sound pressure level are obtained.

A comparison of methods for estimating individual real-ear-to-coupler-differences in hearing aid fitting

The sound pressure at the ear drum is the reference quantity for almost all applications of sound delivery to the ear, especially in hearing aid fitting. Since hearing aids are typically calibrated using the so called 2cc-coupler, the link to the individual sound pressure at the ear drum is given by the real-ear-to-coupler-difference (RECD). Nowadays, averaged RECDs are used for hearing aid fitting, which do not account for inter-individual differences in ear canal acoustics. As a consequence, resulting coupling errors may reach 15 dB for frequencies up to 10 kHz. Alternatively, there are methods for estimating individual RECDs, based on acoustic impedance measurements at the inner face of the ear mold. These methods differ in effort (e.g., the complexity of the ear canal model and fitting algorithm) and accuracy. By using an integrated ear canal microphone, individual RECD estimation could be feasible in future hearing aid fitting. In this research, six different methods to predict individual RECDs were compared using simulations as well as real ear measurements with open and closed ear molds. As a result, it appeared that relatively simple cylindrical and conical ear canal models give the best compromise between effort and accuracy.

Effective Masking Levels for Bone Conduction Auditory Steady State Responses in Infants and Adults Run down Normal Hearing

To obtain ear-specific bone conduction thresholds, masking of the nontest ear is often required. Bone conduction masking has not been formally investigated for infants assessed physiologically. The objective of this study was to determine effective masking levels (EMLs) for auditory steady state responses (ASSRs) elicited by bone-conducted stimuli in a group of normal-hearing infants and adults. Participants were 15 infants younger than 6 mo and 15 adults, all with normal hearing. EML was defined as the lowest level of a binaural air-conducted masker that resulted in absent bone conduction ASSRs. Stimuli were single bone-conducted tones that were 100% amplitude modulated and 25% frequency modulated at 85 and 101 for 1000 and 4000 Hz, respectively. The stimuli were calibrated in dB HL (ANSI S3.6-1996) and expressed in dB HL or dB SL (dB relative to mean bone conduction ASSR thresholds reported in a previous study). The maskers were 1 and 4 kHz narrowband noise generated by a clinical audiometer. Unmasked and masked ASSRs were obtained for each participant. Real ear-to-coupler differences (RECDs) were also obtained for each participant and were used to convert masker dB SPL measured in the coupler to dB SPL in the individual ear canal. Infant EMLs for ASSRs elicited to bone-conducted stimuli in dB HL were 6 to 7 dB higher and 8 to 10 dB lower for 1000 and 4000 Hz, respectively, compared with adults. When masker was adjusted for RECDs, infant EMLs were 12 dB higher at 1000 Hz and similar at 4000 Hz compared with adults. When the stimulus levels were corrected for the mean differences in ASSR bone conduction thresholds between infants and adults and the masker levels adjusted for RECDs, infants had lower EMLs at 1000 Hz and equal EMLs at 4000 Hz, in comparison to adults. Frequency- and level-dependent effects on ASSR amplitude due to masking were found and differed between infants and adults. Our findings indicate that there are frequency- and level-dependent infant-adult differences in EMLs for bone conduction ASSRs and confirm that a 1000 Hz stimulus is 12 dB more effective for infants compared with adults. The following infant preliminary masking levels for bone conduction stimuli are recommended: (i) 1000 Hz: 48 and 58 dB SPL at 15 and 25 dB HL, respectively, and (ii) 4000 Hz: 40 and 45 dB SPL at 25 and 35 dB HL, respectively.

Direct measurement of ear canal volume in a pediatric population: Can we explain its individual variation in terms of age and body weight?

ObjectiveThe aim of this work was to measure the external auditory canal (EAC) volume in children directly and to analyze its variation according to age and body weight. MethodsThis was a prospective study at a university-based, secondary referral hospital. Volumes of the bony and cartilaginous EACs were measured using a 1ml tuberculin syringe filled with 95% ethyl alcohol before inserting ventilation tube(s). Three hundred thirty-eight ears from 194 children (107 boys and 87 girls) were enrolled in this study (mean age=58.8±25.2months). They were between the 10th and 90th percentiles for age and gender based on the 2007 growth chart for Korean children. ResultsEAC volume tended to increase with age. The volumes of cartilaginous and total EACs were significantly larger in boys than in girls. The volume of the bony EAC was significantly larger in right than in left ears. Under the assumption that EAC volume is a linear function of age as well as body weight, these factors explained less than one-third of overall variation. Preferably, the growth of EAC seemed to be not linear with aging in pediatric population. ConclusionsOur cubic model seemed to be more fit to the growth of EAC than simple linear model did and age and body weight alone were not clinically useful predictors of ear canal volume needed for the fitting of hearing aids in pediatric population. Because this variation can result in a large variation of real ear to coupler difference (RECD), this study supports that individual measurement of the RECD is crucial for fitting appropriate hearing aids in children.

METHOD OF OBTAINING SETTINGS OF A HEARING INSTRUMENT, AND A HEARING INSTRUMENT

According to the invention, a real ear acoustic coupling quantity representative of the acoustic coupling of a hearing instrument to the user's ear or an anatomical transfer quantity—for example the Real-Ear-to-Coupler-Difference (RECD), the Microphone Location Effect (MLE), the Coupler Response for Flat Insertion Gain (CORFIG), and/or the Real Ear Open Gain (REOG)—is obtained from a transfer function representative of an acoustic transfer from the receiver to the outer microphone such as a signal feedback threshold gain. The obtained quantity may be used for setting a fitting parameter of the hearing instrument, for example a gain correction.