Real Ear Measurements Research Articles

Development of the speech test signal in Brazilian Portuguese for real-ear measurement

Objective: Recommended practice is to verify the gain and/or output of hearing aids with speech or speech-shaped signals. This study has the purpose of developing a speech test signal in Brazilian Portuguese that is electroacoustically similar to the international long-term average speech spectrum (ILTASS) for use in real ear verification systems. Design: A Brazilian Portuguese speech passage was recorded using standardized equipment and procedures for one female talker and compared to ISTS. The passage consisted of simple, declarative sentences making a total of 148 words. Study sample: The recordings of a Brazilian Portuguese passage were filtered to the ILTASS and compared to the International Speech Test Signal (ISTS). Aided recordings were made at three test levels, for three audiograms for the Brazilian Portuguese passage and the ISTS. Results: The unaided test signals were spectrally matched to within 0.5 dB. Aided evaluation revealed that the Brazilian Portuguese passage produced aided spectra that were within 1 dB on average, within about 2 dB per audiogram, and within about 3 dB per frequency for 95% of fittings. Conclusion: Results indicate that the Brazilian Portuguese passage developed in this study provides similar electroacoustic hearing-aid evaluations to those expected from the standard ISTS passage.

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.

Pole-zero modeling of the middle ear based on acoustic reflectance measurements

Fitting poles and zeros to complex acoustic reflectance (CAR) data using a “rational approximation method” [Gustavsen and Semlyen (1999)] allows for a precise parameterization of complex real-ear measurements. CAR is measured using a foam-tipped probe sealed in the ear canal, containing a microphone and receiver (i.e., MEPA3 system, Mimosa Acoustics). From the complex pressure response to a broadband stimulus, the acoustic impedance and reflectance of the middle ear can be calculated as functions of frequency. The goal of this work is to establish a quantitative connection between the fitted pole-zero locations and underlying physical properties of the CAR and impedance of the middle ear. It was found that (1) the contribution of the ear canal may be approximated as the lossless all-pass component of the factored reflectance fit, (2) individual CAR magnitude variations for normal middle ears in the 1 to 4 kHz range give rise to closely placed pole-zero pairs, and (3) the locations of the poles and zeros in the s-plane may differ between normal and pathological middle ears. Pole-zero fitting allows for concise characterization of individual CAR measurements, providing a foundation for modeling individual and pathological variations of middle ears.

Characterizing the ear canal acoustic impedance and reflectance by pole-zero fitting

This study characterizes middle ear complex acoustic reflectance (CAR) and impedance by fitting poles and zeros to real-ear measurements. The goal of this work is to establish a quantitative connection between pole-zero locations and the underlying physical properties of CAR data. Most previous studies have analyzed CAR magnitude; while the magnitude accounts for reflected power, it does not encode latency information. Thus, an analysis that studies the real and imaginary parts of the data together, being more general, should be more powerful. Pole-zero fitting of CAR data is examined using data compiled from various studies, dating back to Voss and Allen (1994). Recent CAR measurements were taken using the Mimosa Acoustics HearID system, which makes complex acoustic impedance and reflectance measurements in the ear canal over a 0.2–6.0 [kHz] frequency range. Pole-zero fits to measurements over this range are achieved with an average RMS relative error of less than 3% with 12 poles. Factoring the reflectance fit into its all-pass and minimum-phase components estimates the effect of the residual ear canal, allowing for comparison of the eardrum impedance and admittance across measurements. It was found that individual CAR magnitude variations for normal middle ears in the 1–4 [kHz] range often give rise to closely-placed pole-zero pairs, and that the locations of the poles and zeros in the s-plane may systematically differ between normal and pathological middle ears. This study establishes a methodology for examining the physical and mathematical properties of CAR using a concise parametric model. Pole-zero modeling accurately parameterizes CAR data, providing a foundation for detection and identification of middle ear pathologies.This article is part of a Special Issue entitled “MEMRO 2012”.

Real-ear output measures of ear level fluency devices

Objective: The purpose of this study was to measure real-ear aided and saturated responses of SpeechEasy™ devices and compare responses while devices delivered altered auditory feedback (AAF) and non-altered feedback (NAF). Design: A repeated measures quasi-experimental design was employed. Study sample: Ten people fitted with completely-in-the-canal or open fit behind-the-ear devices participated. Probe microphone measures were obtained with speech, and 17 chirp stimuli presented at 75 dB and 85 dB SPL, respectively. Measurements were compared with devices delivering AAF (i.e. delayed and frequency shifted) versus NAF. Results: Maximum outputs were approximately 100–105 dB SPL in the 2000–4000 Hz range. Statistically significant differences in device SPL output as a function of device setting (AAF vs. NAF) were found for seven chirp stimuli (p <.05) when levels were sampled at points that were not temporally aligned with the output chirps but not for speech stimulus (p = .17). Device output varied across individuals and with open fit devices dominated by ear canal resonance effects. Conclusions: Real-ear aided responses were equivalent with speech input when devices delivered AAF and NAF. Real-ear saturated responses were not, however, comparable between AAF and NAF settings and may be underestimated if AAF delay is not accounted for.

Optimizing the Combination of Acoustic and Electric Hearing in the Implanted Ear

The aim of this study was to determine an optimal approach to program combined acoustic plus electric (A+E) hearing devices in the same ear to maximize speech-recognition performance. Ten participants with at least 1 year of experience using Nucleus Hybrid (short electrode) A+E devices were evaluated across three different fitting conditions that varied in the frequency ranges assigned to the acoustically and electrically presented portions of the spectrum. Real-ear measurements were used to optimize the acoustic component for each participant, and the acoustic stimulation was then held constant across conditions. The lower boundary of the electric frequency range was systematically varied to create three conditions with respect to the upper boundary of the acoustic spectrum: Meet, Overlap, and Gap programming. Consonant recognition in quiet and speech recognition in competing-talker babble were evaluated after participants were given the opportunity to adapt by using the experimental programs in their typical everyday listening situations. Participants provided subjective ratings and evaluations for each fitting condition. There were no significant differences in performance between conditions (Meet, Overlap, Gap) for consonant recognition in quiet. A significant decrement in performance was measured for the Overlap fitting condition for speech recognition in babble. Subjective ratings indicated a significant preference for the Meet fitting regimen. Participants using the Hybrid ipsilateral A+E device generally performed better when the acoustic and electric spectra were programmed to meet at a single frequency region, as opposed to a gap or overlap. Although there is no particular advantage for the Meet fitting strategy for recognition of consonants in quiet, the advantage becomes evident for speech recognition in competing-talker babble and in patient preferences.

Reliability of real ear insertion gain in behind-the-ear hearing aids with different coupling systems to the ear canal

Objective: The last decade has offered a multitude of instant fit coupling systems to be fitted with behind-the-ear (BTE) hearing aids. The impact of these designs on the reliability of real ear measurements (REMs) has not been reported. The purpose of this study was to obtain REM reliability data for instant fit coupling systems. Design: REM reliability data was obtained for four different instant-fit coupling systems and for standard size 13 tubing and custom earmolds. REMs were performed for all five coupling systems two times and by two examiners. Study sample: Ten normal-hearing individuals (20 ears) served as participants. Results: The REM test-retest reliability is high for the four instant fit coupling systems as well as for the custom earmolds. The REM inter-examiner reliability is high for three of the four instant fit coupling systems. Conclusions: Carrying out REMs with instant fit coupling systems appears to be fundamentally no different than performing REMs with conventional hearing aids. For either, care should be taken in probe tube placement in terms of insertion depth and maintaining the probe tube placement, and other best practices regarding test environment and test setup should be observed.

REAL EAR MEASUREMENT ADAPTOR WITH INTERNAL SOUND CONDUIT

Methods and apparatus for a hearing assistance device housing for use in real ear measurements. The methods and apparatus for configuration of a hearing assistance device using an apparatus including an opening to receive a sound tube for real ear measurements and providing an opening for connection of a sound hook to a housing of the hearing assistance device.

REAL EAR MEASUREMENT SYSTEM USING THIN TUBE

An embodiment of a hearing assistance apparatus for performing a Real Ear Measurement (REM), comprises a hearing assistance device housing, a microphone within the housing, an earhook connected to the housing, and a flexible tube. The house has a first opening for guiding sound into the housing to the microphone. The housing and the connected earhook form an interface, where the earhook has a shape to provide a slot near the interface of the housing and the earhook. The tube guides sound, and has a first end and a second end. The first end of the flexible tube and the slot of the earhook cooperate to retain the first end of the flexible tube in the slot of the earhook and flush with the housing to provide a sound-tight connection with the first opening.

A Study of Hearing Aid Fitting Characteristics in Patients with Eardrum Perforation

The purpose of this study was to describe hearing aid fitting characteristics and the effects of fitting when using RECD in patients with a tympanic membrane (TM) perforation. 10 subjects with TM perforations and 8 subjects with intact TM participated in this study. RECDs were measured by using a real ear measurement system and used in fitting hearing aids through Speechmap program. Electroacoustic analysis including OSPL 90 and RESP 50 were performed in both Test-box and On-ear conditions. Aided sound field thresholds were also obtained in both conditions. There were no significant differences in hearing aid fitting characteristics and sound field aided thresholds in both Test-box and On-ear conditions for the intact TM group. However, significant differences were shown at lower frequencies below 1,000 Hz for the perforated ears in these conditions. Individual RECD is needed especially for patients with TM perforation because it can prevent from underamplification. These results suggest that individual RECD measurements are strongly recommended in fitting a hearing aid for its best outcome.

Using Average Correction Factors to Improve the Estimated Sound Pressure Level Near the Tympanic Membrane

Sound pressure-based real ear measurements are considered best practice for ensuring audibility among individuals fitting hearing aids. The accuracy of current methods is generally considered clinically acceptable for frequencies up to about 4 kHz. Recent interest in the potential benefits of higher frequencies has brought about a need for an improved, and clinically feasible, method of ensuring audibility for higher frequencies. To determine whether (and the extent to which) average correction factors could be used to improve the estimated high-frequency sound pressure level (SPL) near the tympanic membrane (TM). For each participant, real ear measurements were made along the ear canal, at 2-16 mm from the TM, in 2-mm increments. Custom in-ear monitors were used to present a stimulus with frequency components up to 16 kHz. Twenty adults with normal middle-ear function participated in this study. Two methods of creating and implementing correction factors were tested. For Method 1, correction factors were generated by normalizing all of the measured responses along the ear canal to the 2-mm response. From each normalized response, the frequency of the pressure minimum was determined. This frequency was used to estimate the distance to the TM, based on the ¼ wavelength of that frequency. All of the normalized responses with similar estimated distances to the TM were grouped and averaged. The inverse of these responses served as correction factors. To apply the correction factors, the only required information was the frequency of the pressure minimum. Method 2 attempted to, at least partially, account for individual differences in TM impedance, by taking into consideration the frequency and the width of the pressure minimum. Because of the strong correlation between a pressure minimum's width and depth, this method effectively resulted in a group of average normalized responses with different pressure-minimum depths. The inverse of these responses served as correction factors. To apply the correction factors, it was necessary to know both the frequency and the width of the pressure minimum. For both methods, the correction factors were generated using measurements from one group of ten individuals and verified using measurements from a second group of ten individuals. Applying the correction factors resulted in significant improvements in the estimated SPL near the TM for both methods. Method 2 had the best accuracy. For frequencies up to 10 kHz, 95% of measurements had <8 dB of error, which is comparable to the accuracy of real ear measurement methods that are currently used clinically below 4 kHz. Average correction factors can be successfully applied to measurements made along the ear canals of otologically healthy adults, to improve the accuracy of the estimated SPL near the TM in the high frequencies. Further testing is necessary to determine whether these correction factors are appropriate for pediatrics or individuals with conductive hearing losses.

Difference between the Default Telecoil (T-Coil) and Programmed Microphone Frequency Response in Behind-the-Ear (BTE) Hearing Aids

A telecoil (t-coil) is essential for hearing aid users when listening on the telephone because using the hearing aid microphone when communicating on the telephone can cause feedback due to telephone handset proximity to the hearing aid microphone. Clinicians may overlook the role of the t-coil due to a primary concern of matching the microphone frequency response to a valid prescriptive target. Little has been published to support the idea that the t-coil frequency response should match the microphone frequency response to provide "seamless" and perhaps optimal performance on the telephone. If the clinical goal were to match both frequency responses, it would be useful to know the relative differences, if any, that currently exist between these two transducers. The primary purpose of this study was to determine if statistically significant differences were present between the mean output (in dB SPL) of the programmed microphone program and the hearing aid manufacturer's default t-coil program as a function of discrete test frequencies. In addition, pilot data are presented on the feasibility of measuring the microphone and t-coil frequency response with real-ear measures using a digital speech-weighted noise. A repeated-measures design was utilized for a 2-cc coupler measurement condition. Independent variables were the transducer (microphone, t-coil) and 11 discrete test frequencies (15 discrete frequencies in the real-ear pilot condition). The study sample was comprised of behind-the-ear (BTE) hearing aids from one manufacturer. Fifty-two hearing aids were measured in a coupler condition, 39 of which were measured in the real-ear pilot condition. Hearing aids were previously programmed and verified using real-ear measures to the NAL-NL1 (National Acoustic Laboratories-Non-linear 1) prescriptive target by a licensed audiologist. Hearing aid output was measured with a Fonix 7000 hearing aid analyzer (Frye Electronics, Inc.) in a HA-2 2-cc coupler condition using a pure-tone sweep at an input level of 60 dB SPL with the hearing aid in the microphone program and 31.6 mA/M in the t-coil program. A digital speech weighted noise input signal presented at additional input levels was used in the real-ear pilot condition. A mixed-model repeated-measures analysis of variance (ANOVA) and the Tukey Honestly Significant Difference (HSD) post hoc test were utilized to determine if significant differences were present in performance across treatment levels. There was no significant difference between mean overall t-coil and microphone output averaged across 11 discrete frequencies (F(1,102) = 0, p < 0.98). A mixed-model repeated-measures ANOVA revealed a significant transducer by frequency interaction (F(10,102) = 13.0, p < 0.0001). Significant differences were present at 200 and 400 Hz where the mean t-coil output was less than the mean microphone output, and at 4000, 5000, and 6300 Hz where the mean t-coil output was greater than the mean microphone output. The mean t-coil output was significantly lower than the mean microphone output at 400 Hz, a frequency that lies within the typical telephone bandwidth of 300-3300 Hz. This difference may partially help to explain why some patients often complain the t-coil fails to provide sufficient loudness for telephone communication.

Telessaúde: avaliação da eficácia da teleconsulta na programação e adaptação de aparelho de amplificação sonora individual

To evaluate teleconsultation's efficacy for hearing aid fitting. Fifty hearing impaired individuals with ages ranging from 39 to 88 years and mean audiometric thresholds between 30 and 68.75 dBHL participated in this study. Participants were divided into two groups (stratified randomization): control group (n=25), submitted to face-to-face procedures, and experimental group (n=25), submitted to synchronous teleconsultation with interactive video and remote applicative control. The hearing aids were programmed and verified (with microphone probe), and the subjects received instructions regarding use and care for the device. Time taken for the procedures was measured. Following the consultations, an evaluator (blind to the groups) applied the Hearing in Noise Test (HINT-Brazil). Approximately one month after consultations, the daily time of hearing aid use was verified, and the International Outcome Inventory for Hearing Aids (IOI-HA) was administered. A greater time for programming and verification and a smaller time for orientation were observed for the experimental group. No difference was found between groups for the total consultation time. The real ear measures' matching to their respective targets was similar for both groups. No difference was observed between groups for the HINT results (silence and noise), the daily amount of use of hearing aids in hours, and the IOI-HA scores. Teleconsultation is an efficient procedure for hearing aid programming, verification and fitting when face-to-face services are not available.

Effect of Active Noise Cancelling Earphones on Preferred Listening Level When Listening to Portable Music Players in Noisy Environments

Background and ObjectivesZZActive noise cancelling (ANC) is a technology that can reduce external noise by producing a signal that is similar to noise but different in that it has an opposite phase to noise. Nowadays ANC has become an important technology in the field of hearing aids, but many studies have not focused on the effect of ANC of earphones when listening to portable music players. In this study, we aimed to evaluate whether ANC earphones can effectively reduce external noise and lower the preferred listening level. Subjects and MethodZZThree different earphones (Ear-canal, On-the-ear, Covering-theear) were tested in three different noise environments. Nine participants were tested in 10 experiments. First, through the real ear measurement (REM) system, we evaluated the differences in sound pressure level when the ANC was either turned on or off. Second, we evaluated the effects of ANC on Preferred Listening Level (PLL) for participants listening to the same song with different earphones. Through the REM system, we evaluate the level of sound pressure level when participants controlled the volume and felt most comfortable with the volume level.

Audiologist-Driven Versus Patient-Driven Fine Tuning of Hearing Instruments

Two methods of fine tuning the initial settings of hearing aids were compared: An audiologist-driven approach--using real ear measurements and a patient-driven fine-tuning approach--using feedback from real-life situations. The patient-driven fine tuning was conducted by employing the Amplifit(®) II system using audiovideo clips. The audiologist-driven fine tuning was based on the NAL-NL1 prescription rule. Both settings were compared using the same hearing aids in two 6-week trial periods following a randomized blinded cross-over design. After each trial period, the settings were evaluated by insertion-gain measurements. Performance was evaluated by speech tests in quiet, in noise, and in time-reversed speech, presented at 0° and with spatially separated sound sources. Subjective results were evaluated using extensive questionnaires and audiovisual video clips. A total of 73 participants were included. On average, higher gain values were found for the audiologist-driven settings than for the patient-driven settings, especially at 1000 and 2000 Hz. Better objective performance was obtained for the audiologist-driven settings for speech perception in quiet and in time-reversed speech. This was supported by better scores on a number of subjective judgments and in the subjective ratings of video clips. The perception of loud sounds scored higher than when patient-driven, but the overall preference was in favor of the audiologist-driven settings for 67% of the participants.

Effect of Canal Depth on Sound Pressure Level Distribution in Human Bilateral Ears

This study was to measure the sound pressure level distribution by ear canal resonance in the human left and right external auditory canals (EAC). The gain for different stimulus frequencies was analyzed at four different measuring depths (0.5 cm, 1.0 cm, 1.5 cm and 2.0 cm) from the entrance of the ear canal bilaterally. Comparative evaluation showed that the gain for different stimulus frequencies at a depth of 2.0 cm was consistent with the results of Dillon’s study. In addition, the gain for the right EAC at 4000 Hz was larger than that of the left EAC by 1.2 dB at 0.5 cm, 1.8 dB at 1.0 cm, and 0.8 dB at 1.5 cm. This seems to suggest that gain at 4000 Hz is more affected by depth in the right EAC than in the left EAC. This study further found that the gain at the stimulus frequency of 4000 Hz was more affected by the depth than at 2000 Hz for the bilateral ear canals respectively. These gain differences between the right and left ears were statistically significant (p&lt;0.05) at any of four measuring depths. The findings of this study may have an understanding of gain distribution to have implications for microphone placement of custom-made bilateral hearing aids (i.e. ITC or CIC) as these are placed at different depths within the ear canal. Keywords: Sound pressure level; Canal depth; Ear canal resonance; Real ear measurement; External auditory canal

Real ear measurement methods for open fit hearing aids: Modified pressure concurrent equalization (MPCE) versus modified pressure stored equalization (MPSE)

Objective: The aim of this study was to assess differences between real ear insertion gains (REIG) measured with the modified pressure concurrent equalization (MPCE) and modified pressure stored equalization (MPSE) methods for open fittings in a typical audiology patient population. Design: REIGs were compared for the two methods using a warble tone sweep at 65 dB SPL. The differences between the two methods at 0.25, 0.5, 1, 2, 3, 4 and 6 kHz were recorded. Study sample: Eighty-three ears of a consecutive sample of 48 candidates for open-fit hearing aids were included. Results: The mean difference between MPSE and MPCE REIGs was less than 1 dB at all frequencies. Analysis of variance showed that the main effect of method was not significant, and there was no significant interaction between method and frequency. Conclusions: The results for the MPSE and MPCE methods did not differ significantly for the patients with mild-to-moderate hearing losses tested here, for whom REIGs were generally less than 20 dB. Further research is needed to identify the REIG values at which the differences between MPCE and MPSE methods become clinically significant.

Accuracy and Reliability of a Real-Ear-to-Coupler Difference Measurement Procedure Implemented within a Behind-the-Ear Hearing Aid

Measurement of the real ear response of a fitted hearing aid allows matching of the frequency response to prescriptive targets, as well as comparison of the response to both threshold and loudness discomfort level (LDL). These processes are recommended procedures for hearing aid fittings. The real ear aided response (REAR) is often predicted based on the coupler response of the device, the real-ear-to-coupler difference (RECD), and the microphone location effect (MLE). Individualized measurement of the RECD tends to increase the accuracy of this prediction. A commercial hearing aid has been developed that measures the individual RECD and incorporates the data into the software-assisted fitting process. This study evaluated the test-retest reliability and predictive validity of this particular method for measuring the RECD. A repeated measures design was used to evaluate differences between subsequent measures of the RECD in the same ear, and prediction differences associated with using the RECD (and other information) to predict the REAR. Fifteen ears, on a convenience sample of ten adults (45-86 yr) and five children (6-15 yr) were tested. All participants were hearing aid users. Predicted and measured REARs were collected using normal clinical procedures, on an Audioscan Verifit VF-1 for two test signals/levels. Reliability, mean differences between predicted and measured REARs, and 95% confidence intervals of the prediction accuracy are reported. The RECD procedure had test-retest reliability within 2.5 dB for 14 out of 15 ears between 500 and 4000 Hz, and had predictive accuracy within 5 dB between 500 and 4000 Hz for 14 out of 15 ears. However, errors associated with earhook misalignment were discovered. Also, the RECD values measured using this hearing-aid-specific procedure differ somewhat from the normative data available from insert earphone RECDs. This procedure, when measured according to recommendations, provides a reasonably accurate prediction of the REAR. Functionally, this procedure does not replace the range of measures offered by modern real ear measurement systems. However, given the inaccuracy of software-assisted fittings without a measure of individual ear canal acoustics, use of this procedure may have the potential to improve the accuracy of fittings versus fittings completed without real ear measurement.

Verificação da prótese auditiva realizada face a face e via teleconsulta: medidas repetidas

OBJETIVO: avaliar as medidas repetidas da resposta de ressonância da orelha externa sem (REUR) e com uso de amplificação (REAR) e o ganho de inserção (REIG), realizados face a face e via teleconsulta. MÉTODO: estudo prospectivo longitudinal. Foram realizadas quatro repetições da REUR, REAR e REIG (com estímulo speech noise apresentado em 65 dB NPS e 0º azimute) em 19 orelhas de adultos ouvintes normais, via face a face (F) e teleconsulta síncrona por controle remoto de aplicativo (T) e vídeo interativo. O software Polycom PVX foi utilizado para compartilhamento e transmissão de áudio e vídeo. A conexão foi realizada via LAN (Local Area Network) USP na velocidade de 384 kbps Foi calculado o erro causal (Dalhberg) entre as quatro medidas para frequências de 250 a 8000 Hz. RESULTADOS: os erros casuais entre as medidas F e T foram muito semelhantes, sendo maiores nas frequências acima de 4 kHz. As diferenças e variações entre as medidas F e T estavam dentro da magnitude de variabilidade do procedimento de medidas com microfone sonda. CONCLUSÃO: as medidas com microfone sonda via teleconsulta fornece resultados confiáveis e similares aos obtidos pelo procedimento padrão.

Gain Affected by the Interior Shape of the Ear Canal

This study investigated the correlation of gain distribution and the interior shape of the human external ear canal. Cross-sectional study of gain measurement at the first bend and second bend. Chang Gung Memorial Hospital and Chang Gung University. There were 15 ears in patients aged between 20 and 30 years (8 men/7 women) with normal hearing and middle ears. Stimulus frequencies of 500, 1000, 2000, 3000, and 4000 Hz were based on the standard clinical hearing test. Measurements closer to the tympanic membrane and the positions at the first and second bends were confirmed by using otoscope. Real ear measurement to analyze the canal resonance in human external ears was adopted. This study found that gain at stimulus frequencies of 4000 Hz was affected by the interior shape of the ear canal (P < .005), particularly at the first and second bends, whereas gain was only affected by the length of the ear canal for stimulus frequencies of 2000 Hz (P < .005). This study found that gain was affected not only by the length of the external auditory canal (EAC) but also by the interior shape of the EAC significantly. The findings of this study may have potential clinical applications in canalplasty and congenital aural atresia surgery and may be used to guide surgeries that attempt to reshape the ear canal to achieve more desirable hearing outcomes.