Is the real-ear to coupler difference independent of the measurement earphone?

Direct measurement of real-ear hearing aid performance can be obtained using a probe tube microphone system. Alternatively, it can be derived by adding the real-ear to coupler difference (RECD) to the electroacoustic performance of the hearing instrument measured in a 2-cc coupler. Inherent in this derivation is the assumption that the RECD measured with one transducer can be applied to a coupler measurement performed with a different transducer. For the RECD procedure to be valid, it should be independent of the measurement transducer. The Audioscan RM500 is an example of a commercially available real-ear measurement system that incorporates a clinical protocol for the measurement of the RECD. The RECD can be measured on the Audioscan RM500 using a standard EAR-Tone ER-3A insert earphone or the Audioscan's own RE770 insert earphone. The aim of this study was to compare the RECDs obtained with these two earphones. The Audioscan RM500 was used to measure the RECD from the right ears of 18 adult subjects ranging in age from 22 to 36 years (mean 25 years). Measurements were made with the EAR-Tone ER-3A and RE770 insert earphone and three earmould configurations: (1) the EARLINK foam ear-tip; (2) a hard acrylic shell earmould with the same length of acoustical tubing as the foam ear-tip (25 mm); and (3) the shell ear mould with the appropriate length of tubing for a behind-the-ear (BTE) hearing aid fitting (approximately 35-45 mm). The results show that the mean RECD was around 3 dB higher at 1.5 kHz with the foam ear-tip when measured with the RE770 earphone than when measured with the ER-3A earphone. The same magnitude of difference was obtained with the shell earmould and 25-mm tubing; however, this increased to 9 dB when the tubing was increased to around 40 mm for a BTE fitting. The difference in mean RECD with the two earphones was statistically significant on a repeated-measures ANOVA for every earmould configuration (p<0.001). The results of this study demonstrate that the RECD procedure that uses an HA2 coupler and earmould is not independent of the measurement earphone. This has important implications for clinical practice.     

Earphone termination and the response of behind-the-ear hearing aids.

An investigation was carried out on the effects on hearing aid response of placing the earphone in the earmould rather than in the case of a behind-the-ear hearing aid. Results from a number of physical configurations are reported and discussed and it is shown that it is possible to achieve a considerable reduction in the height of frequency response peaks. On the basis of the research reported some specific recommendations are made about future aid design.     

In situ measurements for determining the effect of additional boring of the earmold

To investigate the effect of earmould venting on the insertion gain of hearing aids in patients' ear canal, the authors sealed 35 earmould ventings with soft silicone after measurement under normal conditions and repeated the measurement. The size of the ventings varied from 0.8 mm to 3.5 mm in diameter. The results show the expected SPL-reducing effect of the ventings between 500 Hz and 1,000 Hz. Below 500 Hz the effect found was only slight, because of the low amplification in this frequency range. Above 1 kHz an increasing sound pressure level was measured as a result of resonance effects. This study illustrates the effect of earmould venting on insertion gain. To improve the hearing aid fitting the earmould venting should be used, deliberately and specifically, far more often than at present. The resulting effects of earmould modifications of real ear gain can only be determined by in situ measurements on the patient's eardrum. This method also enables resonance to be compensationed for in a controlled manner.     

Middle ear pathology can affect the ear-canal sound pressure generated by audiologic earphones

OBJECTIVE: To determine how the ear-canal sound pressures generated by earphones differ between normal and pathologic middle ears. DESIGN: Measurements of ear-canal sound pressures generated by the Etymtic Research ER-3A insert earphone in normal ears (N = 12) were compared with the pressures generated in abnormal ears with mastoidectomy bowls (N = 15), tympanostomy tubes (N = 5), and tympanic-membrane perforations (N = 5). Similar measurements were made with the Telephonics TDH-49 supra-aural earphone in normal ears (N = 10) and abnormal ears with mastoidectomy bowls (N = 10), tympanostomy tubes (N = 4), and tympanic-membrane perforations (N = 5). RESULTS: With the insert earphone, the sound pressures generated in the mastoid-bowl ears were all smaller than the pressures generated in normal ears; from 250 to 1000 Hz the difference in pressure level was nearly frequency independent and ranged from -3 to -15 dB; from 1000 to 4000 Hz the reduction in level increased with frequency and ranged from -5 dB to -35 dB. In the ears with tympanostomy tubes and perforations the sound pressures were always smaller than in normal ears at frequencies below 1000 Hz; the largest differences occurred below 500 Hz and ranged from -5 to -25 dB. With the supra-aural earphone, the sound pressures in ears with the three pathologic conditions were more variable than those with the insert earphone. Generally, sound pressures in the ears with mastoid bowls were lower than those in normal ears for frequencies below about 500 Hz; above about 500 Hz the pressures showed sharp minima and maxima that were not seen in the normal ears. The ears with tympanostomy tubes and tympanic-membrane perforations also showed reduced ear-canal pressures at the lower frequencies, but at higher frequencies these ear-canal pressures were generally similar to the pressures measured in the normal ears. CONCLUSIONS: When the middle ear is not normal, ear-canal sound pressures can differ by up to 35 dB from the normal-ear value. Because the pressure level generally is decreased in the pathologic conditions that were studied, the measured hearing loss would exaggerate substantially the actual loss in ear sensitivity. The variations depend on the earphone, the middle ear pathology, and frequency. Uncontrolled variations in ear-canal pressure, whether caused by a poor earphone-to-ear connection or by abnormal middle ear impedance, could be corrected with audiometers that measure sound pressures during hearing tests.     

Factors affecting the use and perceived benefit of ITE and BTE hearing aids.

The aim of the present study was to investigate factors that might affect hearing aid use, satisfaction and perceived benefit. A further aim was to look at which variables affect the choice of hearing aid, in particular, an in-the-ear (ITE) versus a behind-the-ear (BTE) device. Twenty-nine elderly hearing-impaired people with a mild-to-moderate hearing loss were fitted with both an ITE and a BTE hearing aid with similar electroacoustic performance. Both hearing aids were linear with output compression limiting and were fitted in a randomized order. After wearing each device for a six-week period, subj ets were asked to select the hearing aid they preferred. Variables significantly related to hearing aid choice, use and perceived benefit included ease of management, accuracy with which the NAL-R insertion gain target was achieved, earmould comfort and the type of hearing aid the client preferred initially.     

Audiometric earphone discomfort level and hearing aid saturation sound pressure level for a 90 decibel input signal (SSPL90) as measured in the human ear canal

The acoustical problems involved in matching the saturation sound pressure level for a 90 dB input signal (SSPL90) of a hearing aid to individual discomfort level were investigated. The real ear SPL (RE/SSPL90) produced by a supra-aural earphone used when measuring uncomfortable loudness (UCL), and RE/SSPL90 produced by three different hearing aids at 90 dB SPL input, were measured for nine subjects, using a miniature microphone technique, and compared to the corresponding coupler levels used when matching hearing aid maximum output to UCL. It was found that a hearing aid often gives about 5 dB, and sometimes 10 dB, higher RE/SPLs than the earphone, if the hearing aid output levels, as measured in a 2-cc coupler (IEC126), are equal to the earphone output levels as measured in a 6-cc coupler (NBS9A). It is recommended that a safety margin of at least 5 dB be used in the preliminary fitting when matching hearing aid SSPL90 to the patient's UCL, converted to dB SPL.     

The effect on speech intelligibility of varying compression time constants in a digital hearing aid

The identification of nonsense syllables in quiet and in three types of background (babble, cafeteria and single female speaker) was measured using four hearing aid compression algorithms differing in attack and release time constants, and using linear amplification. The speech level was always 65 dB SPL. The compression algorithms, which were implemented in a Phonak Claro ITE hearing aid, were: (1) 'very fast'--the attack time was 8 ms and the release time was 32 ms, for all 20 channels; (2) 'slow-fast'--the attack and release times decreased from 500 ms for low frequencies to about lOOms for high frequencies; (3) 'fast-slow'-the attack and release times increased from about 50ms for low frequencies to 500 ms for high frequencies; and (4) 'slow + fast'-a very slow-acting gain control signal was combined with a fast-acting gain control signal, for each channel in a 10-channel system. Acoustical stimuli were presented monaurally via a circumaural headphone mounted over the hearing aid. The linear condition did not use the Claro aid; instead, the signal was digitally filtered to implement the Cambridge formula prior to delivery via the earphone. Five subjects with moderate sensorineural hearing loss were tested in a counter-balanced order across conditions. In quiet, performance was best for linear amplification and worst for the slow + fast algorithm. In the presence of background sounds, the highest scores were obtained with the linear-gain Cambridge formula implemented via headphones; a supplementary experiment suggested that this was due to the greater high-frequency gain resulting from the use of this formula. No significant differences were found between scores for the different compression algorithms. We conclude that the intelligibility of speech at a fixed level, presented in background sounds, is not markedly affected by rather substantial variations of the time constants in a multichannel compression system.     

Use of the 'real-ear to dial difference' to derive real-ear SPL from hearing level obtained with insert earphones

The electroacoustic characteristics of a hearing instrument are normally selected for individuals using data obtained during audiological assessment. The precise inter-relationship between the electroacoustic and audiometric variables is most readily appreciated when they have been measured at the same reference point, such as the tympanic membrane. However, it is not always possible to obtain the real-ear sound pressure level (SPL) directly if this is below the noise floor of the probe-tube microphone system or if the subject is unco-operative. The real-ear SPL may be derived by adding the subject's real-ear to dial difference (REDD) acoustic transform to the audiometer dial setting. The aim of the present study was to confirm the validity of the Audioscan RM500 to measure the REDD with the ER-3A insert earphone. A probe-tube microphone was used to measure the real-ear SPL and REDD from the right ears of 16 adult subjects ranging in age from 22 to 41 years (mean age 27 years). Measurements were made from 0.25 kHz to 6 kHz at a dial setting of 70 dB with an ER-3A insert earphone and two earmould configurations: the EAR-LINK foam ear-tip and the subjects' customized skeleton earmoulds. Mean REDD varied as a function of frequency but was typically approximately 12 dB with a standard deviation (SD) of +/- 1.7 dB and +/- 2.7 dB for the foam ear-tip and customized earmould, respectively. The mean test-retest difference of the REDD varied with frequency but was typically 0.5 dB (SD 1 dB). Over the frequency range 0.5-4 kHz, the derived values were found to be within 5 dB of the measured values in 95% of subjects when using the EAR-LINK foam ear-tip and within 4 dB when using the skeleton earmould. The individually measured REDD transform can be used in clinical practice to derive a valid estimate of real-ear SPL when it has not been possible to measure this directly.     

The effect on speech intelligibility of varying compression time constants in a digital hearing aid

The identification of nonsense syllables in quiet and in three types of background (babble, cafeteria and single female speaker) was measured using four hearing aid compression algorithms differing in attack and release time constants, and using linear amplification. The speech level was always 65 dB SPL. The compression algorithms, which were implemented in a Phonak Claro ITE hearing aid, were: (1) ‘very fast’—the attack time was 8 ms and the release time was 32 ms, for all 20 channels; (2) ‘slow–fast’—the attack and release times decreased from 500 ms for low frequencies to about 100 ms for high frequencies; (3) ‘fast–slow’—the attack and release times increased from about 50 ms for low frequencies to 500 ms for high frequencies; and (4) ‘slow+fast’—a very slow-acting gain control signal was combined with a fast-acting gain control signal, for each channel in a 10-channel system. Acoustical stimuli were presented monaurally via a circumaural headphone mounted over the hearing aid. The linear condition did not use the Claro aid; instead, the signal was digitally filtered to implement the Cambridge formula prior to delivery via the earphone. Five subjects with moderate sensorineural hearing loss were tested in a counter-balanced order across conditions. In quiet, performance was best for linear amplification and worst for the slow+fast algorithm. In the presence of background sounds, the highest scores were obtained with the linear-gain Cambridge formula implemented via headphones; a supplementary experiment suggested that this was due to the greater high-frequency gain resulting from the use of this formula. No significant differences were found between scores for the different compression algorithms. We conclude that the intelligibility of speech at a fixed level, presented in background sounds, is not markedly affected by rather substantial variations of the time constants in a multichannel compression system.     

Perceived sound quality in a hearing aid with vented and closed earmould equalized in frequency response.

Nine normal-hearing subjects listened to speech and music in a hearing aid, either through a vented earmould or a closed earmould. The complex frequency responses of the two systems were made equal by compensating the aid and closed mould combination with a digital filter. The subjects rated the perceived sound quality of the systems on seven perceptual scales and a scale for overall impression. The results of the ratings support the hypothesis that there is no difference in perceived sound quality between vented and closed earmoulds that are equalized in frequency response, provided that the perceived loudness is the same in both cases.     

Zur Effektivität der Hörgeräteversorgung

Summary By means of a questionnaire the utilization of hearing aids has been investigated in 550 patients who had received their aids in a way being typical for the Federal Republic of Germany, i.e., first prescribed by the ENT-specialist and then fitted by the hearing aid acoustician. An additional goal was to analyze relevant factors influencing the use of hearing aids. 45% of the patients used their aids always, 52% regularly (on special occasions) and 3,1% never. The most common complaints of patients refusing their hearing aid were disturbing noise and unsatisfactory understanding. A relatively better utilization of hearing aids — as compared with the average use of the whole group — was found in children and in patients with severe and conductive hearing losses, with aids on both ears or with aids having a PC-circuit or dynamic compression. Relatively lower utilization was seen in patients older than 60 years, in workmen and in patients wearing an hearing aid on the worse ear. Further factors related to less regular use were: mild hearing loss and hightone deafness, bone conductive earphone, eyeglass hearing aid and AVC-circuit. There was no correlation between the degree of utilization and the monosyllable discrimination score.     

Factors relating to the under-use of postaural hearing aids

All adult patients issued at Withington Hospital with NHS postaural hearing aids in 1980 (n = 731) were reviewed. Efforts were made to determine the reasons for under-use and dissatisfaction among those who were not using the aid at all or using it minimally and with low satisfaction. The major presenting reason for non-use, accounting for over a quarter of all non-users, was inability to insert the earmould. The next most common reason for non-use and the major reason for poor satisfaction in low level users was related to difficulty in coping with signals in noise. Other significant factors contributing to poor or non-use were (1) lack of recognition of hearing impairment, (2) advanced age and poor health, (3) less than ideal matching of the aid to the loss of hearing. The percentage of under-users was significantly reduced by hearing aid orientation and counselling. Further reduction might be achieved if attitudes to hearing loss among those affected and concerned professionals could be improved so that early referral and treatment became the norm rather than the exception.     

Measuring the real-ear to coupler difference transfer function with an insert earphone and a hearing instrument: are they the same?

OBJECTIVE: The purpose of the study was to compare the real-ear to coupler difference (RECD) measured with an insert earphone and two models of hearing instrument. DESIGN: The RECD was obtained from one ear of 18 normal-hearing subjects by subtracting the 2-cc coupler (HA1 and HA2) response from a real-ear aided response, using a conventional probe-tube microphone system. The measurements were made with a conventional ER-3A earphone and two models of behind-the-ear hearing instrument (Unitron US80, Unitron, Kitchener, Canada; and Widex Diva, Widex, Vaerloese, Denmark). RESULTS: The procedures were very reliable, with mean differences on retest of less than 1 dB. There were statistically significant differences between the mean RECDs obtained using an insert earphone compared with those obtained with each hearing instrument (p < 0.05). The differences were greatest when using the HA2 2-cc coupler. For example, the maximum difference in mean RECD between the insert earphone and the Widex Diva was 6 dB and 11 dB when using the HA1 and the HA2 2-cc coupler, respectively. CONCLUSIONS: The RECD is dependent on the acoustic impedance of the sound source, the coupling system, and the coupler and ear. The acoustic impedance may be different for an insert earphone and a given hearing instrument. Therefore, the RECD measured with an insert earphone may not always accurately represent the difference in performance of a hearing instrument measured in the real ear and the 2-cc coupler.     

The real ear effect of adjusting the tone control and venting a hearing aid system

The effect of modifying the frequency response of a hearing aid system has previously been reported only on 2 cc couplers. Although it is recognized that coupler measurements do not accurately reflect real ear measures, they are frequently quoted when describing the effect of modifying a hearing aid system. To investigate the correlation, the real ear effect was assessed in 43 ears by measuring the effect on the insertion gain of adjusting the tone control of a hearing aid and acoustically venting the mould with a 2 mm parallel vent, singly and in combination. The results were considerably different from those measured in couplers. By comparing insertion gain with 2 cc coupler gain measurements, it was found that: (1) adjusting the tone control had a lesser mean effect than predicted; (2) venting the earmould with a 2 mm parallel vent produced a mean reduction in the frequency response at 0.75 to 1 kHz of 8 dB SPL; (3) by combining a 2 mm earmould vent and adjusting the tone control, a mean reduction in the frequency response of 10 dB SPL was produced at 0.75 to 1 kHz. In addition, the range of acoustical effects was considerable, from virtually none to greater than those predicted in coupler experiments. This was presumably due to variation in the anatomy of normal canals. It is concluded that for both research and clinical purposes, the effect of modifying the frequency response of a hearing aid system should be measured by insertion gain rather than predicted from laboratory results.     

Changing systems of amplification

This paper reports on the changing systems of amplification used by hearing-impaired children in the last decade (1977 to 1987). The major changes noted were in terms of ear-level v. body-worn hearing aids, monaural v. binaural hearing aids and FM-wireless v. hardwire group hearing aids (GHAs). There was an increase in the use of ear-level hearing aids, binaural hearing aids and FM-wireless hearing aids with a corresponding decrease in the use of body-worn hearing aids and hardwire GHAs.     

Test-retest reliability of in situ unaided thresholds in adults

PURPOSE: The purpose of this study was to examine test-retest reliability of in situ unaided thresholds measured using a handheld hearing aid programmer coupled to a hearing aid transducer in adults with normal hearing. METHOD: Randomized in situ thresholds at 4 octave frequencies were established in 1 ear of 43 adults twice using the Widex Diva SP3 device with the stimulus generated by and transduced through a Widex Diva SD-9 behind-the-ear hearing aid. Insert earphone tips were used in each of the measures to couple the hearing aid/transducer to the ear canal. RESULTS: Mean decibel differences between the test and retest thresholds were less than 1 dB at each frequency. Using an 80% statistical test criterion, results revealed test-retest reliability within 5 dB for all frequencies: 98% at 500 Hz, 100% at 1000 and 2000 Hz, and 93% at 4000 Hz. CONCLUSIONS: Test-retest reliability of in situ unaided thresholds using the SP3/SD-9 device is equivalent to that of currently accepted audiometric procedures.