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.     

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.     

Physical and Subjective Correlates of Earmould Occlusion

Physical and subjective aspects of earmould occlusion are examined and related. In particular, measurements made in an ear-like coupler for various venting arrangements are compared with those obtained subjectively by a loudness balance procedure. The results demonstrate the effectiveness of an open (completely non-occluding) earmould at low-frequency sound reduction but indicate some of the factors which make its individual effect difficult to predict. It is further seen the group of hearing-impaired persons was less able to make systematic judgements on sound quality than was the control group of normally hearing persons.

Les facteurs physiques et subjectifs intervenant lors de l'emploi d'embouts d'appareils de correction auditive occlusifs ont été etudies et rapportés. Ont été comparés, en particulier, les mesures faites avec une oreille artiflcielle dans laquelle ont été aménagés plusieurs types d'ouvertures et les résultats obtenus subjectivement par balance alternée de la sonie. Les résultats démontrent l'efficacité de l'embout ouvert (sans occlusion aucune) pour les basses fréquences; mais, ils révèlent également un certain nombre de facteurs qui montrent que son effet peut varier d'un individu à l'autre. Nos résultats ont montré, par ailleurs, que les personnes souffrant de troubles de l'audition éprouvaient plus de difficultés à émettre des appréciations systématiques sur la qualité du son que le groupe témoin, composé de personnes jouissant d'une audition normale.     

Dynamic free-field headphone as hearing aid transducer. A preliminary report

A comparison between a body-worn hearing aid with a conventional earphone/earmould system, and a free-field dynamic headphone demonstrated the significance of the coupling between the hearing aid earphone and the subject's ear. Measurement of the insertion gain revealed destruction of the ear-canal resonance with a conventional earmould, whereas the ear-canal resonance was preserved by the use of a dynamic headphone. The use of a body-worn hearing aid connected to a dynamic headphone showed a greater amplification at low as well as at high frequencies. Furthermore, a significantly better discrimination score and an improved sound quality were demonstrated with the dynamic headphone.     

Acoustic evaluation of earmoulds in situ: a comparison of impression and earmould materials.

Laboratory research has been carried out on the accuracy of both ear impression and earmould materials. The present work was undertaken to assess such materials in vivo. An objective clinical method of earmould evaluation was developed, based on estimation of the attenuation in the acoustic feedback path. The method was used to assess the acoustic performance of earmoulds made from three earmould materials of different texture, when prepared from two different impression materials. It was shown that the choice of impression material made a significant difference to earmould performance. For greatest accuracy, addition cured silicone impression materials are recommended.     

Relationship between earmould venting, comfort and feedback

Although earmould venting is considered to make an earmould more comfortable, whether it does so remains to be proven in hearing-aid users. A hundred and six patients were sequentially fitted with a hearing aid in a randomized order with an unvented, a 0.8 mm vented or a 2 mm vented mould and questioned about various aspects of discomfort at the end of each trial period. The three moulds were equally uncomfortable (approximately 17% overall), moist (approximately 34% overall) and associated with an itchy sensation (approximately 36% overall). However, a 0.8 mm and a 2 mm vent significantly reduced the sensation of blockage from 35 to 22% (P less than 0.05) and 13% (P less than 0.001) respectively. A potential disadvantage of venting is feedback, but patients' reports of this can be confused with feedback due to incorrectly inserting the mould. A separate study showed that a 2 mm vent might cause feedback in approximately 10% of patients when used in conjunction with behind-the-ear aids whose maximum gain was 45 dB, but only when the gain was at 42 dB or greater.     

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.     

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.     

Problems with handling the BE10 series hearing aids among elderly people.

Seven items of activity related to patients' ability to handle behind-the-ear hearing aids (BE11/12) were investigated to establish the effects of age, sex and functional disability. One hundred and thirty-six patients were examined; all were first-time users of hearing aids. Over two-fifths of the sample had problems with manipulating the volume control and over a third had difficulty with inserting the earmould and changing the battery. For both men and women, the difficulties with the volume control and earmould were significantly associated with functional disability. Difficulties with these tasks were also significantly related to age and sex. Patients aged 75 years of age or more had greater difficulties than those who were younger and women had more difficulty than men.     

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.     

A comparison of the effects of different methods of impression build-up on earmoulds

An investigation was carried out into effects of three types of impression build-up (patting down of impressions, special earmould-maker build-up and the multistage impression technique) on the dimensions, static pressure seal, degree of acoustic seal and the subjective tightness and comfort of earmoulds. Patting down the impression significantly improved the degree of acoustic seal provided by earmoulds without making them feel tighter or less comfortable. However, special build-up was much more effective than patting down and the multistage impression technique was slightly more effective than special build-up in improving the degree of acoustic seal. The improvement in acoustic seal provided by both multistage and specially built-up earmoulds can usually be obtained without an unacceptable level of discomfort. Patting down the impression did not improve the chance of obtaining a static pressure seal. Special build-up of the impression by the earmould-maker significantly increased the proportion of earmoulds which provided a static pressure seal but an even higher proportion of earmoulds made from multistage impressions provided a seal. Dimension results indicated that an increase in earmould-maker build-up of the minor axis at the beginning of the canal segment of the impression would improve the acoustic seal provided by specially built-up earmoulds and that earmoulds with rounder tips are more likely to provide a static pressure seal than earmoulds with more elliptical tips. The better the impression material fills the ear canal, the rounder the tip of the impression, and the rounder the tip of the earmould made from the impression.     

耳模和声管长短的声学效果评估

目的：了解耳模和声管长短对声学效果的影响。方法：任选外耳道结构正常的受试者30人（60耳）,并按耳印在第二峡部的平均直径≥4．0mm者为甲组,＜4．0mm者为乙组。采用丹麦产Aurical真耳分析仪,运用台台湾产恒升486笔记本电脑在Noah平台下操作,应用同一固定的助听器,按常规真耳测试方法分析耳模及声管在长短不同的A、B、C三种类型下的声学效果,即A型为耳模与声管等长且距离鼓膜约1．0cm,C型耳模及声管均比A型短0．5cm,B型的声管与A型等长而耳模与C型等长,实验中分别测量A、B、C型耳模在250、500、750、1000、1500、2000、3000、4000、6000Hz时的介入增益值,即A、B及C值,并将测量结果进行SAS软件分析,结果：甲组在250、500Hz处的A、B值较C表显著性差异（P＜0．05）,在3000、4000、6000Hz处A值与C值均有高度显著性差异（P＜0．01）,B值与C值均有显著性差异（P＜0．05）,在750、1000、1500和2000Hz处A、B和C值无明显变化（P＞0．05）;乙组中A、B值较C值仅在250、500Hz有显著性差异（P＜0．05）,在其它频率三者间无显著性差异（P＞0．05）。结论,当外耳道较为宽大时,增加声管的长度可以提高低频和高频的增益,当外耳道较为狭窄时,增加声管的长度仅能提高低频的增益。     

Practical considerations in the fabrication of earmoulds for young babies

The practicalities of fabricating earmoulds for young babies (under the age of 3 months) have been investigated. The results indicate that earmoulds can be satisfactorily fabricated provided there are changes in approach in the fabrication procedure. This applies in both the ear impression taking and in the format of the final earmould.     

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.     

Unusual phonological behavior and the avoidance of homonymy in children

Young children sometimes make use of unusual phonological patterns even when they already possess the appropriate sound or a suitable substitute in their phonological systems. In this investigation, we attempted to determine whether in such instances unusual sound changes enable children to avoid potential homonymy with other words in their lexicons. Novel words were presented to children, half serving as potential homonyms, half as unlikely homonyms. The children's acquisition of these words was monitored. For a group of normally developing children, unusual sound changes were found to be more frequent in the words with the potential for homonymy. In contrast, a group of children with specific language impairment showed the same degree of unusual usage for both types of words. The findings suggest that children with specific language impairment are especially limited in their ability to capitalize on the phonetic regularities of the language.     

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.