Acoustic versus electronic modifications of hearing aid low-frequency output

The rated quality and intelligibility of speech processed by hearing aids in which the low-frequency output had been reduced by either electronic modification (low-cut tone controls) or acoustic modification (vented or open earmolds) was investigated. Fifteen subjects with high-frequency hearing loss provided data for nine commercial hearing aids and both high and low background noise levels. Results for both background noise levels indicated that for hearing aids with a low-frequency cut off at or above 750 Hz (as measured in this investigation), the use of a vented or open earmold significantly improved both quality and intelligibility even when it had essentially no effect on the hearing aid's low-frequency output. The implication of the outcome is that for an individual with essentially normal low-frequency sensitivity and a high-frequency hearing loss, an earmold incorporating an opening should be used whenever possible, even though it may not be used for the purpose of controlling low-frequency amplification.     

The effects of venting on in-the-ear, in-the-canal, and completely-in-the-canal hearing aid shell frequency responses: real-ear measures.

The acoustic effects of 1-, 2-, and 3-mm vents were investigated with in-the-ear, in-the-canal, and completely-in-the-canal hearing aid shells. Real-ear sound pressure level measures were obtained from unvented and vented shells with 12 adults. In general, with increasing vent size, a statistically significant (p < .05) increase in the amount of low-frequency reduction, an upward shift in vent cutoff frequencies, and an upward shift in vent-associated resonances occurred for all hearing aid shell styles. There was no significant change in the slope of the low-frequency reduction across all hearing aid shell styles (p > .05), albeit the frequency response curves were shifted upward in frequency with increasing vent diameters. Only with the in-the-ear and completely-in-the-canal hearing aid shells were statistically significant (p < .05) differences found with the magnitude of vent-associated resonance as a function of vent diameter, and these differences were not consistent across the different styles. These findings suggest that venting may be used effectively to tune low-frequency responses in custom in-the-ear hearing instruments.     

What improvements can be gained by additional boring in hearing aid fitting?]

In several investigations the authors tried to find a objective correlation to the subjective positive reactions after venting an earmold. There was no notable effect neither on insertion gain nor on speech intelligibility in different background noise situations. In this study the most comfortable hearing level has been used. This stimulus is influenced by the suprathreshold loudness growth. The measurement has been carried out with and without venting. Comparing the results there can be seen only a little effect of venting at all frequencies. Might be that patient's report about improvement after venting results from the direct input of low frequencies through the vent to the eardrum. These frequency region plays a special part of hearing comfort to reach a comfortable sound quality.     

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.     

防噪声耳模的应用研究

目的对防噪声耳模的防护作用进行实验室及临床研究。方法制作普通和加芯子的防噪声耳模,通过CT多角度切割分析、不同强度下噪声衰减测试及正常人佩戴前后听阈变化的比较,对普通和加芯子的防噪声耳模声音衰减进行分析。结果普通防噪声耳模的声音衰减随着频率的增高逐渐增加,低频处为10dBHL,高频处为35dBHL。加芯子防噪声耳模的噪声衰减随入射声压级的变化而变化,呈现出非线性效应。入射声压级越高。噪声衰减也越高。入射声压级在120～130dBHL时,噪声衰减比较大的频段在2500～4500Hz。结论佩戴防噪声耳模是听力防护的有效手段,加芯子的防噪声耳模具有有效保留言语会话区域的作用。适用范围更加广泛,具有广阔的应用前景。     

Earmold modification effect measured by coupler, threshold and probe techniques

The validity of probe tube microphone measurements in providing data indicative of the magnitude of the change in subjects' threshold resulting from changes in earmold configuration was investigated. The relationship between these measures in the real ear canal and the changes observed in 2-cm3 and Zwislocki couplers under similar circumstances or earmold modification was also measured. Standard, vented and 'open' earmold conditions were utilized. Threshold and probe-tube measurements were made. Statistical evaluation revealed that these two techniques did not produce significantly different results except at 125--165 Hz, where noise masking may have been a factor influencing the threshold data. Neither coupler as used gave an accurate quantitative estimate of the in-use effects of vented earmolds or the open earmold configuration, but the Zwislocki coupler gave a better approximation than the 2-cm3 coupler.     

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.     

Occlusion effect of earmolds with different venting systems

In this study the occlusion effect was quantified for five types of earmolds with different venting. Nine normal-hearing listeners and ten experienced hearing aid users were provided with conventional earmolds with 1.6 and 2.4 mm circular venting, shell type earmolds with a novel vent design with equivalent cross-sectional vent areas, and nonoccluding soft silicone eartips of a commercial hearing instrument. For all venting systems, the occlusion effect was measured using a probe microphone system and subjectively rated in test and retest sessions. The results for both normal-hearing subjects and hearing aid users showed that the novel vents caused significantly less occlusion than the traditional vents. Occlusion effect associated with the soft silicone eartip was comparable to the nonoccluded ear. Test-retest reproducibility was higher for the subjective occlusion rating than for the objectively measured occlusion. Perceived occlusion revealed a closer relationship to measured occlusion in the ear in which the measured occlusion effect was higher ("high OE" ear) than in the "low OE" ear. As our results suggest that subjective judgment of occlusion is directly related to the acoustic mass of the air column in the vent, the amount of perceived occlusion may be predicted by the vent dimensions.     

The effects of venting and low-frequency gain compensation on performance in noise with directional hearing instruments

The present study investigated the effects of gain compensation and venting on front-to-back ratios (FBRs), speech understanding in noise, and acceptance of noise in 19 listeners with hearing impairment utilizing directional hearing instruments. The participants were separated into two groups based on degree of low-frequency hearing sensitivity. Subjects were fitted binaurally with Starkey Axent II programmable behind-the-ear hearing aids and full-shell earmolds (select-a-vent). Results demonstrated that gain compensation and venting significantly affected FBRs for both groups; however, acceptance of noise was not significantly affected by gain compensation or venting for either group. Results further demonstrated that speech understanding in noise was unaffected by venting but may be improved with the use of gain compensation for some listeners. Clinical implications are discussed.     

Effect of Opening Middle-Ear Cavity on Vibrations of Gerbil Tympanic Membrane

This paper presents in vivo experimental measurements of vibrations on the pars flaccida, along the manubrium and at several points on the pars tensa in the gerbil with open middle-ear cavity. The effects of progressive opening of the middle-ear cavity are presented, with up to five different extents of opening. In all manubrial, pars-tensa and pars-flaccida responses, opening the cavity causes an increase in the low-frequency magnitude and a shift of the main middle-ear resonance to lower frequencies and introduces an antiresonance. However, opening the cavity has little or no effect on either the mode of vibration of the manubrium or the breakup frequency of the pars tensa. When the opening is gradually widened, the antiresonance frequency moves to higher frequencies. When the opening is made as wide as anatomically possible, the antiresonance moves to almost 10 kHz. The main increase in the low-frequency response magnitude happens upon making the smallest hole in the cavity wall, and further progressive enlarging of the opening has little or no effect on the low-frequency magnitude. The antiresonance interferes with the response shapes. An identification method is suggested for eliminating the effect of the antiresonance in order to estimate the ideal open-cavity response. The method is validated and then applied to manubrial and pars-tensa responses. Estimating the ideal open-cavity responses will simplify comparison of the data with numerical models which do not include the air cavity. The data collected at intermediate stages of opening will be useful in validating models that do include the cavity.     

突变截面管式通气孔对耳模声学特性的影响

目的通过改变耳模通气孔的形状，探讨突变截面管式通气孔在耳模声学特性中的优势。方法利用埋管的方法为每位受试者分别制取通气孔为平行、扩张和收缩形状的耳模，然后受试者佩戴每个耳模进行真耳分析，测量佩戴各个耳模时的REOG和REIG值。结果①2 mm平行通气孔耳模与扩张管式通气孔耳模的REOG值相比较，在500 Hz和750 Hz处有显著性差异（P〈0.05）；与收缩管式通气孔耳模的REOG值相比较在各个频率上均无显著性差异（P〉0.05）。②2 mm平行通气孔耳模与扩张管式通气孔耳模的REIG值相比较，在2 kHz处具有显著性差异（P〈0.05）；与收缩管式通气孔耳模的REIG值相比较在2 kHz和3 kHz处具有显著性差异（P〈0.05）。结论突变截面管式通气孔中收缩管式在解决堵耳效应问题上与2 mm平行通气孔有着相似的效果，但突变截面管式通气孔扩张和收缩式耳模可获得更大的助听增益，其中收缩管式通气孔耳模的作用要优于扩张管式通气孔耳模。     

Multivariate analysis using quantitative methods to evaluate the subjective loudness of tinnitus

Factors affecting the subjective loudness of tinnitus were analyzed using quantitative methods. One hundred and eighty-four patients with unilateral tinnitus were studied. Major factors affecting the subjective loudness of tinnitus were found to be subjective tinnitus pitch, annoyance, diagnosis, pitch-matched frequency, insomnia, age, tinnitus loudness level in dB HL, the duration of tinnitus and the tinnitus loudness level in dB SL at the first axis. Tinnitus pitch and pitch-matched frequency strongly affected the loudness of the tinnitus; high-pitch tinnitus and middle and low frequencies were associated with the subjective loudness of the tinnitus. In contrast, low-pitch tinnitus and a high frequency were associated with the subjective softness of the tinnitus. Thus, tinnitus pitch and pitch-matched frequency are inversely related. Sudden deafness and dizziness were associated with subjective softness of tinnitus, while hearing loss in elderly patients was associated with subjective loudness of tinnitus. Our results suggest that the level of annoyance from tinnitus and the subjective loudness of tinnitus are closely related. The relation between these factors should be considered when evaluating patients with tinnitus.     

Relation between comfortable loudness and maximal speech intelligibility in children with sensorineural hearing loss]

The levels of comfortable loudness and those of maximal intelligibility were evaluated in 88 schoolchildren with dull hearing (20-90 dB reduction). All the examinees had the levels of comfortable loudness in the range of the maximal intelligibility, this permitting it to be a criterion in determination of optimal amplification in hearing aids. A significant correlation exists between comfortable loudness and hearing threshold at 500 Hz frequency, mean hearing threshold in the range of the principal speech frequencies 500-2000 Hz and in the range of the safest speech frequencies 250-1000 Hz. However, the range of the individual values of comfortable speech intensity in the same hearing thresholds proved to be 15-25 dB for one-syllable words and 20-40 dB for the standard speech tables making it impossible to recommend the threshold parameters for calculation of optimal intensity of the speech to receive. The most reliable way to do this is the adjustment of the speech loudness level by subjective sensation of the child.     

Predictability of real ear hearing aid performance from coupler measurements

Results comparing hearing aid performance utilizing probe microphones with performance measured in a commercial hearing aid test box using an HA-2 coupler are presented. Sixteen hearing-impaired subjects (23 ears) were divided into two groups. Group I utilized unvented earmolds with short canals and large bores; group II utilized unvented earmolds with long canals and small bores. Results revealed that large individual differences across frequencies as well as within and between groups preclude predicting how a hearing aid will perform on a real ear from test box measurements.     

Perceptual consequence of vents in hearing aids

The perceptual consequence of venting an earmould while maintaining the insertion gain at a preferred listening level was examined on nine hearing-impaired individuals with bilaterally symmetrical sloping sensorineural hearing loss. Subjects wore binaural programmable hearing aids and selected their preferred insertion gain while the hearing aids were coupled to vented (2.2 mm parallel vent) and unvented earmoulds. A modified Simplex procedure with discourse passages presented in quiet was used to determine preferred insertion gain. The results showed that venting enhanced subjects' quality rating of the hearing aids during listening and vocalization tasks, but did not change subjects' word recognition scores. These results suggest that vented earmoulds should be used to achieve target insertion gain in order to maximize patients' acceptance of hearing aids.     

Temporal modulation transfer functions in cochlear implantees using a method that limits overall loudness cues

Temporal modulation transfer functions (TMTFs) were measured for six users of cochlear implants, using different carrier rates and levels. Unlike most previous studies investigating modulation detection, the experimental design limited potential effects of overall loudness cues. Psychometric functions (percent correct discrimination of modulated from unmodulated stimuli versus modulation depth) were obtained. For each modulation depth, each modulated stimulus was loudness balanced to the unmodulated reference stimulus, and level jitter was applied in the discrimination task. The loudness-balance data showed that the modulated stimuli were louder than the unmodulated reference stimuli with the same average current, thus confirming the need to limit loudness cues when measuring modulation detection. TMTFs measured in this way had a low-pass characteristic, with a cut-off frequency (at comfortably loud levels) similar to that for normal-hearing listeners. A reduction in level caused degradation in modulation detection efficiency and a lower-cut-off frequency (i.e. poorer temporal resolution). An increase in carrier rate also led to a degradation in modulation detection efficiency, but only at lower levels or higher modulation frequencies. When detection thresholds were expressed as a proportion of dynamic range, there was no effect of carrier rate for the lowest modulation frequency (50 Hz) at either level.     

Detection of loudness recruitment in patients with retrocochlear lesions using the "Würzburger Hörfeld" loudness scaling

BACKGROUND: The pathogenesis of hearing loss caused by cerebellopontine angle tumors such as acoustic neuromas is unknown. The lack of loudness recruitment is thought to be one of the features of retrocochlear hearing impairment. In contrast to conventional suprathreshold tests, the categorial loudness scaling using the "Würzburger H?rfeld" is a valuable tool to describe the individual perception of sound. The aim of the present study was to analyze the loudness growth rate in patients with acoustic neuroma. PATIENTS AND METHOD: Pure tone and speech audiometry as well as auditory brainstem response and bilateral categorial loudness scaling were performed preoperatively in 54 patients with acoustic neuroma. Loudness scaling was done in free field switching off the contralateral ear by using an ear-plug. RESULTS: An abnormal rapid loudness growth function was found in 38 of the 54 patients (70.4%) at least at one frequency on the tumor side. The contralateral side was effected only in 57.4% of the patients. The incidence of a recruitment depended on the frequency with a maximum at 4 kHz. The slope of the loudness function showed a tendency to increase with increasing hearing loss. CONCLUSIONS: Loudness recruitment is not a rare phenomenon in patients with acoustic neuroma. The underlying cause (a preexisting hair cell damage, hair cell changes resulting from an obstruction of the cochlear blood supply or a disruption of the cochlear efferents) still remains unclear.     

Acoustic effects in in-the-ear hearing aid response: results from a computer simulation

The response of a hearing aid depends on the design of the instrument and on the characteristics of the individual ear. In this paper a computer simulation of an in the ear (ITE) hearing aid is used to determine the effects on the hearing aid response caused by variations in the size of the ear canal, the magnitude of the eardrum impedance, and the vent size and damping. The simulation results indicate that, for an unvented hearing aid, changes in the size of the ear canal or the eardrum impedance shift the average sound pressure level at the eardrum but have relatively small effects on the overall shape of the frequency response. A vented instrument presents a more complicated situation since the vent modifies the low-frequency response in a predictable manner but can have unexpectedly pronounced effects at high frequencies due to the acoustic feedback.     

High-frequency audiometry. Response characteristics of the KH70 vibrator.

Various response characteristics of the Pr?citronic KH70 bone vibrator have been investigated in the frequency range 0.25 through 16 kHz. Masked threshold reproducibility is satisfactory throughout the frequency range. An occlusion effect is present only at frequencies at and below 1 kHz. Stimulus perception lateralizes to the occluded ear through 1 kHz and less consistently at successively higher frequencies. The KH70 does not satisfy the IEC 645 (1979) criterion for acoustic radiation for frequencies below 6 kHz, especially at the intermediate frequencies of 0.5, 1 and 2 kHz. With the restrictions inherent in the occlusion effect, this does not, however, interfere with threshold determination. The vibrator would thus seem suitable for clinical use through 16 kHz.