An acoustic head simulator for hearing protector evaluation. II: Measurements in steady-state and impulse noise environments

The attenuation characteristics of hearing protection devices (HPDs) were measured using a modular acoustic head simulator. The effect in changes in the head configuration was assessed in a steady-state diffuse sound field. The use of artificial circumaural skin had a relatively small influence on the insertion loss of earmuffs (max. 6-7 dB at low frequencies). This contrasts to the very large effects found for the artificial intraaural skin on the insertion loss of earplugs (in excess of 40 dB at low frequencies for some devices). Results were also compared with real-ear attenuation at threshold (REAT) data (ANSI S3.19-1974). In general, there is good agreement between the two methods, especially for earmuffs. Design improvements are proposed for earplugs. The result of an exploratory study aimed at measuring the complex (amplitude and phase) insertion loss of HPDs using an impulse noise source are also reported.     

Modeling sensorineural hearing loss. I. Model and retrospective evaluation

The present article describes an approach to the evaluation of psychoacoustic data from the hearing impaired. The results obtained from the hearing impaired in several studies of frequency resolution, temporal resolution, and speech recognition are compared to the results expected for noise-masked normal listeners. It is presumed in this approach that the hypothetical noise-masked normal listeners have masked thresholds that agree perfectly with the quiet thresholds of the hearing-impaired subjects. Using this approach, most of the results obtained from impaired ears on spectral-resolution and speech-recognition tasks could be accurately predicted, an exception being results from spectral-resolution paradigms using fixed-level signals. Some of the data from hearing-impaired listeners on temporal-resolution tasks, on the other hand, could not be adequately described with this approach. The latter data, however, were much more limited. Additional data are needed to better evaluate the adequacy of this approach in describing the performance of the hearing impaired on temporal-resolution tasks.     

Design of a pulse generator and shock tube for measuring hearing protector attenuation of high-amplitude impulsive noise

The effectiveness of hearing protectors against high amplitude impulse noise levels remains the subject of research with objective testing techniques using acoustic test fixtures offering the only realistic method of providing rapid performance data for protector design and qualification. The work presented in this paper examines a prototype test method based on a shock tube and acoustic test fixture for the evaluation of protectors against high-level impulsive noise where established real ear attenuation at threshold methods would be impractical to apply. The results show that the system is capable of producing controlled repeatable high amplitude pressure pulses of variable duration for testing hearing protection devices in a grazing wave type test. A series of pilot tests illustrate how the system can have a sufficient self-insertion loss to reject flanking noise and allow the measurement of protector attenuations of up to 45 dB with little corruption from flanking noise.     

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part I: Review of previous work and the design of an improved test fixture

This paper gives a comprehensive progress report on the development of objective methods for measuring the attenuation of hearing protection devices (HPD's), and focuses on the use of acoustic test fixtures (ATF's), i.e., artificial heads. While there are many publications on ATF's for the evaluation of circumaural HPD's (earmuffs), only one serious attempt to construct an ATF for the evaluation of intra-aural HPD's (earplugs) could be found. Consequently, no ATF for testing earplugs has been standardized so far, while two standardized ATF's currently exist for testing earmuffs [see ANSI S3.19-1974 (1975) and ISO/DIS 6290 (1983)]. Both ATF's are suited, however, only for production testing and are not designed for HPD-type testing. It is believed that both ATF's do not provide sufficiently high accuracy for HPD-type testing. A new ATF with appropriate circumaural and intra-aural flesh simulations was constructed, including a suitable ear simulator and a cast of an average pinna. Objectives for design and construction of the new ATF are discussed. The effect of using artificial flesh on the insertion loss of earmuffs (max. 5 dB at 125 and/or 250 Hz) and the effect of using a pinna (max. 12 dB lower insertion loss at 2 kHz) were evaluated.     

不对称结构的分布式负载有界波电磁脉冲模拟器

 设计、建造了一台不对称结构、分布式负载有界波电磁脉冲（EMP）模拟器（MDES-60）。模拟器平行极板间区域长5 m，宽2 m，高1 m。测试结果显示模拟器工作空间电场幅值分布均匀、波形后沿基本无反射。表明通过缩小前过渡段的锥角、加宽下极板调整特性阻抗及采用分布式负载等措施取得了很好效果。配套不同的脉冲源，该模拟器可模拟IEC61000-2-9、Bell实验室、1976年出版物等多种脉宽标准的EMP波形，场强幅度范围15~60 kV/m，可用于短线缆响应实验或小型电子设备的考核效应实验。     

On the behaviour of artificial head transfer system applied to acoustic evaluation researches for halls

The author has made tests for an artificial head transfer system whichis modelled on a Chinese male on its main physical behaviour such as frequencyresponses,frequency response differences between the front and the rear inci-dences,as will as on its important hearing behaviour such as localization,theperception of distance and room dimensions.The results verify that this kind ofartificial head transfer system can be used as one of effective tools of acousticevaluation researches for halls.     

An acoustic analysis of laughter produced by congenitally deaf and normally hearing college students

Relatively few empirical data are available concerning the role of auditory experience in nonverbal human vocal behavior, such as laughter production. This study compared the acoustic properties of laughter in 19 congenitally, bilaterally, and profoundly deaf college students and in 23 normally hearing control participants. Analyses focused on degree of voicing, mouth position, air-flow direction, temporal features, relative amplitude, fundamental frequency, and formant frequencies. Results showed that laughter produced by the deaf participants was fundamentally similar to that produced by the normally hearing individuals, which in turn was consistent with previously reported findings. Finding comparable acoustic properties in the sounds produced by deaf and hearing vocalizers confirms the presumption that laughter is importantly grounded in human biology, and that auditory experience with this vocalization is not necessary for it to emerge in species-typical form. Some differences were found between the laughter of deaf and hearing groups; the most important being that the deaf participants produced lower-amplitude and longer-duration laughs. These discrepancies are likely due to a combination of the physiological and social factors that routinely affect profoundly deaf individuals, including low overall rates of vocal fold use and pressure from the hearing world to suppress spontaneous vocalizations.     

Effect of filter spacing on melody recognition: acoustic and electric hearing

This paper assesses the effect of filter spacing on melody recognition by normal-hearing (NH) and cochlear implant (CI) subjects. A new semitone filter spacing is proposed for music. The quality of melodies processed by the various filter spacings is also evaluated. Results from NH listeners showed nearly perfect melody recognition with only four channels of stimulation, and results from CI users indicated significantly higher scores with a 12-channel semitone spacing compared to the spacing used in their daily processor. The quality of melodies processed by the semitone filter spacing was preferred over melodies processed by the conventional logarithmic filter spacing.     

Speech recognition in noise for cochlear implant listeners: benefits of residual acoustic hearing

The purpose of this study was to explore the potential advantages, both theoretical and applied, of preserving low-frequency acoustic hearing in cochlear implant patients. Several hypotheses are presented that predict that residual low-frequency acoustic hearing along with electric stimulation for high frequencies will provide an advantage over traditional long-electrode cochlear implants for the recognition of speech in competing backgrounds. A simulation experiment in normal-hearing subjects demonstrated a clear advantage for preserving low-frequency residual acoustic hearing for speech recognition in a background of other talkers, but not in steady noise. Three subjects with an implanted "short-electrode" cochlear implant and preserved low-frequency acoustic hearing were also tested on speech recognition in the same competing backgrounds and compared to a larger group of traditional cochlear implant users. Each of the three short-electrode subjects performed better than any of the traditional long-electrode implant subjects for speech recognition in a background of other talkers, but not in steady noise, in general agreement with the simulation studies. When compared to a subgroup of traditional implant users matched according to speech recognition ability in quiet, the short-electrode patients showed a 9-dB advantage in the multitalker background. These experiments provide strong preliminary support for retaining residual low-frequency acoustic hearing in cochlear implant patients. The results are consistent with the idea that better perception of voice pitch, which can aid in separating voices in a background of other talkers, was responsible for this advantage.     

The use of acoustic cues for phonetic identification: effects of spectral degradation and electric hearing

Although some cochlear implant (CI) listeners can show good word recognition accuracy, it is not clear how they perceive and use the various acoustic cues that contribute to phonetic perceptions. In this study, the use of acoustic cues was assessed for normal-hearing (NH) listeners in optimal and spectrally degraded conditions, and also for CI listeners. Two experiments tested the tense/lax vowel contrast (varying in formant structure, vowel-inherent spectral change, and vowel duration) and the word-final fricative voicing contrast (varying in F1 transition, vowel duration, consonant duration, and consonant voicing). Identification results were modeled using mixed-effects logistic regression. These experiments suggested that under spectrally-degraded conditions, NH listeners decrease their use of formant cues and increase their use of durational cues. Compared to NH listeners, CI listeners showed decreased use of spectral cues like formant structure and formant change and consonant voicing, and showed greater use of durational cues (especially for the fricative contrast). The results suggest that although NH and CI listeners may show similar accuracy on basic tests of word, phoneme or feature recognition, they may be using different perceptual strategies in the process.     

100 mK bolometers for the submillimetre common-user bolometer array (scuba) I. Design and construction

We describe the design and construction of bolometric detectors for SCUBA - the Submillimetre Common-User Bolometer Array for the James Clerk Maxwell Telescope in Hawaii. The instrument contains 131 individual detectors, in two arrays, optimized for the submillimetre atmospheric transmission windows. The detectors are cooled by dilution refrigeration to a temperature of 100 mK, so that the receiver performance will be limited by photon noise from the sky and telescope background in all wavebands. A future paper will describe the performance of the detectors with reference to typical data obtained during the laboratory commissioning period.     

A glimpsing account for the benefit of simulated combined acoustic and electric hearing

The benefits of combined electric and acoustic stimulation (EAS) in terms of speech recognition in noise are well established; however the underlying factors responsible for this benefit are not clear. The present study tests the hypothesis that having access to acoustic information in the low frequencies makes it easier for listeners to glimpse the target. Normal-hearing listeners were presented with vocoded speech alone (V), low-pass (LP) filtered speech alone, combined vocoded and LP speech (LP+V) and with vocoded stimuli constructed so that the low-frequency envelopes were easier to glimpse. Target speech was mixed with two types of maskers (steady-state noise and competing talker) at -5 to 5 dB signal-to-noise ratios. Results indicated no advantage of LP+V in steady noise, but a significant advantage over V in the competing talker background, an outcome consistent with the notion that it is easier for listeners to glimpse the target in fluctuating maskers. A significant improvement in performance was noted with the modified glimpsed stimuli over the original vocoded stimuli. These findings taken together suggest that a significant factor contributing to the EAS advantage is the enhanced ability to glimpse the target.     

A modal analysis for the acoustic radiation problems, I. Theory

For the acoustic radiation problems from a complex vibrating body surface, a modal analysis approach is put forward. All the normal vibration velocities on a vibrating surface form the Hilbert space. In the Hilbert space, an operator is defined, which includes the radiation property of the vibrating surface and is linear, self-adjoint and positive. Using the operator, a set of basis functions in the Hilbert space are obtained, which describe the radiation patterns and are called the radiation modes. Based on the radiation modes, a set of basis functions of the radiation field are obtained by the Helmholtz simple layer potentials, which describe the distribution patterns of the radiation field and are called the field distribution modes. The radiation behavior can be expressed by expansions of the radiation modes and the field distribution modes. The modal analysis approach is introduced into the acoustic radiation problems.     

Monocrystalline high-saturation magnetization ferrites for video recording head application: I. Zn ferrous ferrites

Monocrystalline Zn ferrous ferrites Zn_xFe_3-xO₄, with x ? 0.4, are considered as candidate materials for video recording heads, to be used for writing on magnetic tapes of high coercivity. The saturation magnetization of these ferrites can be as high as 0.7 T at 20°C. We show that because of the small dimensions of modern video recording heads, the relatively high electrical conductivity of the Zn ferrous ferrites is not an obstacle to their use at video frequencies. Measurements are reported of magnetic and electrical parameters relevant to recording head application. It is shown that some of the magnetic parameters can be influenced positively by Co^II additions. The present paper is the first of a series of three dealing with Fe^II-rich ferrites for video recording head application.     

A comparison of intergestural patterns in deaf and hearing adult speakers: implications from an acoustic analysis of disyllables.

Coarticulation studies in speech of deaf individuals have so far focused on intrasyllabic patterning of various consonant-vowel sequences. In this study, both inter- and intrasyllabic patterning were examined in disyllables /symbol see text #CVC/ and the effects of phonetic context, speaking rate, and segment type were explored. Systematic observation of F2 and durational measurements in disyllables minimally contrasting in vocalic ([i], [u,][a]) and in consonant ([b], [d]) context, respectively, was made at selected locations in the disyllable, in order to relate inferences about articulatory adjustments with their temporal coordinates. Results indicated that intervocalic coarticulation across hearing and deaf speakers varied as a function of the phonetic composition of disyllables (b_b or d_d). The deaf speakers showed reduced intervocalic coarticulation for bilabial but not for alveolar disyllables compared to the hearing speakers. Furthermore, they showed less marked consonant influences on the schwa and stressed vowel of disyllables compared to the hearing controls. Rate effects were minimal and did not alter the coarticulatory patterns observed across hearing status. The above findings modify the conclusions drawn from previous studies and suggest that the speech of deaf and hearing speakers is guided by different gestural organization.     

Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. I: The contribution of selected frequency regions

The purpose of this study is to specify the contribution of certain frequency regions to consonant place perception for normal-hearing listeners and listeners with high-frequency hearing loss, and to characterize the differences in stop-consonant place perception among these listeners. Stop-consonant recognition and error patterns were examined at various speech-presentation levels and under conditions of low- and high-pass filtering. Subjects included 18 normal-hearing listeners and a homogeneous group of 10 young, hearing-impaired individuals with high-frequency sensorineural hearing loss. Differential filtering effects on consonant place perception were consistent with the spectral composition of acoustic cues. Differences in consonant recognition and error patterns between normal-hearing and hearing-impaired listeners were observed when the stimulus bandwidth included regions of threshold elevation for the hearing-impaired listeners. Thus place-perception differences among listeners are, for the most part, associated with stimulus bandwidths corresponding to regions of hearing loss.     

Beamforming for directional sources: additional estimator and evaluation of performance under different acoustic scenarios

Beamforming is done with an array of sensors to achieve a directional or spatially-specific response by using a model of the arriving wavefront. Conventionally, a plane wave or point source model is used and this can cause decreased array gain or even total breakdown of beamforming when the source is directional. To avoid this, the authors proposed in recent work an alternative beamforming method which defines a set of "sub-beamformers," each designed to respond to a different spatial mode of the source. The outputs of the individual sub-beamformers are combined in a weighted sum to give an overall output of better quality than that of a monopole beamformer. This paper extends the previous work by introducing an additional estimator for the weighted sum and by presenting simulation results to demonstrate the relative performance of the proposed method and the different estimators for a directional source in the presence of diffuse noise, reverberation, and an interfering source. Gain optimization subject to a constraint on the white-noise gain with the proposed beamforming method is also introduced. Generally, when beamforming on directional sources, the proposed method outperforms beamforming with a point source model when the input signal-to-noise ratio (SNR) is 0 dB or higher.     

The use of acoustical test fixtures for the measurement of hearing protector attenuation. Part II: Modeling the external ear, simulating bone conduction, and comparing test fixture and real-ear data

This paper investigates two main features of the human head which influence the measured attenuation of circumaural and intraaural hearing protection devices (HPDs): the external ear and the different pathways of bone conduction. A theoretical model for the external ear shows that its influence on the insertion loss of HPDs, on the sensitivity level of headphones or earphones, and on the insertion gain of hearing aids, all can be described by one equation. While it is not necessary to simulate the eardrum impedance in order to measure the insertion loss of earmuffs and the sensitivity level of headphones with acoustical test fixtures (ATFs), the required accuracy of an ear simulator is more stringent when the same measurements are performed on intraaural devices. For the evaluation of HPDs, bone conduction plays an important role. We have developed a model to estimate HPD-dependent bone conduction effects. The model includes two bone conduction sources: one in the external ear and one in the middle ear. The model explains, for example, the occlusion effect of HPDs and the masking error at low frequencies due to physiological noise that arises when real-ear attenuation at threshold (REAT) measurements are made. Consequently, objectively measured insertion loss can now be used to predict REAT with improved accuracy. ATF and REAT data are compared using nine earmuffs and nine earplugs. In the majority of cases, the two sets of data agree well. Discrepancies are discussed.