真人头部骨导效应实验和分析

利用耳声发射原理,借鉴三间隔范式分离方法,提出对骨导振子施加扫频音,以快速准确获取全频段刺激频率耳声发射(SFOAE)信号的方法,以此研究真人头部的骨导效应,将测得的耳声信号和骨导振子激励信号之间的相对关系定义为耳声相关骨传导响应函数(OAR-BCRF).10名听力正常的受试者的OAR-BCRF实验结果表明,不同刺激强...     

骨导超声听觉感知进展与研究*

骨导超声听觉感知是超声振动通过头骨传导产生听觉感知的一种特殊现象。本文首先介绍了骨导超声听觉感知研究领域的国内外发展现状,在此基础上设计了一套骨导超声听觉感知测试系统,并完成了系统的软、硬件平台实现。利用该系统,分别对听力正常和听力障碍被试者进行了主观测试,围绕单频超声感知效果及单频可听声、汉语语音由超声载波调制后的感知效果开展研究,比较了多种不同调制方式下的主观感知效果,并分析了空气传导声对实验结果的影响。     

稳态和动态虚拟听觉重放对近场距离感知的影响*

虚拟听觉重放是研究距离感知的一种重要工具,它可分为传统的稳态虚拟听觉重放和动态虚拟听觉重放。然而,稳态虚拟听觉重放经常会产生头中定位而影响距离感知的判断,从而影响最终的实验结果。过去的实验大多采用稳态虚拟听觉重放,因此其结论也存在较大的争议性结论。本文对比研究稳态和动态的虚拟听觉重放对绝对距离感知效果的影响。实验采用非个性化HRTF进行双耳合成,将分布在水平面0.20 m至1.00 m的七个距离、0°至180°的七个方位角下的信号通过耳机进行虚拟重放。心理声学实验结果表明,在稳态虚拟听觉重放条件下,受试者不同程度地报告了存在头中定位。而动态虚拟听觉重放系统能够利用动态因素,从而产生头外化的听觉感知。统计分析表明动态虚拟听觉重放下的距离感知效果与稳态重放存在明显的差异。由于动态虚拟重放更接近真实声源的感知效果,应选用这种方法作为实验工具。同时,在实际的空间声应用中,也应该采用动态虚拟听觉重放产生不同的距离感知。     

压电陶瓷复合振子的电声效率与振子压电片位置关系的实验研究

压电陶瓷组成的功率超声复合振子,虽然有不少优点,但是在实际负载中,有时声负载匹配不够理想,声能不易辐射出去。如果压电片的位置放的不妥当,其声能就更辐射不出去,增加了换能器的损耗,降低了电声效率。本文从振子的晶片位置上研究了这个问题。 一、引言 关于复合振子的压电片位置,有人曾作过研究。例如:Shoh研究了压电片位置对振子内部功率损耗的影响。Lemaser在频率为10kHz下,研究了压电片的位置对阻抗、Q值和辐射端头位移的影响。汪承灏研究了压电片的位置对有效耦合系数的影响。我们根据压电片在振子中的位置不同,设计了多种20kHz的压电陶瓷复合振子。在超声工程常用的功率和位移振幅下,分两种情况试验:第一情况,向空气中辐射;第二种情况向水中辐射。通过这些实验,从压电陶瓷片在振子中的不同位置,观察它们的内部损耗功率和电声效率的变化。     

两扬声器虚拟声重放的双耳声压控制与定位性能

在两扬声器虚拟声重放中,通过精确重构双耳声压而产生不同的空间听觉感知。其重放的定位性能应该是由双耳声压控制的代价和稳定性所共同决定的。过去研究主要对双耳声压控制的稳定性进行分析,并以此作为扬声器布置和信号处理的依据。该文研究表明仅对双耳声压的稳定性分析是不足以完全衡量扬声器虚拟声重放的定位性能的。进一步采用虚拟声信号处理滤波器响应平均功率对双耳声压控制的代价进行分析。结果表明,缩窄左右对称扬声器布置的张角或采用非对称扬声器布置会明显增加产生侧向目标虚拟源时的双耳声压控制代价。虚拟源(虚拟声像)定位实验表明,双耳声压控制代价增加会引起虚拟源定位缺陷。实际应用中,为了有效产生侧向虚拟源,应避免采用过窄张角(如立体声偶极)和非对称的扬声器布置。     

低温下三角绝缘铁磁体的磁振子软化

在二维绝缘铁磁系统基础上建立了一个磁振子声子相互作用模型.利用格林函数方法研究了磁振子声子相互作用下的三角绝缘铁磁体的磁振子谱,计算了布里渊区的Λ线上的磁振子色散曲线.发现在布里渊区边界区域磁振子谱的软化和磁振子谱线增宽最明显.比较了纵向声子与横向声子对磁振子谱的软化与磁振子谱线增宽的影响,也讨论了各项参数,以及温度的变化对磁振子谱的软化与磁振子谱线增宽的影响.     

基于Duffing振子的微弱周期信号混沌检测性能研究

不同的混沌振子具有不同的混沌检测性能. 本文围绕Duffing振子的混沌检测方法, 从混沌系统临界点相图的突变性、混沌区间保持性以及混沌临界点的容噪性等三个方面的检测性能做了进一步研究, 并分别分析了影响这些性能的因素, 最后围绕这三个方面对两个不同混沌振子的混沌检测性能做了分析和比较. 关键词： 混沌检测 微弱信号检测 Duffing方程 检测性能     

T→0K下光频支声子-磁振子相互作用对磁振子衰减的影响

在二维复式正方Heisenber铁磁系统的基础上建立了磁振子-声子相互作用模型.利用松原格林函数理论研究了系统T→0K下的磁振子衰减,计算了布里渊区的主要对称点线上的磁振子衰减的变化曲线,比较了磁性离子的与非磁性离子的光频支声子对磁振子衰减的影响以及各项参数的变化对磁振子衰减的影响.发现光频支声子-磁振子耦合对磁振子衰减起主要作用,尤其是纵向光频支声子对磁振子衰减起更大的作用,并且非磁性离子的光频支声子对磁振子衰减的作用比磁性离子的光频支声子对磁振子衰减的作用更显著.根据关系式-Im∑*(1)(k)=/(2τ)可以对磁振子寿命和磁振子线宽进行判断.     

低温下二维绝缘铁磁体的磁振子软化

在二维正方绝缘铁磁系统基础上建立了一个磁振子-声子相互作用模型.利用格林函数方法研 究了磁振子-声子相互作用下的二维绝缘铁磁体的磁振子谱, 计算了布里渊区的主要对称点 线上的磁振子色散曲线.发现在布里渊区边界区域磁振子谱的软化和磁振子谱线增宽最明显. 比较了纵向声子与横向声子对磁振子谱的软化与磁振子谱线增宽的影响，也讨论了各项参数 的变化对磁振子谱的软化与磁振子谱线增宽的影响. 关键词： 磁振子-声子相互作用 磁振子软化 铁磁体 磁振子谱线增宽     

东印度洋热带偶极子对声会聚区影响分析

大洋中的物理海洋现象影响着水体的变化,从而对其中的声波传播产生重要的影响.首次在东印度洋海域进行的声学调查实验,发现了印度洋热带偶极子物理海洋现象对声传播的影响,利用穿越热带偶极子的声传播实验数据,分析了声源深度和水体起伏对深海会聚区的影响,并对实验中的声传播现象形成机理进行了理论解释.结果表明:东印度洋深海非完全声道环境下,受热带偶极子形成暖水团和声源深度起伏的影响,第2会聚区没有形成,声源深度变深时,更容易形成深海会聚区;印度洋热带偶极子影响下第2会聚区位置处的水体跃层起伏会对下一个会聚区的形成及位置产生重要影响,使得第3会聚区提前形成,会聚区位置向声源方向偏移2—3 km.研究结果对探测及通信声纳在深海复杂环境下应用具有重要指导意义.     

Acoustic method for calibration of audiometric bone vibrators

The standard method for the calibration of audiometric bone vibrators requires the use of an artificial mastoid, a device that converts vibratory energy to an electrical analog. The mechanical input impedance of the device is designed to represent the average mechanical impedance of the human head. For calibration purposes, it is not necessary that the coupling device represent the impedance of the head. It is only necessary that it provides a repeatable measurement of the output of the vibrator that can be related to the normal threshold of hearing at each test frequency. In addition to the mechanical output that serves as the stimulus for the hearing test, bone vibrators produce an acoustic signal that is proportional to the mechanical force delivered to the head. By determining the transfer function relating the acoustic sound pressure to the mechanical force, the acoustic signal can serve as a proxy for the vibratory stimulus. This article describes the design and validation of an acoustic coupler for the calibration of audiometric bone vibrators.     

Factors contributing to bone conduction: the outer ear

The ear canal sound pressure and the malleus umbo velocity with bone conduction (BC) stimulation were measured in nine ears from five cadaver heads in the frequency range 0.1 to 10 kHz. The measurements were conducted with both open and occluded ear canals, before and after resection of the lower jaw, in a canal with the cartilage and soft tissues removed, and with the tympanic membrane (TM) removed. The sound pressure was about 10 dB greater in an intact ear canal than when the cartilage part of the canal had been removed. The occlusion effect was close to 20 dB for the low frequencies in an intact ear canal; this effect diminished with sectioning of the canal. At higher frequencies, the resonance properties of the ear canal determined the effect of occluding the ear canal. Sectioning of the lower jaw did not significantly alter the sound pressure in the ear canal. The sound radiated from the TM into the ear canal was investigated in four temporal bone specimens; this sound is significantly lower than the sound pressure in an intact ear canal with BC stimulation. The malleus umbo velocity with air conduction stimulation was investigated in nine temporal bone specimens and compared with the umbo velocity obtained with BC stimulation in the cadaver heads. The results show that for a normal open ear canal, the sound pressure in the ear canal with BC stimulation is not significant for BC hearing. At threshold levels and for frequencies below 2 kHz, the sound in the ear canal caused by BC stimulation is about 10 dB lower than air conduction hearing thresholds; this difference increases at higher frequencies. However, with the ear canal occluded, BC hearing is dominated by the sound pressure in the outer ear canal for frequencies between 0.4 and 1.2 kHz.     

Influence of the Number of Loudspeakers on the Timbre in Horizontal and Mixed-Order Ambisoncis Reproduction

Ambisonics is a series of flexible spatial sound reproduction systems based on spatial harmonics decomposition of sound field. Traditional horizontal and spatial Ambisonics reconstruct horizontal and spatial sound field with certain order of spatial harmonics, respectively. Both the Shannon-Nyquist spatial sampling frequency limit for accurately reconstructing sound field and the complexity of system increase with the increasing order of Ambisonics. Based on the fact that the horizontal localization resolution of human hearing is higher than vertical resolution, mixed-order Ambisonics (MOA) reconstructs horizontal sound field with higher order spatial harmonics, while reconstructs vertical sound field with lower order spatial harmonics, and thereby reaches a compromise between the perceptual performance and the complexity of system. For a given order horizontal Ambisoncis or MOA reproduction, the number of horizontal loudspeakers is flexible, providing that it exceeds some low limit. By using Moore’s revised loudness model, the present work analyzes the influence of the number of horizontal loudspeakers on timbre both in horizontal Ambisonics and MOA reproduction. The binaural loudness level spectra (BLLS) of Ambisoncis reproduction are calculated and then compared with those of target sound field. The results indicate that below the Shannon-Nyquist limit of spatial sampling, increasing the number of horizontal loudspeakers influence little on BLLS then timbre. Above the limit, however, the BLLS for Ambisoncis reproduction deviate from those of target sound field. The extent of deviation depends on both the direction of target sound field and the number of loudspeakers. Increasing the number of horizontal loudspeakers may increase the change of BLLS then timbre in some cases, but reduce the change in some other cases. For MOA, the influence of the number of horizontal loudspeakers on BLLS and timbre reduces when virtual source departs from horizontal plane to the high or low elevation. The subjective evaluation experiment also validates the analysis.     

Adaptive wave field synthesis for active sound field reproduction: experimental results

Sound field reproduction has applications in music reproduction, spatial audio, sound environment reproduction, and experimental acoustics. Sound field reproduction can be used to artificially reproduce the spatial character of natural hearing. The objective is then to reproduce a sound field in a real reproduction environment. Wave field synthesis (WFS) is a known open-loop technology which assumes that the reproduction environment is anechoic. The room response thus reduces the quality of the physical sound field reproduction by WFS. In recent research papers, adaptive wave field synthesis (AWFS) was defined as a potential solution to compensate for these quality reductions from which WFS objective performance suffers. In this paper, AWFS is experimentally investigated as an active sound field reproduction system with a limited number of reproduction error sensors to compensate for the response of the listening environment. Two digital signal processing algorithms for AWFS are used for comparison purposes, one of which is based on independent radiation mode control. AWFS performed propagating sound field reproduction better than WFS in three tested reproduction spaces (hemianechoic chamber, standard laboratory space, and reverberation chamber).     

Sound radiation and sound quality characteristics of refrigerator noise in real living environments

The characteristics of various types of refrigerator noise were investigated in an anechoic chamber and in a real living environment - a 100 m² apartment which is a common size in Korea. It was found that the sound pressure level of the refrigerator noise in the real living room was about 10 dB higher than the level in the anechoic chamber at the same position (1 m in front of refrigerator). In addition, a tolerance level for refrigerator noise was determined by subjective evaluation experiments. Refrigerator noise was presented by a loudspeaker placed in the kitchen where the refrigerator is normally located. Level 2 responses to the subjective evaluation (“hardly perceivable”) corresponded to a sound pressure level of about 26 dB(A), for which 90% of participants were satisfied with the level of refrigerator noise. A semantic differential test using various adjectives was also conducted to evaluate the sound quality of refrigerator noise. With the semantic differential and the factor analysis, adjectives used in this experiment were grouped into three factors. From the results of correlation and multiple regression analyses on the psychoacoustical parameters and subjective evaluations of 30 kinds of refrigerators, sound quality index which predict the subjective rating score were proposed.     

Examination of bone-conducted transmission from sound field excitation measured by thresholds, ear-canal sound pressure, and skull vibrations

Bone conduction (BC) relative to air conduction (AC) sound field sensitivity is here defined as the perceived difference between a sound field transmitted to the ear by BC and by AC. Previous investigations of BC-AC sound field sensitivity have used different estimation methods and report estimates that vary by up to 20 dB at some frequencies. In this study, the BC-AC sound field sensitivity was investigated by hearing threshold shifts, ear canal sound pressure measurements, and skull bone vibrations measured with an accelerometer. The vibration measurement produced valid estimates at 400 Hz and below, the threshold shifts produced valid estimates at 500 Hz and above, while the ear canal sound pressure measurements were found erroneous for estimating the BC-AC sound field sensitivity. The BC-AC sound field sensitivity is proposed, by combining the present result with others, as frequency independent at 50 to 60 dB at frequencies up to 900 Hz. At higher frequencies, it is frequency dependent with minima of 40 to 50 dB at 2 and 8 kHz, and a maximum of 50 to 60 dB at 4 kHz. The BC-AC sound field sensitivity is the theoretical limit of maximum attenuation achievable with ordinary hearing protection devices.     

An acoustic head simulator for hearing protector evaluation. I: Design and construction

As an alternative to subjective methods, an acoustic head simulator was constructed for hearing protector evaluation. The primary purpose of the device is for hearing protector testing and research under high-level steady-state and impulse noise environments. The design is based on the KEMAR manikin and therefore approximates the physical dimensions and the acoustical eardrum impedance of the median human adult. The head simulator includes a mechanical reproduction of the human circumaural and intraaural tissues with a silicone rubber material. A compliant head-neck system was constructed to approximate the vibrational characteristics of the human head in a sound field in order to simulate the inertia effect of earmuffs. The bone-conducted sounds are not mechanically reproduced in the design. Applications for the device are reported in a companion article [C. Giguère and H. Kunov, J. Acoust. Soc. Am. 85, 1197-1205 (1989)].     

Hearing protector attenuation: A perspective view

The design, performance and evaluation of hearing protectors are matters of substantial current interest. The specific scientific questions which command attention include the accuracy of the shift in free field hearing threshold as a measure of protection, the relationship between physical measurements of sound attenuation with real heads and psycho-physical methods of measurement, the relationship between physical measurements with real and artificial heads, the acoustical behaviour of hearing protectors and the factors which limit their performance, and the relationship between hearing protector attenuation and speech intelligibility. These questions have received considerable attention during the past twenty years but are not yet fully answered.     

Responses of pigeon vestibular nerve fibers to sound and vibration with audiofrequencies

Single unit recordings were made from the nerve branch innervating the crista in the horizontal semicircular canal of a pigeon. The vestibular organ was either stimulated with sound through the ear canal or with a vibrator in contact with the membraneous ampulla roof. Units responding to sound or vibration showed tuning with a best frequency of approximately 0.7 kHz. The average low-frequency slope of the tuning curves is--16 dB/oct; the average high-frequency slope 20 dB/oct. The threshold amplitude for vibrator stimulation is 30 nm. This value comes close to the calculated threshold value for cupula deflection in the human semicircular canal.     

Is real-ear attenuation at threshold a function of hearing level?

In the course of measuring the real-ear attenuation at threshold (REAT) of experimenter-inserted E-A-R foam earplugs on 100 subjects, a statistically significant correlation was observed between attenuation and hearing level (for normal listeners, HTL less than or equal to 20 dB) at test frequencies from 2-8 kHz. Listeners with more sensitive hearing obtained better protection. The relationship was most robust at 6 and 8 kHz. For hearing levels greater than 20 dB, attenuation appeared independent of hearing level. A hypothesis was developed to explain the relationship for the normal listeners, based upon the fact that the high-frequency attenuation of the earplug was nearly bone-conduction limited. The hypothesis suggested that the attenuation of a hearing protector that provided substantially lower protection would not exhibit the same relationship. Data for such a device were collected for 70 subjects, and indeed demonstrated reduced correlation between attenuation and hearing level. Implications of the results of the experiments are discussed with regard to hearing level requirements for hearing protector attenuation test subjects, utilization of hearing-impaired listeners to measure REAT at suprathreshold (with respect to normal listeners) sound pressure levels, and linearity of hearing protector attenuation as a function of sound level.