Specification of the acoustical input to the ear at high frequencies

The sound fields that arise in the auditory canals of cats have been examined both experimentally and theoretically. Of particular interest was the spatial variation of sound pressure near the eardrum, where reference probes are typically located. Using a computer controlled data acquisition system, sound pressure was measured between 100 Hz and 33 kHz for constant driver input at 14 different locations in the ear canal of a cat, and the standing wave patterns formed. The shape of the patterns could be predicted quite well above 12 kHz using a theory that requires specification of only the geometry of the ear canal. This theory, an extension of the one-dimensional horn equation, applies to three-dimensional, rigid-walled tubes that have both variable cross section and curvature along their lengths. Large variations of sound pressure along the ear canal and over the surface of the eardrum are found above about 10 kHz. As a consequence it is not possible to define the acoustical input to the ear from sound pressure level measured at any single location. Even in comparative experiments, in which only the constancy of the acoustical input is important, any uncertainty in reference probe location would lead to an uncertainty in sound pressure level when different sets of measurements are compared. This error, calculated for various probe locations and frequencies, is especially large when the probe is near a minimum of the sound field. Spatial variations in pressure can also introduce anomalous features into the measured frequency response of other auditory quantities when eardrum sound pressure is used as a reference. This is illustrated with measurements of the round window cochlear microphonic.     

Intratympanic manganese administration revealed sound intensity and frequency dependent functional activity in rat auditory pathway

The cochlear plays a vital role in the sense and sensitivity of hearing; however, there is currently a lack of knowledge regarding the relationships between mechanical transduction of sound at different intensities and frequencies in the cochlear and the neurochemical processes that lead to neuronal responses in the central auditory system. In the current study, we introduced manganese-enhanced MRI (MEMRI), a convenient in vivo imaging method, for investigation of how sound, at different intensities and frequencies, is propagated from the cochlear to the central auditory system. Using MEMRI with intratympanic administration, we demonstrated differential manganese signal enhancements according to sound intensity and frequencies in the ascending auditory pathway of the rat after administration ofintratympanicMnCl₂.Compared to signal enhancement without explicit sound stimuli, auditory structures in the ascending auditory pathway showed stronger signal enhancement in rats who received sound stimuli of 10 and 40 kHz. In addition, signal enhancement with a stimulation frequency of 40 kHz was stronger than that with 10 kHz. Therefore, the results of this study seem to suggest that, in order to achieve an effective response to high sound intensity or frequency, more firing of auditory neurons, or firing of many auditory neurons together for the pooled neural activity is needed.     

Gerbil middle-ear sound transmission from 100 Hz to 60 kHz

Middle-ear sound transmission was evaluated as the middle-ear transfer admittance H(MY) (the ratio of stapes velocity to ear-canal sound pressure near the umbo) in gerbils during closed-field sound stimulation at frequencies from 0.1 to 60 kHz, a range that spans the gerbil's audiometric range. Similar measurements were performed in two laboratories. The H(MY) magnitude (a) increased with frequency below 1 kHz, (b) remained approximately constant with frequency from 5 to 35 kHz, and (c) decreased substantially from 35 to 50 kHz. The H(MY) phase increased linearly with frequency from 5 to 35 kHz, consistent with a 20-29 micros delay, and flattened at higher frequencies. Measurements from different directions showed that stapes motion is predominantly pistonlike except in a narrow frequency band around 10 kHz. Cochlear input impedance was estimated from H(MY) and previously-measured cochlear sound pressure. Results do not support the idea that the middle ear is a lossless matched transmission line. Results support the ideas that (1) middle-ear transmission is consistent with a mechanical transmission line or multiresonant network between 5 and 35 kHz and decreases at higher frequencies, (2) stapes motion is pistonlike over most of the gerbil auditory range, and (3) middle-ear transmission properties are a determinant of the audiogram.     

Delays of stimulus-frequency otoacoustic emissions and cochlear vibrations contradict the theory of coherent reflection filtering

When stimulated by tones, the ear appears to emit tones of its own, stimulus-frequency otoacoustic emissions (SFOAEs). SFOAEs were measured in 17 chinchillas and their group delays were compared with a place map of basilar-membrane vibration group delays measured at the characteristic frequency. The map is based on Wiener-kernel analysis of responses to noise of auditory-nerve fibers corroborated by measurements of vibrations at several basilar-membrane sites. SFOAE group delays were similar to, or shorter than, basilar-membrane group delays for frequencies >4 kHz and <4 kHz, respectively. Such short delays contradict the generally accepted "theory of coherent reflection filtering" [Zweig and Shera, J. Acoust. Soc. Am. 98, 2018-2047 (1995)], which predicts that the group delays of SFOAEs evoked by low-level tones approximately equal twice the basilar-membrane group delays. The results for frequencies higher than 4 kHz are compatible with hypotheses of SFOAE propagation to the stapes via acoustic waves or fluid coupling, or via reverse basilar membrane traveling waves with speeds corresponding to the signal-front delays, rather than the group delays, of the forward waves. The results for frequencies lower than 4 kHz cannot be explained by hypotheses based on waves propagating to and from their characteristic places in the cochlea.     

压力罐中水声材料声学特性的参量源测量法

设计了一种原波频率500 kHz、差频范围1~30 kHz的截断宽带参量阵,作为水声材料测量系统的声源。通过分析典型频率下的宽带参量源指向性理论计算和实际测量结果,发现两者结果的曲线基本吻合,证明计算模型是正确的。应用钟形短时脉冲实现水声材料声特性的宽带测量,有益于降低样品边缘衍射干扰。并建立了测量水声材料大面积板状样品声压反射系数、声压透射系数和吸声系数的压力罐测量系统,罐体内尺寸Φ4 m×12 m,最高静水压4.5 MPa,测量频率范围1~30 kHz。对标准样品(尺寸1m×1m)进行了测量实验,其测量结果和理论曲线有很好的吻合,参量源测量法得到了验证;之后,通过对一块橡胶板样品在不同静压力下的吸声性能进行了测量和有效评估,进一步确认了参量源测量法在压力罐这样有限水域中的潜在应用价值。      

Active control of the volume acquisition noise in functional magnetic resonance imaging: method and psychoacoustical evaluation.

Functional magnetic resonance imaging (fMRI) provides a noninvasive tool for observing correlates of neural activity in the brain while a subject listens to sound. However, intense acoustic noise is generated in the process of capturing MR images. This noise stimulates the auditory nervous system, limiting the dynamic range available for displaying stimulus-driven activity. The noise is potentially damaging to hearing and is distracting for the subject. In an active noise control (ANC) system, a reference sample of a noise is processed to form a sound which adds destructively with the noise at the listener's ear. We describe an implementation of ANC in the electromagnetically hostile and physically compact MRI scanning environment. First, a prototype system was evaluated psychoacoustically in the laboratory, using the electrical drive to a noise-generating loudspeaker as the reference. This system produced 10-20 dB of subjective noise-reduction between 250 Hz and 1 kHz, and smaller amounts at higher frequencies. The system was modified to operate in a real MR scanner where the reference was obtained by recording the acoustic scanner noise. Objective reduction by 30-40 dB of the most intense component in scanner noises was realized between 500 Hz and 3500 Hz, and subjective reduction of 12 dB and 5 dB in tests at frequencies of 600 Hz and at 1.9 kHz, respectively. Although the benefit of ANC is limited by transmission paths to the cochlea other than air-conduction routes from the auditory meatus, ANC achieves worthwhile attenuation even in the frequency range of maximum bone conduction (1.5-2 kHz). ANC should, therefore, be generally useful during auditory fMRI.     

Equal autophonic level curves under different room acoustics conditions

The indirect auditory feedback from one's own voice arises from sound reflections at the room boundaries or from sound reinforcement systems. The relative variations of indirect auditory feedback are quantified through room acoustic parameters such as the room gain and the voice support, rather than the reverberation time. Fourteen subjects matched the loudness level of their own voice (the autophonic level) to that of a constant and external reference sound, under different synthesized room acoustics conditions. The matching voice levels are used to build a set of equal autophonic level curves. These curves give an indication of the amount of variation in voice level induced by the acoustic environment as a consequence of the sidetone compensation or Lombard effect. In the range of typical rooms for speech, the variations in overall voice level that result in a constant autophonic level are on the order of 2 dB, and more than 3 dB in the 4 kHz octave band. By comparison of these curves with previous studies, it is shown that talkers use acoustic cues other than loudness to adjust their voices when speaking in different rooms.     

Mechanisms for subcritical penetration into a sandy bottom: experimental and modeling results

This paper presents preliminary results of a recent study whose overall objectives are to determine the mechanisms contributing significantly to subcritical acoustic penetration into ocean sediments, and to quantify the results for use in sonar performance prediction for the detection of buried objects. In situ acoustic measurements were performed on a sandy bottom whose geoacoustical and geomorphological properties were also measured. A parametric array mounted on a tower moving on a rail was used to insonify hydrophones located above and below the sediment interface. Data covering grazing angles both above and below the nominal critical angle and in the frequency range 2-15 kHz were acquired and processed. The results are compared to two models that account for scattering of sound at the rough water-sediment interface into the sediment. Although all possible mechanisms for subcritical penetration are not modeled, the levels predicted by both models are consistent with the levels observed in the experimental data. For the specific seafloor and experimental conditions examined, the analysis suggests that for frequencies below 5-7 kHz sound penetration into the sediment at subcritical insonification is dominated by the evanescent field, while scattering due to surface roughness is the dominant mechanism at higher frequencies.     

Localization by interaural time difference (ITD): effects of interaural frequency mismatch.

A commonly accepted physiological model for lateralization of low-frequency sounds by interaural time delay (ITD) stipulates that binaural comparison neurons receive input from frequency-matched channels from each ear. Here, the effects of hypothetical interaural frequency mismatches on this model are reported. For this study, the cat's auditory system peripheral to the binaural comparison neurons was represented by a neurophysiologically derived model, and binaural comparison neurons were represented by cross-correlators. The results of the study indicate that, for binaural comparison neurons receiving input from one cochlear channel from each ear, interaural CF mismatches may serve to either augment or diminish the effective difference in ipsilateral and contralateral axonal time delays from the periphery to the binaural comparison neuron. The magnitude of this increase or decrease in the effective time delay difference can be up to 400 microseconds for CF mismatches of 0.2 octaves or less for binaural neurons with CFs between 250 Hz and 2.5 kHz. For binaural comparison neurons with nominal CFs near 500 Hz, the 25-microsecond effective time delay difference caused by a 0.012-octave CF mismatch is equal to the ITD previously shown to be behaviorally sufficient for the cat to lateralize a low-frequency sound source.     

液体材料超声处理过程中声场和流场的分布规律研究

针对合金熔体等液体材料的超声处理过程,选取水作为透明模型材料,采用数值模拟计算和示踪粒子实验方法,研究了20和490 kHz两种频率超声作用下水中的声场和流场分布.结果表明,增大变幅杆半径能够提高水中声压水平,扩大空化效应的发生区域.当超声频率为20 kHz时,水中声压最大值出现在超声变幅杆下端面处,且声压沿传播距离的增大而显著减小.如果超声频率增加至490 kHz,水中的声压级相比于20 kHz时明显提高,且声压沿着超声传播方向呈现出周期性振荡特征.两种频率超声作用下水中的流场呈现相似的分布特征,且平均流速均随着变幅杆半径增大表现出先升高后降低的趋势.变幅杆半径相同时,20 kHz频率超声作用下水中的平均流速高于490 kHz频率超声.采用示踪粒子图像测速技术实时观察和测定了水中的流速分布,发现其与计算结果基本一致.     

The auditory periphery of the ferret. I: Directional response properties and the pattern of interaural level differences

The transformations of sound by the auditory periphery of the ferret have been investigated using an impulse response technique for a large number of sound locations surrounding the animal. Individual frequencies were extracted from the detailed spectral transformation functions (STFs) obtained for each stimulus location and, using sophisticated spatial interpolation routines, were used to calculate the directional response of the periphery at that frequency. The strength of the directional response was directly related to the analysis frequency. Furthermore, as the analysis frequency was increased to 20 kHz, the orientation of the directional response increased in elevation from the horizon (E0 degrees) to about E30 degrees, while the azimuthal location remained fairly constant at 30 degrees to 40 degrees from the midline. For analysis frequencies above 20 kHz, the response became increasingly directional toward the ipsilateral interaural axis. The interaural level differences (ILDs) were also calculated for all animals studied. ILDs increased from around 5 to 25 dB over the range of frequencies from 3-24 kHz. The two-dimensional patterns of iso-ILD contours were roughly concentric and centered on the interaural axis for frequencies below 16 kHz. For higher frequencies, there was a tendency for the ILD contours to be centered on more anterior and inferior locations. The increased directionality of the auditory periphery with increasing analysis frequency, together with the presence of sharp nulls in the response at high analysis frequencies, is consistent with a diffractive effect produced by the aperture of the pinna. However, this simple model does not predict the directional responses over the low to middle frequency range.     

Experimental measurements of acoustical properties of snow and inverse characterization of its geometrical parameters

Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63–6300 Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1 kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1 kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45 dB cm⁻¹ to 3.77 dB cm⁻¹ for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and −6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.     

An efficient sound speed estimation method to enhance image resolution in ultrasound imaging

Most of clinical ultrasound imaging systems use a pre-determined sound speed, mostly 1540 m/s, in transmit- and receive-beamforming while actual sound speed varies depending on tissue composition and temperature. Sound speed errors, particularly in receive-beamforming, lead to resolution degradation and sensitivity loss in ultrasound imaging. In this paper, we propose a sound speed estimation method in which an optimal sound speed, the speed that makes the echo signal delays at the transducer elements be best matched to the theoretical delays, is estimated by maximizing the beamformed echo signal amplitude with respect to the sound speed and the reflector displacement from the central axis of the ultrasound beam. Since the sound speed can be estimated from the echo signals on several scan lines, the proposed method does not require excessive computation. Experimental imaging studies of phantoms and porcine tissue with a 6 MHz 128-element linear probe and a 3 MHz 128-element convex probe have shown that spatial resolution, particularly in the lateral direction, can be improved by the proposed method.     

Frequency characteristics of sound transmission in middle ears from Norwegian cattle, and the effect of static pressure differences across the tympanic membrane and the footplate

For 23 cadaver ears from Norwegian cattle, frequency characteristics for the round-window volume displacement relative to the sound pressure at the eardrum have been measured, and are compared to earlier results for human ears [M. Kringlebotn and T. Gundersen, J. Acoust. Soc. Am. 77(1), 159-164 (1985)]. For human as well as for cattle ears, mean amplitude curves have peaks at about 0.7 kHz. At lower frequencies, the mean amplitude for cattle ears is about 5 dB smaller than for human ears. The amplitude curves cross at about 2 kHz, and toward higher frequencies the amplitude for cattle ears becomes increasingly larger. If amplitude curves are roughly approximated by straight lines above 1 kHz, the slope for cattle ears is about -5 dB/octave as compared to about -15 dB/octave for human ears. The phase of the round-window volume displacement lags behind the phase of the sound pressure at the tympanic membrane. The phase lag is close to zero below 0.2 kHz, but increases to about 3.5 pi at 20 kHz for cattle ears, as compared to less than 2 pi for human ears. Further investigations are needed in order to explain the observed differences. Sound transmission in the ear decreases with an increasing static pressure difference across the tympanic membrane, especially at frequencies below 1 kHz, where pressure differences of 10 and 60 cm water cause mean transmission losses of about 10 and 26 dB, respectively, the losses being somewhat larger for overpressures than for underpressures in the ear canal. At higher frequencies, the transmission losses are smaller. For small overpressures, and in a limited frequency range near 3 kHz, even some transmission enhancement may occur. Static pressure variations in the inner ear have only a minor influence on sound transmission. Static pressures relative to the middle ear in the range 0-60 cm water cause mean sound transmission losses less than 5 dB below 1 kHz, and negligible losses at higher frequencies.     

Toneburst-evoked auditory brainstem response in a leopard seal, Hydrurga leptonyx

Toneburst-evoked auditory brainstem responses (ABRs) were recorded in a captive subadult male leopard seal. Three frequencies from 1 to 4 kHz were tested at sound levels from 68 to 122 dB peak equivalent sound pressure level (peSPL). Results illustrate brainstem activity within the 1-4 kHz range, with better hearing sensitivity at 4 kHz. As is seen in human ABR, only wave V is reliably identified at the lower stimulus intensities. Wave V is present down to levels of 82 dB peSPL in the right ear and 92 dB peSPL in the left ear at 4 kHz. Further investigations testing a wider frequency range on seals of various sex and age classes are required to conclusively report on the hearing range and sensitivity in this species.     

Monaural and binaural hearing directivity in the bottlenose dolphin: evoked-potential study

Hearing thresholds as a function of sound-source azimuth were measured in bottlenose dolphins using an auditory evoked potential (AEP) technique. AEP recording from a region next to the ear allowed recording monaural responses. Thus, a monaural directivity diagram (a threshold-vs-azimuth function) was obtained. For comparison, binaural AEP components were recorded from the vertex to get standard binaural directivity diagrams. Both monaural and binaural diagrams were obtained at frequencies ranging from 8 to 128 kHz in quarter-octave steps. At all frequencies, the monaural diagram demonstrated asymmetry manifesting itself as: (1) lower thresholds at the ipsilateral azimuth as compared to the symmetrical contralateral azimuth and (2) ipsilateral shift of the lowest-threshold point. The directivity index increased with frequency: at the ipsilateral side it rose from 4.7 to 17.8 dB from 11.2 to 128 kHz, and from 10.5 to 15.6 dB at the contralateral side. The lowest-threshold azimuth shifted from 0 degrees at 90-128 kHz to 22.5 degrees at 8-11.2 kHz. The frequency-dependent variation of the lowest-threshold azimuth indicates the presence of two sound-receiving apertures at each head side: a high-frequency aperture with the axis directed frontally, and a low-frequency aperture with the axis directed laterally.     

Measurement of sound-pressure distribution in replicas of the oral cavity.

The spatial distributions of sound pressure in artificial oral cavities were measured to examine the characteristics of wave propagation in the vocal tract. The measurement was performed with plaster replicas of the oral cavity, and pure tones were used as the driving signals to obtain both amplitude and phase distributions at varied frequencies. Plane-wave propagation, which has been widely assumed for speech production models, was examined from the measured spatial distributions of sound pressure. Trajectories of media particles and vectorial maps of acoustic intensity, which can be computed from the measured pressure distributions, were also presented to visualize the acoustic field in the oral cavity. The results showed that at certain frequencies there existed points where sound pressure was absolutely zero, with the phase spatially circulating around them. Up to about 4 kHz, except at these certain frequencies, the wave front was almost one-dimensional, though an amplitude gradient was seen in the vertical direction.     

Responses of neurons to click-pairs as simulated echoes: auditory nerve to auditory cortex

When two identical sounds are presented from different locations with a short interval between them, the perception is of a single sound source at the location of the leading sound. This "precedence effect" is an important behavioral phenomenon whose neural basis is being increasingly studied. For this report, neural responses were recorded to paired clicks with varying interstimulus intervals, from several structures of the ascending auditory system in unanesthetized animals. The structures tested were the auditory nerve, anteroventral cochlear nucleus, superior olivary complex, inferior colliculus, and primary auditory cortex. The main finding is a progressive increase in the duration of the suppressive effect of the leading sound (the conditioner) on the response to the lagging sound (the probe). The first major increase occurred between the lower brainstem and inferior colliculus, and the second between the inferior colliculus and auditory cortex. In neurons from the auditory nerve, cochlear nucleus, and superior olivary complex, 50% recovery of the response to the probe occurred, on average, for conditioner and probe intervals of approximately 2 ms. In the inferior colliculus, 50% recovery occurred at an average separation of approximately 7 ms, and in the auditory cortex at approximately 20 ms. Despite these increases in average recovery times, some neurons in every structure showed large responses to the probe within the time window for precedence (approximately 1-4 ms for clicks). This indicates that during the period of the precedence effect, some information about echoes is retained. At the other extreme, for some cortical neurons the conditioner suppressed the probe response for intervals of up to 300 ms. This is in accord with behavioral results that show dominance of the leading sound for an extended period beyond that of the precedence effect. Other transformations as information ascended included an increased variety in the shapes of the recovery functions in structures subsequent to the nerve, and neurons "tuned" to particular conditioner-probe intervals in the auditory cortex. These latter are reminiscent of neurons tuned to echo delay in bats, and may contribute to the perception of the size of the acoustic space.     

Behavioral responses of two captive bottlenose dolphins (Tursiops truncatus) to a continuous 50 kHz tone

At present, the fundamental frequencies of signals of most commercially available acoustic alarms to deter small cetaceans are below 20 kHz, but it is not well ascertained whether higher frequencies have a deterrent effect on bottlenose dolphins (Tursiops truncatus). Two captive bottlenose dolphins housed in a floating pen were subjected to a continuous pure tone at 50 kHz with a source level of 160 ± 2 dB (re 1 μPa, rms). The behavioral responses of dolphins were judged by comparing surfacing distance relative to the sound source, number of surfacings, and number of echolocation clicks produced, during forty 15 min baseline periods with forty 15 min test periods (four sessions per day, 40 sessions in total). On all 10 study days, surfacing distance and the number of surfacings increased while click production decreased during broadcasts of test sound. The avoidance threshold sound pressure level for a continuous 50 kHz tone for the bottlenose dolphins, in the context of this study, was estimated to be 144 ± 2 dB (re 1 μPa, rms). The results indicated that a continuous 50 kHz tonal signal can deter bottlenose dolphins from an area.     

Research of the planar optical fiber Bragg grating hydrophone probe

This paper presents the planar Fiber Bragg Grating （FBG） hydrophone probe sensing principle, and theoretically and experimentally researches the probe structure sensitivity, the receiving sensitivity frequency response characteristic and the acceleration response property. Planar sheet is made of stainless steel, its thickness is 0.15 mm, its diameter is 15mm, and the length of hollow circular shell is 20 mm. For this size of the structure, the probe structure sensitivity is up to 23 fm/Pa, which is about 7300 times of the value of the bare fiber. The resonance frequency is 6.5 kHz, and the amplitude-frequency curve of the receiving sensitivity response is relatively flat within the frequency range of 100 Hz to 5.5 kHz. The output yielded by one unit acceleration （1m/s2） is equivalent to （2.52 to 3.26 Pa） acoustic pressure acting output. This probe structure is easy to form FBG hydrophone array by multiplexing technique. The research shows that this planar structure not only can form FBG hydrophone probe, but also can constitute optical FBG laser hydrophone probe. The structure can realize different bandwidth, different range acoustic pressure measurement by adjusting the geometrical size of the sheet.