Showing papers in "Journal of the Acoustical Society of America in 2010"

Systems and methods for responding to natural language speech utterance

Abstract: Systems and methods are provided for receiving speech and non-speech communications of natural language questions and/or commands, transcribing the speech and non-speech communications to textual messages, and executing the questions and/or commands. The invention applies context, prior information, domain knowledge, and user specific profile data to achieve a natural environment for one or more users presenting questions or commands across multiple domains. The systems and methods creates, stores and uses extensive personal profile information for each user, thereby improving the reliability of determining the context of the speech and non-speech communications and presenting the expected results for a particular question or command.

Ultrasound treatment system

Abstract: An ultrasound treatment system comprises an ultrasonic transducer, a handpiece, a probe, a sheath, a clamping member, an operation unit, an operating member, a suction base, and a perfusion base. The ultrasonic transducer generates ultrasonic vibrations. The handpiece has the ultrasonic transducer incorporated therein. The probe is connected to the ultrasonic transducer for transmitting ultrasonic vibrations to a distal member realizing a stationary portion that is a treatment portion for treating a living tissue. The sheath serves as a protecting member for shielding the probe. The clamping member is opposed to the distal member at the distal end of the sheath for clamping a living tissue in cooperation with the distal member. The operation unit is manipulated for clamping a living tissue with the clamping member and distal member or freeing the living tissue therefrom.

A principal components model of soundscape perception

Abstract: There is a need for a model that identifies underlying dimensions of soundscape perception, and which may guide measurement and improvement of soundscape quality With the purpose to develop such a model, a listening experiment was conducted One hundred listeners measured 50 excerpts of binaural recordings of urban outdoor soundscapes on 116 attribute scales The average attribute scale values were subjected to principal components analysis, resulting in three components: Pleasantness, eventfulness, and familiarity, explaining 50, 18 and 6% of the total variance, respectively The principal-component scores were correlated with physical soundscape properties, including categories of dominant sounds and acoustic variables Soundscape excerpts dominated by technological sounds were found to be unpleasant, whereas soundscape excerpts dominated by natural sounds were pleasant, and soundscape excerpts dominated by human sounds were eventful These relationships remained after controlling for the overall soundscape loudness (Zwicker's N(10)), which shows that 'informational' properties are substantial contributors to the perception of soundscape The proposed principal components model provides a framework for future soundscape research and practice In particular, it suggests which basic dimensions are necessary to measure, how to measure them by a defined set of attribute scales, and how to promote high-quality soundscapes

Modeling power law absorption and dispersion for acoustic propagation using the fractional Laplacian

Abstract: The efficient simulation of wave propagation through lossy media in which the absorption follows a frequency power law has many important applications in biomedical ultrasonics. Previous wave equations which use time-domain fractional operators require the storage of the complete pressure field at previous time steps (such operators are convolution based). This makes them unsuitable for many three-dimensional problems of interest. Here, a wave equation that utilizes two lossy derivative operators based on the fractional Laplacian is derived. These operators account separately for the required power law absorption and dispersion and can be efficiently incorporated into Fourier based pseudospectral and k-space methods without the increase in memory required by their time-domain fractional counterparts. A framework for encoding the developed wave equation using three coupled first-order constitutive equations is discussed, and the model is demonstrated through several one-, two-, and three-dimensional simulations.

Perceptual assessment of quality of urban soundscapes with combined noise sources and water sounds

Abstract: In this study, urban soundscapes containing combined noise sources were evaluated through field surveys and laboratory experiments. The effect of water sounds on masking urban noises was then examined in order to enhance the soundscape perception. Field surveys in 16 urban spaces were conducted through soundwalking to evaluate the annoyance of combined noise sources. Synthesis curves were derived for the relationships between noise levels and the percentage of highly annoyed (%HA) and the percentage of annoyed (%A) for the combined noise sources. Qualitative analysis was also made using semantic scales for evaluating the quality of the soundscape, and it was shown that the perception of acoustic comfort and loudness was strongly related to the annoyance. A laboratory auditory experiment was then conducted in order to quantify the total annoyance caused by road traffic noise and four types of construction noise. It was shown that the annoyance ratings were related to the types of construction noise in combination with road traffic noise and the level of the road traffic noise. Finally, water sounds were determined to be the best sounds to use for enhancing the urban soundscape. The level of the water sounds should be similar to or not less than 3 dB below the level of the urban noises.

Remote control signaling using audio watermarks

Abstract: A system for using a watermark embedded in an audio signal to remotely control a device. Various devices such as toys, computers, and appliances, equipped with an appropriate detector, detect the hidden signals, which can trigger an action, or change a state of the device. The watermarks can be used with a “time gate” device, where detection of the watermark opens a time interval within which a user is allowed to perform an action, such as pressing a button, typing in an answer, turning a key in a lock, etc.

Resonator and a method of manufacturing the same, and oscillator and electronic apparatus including the same

Abstract: Disclosed herein is a resonator including, a vibrating portion having a conductor portion, and three or more insulating portions provided so as to electrically separate the conductor portion into a plurality of blocks, wherein when a potential difference is caused across both ends in each of the three or more insulating portions, the vibrating portion carries out a resonance vibration based on a longitudinal vibration in accordance with a frequency of an A.C. signal inputted to each of corresponding ones of the plurality of blocks in the conductor portion.

Suspension control apparatus

Abstract: A suspension control apparatus includes a variable damping coefficient type shock absorber disposed between sprung mass and unsprung mass of a vehicle and an actuator for setting and adjusting a damping coefficient of the variable damping coefficient type shock absorber on the basis of a control signal. An upward and downward absolute velocity detector for detecting an upward absolute velocity and a downward absolute velocity of the vehicle is provided. A control unit changes a signal from the upward and downward absolute velocity detector in accordance with a running condition of the vehicle to obtain a control target signal. A control signal generator outputs the control signal for the actuator on the basis of the control target signal from the control unit. A signal representative of the roughness of a road surface on which the vehicle is running is generated and a feature of the control unit is adjusted for changing the control signal on the basis of the signal representative of the road surface roughness.

Systems and methods for making and using a motor distally-positioned within a catheter of an intravascular ultrasound imaging system

Abstract: A catheter assembly for an intravascular ultrasound system includes an imaging core configured and arranged for inserting into a distal end of a lumen of a catheter. The imaging core includes at least one transducer mounted to a driveshaft and configured and arranged for transforming applied electrical signals to acoustic signals and also for transforming received echo signals to electrical signals. A motor is coupled to the driveshaft between the one or more transducers and the transformer. The motor includes a rotatable magnet and at least two magnetic field windings disposed around at least a portion of the magnet.

Personal acoustic device position determination

Abstract: A apparatus and method for determining an operating state of an earpiece of a personal acoustic device and/or the entirety of the personal acoustic device by analyzing signals output by at least an inner microphone disposed within a cavity of a casing of the earpiece and an outer microphone disposed on the personal acoustic device in a manner acoustically coupling it to the environment outside the casing of the earpiece.

Characteristics of second harmonic generation of Lamb waves in nonlinear elastic plates

Abstract: This paper investigates the characteristics of the second harmonic generation of Lamb waves in a plate with quadratic nonlinearity. Analytical asymptotic solutions to Lamb waves are first obtained through the use of a perturbation method. Then, based on a careful analysis of these asymptotic solutions, it is shown that the cross-modal generation of a symmetric second harmonic mode by an antisymmetric primary mode is possible. These solutions also demonstrate that modes showing internal resonance-nonzero power flux to the second harmonic mode, plus phase velocity matching-are most useful for measurements. In addition, when using finite wave packets, which is the case in most experimental measurements, group velocity matching is required for a cumulative increase in the second harmonic amplitude with propagation distance. Finally, five mode types (which are independent of material properties) that satisfy all three requirements for this cumulative increase in second harmonic amplitude-nonzero power flux, plus phase and group velocity matching-are identified. These results are important for the development of an experimental procedure to measure material nonlinearity with Lamb waves.

Individual variability in cue-weighting and lexical tone learning

Abstract: Speech sound patterns can be discerned using multiple acoustic cues. The relative weighting of these cues is known to be language-specific. Speech-sound training in adults induces changes in cue-weighting such that relevant acoustic cues are emphasized. In the current study, the extent to which individual variability in cue weighting contributes to differential success in learning to use foreign sound patterns was examined. Sixteen English-speaking adult participants underwent a sound-to-meaning training paradigm, during which they learned to incorporate Mandarin linguistic pitch contours into words. In addition to cognitive tests, measures of pitch pattern discrimination and identification were collected from all participants. Reaction time data from the discrimination task was subjected to 3-way multidimensional scaling to extract dimensions underlying tone perception. Two dimensions relating to pitch height and pitch direction were found to underlie non-native tone space. Good learners attended more to pitch direction relative to poor learners, before and after training. Training increased the ability to identify and label pitch direction. The results demonstrate that variability in the ability to successfully learn to use pitch in lexical contexts can be explained by pre-training differences in cue-weighting.

Beyond arousal: Valence and potency/control cues in the vocal expression of emotion

Abstract: The important role of arousal in determining vocal parameters in the expression of emotion is well established. There is less evidence for the contribution of emotion dimensions such as valence and potency/control to vocal emotion expression. Here, an acoustic analysis of the newly developed Geneva Multimodal Emotional Portrayals corpus, is presented to examine the role of dimensions other than arousal. This corpus contains twelve emotions that systematically vary with respect to valence, arousal, and potency/control. The emotions were portrayed by professional actors coached by a stage director. The extracted acoustic parameters were first compared with those obtained from a similar corpus [Banse and Scherer (1996). J. Pers. Soc. Psychol. 70, 614-636] and shown to largely replicate the earlier findings. Based on a principal component analysis, seven composite scores were calculated and were used to determine the relative contribution of the respective vocal parameters to the emotional dimensions arousal, valence, and potency/control. The results show that although arousal dominates for many vocal parameters, it is possible to identify parameters, in particular spectral balance and spectral noise, that are specifically related to valence and potency/control.

Effects of the acoustic properties of infant-directed speech on infant word recognition

Abstract: A number of studies have examined the acoustic differences between infant-directed speech (IDS) and adult-directed speech, suggesting that the exaggerated acoustic properties of IDS might facilitate infants’ language development. However, there has been little empirical investigation of the acoustic properties that infants use for word learning. The goal of this study was thus to examine how 19-month-olds’ word recognition is affected by three acoustic properties of IDS: slow speaking rate, vowel hyper-articulation, and wide pitch range. Using the intermodal preferential looking procedure, infants were exposed to half of the test stimuli (e.g., Where’s the book?) in typical IDS style. The other half of the stimuli were digitally altered to remove one of the three properties under investigation. After the target word (e.g., book) was spoken, infants’ gaze toward target and distractor referents was measured frame by frame to examine the time course of word recognition. The results showed that slow speaking rate and vowel hyper-articulation significantly improved infants’ ability to recognize words, whereas wide pitch range did not. These findings suggest that 19-month-olds’ word recognition may be affected only by the linguistically relevant acoustic properties in IDS.

Spectral and temporal changes to speech produced in the presence of energetic and informational maskers.

Abstract: Talkers change the way they speak in noisy conditions. For energetic maskers, speech production changes are relatively well-understood, but less is known about how informational maskers such as competing speech affect speech production. The current study examines the effect of energetic and informational maskers on speech production by talkers speaking alone or in pairs. Talkers produced speech in quiet and in backgrounds of speech-shaped noise, speech-modulated noise, and competing speech. Relative to quiet, speech output level and fundamental frequency increased and spectral tilt flattened in proportion to the energetic masking capacity of the background. In response to modulated backgrounds, talkers were able to reduce substantially the degree of temporal overlap with the noise, with greater reduction for the competing speech background. Reduction in foreground-background overlap can be expected to lead to a release from both energetic and informational masking for listeners. Passive changes in speech rate, mean pause length or pause distribution cannot explain the overlap reduction, which appears instead to result from a purposeful process of listening while speaking. Talkers appear to monitor the background and exploit upcoming pauses, a strategy which is particularly effective for backgrounds containing intelligible speech.

Effect of age at onset of deafness on binaural sensitivity in electric hearing in humans

Abstract: Sensitivity to binaural cues was studied in 11 bilateral cochlear implant users, all of whom received both of their cochlear implants as adults, but who varied in the age at onset of deafness, from pre-lingual to childhood-onset to adult-onset. Sensitivity to interaural timing difference (ITD) and interaural level difference (ILD) cues was measured at basal, middle, and apical pitch-matched places of stimulation along the cochlear arrays, using a stimulation rate of 100 Hz. Results show that there is a trend for people whose onset of deafness occurred during adult life or late childhood to retain at least some sensitivity to ITDs, whereas people with onset of deafness earlier in life were insensitive to ITDs. In contrast, ILD cue sensitivity was present in all subjects. There were no effects of place of stimulation on binaural sensitivity, suggesting that there is no indication of a dependence of ITD sensitivity on apical vs basal electrode location.

Between-speaker and within-speaker variation in speech tempo of American English.

Abstract: This study characterizes the speech tempo (articulation rate, excluding pauses) of two distinct varieties of American English taking into account both between-speaker and within-speaker variation. Each of 192 speakers from Wisconsin (the northern variety) and from North Carolina (the southern variety), men and women, ranging in age from children to old adults, read a set of sentences and produced a spontaneous unconstrained talk. Articulation rate in spontaneous speech was modeled using fixed-mixed effects analyses. The models explored the effects of the between-speaker factors dialect, age and gender and included each phrase and its length as a source of both between- and within-speaker variation. The major findings are: (1) Wisconsin speakers speak significantly faster and produce shorter phrases than North Carolina speakers; (2) speech tempo changes across the lifespan, being fastest for individuals in their 40s; (3) men speak faster than women and this effect is not related to the length of phrases they produce. Articulation rate in reading was slower than in speaking and the effects of gender and age also differed in reading and spontaneous speech. The effects of dialect in reading remained the same, showing again that Wisconsin speakers had faster articulation rates than did North Carolina speakers.

Multicenter evaluation of signal enhancement algorithms for hearing aids.

Abstract: In the framework of the European HearCom project, promising signal enhancement algorithms were developed and evaluated for future use in hearing instruments. To assess the algorithms' performance, five of the algorithms were selected and implemented on a common real-time hardware/software platform. Four test centers in Belgium, The Netherlands, Germany, and Switzerland perceptually evaluated the algorithms. Listening tests were performed with large numbers of normal-hearing and hearing-impaired subjects. Three perceptual measures were used: speech reception threshold (SRT), listening effort scaling, and preference rating. Tests were carried out in two types of rooms. Speech was presented in multitalker babble arriving from one or three loudspeakers. In a pseudo-diffuse noise scenario, only one algorithm, the spatially preprocessed speech-distortion-weighted multi-channel Wiener filtering, provided a SRT improvement relative to the unprocessed condition. Despite the general lack of improvement in SRT, some algorithms were preferred over the unprocessed condition at all tested signal-to-noise ratios (SNRs). These effects were found across different subject groups and test sites. The listening effort scores were less consistent over test sites. For the algorithms that did not affect speech intelligibility, a reduction in listening effort was observed at 0 dB SNR.

A direct approach for the design of chirp stimuli used for the recording of auditory brainstem responses

Abstract: A recent study evaluates auditory brainstem responses (ABRs) evoked by chirps of different durations (sweeping rates) [Elberling et al. (2010). J. Acoust. Soc. Am. 128, 215–223]. The study demonstrates that shorter chirps are most efficient at higher levels of stimulation whereas longer chirps are most efficient at lower levels. Mechanisms other than the traveling wave delay, in particular, upward spread of excitation and changes in cochlear-neural delay with level, are suggested to be responsible for these findings. As a consequence, delay models based on estimates of the traveling wave delay are insufficient for the design of chirp stimuli, and another delay model based on a direct approach is therefore proposed. The direct approach uses ABR-latencies from normal-hearing subjects in response to octave-band chirps over a wide range of levels. The octave-band chirps are constructed by decomposing a broad-band chirp, and constitute a subset of the chirp. The delay compensations of the proposed model are similar to those found in the previous experimental study, which thus verifies the results of the proposed model.

Revision, extension, and evaluation of a binaural speech intelligibility model.

Abstract: This study presents revision, extension, and evaluation of a binaural speech intelligibility model (Beutelmann, R, and Brand, T (2006) J Acoust Soc Am 120, 331-342) that yields accurate predictions of speech reception thresholds (SRTs) in the presence of a stationary noise source at arbitrary azimuths and in different rooms The modified model is based on an analytical expression of binaural unmasking for arbitrary input signals and is computationally more efficient, while maintaining the prediction quality of the original model An extension for nonstationary interferers was realized by applying the model to short time frames of the input signals and averaging over the predicted SRT results Binaural SRTs from 8 normal-hearing and 12 hearing-impaired subjects, incorporating all combinations of four rooms, three source setups, and three noise types were measured and compared to the model's predictions Depending on the noise type, the parametric correlation coefficients between observed and predicted SRTs were 080-093 for normal-hearing subjects and 059-080 for hearing-impaired subjects The mean absolute prediction error was 3 dB for the mean normal-hearing data and 4 dB for the individual hearing-impaired data 70% of the variance of the SRTs of hearing-impaired subjects could be explained by the model, which is based only on the audiogram

The effect of tectorial membrane and basilar membrane longitudinal coupling in cochlear mechanics

Abstract: Most mathematical models of the mammalian cochlea neglect structural longitudinal coupling. However, recent experimental data suggest that viscoelastic longitudinal coupling, in the basilar membrane (BM) and the tectorial membrane (TM), is non-negligible. In this paper, mathematical models for BM and TM longitudinal coupling are presented to determine the influence of such a coupling on the tuning of the BM. The longitudinal coupling models are added to a macroscopic linear model of the guinea pig cochlea that includes the micromechanics of the organ of Corti and outer hair cell (OHC) somatic motility. The predictions of the BM response to acoustic stimulus show that the characteristic frequency is controlled by a TM radial resonance and that TM longitudinal coupling has a more significant effect than BM longitudinal coupling. TM viscoelasticity controls the sharpness of the BM frequency response and the duration of the impulse response. The results with realistic TM longitudinal coupling are more consistent with experiments. The model predicts that OHC somatic electromotility is able to supply power to the BM at frequencies well above the cutoff of the OHC basolateral membrane. Moreover, TM longitudinal coupling is predicted to stabilize the cochlea and enable a higher BM sensitivity to acoustic stimulation.

Trans-dimensional geoacoustic inversion

Abstract: This paper develops a general trans-dimensional Bayesian methodology for geoacoustic inversion. Trans-dimensional inverse problems are a generalization of fixed-dimensional inversion that includes the number and type of model parameters as unknowns in the problem. By extending the inversion state space to multiple subspaces of different dimensions, the posterior probability density quantifies the state of knowledge regarding inversion parameters, including effects due to limited knowledge about appropriate parametrization of the environment and error processes. The inversion is implemented here using a reversible-jump Markov chain Monte Carlo algorithm and the seabed is parametrized using a partition model. Unknown data errors are addressed by including a data-error model. Jumps between dimensions are implemented with a birth–death methodology that allows transitions between dimensions by adding or removing interfaces while maintaining detailed balance in the Markov chain. Trans-dimensional inversion results in an inherently parsimonious solution while partition modeling provides a naturally self-regularizing algorithm based on data information content, not on subjective regularization functions. Together, this results in environmental estimates that quantify appropriate seabed structure as supported by the data, allowing sharp discontinuities while approximating smooth transitions where needed. This approach applies generally to geoacoustic inversion and is illustrated here with seabed reflection-coefficient data.

Passive cavitation mapping for localization and tracking of bubble dynamics

Abstract: Current acoustic techniques for studying cavitation dynamics are only readily applicable to single-bubble activity, while optical methods can only be used in transparent media. However, multi-bubble cavitation often occurs in opaque media such as biological tissue. Here, the signals received passively by each of the 64 channels of a diagnostic ultrasound array are used to localize and separate emissions from several bubble clusters cavitating in agar gel, thereby providing a method of observing cavitation dynamics. The method has a high spatiotemporal resolution and is applicable to cavitation in opaque media.

Acoustic resonator performance enhancement using selective metal etch

Abstract: An acoustic resonator that includes a substrate, a first electrode, a layer of piezoelectric material, and a second electrode. The substrate has a first surface and the first electrode is adjacent the first surface of the substrate. The layer of piezoelectric material is adjacent the first electrode. The second electrode is adjacent the layer of piezoelectric material, and the second electrode lies in a first plane and has an edge. The layer of piezoelectric material has a recessed feature adjacent the edge of the second electrode.

Subharmonic behavior of phospholipid-coated ultrasound contrast agent microbubbles.

Abstract: Coated microbubbles, unlike tissue are able to scatter sound subharmonically. Therefore, the subharmonic behavior of coated microbubbles can be used to enhance the contrast in ultrasound contrast imaging. Theoretically, a threshold amplitude of the driving pressure can be calculated above which subharmonic oscillations of microbubbles are initiated. Interestingly, earlier experimental studies on coated microbubbles demonstrated that the threshold for these bubbles is much lower than predicted by the traditional linear viscoelastic shell models. This paper presents an experimental study on the subharmonic behavior of differently sized individual phospholipid coated microbubbles. The radial subharmonic response of the microbubbles was recorded with the Brandaris ultra high-speed camera as a function of both the amplitude and the frequency of the driving pulse. Threshold pressures for subharmonic generation as low as 5 kPa were found near a driving frequency equal to twice the resonance frequency of the bubble. An explanation for this low threshold pressure is provided by the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499–3505 (2005)] . It is shown that the change in the elasticity of the bubble shell as a function of bubble radius as proposed in this model, enhances the subharmonic behavior of the microbubbles.

Prediction of binaural speech intelligibility against noise in rooms.

Abstract: In the presence of competing speech or noise, reverberation degrades speech intelligibility not only by its direct effect on the target but also by affecting the interferer. Two experiments were designed to validate a method for predicting the loss of intelligibility associated with this latter effect. Speech reception thresholds were measured under headphones, using spatially separated target sentences and speech-shaped noise interferers simulated in virtual rooms. To investigate the effect of reverberation on the interferer unambiguously, the target was always anechoic. The interferer was placed in rooms with different sizes and absorptions, and at different distances and azimuths from the listener. The interaural coherence of the interferer did not fully predict the effect of reverberation. The azimuth separation of the sources and the coloration introduced by the room also had to be taken into account. The binaural effects were modeled by computing the binaural masking level differences in the studied configurations, the monaural effects were predicted from the excitation pattern of the noises, and speech intelligibility index weightings were applied to both. These parameters were all calculated from the room impulse responses convolved with noise. A 0.95–0.97 correlation was obtained between the speech reception thresholds and their predicted value.

A unifying fractional wave equation for compressional and shear waves.

Abstract: This study has been motivated by the observed difference in the range of the power-law attenuation exponent for compressional and shear waves. Usually compressional attenuation increases with frequency to a power between 1 and 2, while shear wave attenuation often is described with powers less than 1. Another motivation is the apparent lack of partial differential equations with desirable properties such as causality that describe such wave propagation. Starting with a constitutive equation which is a generalized Hooke's law with a loss term containing a fractional derivative, one can derive a causal fractional wave equation previously given by Caputo [Geophys J. R. Astron. Soc. 13, 529-539 (1967)] and Wismer [J. Acoust. Soc. Am. 120, 3493-3502 (2006)]. In the low omegatau (low-frequency) case, this equation has an attenuation with a power-law in the range from 1 to 2. This is consistent with, e.g., attenuation in tissue. In the often neglected high omegatau (high-frequency) case, it describes attenuation with a power-law between 0 and 1, consistent with what is observed in, e.g., dynamic elastography. Thus a unifying wave equation derived properly from constitutive equations can describe both cases.

Maximization of acoustic energy difference between two spaces

Abstract: There has recently been an increasing interest in the generation of a sound field that is audible in one spatial region and inaudible in an adjacent region. The method proposed here ensures the control of the amplitude and phase of multiple acoustic sources in order to maximize the acoustic energy difference between two adjacent regions while also ensuring that evenly distributed source strengths are used. The performance of the method proposed is evaluated by computer simulations and experiments with real loudspeaker arrays in the shape of a circle and a sphere. The proposed method gives an improvement in the efficiency of radiation into the space in which the sound should be audible, while maintaining the acoustic pressure difference between two acoustic spaces. This is shown to give an improvement of performance compared to the contrast control method previously proposed.

Noise suppression device

Abstract: A noise suppression device comprises subband SN ratio calculation means which receives a noise likeness signal, an input signal spectrum and a subband-based estimated noise spectrum, calculates the subband-based input signal average spectrum, calculates a subband-based mixture ratio of the subband-based estimated noise spectrum to the subband-based input signal average spectrum on the basis of the noise likeness signal, and calculates the subband-based SN ratio on the basis of the subband-based estimated noise spectrum, the subband-based input signal average spectrum and the mixture ratio.

Sound absorption of a micro-perforated panel backed by an irregular-shaped cavity.

Abstract: In the pursuit of more effective noise control devices, the cavity backed micro-perforated panel absorber (CBMPPA) is developed in this study. A CBMPPA differs from the conventional micro-perforated panel (MPP) absorber in that the MPP is backed by a trapezoidal cavity, which allows more effective vibroacoustic coupling between the MPP and the cavity. A two-dimensional theoretical model is established and tested both numerically and experimentally. Based on the verified theoretical model, sound absorption performance of a trapezoidal CBMPPA is investigated numerically. Results show that the shape of the backing cavity can significantly alter the sound absorption mechanisms and frequency distribution of overall sound absorption coefficient of the absorber. Further analyses show that acoustic modes that are initially decoupled from the MPP in the rectangular configuration are coupled with the air motion in the MPP, which accounts for the change in absorption pattern of the trapezoidal CBMPPA. By the same token, it also provides the flexibility for tuning the effective absorption range of the absorber. Due to the varying impedance matching conditions, the absorption performance of the trapezoidal CBMPPA exhibits obvious local characteristics over the MPP surface, which contrasts with the spatially uniform absorption in the conventional MPP absorber.