Acoustic Reverberation Research Articles

Reverberation measurement set for the interrupted noise method

This paper describes the methodology of measuring the sound absorption coefficient in a reverberation room. For its purpose, a measuring set was created combining professional with widely available hardware suitable for acoustic reverberation measurements. For the measurement itself, the interrupted noise method was chosen based on the standard ČSN EN ISO 354. Measurement and evaluation of data take place using scripts written in the Python programming language. An effective measuring set was developed both in terms of operation during measurement and in terms of subsequent data processing, accessing and graphical presentation.

Observation of the Relationship between Ocean Bathymetry and Acoustic Bearing-Time Record Patterns Acquired during a Reverberation Experiment in the Southwestern Continental Margin of the Ulleung Basin, Korea

We observed a distinct drop-off region in the bearing-time record of acoustic reverberation data acquired from the south-western continental margin of the Ulleung Basin, East Sea, in the summer of 2015. 3 kHz continuous waves with pulse lengths of 0.1, 0.3, and 1.0 s were used as source pulses, with an R/V Cheonghae vessel towing a variable depth source and a triplet towed array toward the deep sea from shallow water. The observed pattern changed as the R/V Cheonghae moved across the continental slope further into the sea. This pattern arises as a result of the downward-refracted beams in the 1/2 convergence zone interacting with the soft bottom. In addition, the boundary of the drop-off region was modeled with the two-way maximum travel time of the first bottom-reflected rays using the bathymetry model of the General Bathymetric Chart of the Oceans, 2020. Some discrepancies were observed when comparing the modeled curve to the measured results, and the inaccuracy of the bathymetry model on the continental slope could be the main cause of these discrepancies. This pattern could be useful for bathymetry mapping, as well as estimations of source and receiver configurations.

Real-time joint dereverberation and speech enhancement for hearing aid applications using edge devices

In this work, we propose a joint dereverberation and speech enhancement technique for real-time applications. Speech dereverberation is based on the coherent-to-diffuse energy ratio (CDR) measured from the direction-of-arrival (DOA) dependent complex spatial coherence function. A personalized speech enhancement (SE) technique based on joint maximum a posteriori probability (JMAP) estimation that inherently accounts for the effects of changes in acoustic path and reverberation is used. The combination of these masking functions is used to enhance the speech corrupted by reverberation and noise in a frame-by-frame process. The proposed method is implemented on the smartphone (edge device), to illustrate real-time usability. The efficiency of the proposed method is evaluated using speech quality and intelligibility measures and compared with that of other benchmark techniques.

An Energy Model for the Calculation of Room Acoustic Parameters in Rectangular Rooms with Absorbent Ceilings

The most common acoustical treatment of public rooms, such as schools, offices, and healthcare premises, is a suspended absorbent ceiling. The non-uniform distribution of the absorbent material, as well as the influence of sound-scattering objects such as furniture or other interior equipment, has to be taken into account when calculating room acoustic parameters. This requires additional information than what is already inherent in the statistical absorption coefficients and equivalent absorption areas provided by the reverberation chamber method ISO 354. Furthermore, the classical diffuse field assumption cannot be expected to be valid in these types of rooms. The non-isotropic sound field has to be considered. In this paper, a statistical energy analysis (SEA) model is derived. The sound field is subdivided into a grazing and non-grazing part where the grazing part refers to waves propagating almost parallel to the suspended ceiling. For estimation of all the inherent parameters in the model, the surface impedance of the suspended ceiling has to be known. A method for estimating the scattering and absorbing effects of furniture and objects is suggested in this paper. The room acoustical parameters reverberation time T20, speech clarity C50, and sound strength G were calculated with the model and compared with calculations according to the classical diffuse field model. Comparison with measurements were performed for a classroom configuration. With regard to all cases, the new model agrees better with measurements than the classical one.

A hydroacoustic approach to oil detection in ice covered water

A method of detecting oil spills in ice-covered lakes and seas, by observing changes in underwater acoustic reverberation time, had earlier been proposed; testing in a small tank environment showed it to hold some promise. Work now continues to improve the method, to further validate it, and to extend it to large bodies of water. The current work carries such scale testing further, establishing, by hypothesis testing, the level of confidence with which the presence of an oil layer underlying the ice can be discerned. Moreover, it expands the study to full scale experimentation in lakes and seas, including a portion of the Great Lakes across which a pipeline lies. These experiments seek to determine representative reverberation times (albeit without oil contamination, for obvious ethical reasons), and to explore whether natural impulsive sounds from ice fissuring may serve as a basis for passive hydroacoustic monitoring. The experiments at both scales are mutually complementary; while the tank tests serve to more rigorously validate that reverberation time is measurably affected by an oil layer, the lake-scale tests suggest those frequency bands an eventual passive monitoring using naturally arising sound would actually use, and establish the “control case” (oil-free) reverberation times.

Acoustic impact of the human skull on transcranial photoacoustic imaging.

With balanced spatial resolution, imaging depth, and functional sensitivity, photoacoustic tomography (PAT) hold great promise for human brain imaging. However, the strong acoustic attenuation and aberration of the human skull (∼8 mm thick) are longstanding technical challenges for PAT of the human brain. In this work, we numerically investigated the impacts of the stratified human skull on photoacoustic wave propagation (i.e., the forward model) and PAT image formation (i.e., the inverse model). We simulated two representative transcranial PAT implementations: photoacoustic computed tomography (PACT) and photoacoustic macroscopy (PAMac). In the forward model, we simulated the detailed photoacoustic wave propagation from a point or line source through a digital human skull. The wave attenuation, refraction, mode conversation, and reverberation were thoroughly investigated. In the inverse model, we reconstructed the transcranial PACT and PAMac images of a point or line target enclosed by the human skull. Our results demonstrate that transcranial PAMac suffers mainly from wave reverberation within the skull, leading to prolonged signal duration and reduced axial resolution. Transcranial PACT is more susceptible to the skull's acoustic distortion, mode conversion, and reverberation, which collectively lead to strong image artifacts and deteriorated spatial resolutions. We also found that PACT with a ring-shaped transducer array shows more tolerance of the skull's adverse impacts and can provide more accurate image reconstruction. Our results suggest that incorporating the skull's geometry and acoustic properties can improve transcranial PAT image reconstruction. We expect that our results have provided a more comprehensive understanding of the acoustic impact of the human skull on transcranial PAT.

On the Robustness of the Superdirective Beamformer

In microphone array beamforming, a high directional gain is always desired for acoustic noise and reverberation suppression; as a result, the superdirective beamformer has been of great interest in many applications. However, this beamformer is well known to be very sensitive to array imperfections. While much effort has been made to improve its robustness, it is still a major problem. This paper is essentially devoted to the study of the robustness of the superdirective beamformer and derivation of better ways to deal with this important issue. We first prove that any distortionless fixed beamformer can be written as the sum of two orthogonal beamformers, i.e., the sum of the classical delay-and-sum (DS) beamformer and a reduced-rank beamformer. Based on this property, different kinds of robust superdirective beamformers are then developed. We also show that the robust design problem can be transformed into a quadratic eigenvalue problem (QEP), which leads to a solution that achieves the maximum possible directivity factor (DF) while meets the white noise gain (WNG) constraint over a frequency band of interest.

Sonographic Evaluation of Coprostatic Impaction with Sand and Ingesta in Draft Equids

Background: Impaction of colons is a major cause of deaths in equines; therefore the objective of the current study was to perform the detailed ultrasonographic examination of equids suffering from abdominal discomfort and to identify which measurable parameters were important in reaching a diagnosis of small intestinal abnormality and determining treatment options. Methods: In this study twenty five equids (age 10-13 years) with history of cessation of defecation ranging from 2-4 days were subjected to sonography. Result: The impaction of left ventral colon in all animals was imaged as hyperechoic intraluminal structure casting a strong acoustic shadow with loss of normal sacculations, edema, increase in wall thickness and absence of peristaltic activity. Findings giving an indication of sand colic were the flattening of left ventral colon wall against the ventral body wall with loss of normal sacculations, peristaltic activity, presence of small pinpoint hyperechoic structures on the mucosal surface seen casting small acoustic shadows and reverberation artifacts in different directions were highly suggestive of sand impaction. In all animals the loops of small intestine were observed in transverse as well as longitudinal sections as hypermotile distended with fluidy ingesta and hyperechoic feed particles swirling inside that fluidly ingesta. The presence of dilated multiple loops of intestine in a single scanning area was a consistent feature of left ventral colon impaction. Hence detailed ultrasonographic examination was useful to delineate normal and abnormal conditions and to distinguish between true and false colic which provided an important diagnostic lead in management of affections of left ventral colon.

Flow conditions analysis of Gas Turbine Combustor

Gas turbines are equipped for working effectively on a wide assortment of energizes. Combustor is directed to a great extent by the requirement for its length and frontal territory to stay inside the cut-off points set by other motor segments by the need for a diffuser to limit pressure problems, another issue of expanding significance is that acoustic reverberation. The decrease of combustor size and weight is another significant necessity for air motors. The aim of the present work is to analyse the combustion chamber geometry using FINE/OPEN of NUMECA software and to predict the hot and cold total pressure loss, (circumferential and radial) pattern factors and combustion efficiency. This paper mainly work towards understanding the effect of cold and hot flow in a practical combustor systems using CFD and to estimate the various parameters like pressure loss, pattern factor (circumferential and radial), velocity distribution through diffuser, dome, swirler, three zones and combustor holes. The flow analysis is further extended to investigate the effects of temperature distribution of the flow that reaches the turbine inlet. The combustor model is created using CATIA and parts are then cleaned individual using CADfix suitable for meshing. The performance of the turbulence model is analysed and compared. Present work deals with the implementation of Computational Fluid Dynamics (CFD) for three-dimensional analysis of flow in an annular combustor of an aero gas turbine engine. FINE/OPEN of NUMECA commercial code will be used to analyse the Combustion chamber geometry. The analysis is carried out both in FLUENT and NUMECA and the results are compared.

Acoustic propagation and reverberation in shallow water with a gassy bottom: Experiments in the Sea of Galilee and preliminary data analysis

Acoustic propagation and reverberation in shallow water with a gassy bottom: Experiments in the Sea of Galilee and preliminary data analysis

Object Detection in Sonar Images

The scope of the project described in this paper is the development of a generalized underwater object detection solution based on Automated Machine Learning (AutoML) principles. Multiple scales, dual priorities, speed, limited data, and class imbalance make object detection a very challenging task. In underwater object detection, further complications come in to play due to acoustic image problems such as non-homogeneous resolution, non-uniform intensity, speckle noise, acoustic shadowing, acoustic reverberation, and multipath problems. Therefore, we focus on finding solutions to the problems along the underwater object detection pipeline. A pipeline for realizing a robust generic object detector will be described and demonstrated on a case study of detection of an underwater docking station in sonar images. The system shows an overall detection and classification performance average precision (AP) score of 0.98392 for a test set of 5000 underwater sonar frames.

The acoustic of Roman theatres in Southern Italy and some reflections for their modern uses

Ancient Roman theatres represent a unique cultural heritage which is still used nowadays to host a variety of cultural activities and performances. Acoustic measurements show that the acoustics of these theatres does not always support the listening of music, which is common in modern performances. Although the acoustics of these theatres for modern use performances may be challenging, this cultural heritage offers a unique experience to the audience who can assist to a performance on the same seats once used by Romans. Nowadays, these unroofed theatres, whose walls behind and at the sides of the stage have rarely been restored, are often criticized for the weak sound strength. Moreover, these theatres are often exposed to urban modern background noise. The significant sound absorption due to the presence of the audience on the seating area (named cavea) and to the tapestries used in modern scenes makes challenging to support the acoustic reverberation in these theatres. In this paper, these aspects are described focusing on five ancient Roman theatres located in Southern Italy. The study reports acoustic measurements followed by virtual simulation results. As it was impossible to perform acoustic measurements with full audience occupancy, the presence of the audience was simulated using room acoustic software. The paper compares the acoustic characteristics of these five theatres considering their architectural characteristics, and discusses the role that the material used for their restoration had on their acoustics. Finally, some considerations about some reversible interventions to improve the acoustics of these ancient theatres for modern uses are reported.

Joint NN-Supported Multichannel Reduction of Acoustic Echo, Reverberation and Noise

We consider the problem of simultaneous reduction of acoustic echo, reverberation and noise. In real scenarios, these distortion sources may occur simultaneously and reducing them implies combining the corresponding distortion-specific filters. As these filters interact with each other, they must be jointly optimized. We propose to model the target and residual signals after linear echo cancellation and dereverberation using a multichannel Gaussian modeling framework and to jointly represent their spectra by means of a neural network. We develop an iterative block-coordinate ascent algorithm to update all the filters. We evaluate our system on real recordings of acoustic echo, reverberation and noise acquired with a smart speaker in various situations. The proposed approach outperforms in terms of overall distortion a cascade of the individual approaches and a joint reduction approach which does not rely on a spectral model of the target and residual signals.

The study of the effectiveness of sound insulation of gypsum wall boards with “Shimast” coating

The article presents the experimental studies of sound insulation of a single-layer barrier made of gypsum wall boards with a thin-layer coating. The coating consists of a viscous base and glass airless microgranules. The coating increases the efficiency of reducing air noise. The material is applied as a normal paint by spraying on the surface. The research results have been obtained in an acoustic reverberation chamber designed to study the partition walls effectiveness.

Application of elastic parabolic equation solutions to acoustic reverberation in ice-covered underwater environments

Parabolic equation solutions can be obtained for underwater acoustic environments where elastic boundaries affect the acoustic propagation. One example of this situation is in the Arctic where a (potentially rough) ice layer is on top of the water column. The parabolic equation method shown here rigorously applies the zero-traction and fluid-elastic interface boundary conditions to obtain full field Green’s function estimates near the ice-water interface. This solution is crucial for calculation of recently derived reverberation estimates that require both horizontal and vertical derivatives of the complex acoustic field. Monostatic reverberation estimates for a rough under-ice interface are calculated for an upward refracting water sound speed profile and an elastic ocean bottom with a nearly fluid mud layer. These calculations could be used, for example, to estimate areal distribution of the ice layer roughness from azimuth-time dependence of acoustic reverberation measured in Arctic environments. Performance of the Pade rational function approach in the presence of thin ice cover and low shear speed ocean bottom layers will be addressed.

Research on creation and evolution of artificial diffuse sound field

In a closed space, it is difficult to create a diffuse sound field by using a single source in the reverberation tank. In this paper, a methodology for construction of diffuse sound field using multiple source excitation is proposed. Proposed methodology is based on space processing technique for a single source sound field and also involves reciprocity of sound field transfer function. Firstly, the analytical method of acoustic excitation reverberation field is studied and subsequently the sound pressure equation for excitation reverberation sound field in case of multi sound is obtained. In addition, the numerical method to observe the influence of sound source distribution upon uniformity of sound field is studied by the acoustic analysis software ACTRAN. Finally, diffuse sound field in a glass tank of 1.5 m × 0.9 m × 0.6 m dimensions, is constructed by using 30 emission transducers of the same type. In the end, the diffuse sound field is scanned using scanning array and is then evaluated by measuring the standard difference of the space distribution of sound field. The results show that the standard deviation of the sound pressure distribution in the diffused sound field in comparison with 30 transmitting transducers simultaneously within the reverberation control area is not greater than 3.9 dB under the narrow band condition. Hence, it clearly illustrates that construction of diffused sound field by this method is definitely a viable option.

The acoustic design of higher education music rehearsal spaces

This paper will update our paper presented in 2007 in New Orleans which analyzed our firm's acoustic design parameters for instrumental, band and choral rehearsal rooms along with measured results. In the subsequent 12 years, we have designed and opened numerous more facilities to add to the databakse of knowledge. Acoustic design parameters such as ideal room size per ensemble type, room dimensions, room height and volume, size and openess of any reflecting clouds, permanent absorption, adjustable acoustic systems, reverberation time and client specific user preferences will be examined. Project examples will be discussed to illustrate the discussion.

Preliminary analysis of operating conditions of acoustic sounder (SODAR) before the installation

The SOnic Detection And Ranging (SODAR) is a surface-based remote sensing instrument, based on Doppler effect and sound signal. This paper discusses the operating conditions of Monostatic SODAR system, error in the measured Atmospheric Boundary Layer (ABL) height by taking account of the antenna characteristics which are pulse transmission, receiving durations, spectral augmentation of the received echo and atmospheric refraction effects. The Monostatic SODAR is able to receive even very weak echo by providing a good directional response with high conversion efficiency. The location and orientation of the antenna are finalized after a detailed analysis of the site with relative to several parameters like comparative measurement of acoustic background noise and frequency response of noise. Also, before installation of the system, the transducer has to be individually characterized for it’s transmitted and received conversion efficiency, and variations in the product of these efficiencies (conversion gain). The antenna is systematically characterized, in an acoustic anechoic and reverberation chamber, with respect to its conversion efficiencies and directional response.

Feature Extraction for Acoustic Scattering from a Buried Target

Elastic acoustic scattering is important for buried target detection and identification. For elastic spherical objects, studies have shown that a series of narrowband energetic arrivals follow the first specular one. However, in practice, the elastic echo is rather weak because of the acoustic absorption, propagation loss, and reverberation, which makes it difficult to extract elastic scattering features, especially for buried targets. To remove the interference and enhance the elastic scattering, the de-chirping method was adopted here to address the target scattering echo when a linear frequency modulation (LFM) signal is transmitted. The parameters of the incident signal were known. With the de-chirping operation, a target echo was transformed into a cluster of narrowband signals, and the elastic components could be extracted with a band-pass filter and then recovered by remodulation. The simulation results indicate the feasibility of the elastic scattering extraction and recovery. The experimental result demonstrates that the interference was removed and the elastic scattering was visibly enhanced after de-chirping, which facilitates the subsequent resonance feature extraction for target classification and recognition.

Speech Enhancement Based on Adaptive Noise Cancellation and Particle Swarm Optimization

Speech enhancement is used in almost all modern communication systems. This is due to the quality of speech being degraded by environmental interference factors, such as: Acoustic additive noise, acoustic reverberation or white Gaussian noise. This paper, explores the potential of different benchmark optimization techniques for enhancing the speech signal. This is accomplished by fine tuning filter coefficients using a diverse set of adaptive filters for noise suppression in speech signals. We consider the Particle Swarm Optimization (PSO) and its variants in conjunction with the Adaptive Noise Cancellation (ANC) approach, for delivering dual speech enhancement. Comparative simulation results demonstrate the potential of an optimized coefficient ANC over a fixed one. Experiments are performed at different signal to noise ratios (SNRs), using two benchmark datasets: the NOIZEUS and Arabic dataset. The performance of the proposed algorithms is evaluated by maximising the perceptual evaluation of speech quality (PESQ) and comparing to the audio-only Wiener Filter (AW) and the Adaptive PSO for dual channel (APSOforDual) algorithms.