Omnidirectional Sound Source Research Articles

A Highly-Sensitive Omnidirectional Acoustic Sensor for Enhanced Human-Machine Interaction.

Acoustic sensor-based human-machine interaction (HMI) plays a crucial role in natural and efficient communication in intelligent robots. However, accurately identifying and tracking omnidirectional sound sources, especially in noisy environments still remains a notable challenge. Here, a self-powered triboelectric stereo acoustic sensor (SAS) with omnidirectional sound recognition and tracking capabilities by a 3D structure configuration is presented. The SAS incorporates a porous vibrating film with high electron affinity and low Young's modulus, resulting in high sensitivity (3172.9 mVpp Pa-1) and a wide frequency response range (100-20 000 Hz). By utilizing its omnidirectional sound recognition capability and adjustable resonant frequency feature, the SAS can precisely identify the desired audio signal with an average deep learning accuracy of 98%, even in noisy environments. Moreover, the SAS can simultaneously recognize multiple individuals in the auxiliary conference system and the driving commands under background music in self-driving vehicles, which marks a notable advance in voice-based HMI systems.

A Performance Improvement Method of Omnidirectional Sound Source Tracking using a Square Microphone Array

A Performance Improvement Method of Omnidirectional Sound Source Tracking using a Square Microphone Array

Visar: Projecting Virtual Sound Spots for Acoustic Augmented Reality Using Air Nonlinearity

Augmented reality that integrates virtual content in real-world surroundings has attracted lots of concentration as the growing trend of the metaverse. Acoustic augmented reality (AAR) applications have proliferated due to readily available earphones and speakers. AAR can provide omnidirectional engagement through the all-around sense of spatial information. Most existing AAR approaches offer immersive experiences by playing binaural spatial audios according to head-related transfer functions (HRTF). These involve complex modeling and require the user to wear a headphone. Air nonlinearity that can reproduce audible sounds from ultrasound offers opportunities to achieve device-free and omnidirectional sound source projection in AAR. This paper proposes Visar, a device-free virtual sound spots projection system leveraging air nonlinearity. Visar achieves simultaneous tracking and sound spot generation while suppressing unintended audio leakages caused by grating lobes and nonlinear effects in mixing lobes through optimization. Considering multi-user scenarios, Visar also proposed a multi-spot scheduling scheme to mitigate the mutual interference between the spots. Extensive experiments show the tracking error is 7.83cm and the orientation estimation error is 10.06°, respectively, envisioning the considerable potential of Visar in AAR applications.

Dispersion Influence of Electroacoustic Transducer Parameters in the Design Process of Miniature Loudspeaker Arrays and Omnidirectional Sound Sources.

Electroacoustic transducers represent one of the crucial materials used in the construction of loudspeaker arrays. The dispersion in their parameters may influence the performance of a speaker set. Parametric loudspeaker arrays and omnidirectional sound sources have been used for years. However, the possible influence of transducer manufacturing tolerances on the arrays' performance has not been investigated. In previous research, the sources of possible dispersion in acoustic measurements carried out with omnidirectional sources were studied, pointing out that the problems with sound sources may be a significant reason behind the small measurement repeatability in standards. This paper investigated the measurement of several common types of miniature speakers, using 10 pieces of each type and investigating the influence of their parameter dispersion in electric and acoustic ways. Numerical simulations of omnidirectional sound sources were performed to investigate the drivers' dispersion influence sensitivity. The results provided proof of the small-signal parameter dispersion reaching 20% of the variation. The acoustic measurements show that the loudspeakers may differ in sensitivity parameters by up to 4 dB in 10 transducer tests. The analysis of an example multitransducer array indicated that a dispersion of a sensitivity higher than 1 dB might lead to significant misperformance in constructed arrays and measurement deviations with this type of array.

Evaluation of the influence of Mihrab shape on sound quality in Mosques

A mihrab, a niche in the mosque wall indicating the qibla or the direction of Mecca, plays a crucial role in determining the acoustics within the mosque space. This study explores the impact of mihrab shape on sound characteristics in a mosque. Various mihrab shapes, including a flat wall and seven distinct shapes, were tested. Steady State Diffusivity (Dss) values were calculated. Polar response, Echo Criterion (EC), and Sound Transmission Index (STI) measurements were conducted using a 1:10 scale model omni-directional sound source with Dirac measurement system. The outcomes of this study show that the Trapezium Mihrab, Triangular Mihrab, and Flat Wall configurations demonstration distribution across all proposed parameters. This research lights the significant impact of mihrab shape on the acoustic environment within mosques, offering valuable insights for architects and designers and seeking to optimize its sound quality. The Trapezium Mihrab, characterized by its unique shape, demonstrates notable efficiency in acoustic performance. Similarly, the Triangular Mihrab and Flat Wall configurations also prove to be conducive to effective sound distribution within the mosque main hall. These findings highlight the crucial role that mihrab design plays in shaping the overall acoustics of a mosque. By recognizing the influence of mihrab shape on acoustic elements, architects and designers can make good decisions to enhance the acoustical environment for worshippers. This could contribute to the creation of harmonious and acoustically optimized mosque spaces.

Robust 3D localization of anomalies in reverberation time measurements using the sound field scanning method

Reverberation time measurements form the basis for room acoustic optimizations of existing building structures. During the verification of the achieved room acoustic improvements, anomalies may appear in the reverberation time signal which may be hard to spatially localize, especially in spaces with demanding acoustic requirements such as large, open workspaces, or concert halls. This contribution focuses on the application of the Sound Field Scanning technology to the fast spatial localization of room reflections. In this process, an omnidirectional sound source is positioned at an observation point in the room and periodically excited with band-limited pulses. At the same observation point, an acoustic camera system consisting of a rotating linear microphone array is oriented towards the preferred spatial direction. The emitted pulses and associated room reflections are captured on the measurement surface of the rotating microphone array. Acoustic images with high depth resolution are generated in parallel planes to the measurement surface. In complex situations, the task of spatially localizing anomalies in the reverberation time signal can be reduced to a few measurements from different viewing angles, thus, significantly accelerating the problem-solving process with high confidence. The method is exemplarily described through the room acoustic analysis of a University Lecture Hall.

Comparison of Different Omnidirectional Sound Sources with the Validation of Coupled Speakers as a Measurement Source for Room Acoustics

Omnidirectional sources used in room acoustics usually take the form of multi-speaker sources. Few alternatives for the most commonly used dodecahedral sound source have been derived recently. The project aimed to measure room acoustic parameters using three different sound sources: a dodecahedron, a cube, and a new source of two coupled loudspeakers. The measurements were made by rotating the sources every 15 degrees. The differences in the EDT, T30, D50, and C80 parameters in the function of the rotation angle of the sources were analyzed. Statistical analysis was carried out to examine the sensitivity of the measured parameters’ JND (just a noticeable difference) on the source’s rotation angle. This presentation will show the results and analysis of measurements showing the influence of the used source on obtained parameters and the validation of coupled speakers’ use. A comprehensive discussion of the results obtained with different sources (coupled, dodecahedral, cubic) will be provided. The results confirmed using the coupled speakers as an alternative for omnidirectional sound source in the range of 250–2000 Hz.

Comparison of microphone array techniques and standardized methods for sound power estimation

The sound power level can be estimated using several well-established techniques available in the market. However, the variety of methods can be overwhelming when choosing among them due to environmental restrictions, standard requirements, and the necessary expertise to acquire valid data. In this study, we aim to compare the results obtained with different techniques, either standardized, as described in ISO 3744 in hemi anechoic rooms and ISO 9614-1, engineering method, using sound intensity, and non-standardized microphone array methods, as optimized acoustic beamforming and acoustic holography algorithms. The sound power levels of an omnidirectional sound source with pink noise as input and a printer were measured in a hemi-anechoic chamber using all the techniques. In addition, the measurement with the omnidirectional sound source were carried in a meeting room to check the effect of room and background noise. Considering the results of the sound intensity method as the baseline, all the overall sound power level results varied within the uncertainty stipulated by ISO 9614-1 for both sources. The results in one-third octave bands were within the uncertainty for all bands except one case for both sources in the case of refined beamforming.

Prediction accuracies of ray-tracing and regression models in open-plan offices

The purpose was to determine the prediction accuracies of an empirical regression model (Model 1) and a ray-tracing model (Model 2) in acoustically different open-plan offices. The measurement data was obtained from an open-plan office (81 m2) in which 22 completely different room acoustic conditions were built using alternative room absorption areas in ceiling, walls, and screens, and alternative screen heights. The sound pressure level (SPL) produced by an omnidirectional sound source was measured in six positions in each condition. The corresponding SPLs in 22 conditions were predicted using Models 1 and 2. The prediction accuracies were determined for the A-weighted SPL of speech in each position. In addition, the prediction accuracy was determined for the basic quantities of ISO 3382 standard: spatial decay rate of speech, D2,S, A-weighted SPL of speech at 4 m distance, Lp,A,S,4m, comfort distance, rC, and mean reverberation time T. The mean prediction accuracy of A-weighted SPL of speech was 4.2 dB for Model 1 and 3.4 dB for Model 2. Model 1 predicted D2,S, rC, and T more accurately than Model 2, while the opposite ranking order was found for Lp,A,S,4m. The prediction accuracies of both Models were sufficient when the effects of sound absorption materials and screen heights is simulated. The finding suggests that simple empirical regression models can provide sufficient prediction accuracy in most room acoustic conditions of open-plan offices.

Impact of Mihrab geometry on the acoustics of the mosque

Mihrab is a niche in the wall of a mosque that indicates the qibla, the direction of the Kaaba in Mecca towards which Muslims should face when praying. The wall in which a mihrab appears is thus the "qibla wall". Mihrab geometry has an impact on daily prayer recitation and others. This paper investigates the impact of new type of the Mihrab geometry on the acoustics of the mosque. Flat wall and 7 types of mihrab were modeled. Polar response measurements were carried out using 1:10 scale model. Measurements had been realized using 1:10 omni-directional sound source and Dirac room acoustics software. It is found that flat wall and Mihrab with trapezium and triangle shapes can generate a uniform polar response over the frequency range we are interested in (500-2000 Hz).

Acoustical characterization of Taramati Baradari

India has a very rich and diverse cultural heritage and when studying from one built form to another, it can be observed that each plan and architectural form has a very close association with the purpose it was built for. The use of daylight in these structures is very well documented and studied, the acoustics of the structure are hidden, especially for a place of worship and performance. It needs special attention and should be addressed subjectively. The effect of architectural form and elements on the acoustics of the structure needs to be documented and studied. It should be documented using acoustical instruments like omnidirectional sound source and handheld analysers and ODEON and EASE 4.3, a simulation of the space should be done to understand the original setting of that structure. Taramati Baradari in Hyderabad will be used as a case study.

A practical approach to modelling railway vehicle interior acoustics

The aim of the current work is to propose a practical approach for modelling the interior acoustics of railway vehicles by investigating the spatial decay of sound within the vehicle and its relation to the reverberation time and absorption. Measurements are presented of the longitudinal distribution of sound level inside five railway vehicles as well as the corresponding reverberation times. Both quantities are determined using an omnidirectional sound source located near one end of the vehicle. The measured sound pressure level follows a roughly linear dependence with longitudinal distance and the rate of decay is found to follow a consistent trend over all five datasets when plotted against reverberation time. To interpret these results, three different modelling approaches are considered: ray tracing, Statistical Energy Analysis, and an analytical corridor model. Ray tracing models with a simple geometry resembling the interior of a railway carriage are used to explore the dependence of the spatial decay and reverberation time on the absorption and scattering coefficients of the surfaces. For high values of scattering coefficient, the reverberation time approaches the Sabine estimate but for low values of scattering coefficient it can be up to a factor of 2.5 greater than this estimate. This implies difficulties in deducing the average absorption coefficients from the measured reverberation times. The spatial decay rates obtained from the ray tracing model do not have the same consistent dependence on reverberation time as the measured results, although the results for low values of scattering coefficient are closer to the measured trend than those for higher values. Investigation of the Statistical Energy Analysis approach shows that it predicts a spatial decay rate that depends explicitly on length of the subsystems used in the model; consequently, the results do not converge as the model is refined. It is possible to use modified coupling loss factors based on an analytical corridor model to give a better approximation to the spatial decay. This corridor model is shown to give results that are consistent with the measurements if the average absorption is obtained from the reverberation time using a modified formula for the mean free path length, and if the cross-section area is reduced to allow for the blocking effect of the seats. This provides a practical way forward for using SEA for the interior sound in railway vehicles.

Technical and electroacoustic aspects of miniature omnidirectional sound sources used in acoustic scale modeling

Acoustic similarity theory allows us to create scaled room acoustic models which are simple to construct but usually difficult to measure correctly. One of the most common problems is the sound source, which works in the wide frequency range (800–40000 Hz, 500–63000 Hz) and has an omnidirectional sound propagation pattern. The lecture will present the novel approach for miniature sound sources design and creation for the most common measurement functions—laboratory objects and materials measurements (absorption, diffusion) in the scaled reverberation chamber, sound insulation scale modeling, and the room acoustic measurements in reduced models. Each of those applications has special sound source requirements, which allow us to differentiate their construction type. The most important aspects of the designing process were investigated, such as the number of transducers used and their placement, types of speakers, enclosure shape, and dimensions. The lecture will expose the sound sources used in Technical Acoustic Laboratory in AGH, Cracow, for the given measurement functions. The design recommendations developed based on FEM modeling, and experimental testing will be discussed regarding the existing objects, allowing future users to recreate in similar shape or adjust to other, predefined scale modeling measurement functions.

Acoustic surface impedance of sandy shores

This work presents an effort to characterize the relationship between moisture content and acoustic surface impedance of sandy soils. This effort is part of a larger project seeking to model long-range acoustic transmission loss over coastal areas. Previous studies were done to measure moisture content along the shore and collect samples for bench-testing with an impedance tube. This work seeks to build on those experiments by performing in situ acoustic surface impedance measurements with an omnidirectional sound source and two microphone receivers. These measurements follow the protocol set forth by the ANSI/ASA S1.18 and are recorded at multiple distances from the water on the shore. At each measurement location, sand samples are collected for gravimetric moisture analysis. Atmospheric conditions and ambient noise level are also recorded in accordance with the standard. These results demonstrate the variation of sand surface impedance from the fully saturated swash zone to nominally dry sand.

The Acoustics of the Benevento Roman Theatre

During the Imperial Roman period, thousands of theatres were built. The theatres have three principal elements: the scene building (actor position), the orchestra and the cavea (spectator seating). The theatres were built without a roof, so they were open-air spaces. The theatres were abandoned afterward the barbarian invasions, and during the Middle Ages, homes were built inside the cavea. The theatres were rediscovered during the Renaissance period. Today, ancient theatres are the center of cultural events and are used for various kinds of shows. This work discussed the acoustics of the Roman theatre of Benevento, which was built during the Imperial Age. The theatre was destroyed after the barbaric invasion and it was rebuilt in the first half of the 1900s. The theatre was opened in 1957, and today it is the center of social and cultural activities. Acoustic measurements were carried out according to ISO 3382 standard, placing an omnidirectional sound source on the scene building and in the orchestra, with the measurement microphones along three directions in the cavea. The acoustic characteristics in various seating areas of the cavea were evaluated. Therefore, it possible to understand in which sectors of the theatre the acoustic characteristics are optimal for different types of theatrical performances.

Full Range Omnidirectional Sound Source for Near-Field Head-Related Transfer-Functions Measurement

Full Range Omnidirectional Sound Source for Near-Field Head-Related Transfer-Functions Measurement

Acoustic performance enhancement in a railway passenger carriage using hybrid ray-tracing and image-source method

Geometry of cabins, corridors, and materials used in railway passenger carriages can play important roles in acoustic performance inside the rail cars. In order to evaluate the noise level inside a rail car, a hybrid method based on the ray-tracing and image-source techniques is employed. A parametric model is constructed based on the field experiment performed in a typical coach cabin namely Fadak train in Iranian Railway. An Omni-directional sound source inside the passenger carriage is employed inside the cabin once for an unequipped cabin and once for operational one. Acoustic parameters such as reverberation time (T30), Center time (Ts), and the sound pressure level have been calculated and results are validated with experimental acoustic measurements. The model is experimentally calibrated and then acoustics performance of the passenger coach is enhanced by modifying the materials and absorption coefficients against two dominant sound sources in low to middle speed ranges. It is found the simple recommendation can remarkably enhance the acoustic performance over a broad range of frequencies.

1Pb4-4 Design and Development of Omnidirectional Sound Source Using Facing Ultrasonic Transducer Arrays

1Pb4-4 Design and Development of Omnidirectional Sound Source Using Facing Ultrasonic Transducer Arrays

Balloon dielectric elastomer actuator speaker

A balloon dielectric elastomer actuator (DEA) speaker is constructed by forming a disk-shaped DEA film into a sphere using air, increasing its surface area by 3033%. Sound is generated via expansion and contraction. Shaping the DEA film into a sphere decreases the film thickness and applies a significant amount of pre-strain (prestretch) to the film. In the experiment, sound pressure levels in an audible frequency response up to 16 kHz is the approximately same as both our previous hemispherical DEA speaker and this balloon DEA speaker, allowing an actuating voltage of the balloon speaker lower (800 V p-p signal with an offset of 400 V) than that of our previous hemispherical DEA speaker (2 kV). This is the first time to achieve the audible frequency response of the acrylic balloon DEA speaker. Furthermore, the acoustic radiation pattern of the speaker extends over a 270° range. Compared to polyhedron loudspeakers, which are currently used as omnidirectional sound sources in general acoustic tests, a balloon DEA speaker is compact and lightweight. Therefore, balloon DEA speakers have sufficient potential to contribute to the proper assessment of indoor acoustic characteristics using a scale model.

Construction of an Omnidirectional Parametric Loudspeaker Consisting in a Spherical Distribution of Ultrasound Transducers.

Omnidirectional sound sources are needed to perform a large variety of tests in acoustics. Typically, they consist of conventional speaker drivers arranged in a dodecahedron. However, the directivity of the speaker drivers sharpens with frequency, which induces an intense decrease of the sound pressure levels at the edges of the dodechaedron. In this work, the problem is mitigated by building an Omnidirectional Parametric Loudspeaker (OPL), which contains hundreds of small ultrasound transducers set on a sphere. Each transducer emits an ultrasonic carrier wave modulated by an audible signal. Thanks to nonlinear propagation, the air itself demodulates the signal bringing it back to the audible range. The construction of an OPL prototype is challenging. The structure has been built by 3D-printing a set of pieces that conform to the sphere. Each piece contains the exact location of the transducers, which are aligned in parallels to facilitate the structural assembly and the wiring. The performance of the OPL has been tested in an anechoic chamber. Measurements show that the OPL has a good omnidirectional behavior for most frequencies. It clearly improves the directivity of dodechaedral sources in the high frequency range, but performs worse at low frequencies.