Loudspeaker System Research Articles

3D audio recording of complex underwater sound fields

In this study, we developed a method to capture underwater sound fields and reproduce them for human listeners, providing an immersive 3D auditory experience. We recorded the sound field with an array of four hydrophones arranged in a tetrahedral structure. The side length of the tetrahedron (around 70 cm) was a compromise between capturing accurately the low frequency pressure gradients and spatial aliasing effects at higher frequencies. Subsequently, we transformed the signals into the domain of spherical harmonics facilitating a representation as first-order Ambisonics that is independent of the recording. For playback on devices such as headphones or loudspeaker systems, we used established decoding routines that enhance the immersive audio experience with techniques such as parametric decoding and diffuse sound field equalization. During an expedition to northern Norway, we recorded the underwater soundscape in deep fjords with vocalizing killer whales and singing humpback whales. The resulting binaural renderings for headphones of these sound scenes are astonishing and sparked interest among scientist, artists and general public. This research also helps to enhance our understanding and perception of these intelligent marine mammals and their unique acoustic underwater world, ultimately aiding in better protecting them from noise pollution.

Latency-free real-time auralisation in hemi-anechoic chambers

Real-time auralisation allows users to interact with a simulated acoustical room, providing a more responsive way of evaluating acoustical performance than pre- recorded auralisation. Nevertheless, real-time auralisation is computationally intensive and, therefore, susceptible to latency. This paper presents a novel latency-free real-time auralisation method that enables users to auralise a simulated acoustical event with self-excitation more accurately than current methods. The method uses a loudspeaker system inside a hemi-anechoic chamber. By exploiting the inherent floor reflection of the hemi-anechoic chamber, the impulse response can be trimmed to compensate for the total latency of the loudspeaker system. The method's validity is demonstrated with measurements presenting virtual wall reflections arriving at the correct time at the listening position. The influence of the speaker placement regarding latency is discussed. This method enables users to evaluate a given response more accurately than conventionally possible.

Exploring acoustic wave transmission in micropolar plate in air

This study explores the behavior of sound wave propagation across a micropolar plate at diverse incident angles, specifically crafted from expanded polystyrene. Through a blend of theoretical formulations and practical experimentation, we scrutinize the alterations in transmission coefficients within the frequency spectrum, shedding light on the dynamic shifts in various vibrational modes. Utilizing a comprehensive setup comprising a loudspeaker, microphone, and National Instruments acquisition system, we meticulously discerned the initial trio of longitudinal vibration modes across a broad frequency span extending up to 70 kHz. Notably, despite the plate's inherent dispersion and attenuation traits, this experimental setup proved effective. A distinctive facet of our approach lies in the deliberate incorporation of multiple incident angles, which yielded crucial insights. Notable is the identification, within the experiments, of a critical angle, marking a transitional zone. Below this threshold, distinct Lamb modes dominate, while beyond it, the emergence of micropolar modes becomes apparent. These empirically validated findings, in alignment with theoretical projections, substantially enrich our comprehension of these materials' engineering applications.

Comparison of the noise perception of conventional aircraft and Unmanned Aircraft Systems

The use of Unmanned Aircraft Systems (UAS) for commercial applications is seeing steady growth in numerous sectors as the technology improves and more applications are realised. Whilst research into human response to UAS noise is a relatively new field, there is a far greater understanding of the perception and impacts of conventional aircraft noise. Therefore, a listening experiment was designed to investigate the relationship between perception of conventional aircraft and UAS flyover noise. The experiment used mono ground plate recordings of flyovers from several different aircraft and UAS, these recordings were re-spatialised to simulate flyovers over a multi-channel loudspeaker system. Participants were then asked to rate the annoyance of the sounds through a series of A/B comparisons. Results of the experiment demonstrate a clear positive correlation between Loudness and annoyance. However, Sound Quality Metric analysis also suggests that Sharpness of the UAS sound and Tonality and/or Roughness of aircraft sounds can also be a significant factor for annoyance. The finding of this experiment may contribute to the understanding and development of exposure-response relationships for UAS noise, building upon the extensive existing evidence on human response to conventional aircraft noise.

Measuring the radiation of sound sources with the radiation mode method: Towards realistic problems.

The measurement of the pressure field radiated by a sound source has many applications in the fields of noise control and loudspeaker system design. In this paper, the radiation mode method is used to measure the field radiated by a complex acoustic source whose surface impedance is arbitrary and does not correspond to the Neumann boundary condition used for the calculation of radiation modes. The most effective radiation modes are used as test functions to calculate a pressure expansion around the source under test, an expansion that matches the measured pressure at a limited number of points close to the source. This expansion is then used to calculate the radiated pressure at a greater distance at unmeasured locations. In a first step, numerical simulations are performed to evaluate the method's most influential parameters. Then, measurements are performed in a semi-anechoic room on two real sources of increasing complexity. Obtained results show that the radiation mode method allows an accurate evaluation of the pressure field radiated by the test object over a fairly wide frequency band (between 100 Hz and 2 kHz) even for complex sources.

Virtual acoustics in distributed performance over a closed audio network

We explore an application of active acoustics used to produce a shared virtual environment for live musical performance. As part of a concert given in the Immersive Media Lab at McGill University, musicians and audience members were located in adjacent but acoustically isolated spaces on the same digital audio network. With computer generated effects and live instruments, the concert consisted of electroacoustic performances that utilized dynamic virtual environments produced by our Virtual Acoustic Technology (VAT) system as an improvisatory partner and a mixing device to blend the diffusion of electronic and acoustic musical sources. The performance, including its evolving virtual environment, was captured using spatial microphone techniques and distributed in real-time to the audience over an immersive loudspeaker system in an adjacent control room. Audience members were given the opportunity to visit the musicians’ performance space in order to compare the reproduction to the original environment. Overall, the blending of computer-generated and acoustic sources created a specific use case for virtual acoustics, while the immersive capture and distribution method examined an avenue for producing a real-time shared experience. Future work in this area includes audio networks with multiple virtual acoustic environments and distributions.

Enhancement of virtual acoustics rendering using boundary mounted dipole loudspeakers

The Immersive Media Lab at McGill University hosts a Virtual Acoustics Technology (VAT) system incorporating a suspended array of omnidirectional loudspeakers. Using a convolution reverb engine, acoustic simulations of real spaces can be realized via a catalog of Room Impulse Response measurements. Reflected sound in the room helps to disguise the location of the sound emitters rendering virtual acoustics. One limitation of the system, however, is the interference between the lab’s natural acoustics and the virtual environment generated by the VAT system. The improvement under consideration is to enhance diffusion along the walls of the lab, in order to mask the acoustical characteristics related to the physical dimensions of the room. Dipole loudspeakers are installed on the room boundaries and used to scatter reflections and reverberation along the wall surfaces enlarging the effective radiation surface of the walls. The scattered energy may mask specular reflections and reduce localization of the virtual acoustic sources. Investigations compare the result of scattering reflected sound vertically as opposed to horizontally across the boundaries. Measurements illustrate the effect of the dipole loudspeaker system when used on its own as well as working in conjunction with the existing omnidirectional loudspeaker array.

Linear enhancement of mechanical compliance by zeolite filling in a compact loudspeaker

A zeolite filling in the rear cavity of a compact loudspeaker enhances the sound pressure amplitude of the loudspeaker system with a frequency range up to ∼500 Hz, but its intrinsic mechanisms remain elusive. We theoretically consider the gas adsorption–desorption behavior on zeolite that can be dynamically perturbed by sound pressure from the diaphragm of the loudspeaker. By merging equivalent circuit theory with gas thermodynamic theory, a linear relationship between mechanical compliance and zeolite volume in the rear cavity is quantitatively modeled. Confirmed by electroacoustic impedance experiments, the linear relationship with a slope of 1.92 mF cm−3 reveals the intrinsic ability of porous material to enhance mechanical compliance by adsorption of gas onto the zeolite in the rear cavity. This study correlates the kinetic behavior of air molecules on zeolite and acoustic behavior; it offers a novel insight to improve the performance of a compact loudspeaker by simple filling with porous material and introduces a comprehensive method for evaluating gas adsorption–desorption dynamics in porous media.

The impact of rural loudspeaker systems on typhoon disasters: Guangdong Province of China

Rural Loudspeaker Systems (RLS) are interrelated with the management of typhoons in Guangdong Province, China. The study aims to determine the effectiveness of RLS devices in reducing injuries, fatalities, and house damage caused by typhoons. Additionally, it examines the role of Typhoon Warning Signals (TWS) level, which can indicate the severity of typhoon that people are alerted about, in conveying typhoon intensity and their impact on disaster outcomes. The analysis used multiple datasets, including RLS coverage, TWS-level, and typhoon disaster records. Poisson regression models are used to estimate the impact of RLS coverage on injuries, fatalities, and house damage. The results reveals that an increase in RLS coverage by one percentage point is associated with an 3% reduction in injury events and an 1% reduction in casualty (injury and fatality) events, highlighting the importance of the RLS as a dissemination tool to inform individuals and guide their behavior during typhoon events. However, house damage, a fixed asset, is not significantly influenced by RLS coverage but is more affected by the severity of the typhoon or TWS-level. These findings enhance the understanding of the influence of RLS devices on mitigating typhoon disasters and underscore the crucial need for implementing effective early warning systems in areas prone to vulnerabilities.

Investigation of flow characteristics and velocity fields of excited two parallel plane jets

An experimental investigation was conducted to study the flow characteristics and velocity fields of excited two parallel plane jets. The experiments were carried out at a jet Reynolds number of 200. A loudspeaker system was used to create the jets pulsation and to vary the intensity of jet pulsations at a constant excitation frequency of 40 Hz. A hot-wire anemometer was used to measure the velocities of the jets as they exited. The flow patterns were visualized using a laser-light sheet technique combined with smoke flow visualization. The jet spread widths were determined from images taken with a long-exposure method using binary edge detection. A particle image velocimetry measurement technique was used to render the flow field behaviors of the parallel jets. The introduction of jet pulsation by the speaker led to the roll-up of coherent vortices along the shear layers of the jets. These vortices became more prominent as the intensity of jet pulsations increased. These coherent vortices broke apart into turbulent eddies, resulting in wider jet spread with higher pulsation intensities. Two counter-rotating vortices were detected at the jet exit. These vortices moved closer to the jet exits as the jet pulsation intensity was increased. The intensity of turbulence and the presence of vortices were both influenced by the magnitude of the jet pulsation. Greater jet pulsation led to higher turbulence levels, a more pronounced vorticity field, and a more efficient transfer of momentum, consequently enhancing the mixing process.

Synthesis of a zeolite@mesoporous silica composite to improve the low-frequency acoustic performance of a miniature loudspeaker system.

Herein, a zeolite@mesoporous silica composite (Z@MS) with a hierarchical porous structure was synthesized and employed as the filling material in miniature loudspeakers. The material was synthesized via a simple surfactant-directed sol-gel process in which MFI zeolites with a high silica-alumina ratio (>1000) were encapsulated in mesoporous silica with worm-like pores templated by Brij 72 under acidic conditions. Pressure spray drying technology was adopted to reassemble the intermediate slurry into hierarchical porous microspheres with large particle sizes (∼200 μm). The resonance frequency of the miniature loudspeaker system decreased by 339.77 Hz upon loading Z@MS as the filling material. The excellent acoustic performance can be considered as the result of a synergy of respective energy transmission effects among hierarchical porous structures.

A Stable Sound Field Control Method for a Personal Audio System

A personal audio system has a wide application prospect in people’s lives, which can be implemented by sound field control technology. However, the current sound field control technology is mainly based on sound pressure or its improvement, ignoring another physical property of sound: particle velocity, which is not conducive to the stability of the entire reconstruction system. To address the problem, a sound field method is constructed in this paper, which minimizes the reconstruction error in the bright zone, minimizes the loudspeaker array effort in the reconstruction system, and at the same time controls the particle velocity and sound pressure of the dark zone. Five unevenly placed loudspeakers were used as the initial setup for the computer simulation experiment. Simulation results suggest that the proposed method is better than the PM (pressure matching) and EDPM (eigen decomposition pseudoinverse method) methods in the bright zone in an acoustic contrast index, the ACC (acoustic contrast control) method in a reconstruction error index, and the ACC, PM, and EDPM methods in the bright zone in a loudspeaker array effort index. The average array effort of the proposed method is the smallest, which is about 9.4790, 8.0712, and 4.8176 dB less than that of the ACC method, the PM method in the bright zone, and the EDPM method in the bright zone, respectively, so the proposed method can produce the most stable reconstruction system when the loudspeaker system is not evenly placed. The results of computer experiments demonstrate the performance of the proposed method, and suggest that compared with traditional methods, the proposed method can achieve more balanced results in the three indexes of acoustic contrast, reconstruction error, and loudspeaker array effort on the whole.

Influence of indoor and outdoor noises on the speech intelligibility in classrooms

There are many noise sources inside the classrooms such as heating, ventilating, and air-conditioning(HVAC) noises. Also, there are outdoor noises near classrooms such as road traffic noises. Under these situations, teachers are using loudspeaker system in order to enhance the speech transmission. The present study aims to investigate the students’ subjective responses to teacher’s speech under many different noise situations. in order to this, questionnaire survey was undertaken to 60 students in two different classrooms. They were asked to mark their subjective listening comprehension and speech intelligibility in 5-points scale at every cases when three conditions were changed including opening status of doors and windows, operating HVAC system, and usage of loudspeaker system. Also, sound levels were measured in each case. As a result, it was found that only 17% of subjects responded that they were prevented from noises from outdoor and HVAC system. Also, it was responded that using loudspeaker system can enhance the listening conditions 2.7 times more than normal condition. Nevertheless, there are 33% of negative responses to loudspeaker system due to the artificial tone of speech. Thus, it can be concluded that indoor and outdoor noises cause by opening windows and operating HVAC system do not affect student’s speech intelligibility much in general cases, Also, using loudspeaker system in small classroom should be used cautiously considering students’ preferences.

Modeling a loudspeaker system with a flexible enclosure using finite element and lumped parameter model

A modeling method combining finite element and lumped parameter (FE-LP) model is proposed for accurately simulating loudspeaker systems with flexible enclosures, such as speakerphones, AI speakers, and portable Bluetooth speakers. In this approach, the mechanical components of the driver unit, except for the cone assembly (consisting of the dust cap, cone, and surround), are represented by lumped parameters, while the cone assembly and enclosure are modeled using the finite element method. The coupled equations of motion for the cone assembly and enclosure are derived to describe their dynamic behavior accurately. The coupling between the lumped parameters and finite elements is achieved through the manipulation of the system matrix. The validity of the proposed FE-LP method is demonstrated through numerical examples, including tests for the case of a loudspeaker system with a rigid enclosure. The results of these tests confirm that the proposed method can be applied to loudspeaker systems with enclosures of any rigidity.

Identification of the parametric array loudspeaker system using differential Volterra filter

The self-demodulation property of a parametric array loudspeaker (PAL) system can peel off audible sound modulated on ultrasonic wave and deliver it with high directivity, but also introduces nonlinear distortion. The PAL system can be modeled by the Volterra series expansion in any acoustic field region. However, measurements of Volterra kernel using simple frequency sweep excitation signals may not provide adequate information about the nonlinear system, and the use of wideband signals such as speech signals makes convergence difficult. Based on the Westervelt model, we propose a PAL system identification method utilizing the differential Volterra kernel. The results demonstrate superior fitting performance for real swept frequency output data and speech signal output data compared to the existing one-dimensional Volterra filter (ODVF). Additionally, the proposed method exhibits fewer parameters and faster convergence speed than the traditional volterra kernel.

Effects of sounds on the visitors' experience in museums

Museums increasingly recognize the significance of acoustics for a high-quality visitor experience. Objective/physical parameters have been extensively studied, but there is a need for research focusing on user perception. This study addressed this gap by investigating visitors' soundscape preferences and the effects of different soundscapes on the museum experience. We hypothesized that exhibition-congruent sounds are more effective than conventional masking sounds in reducing distractions, enhancing engagement with artwork, and creating immersive experiences. The research utilized the Cognitive Immersive Room (CIR) at Rensselaer Polytechnic Institute, featuring a 360° visual display with a multi-channel loudspeaker system for spatial audio rendering to project panoramic photographs and ambisonic audio recordings recorded in 16 exhibitions in five relevant museums—for example, MASSMoca and the New York State Museum. Four scenarios were presented to the participants: originally recorded soundscape, recorded soundscape combined with a conventional sound masker, recorded soundscape combined with a congruent sound masker, and silence. After experiencing the immersive environment, 23 subjects responded to a questionnaire. The results showed congruent sounds increased focus and engagement and contributed to a more comprehensive and immersive experience. In 58% of cases, the participants preferred the congruent-sound scenario over the others.

Error Analysis of Sound Source Directivity Interpolation Based on Spherical Harmonics

Precise measurement of the sound source directivity not only requires special equipment, but also is time-consuming. Alternatively, one can reduce the number of measurement points and apply spatial interpolation to retrieve a high-resolution approximation of directivity function. This paper discusses the interpolation error for different algorithms with emphasis on the one based on spherical harmonics. The analysis is performed on raw directivity data for two loudspeaker systems. The directivity was measured using sampling schemes of different densities and point distributions (equiangular and equiareal). Then, the results were interpolated and compared with these obtained on the standard 5° regular grid. The application of the spherical harmonic approximation to sparse measurement data yields a mean error of less than 1 dB with the number of measurement points being reduced by 89%. The impact of the sparse grid type on the retrieval error is also discussed. The presented results facilitate optimal sampling grid choice for low-resolution directivity measurements.

선거운동에 관한 내용 중립적 규제의 위헌심사강도 세분화 가능성

Regulation of speech can be categorized into content-based regulation and content-neutral regulation. This classification is widely accepted by both the Constitutional Court of Korea and the U.S. Supreme Court. However, distinguishing between the two types is not always clear in actual legislation. Therefore, a flexible approach is necessary when conducting constitutional review. In particular, regarding content-neutral regulation - even if a certain regulation is deemed to be content-neutral on its face -, it is necessary to consider the legislative purpose and the secondary effects caused by the legislation in order to determine whether the regulation functions as a form of censorship that prohibits expression itself or its content. Prior to such a discussion, it should be determined whether the regulation focuses on restricting actions rather than the expression itself, which may require a relaxed intensity of constitutional review. Based on the above, the Restriction on Use of Loudspeaker Systems clause in Public Official Election Act can be considered as a form of conduct-regulation rather than speech-regulation. The Prohibition of Installing of Facilities and Prohibition of Unlawful Distribution or Posting of Documents and Pictures in Public Official Election Act require alternative measures to minimize the restriction of political speech. The Restriction on Various Assemblies in Public Official Election Act is considered unconstitutional. In this regard, the recent decisions of the Constitutional Court of Korea are considered justifiable.

Real-time co-location in dynamic virtual soundscapes across multi-occupant immersive rooms

Immersive rooms, a type of virtual reality system consisting of human-scale panoramic visual and acoustic display systems and distributed sensing apparatus for occupant motion, have been increasingly adopted for dynamic and interactive applications. While these applications enable multi-user audiovisual immersion and navigation from a single physical location, they have yet to propagate along multiple homogeneous system infrastructures in a networked manner. In this work, we intend to co-locate two physically-remote immersive rooms – at EMPAC and the CRAIVE-Lab, respectively – in a single system of shared environments developed in Unity and embedded with virtual soundscapes. This system actively monitors spatial properties of both immersive rooms’ dynamic virtual footprint and their corresponding occupants. It generates virtual sound sources. both procedurally and through spatially-aware user inputs. The sound sources are rendered in real time via an algorithm synthesizing a ray-traced early reflection window and a parameterized late reverberation estimate from in-scene geometries. The co-located virtual soundscapes, displayed in individual immersive rooms through their respective multi-channel wave field synthesis loudspeaker systems, are shared as such that the user interaction in one physical location has holistic effects on the experience of virtual environments across all associated physical locations. [Work supported by NSF IIS-1909229 & CNS-1229391.]

Transforming Energy and Pedagogy

Transforming Energy and Pedagogy