Sound Reproduction System Research Articles

Sound system in a small college auditorium

A new 220 seats college auditorium needed an electro acoustics system in order to adequately perform all its normal activities, which included live voices for lectures and conferences, a sound reproduction system working alone or together with the projection equipment, sometimes background music, and eventually some small groups with live music presentations as requested in the specs of the auditorium usage; it also needed recording capabilities for the most important lectures and presentations. A 12/8 channel with stereo output system with peripherals was chosen for the installation, where three microphones were reserved for the front table, six distributed in fixed stands located in the aisles of the audience area for questions and dialog, and the other three were movable. Background noise was not an issue because the auditorium is located in a tree full area within the university campus, away from busy streets. Budget for the acoustical conditioning and the electronic equipment was very limited.

Sound Cask: Music and voice communications system with three-dimensional sound reproduction based on boundary surface control principle

To reproduce a highly realistic sound field reproduction, we have developed a three dimensional sound reproduction system based on the boundary surface control principle. We set up an Internet connection among multiple systems, which enables distant speakers to carry out voice telecommunication by simultaneously hearing the same sound field and perceiving the other speakers' simulated positions as if they were in the same location. In this reproduction system, a listener can freely move his head and rotate his body because the system reproduces the sound not only at the point but at the area. In this paper, we introduce a 'Sound Cask', which is a 96-channel sound reproduction system based on the boundary surface control principle. The 'Sound Cask' is used to realize such musical telecommunication as if musical performers were all playing in the same hall. The system provides space large enough to play a small musical instrument such as violin, which allows listening and communication accompanied with natural body movements by the performer. Another specific feature of the system is that loudspeakers are installed aiming every possible direction excluding the floor. The system design is suitable for relocation as it can be assembled or disassembled when needed.

Wave Field Synthesis: The Future of Spatial Audio

We all are used to perceiving sound in a three-dimensional (3-D) world. In order to reproduce real-world sound in an enclosed room or theater, extensive study on how spatial sound can be created has been an active research topic for decades. Spatial audio is an illusion of creating sound objects that can be spatially positioned in a 3-D space by passing original sound tracks through a sound-rendering system and reproduced through multiple transducers, which are distributed around the listening space. The reproduced sound field aims to achieve a perception of spaciousness and sense of directivity of the sound objects. Ideally, such a sound reproduction system should give listeners a sense of an immersive 3-D sound experience. Spatial audio can primarily be divided into three types of sound reproduction techniques, namely, loudspeaker stereophony, binaural technology, and reconstruction using synthesis of the natural wave field [which includes Ambisonics and wave field synthesis (WFS)], as shown in Fig. 1(a).

Sound Field Reproduction of a Virtual Source Inside a Loudspeaker Array With Minimal External Radiation

We derived an integral equation for reproducing the sound field of a virtual source inside an array of loudspeakers with reduced radiation to the outside. Reproduction of a sound field over a finite interior region inevitably generates sound waves that propagate outside the region. This undesirable radiation is reflected from walls and can induce artifacts in the interior region. In principle, the Kirchhoff-Helmholtz (KH) integral can be used to reproduce the interior sound field from an exterior virtual source without any external radiation. However, if there is a virtual source inside the array, the integral formula does not explicitly demonstrate how one can reproduce the sound field or minimize the external radiation. In this work, we derive an explicit formula for reproducing a sound field with minimal external radiation when a virtual source is located inside a loudspeaker array. The theory shows that external radiation can be effectively reduced without solving any inverse problem. The proposed formula follows the form of the KH integral and thus requires monopole and dipole sources. Although dipole sources are difficult to build in practice, the theory predicts that sound field reproduction with minimal external radiation is possible and that the room dependency of the sound field reproduction system can be decreased.

HORN-LOADED ACOUSTIC SOURCE WITH CUSTOM AMPLITUDE DISTRIBUTION

A sound reproduction system is disclosed in which at least one driver is provided, along with a horn member in acoustic loading relationship to the driver. The horn member defines an internal passageway having a first end and a second open end, with the driver at the first end, producing a driver soundwave having an initial central axis and an initial amplitude distribution. A plurality of vanes are disposed in the internal passageway, at different angles from the central axis to deflect respective portions of the driver soundwave so as to alter the initial amplitude distribution.

SOUND REPRODUCTION WITH IMPROVED LOW FREQUENCY CHARACTERISTICS

A sound reproduction system (10) is disclosed in which a sound barrier (14) defines a horn passageway having an upstream (22) and a downstream section (24). A driver (12) is mounted at the throat (16) of the upstream section (22) so that its rearward directed output communicates with the downstream section (24). Output from the upstream section and the rearward directed output of the driver are merged at a tap point located at the beginning of the downstream section. By altering the respective areas and lengths of the upstream and downstream sections a variety of different frequency dependent responses are obtained. In one example, low-frequency response systems of heretofore unobtainable compact size are realized.

HORN-LOADED ACOUSTIC LINE SOURCE

A sound reproduction system is disclosed in which a sound enclosure defines a soundwave path having a first end, a second open end and at least one bend therebetween. At least one driver is provided at the first end for producing a driver soundwave that is confined by the sound enclosure for travel along the soundwave path. At least one baffle member is situated in the soundwave path, defining a reflective surface of preselected shape that reflects and constricts the soundwave therethrough.

SOUND REPRODUCTION METHOD AND APPARATUS FOR ASSESSING REAL-WORLD PERFORMANCE OF HEARING AND HEARING AIDS

A sound recording and reproduction system for testing hearing and hearing aids is disclosed. Recordings of sound are made in a real word acoustic environment, for example, which are stored as audio signals. In a testing environment, a plurality of loudspeakers is located about a listening position where a test subject is placed during a testing procedure. The plurality of loudspeakers receive at least a portion of the plurality of the stored audio signals, and convert those audio signals received into a combination of sounds that produce, at the listening position, acoustic elements of the real world acoustic environment where the recordings were made. The system enables, in a clinical or other test setting, the evaluation of hearing and/or hearing aid performance as if in a real world environment.

FRONT SURROUND SOUND REPRODUCTION SYSTEM USING BEAM FORMING SPEAKER ARRAY AND SURROUND SOUND REPRODUCTION METHOD THEREOF

A front surround sound reproduction system using a speaker array, a front surround sound reproduction system to perform stereo localization using a beam forming speaker array, and a surround sound reproduction method thereof. A front surround sound reproduction apparatus using a plurality of speakers includes a first signal processing unit to adjust a frequency characteristic of each first and second channel signal and to output the adjusted signals to left and right speakers assigned according to a frequency band, a second signal processing unit to generate a plurality of channel signals by copying the first and second channel signals, to adjust a signal characteristic of each of the plurality of channel signals, and to output the adjusted signals to a speaker array in the center, and a speaker unit having a plurality of speakers to reproduce the signals output from the first signal processing unit and the second signal processing unit.

SOUND REPRODUCTION SYSTEM COMPRISING A LOUDSPEAKER ENCLOSURE WITH PORTS, AND ASSOCIATED PROCESSING CIRCUIT

A sound reproduction system includes a loudspeaker enclosure that has a first loudspeaker and a second loudspeaker which are mounted on a surface of the enclosure. The first and second loudspeakers are respectively accommodated in a first space and a second space of the enclosure, the spaces being separated by a partition and being in communication with a first port and a second port, respectively. The first and second ports are located on opposite sides of the unit formed by the first and second loudspeakers. Processing elements are used for respectively applying a first and a second electric signal to the first and second loudspeaker, the first and second electric signals being generated from a single signal by differentiated phase processing that varies according to the frequency such that the first and second electric signals are offset relative to one another by a variable period of time which is proportionate to the acoustic distance between the first half of the loudspeaker enclosure including the first space, the first loudspeaker, and the first port, and the second half of the loudspeaker enclosure including the second space, the second loudspeaker, and the second port.

Unidirectional Sound Signage for Speech Frequency Range Using Multiple-Loudspeaker Reproduction System

Human safety is the most important issue in disaster management. Speech is a sound signal containing information that is easily and quickly understood by humans. Using speech as sound signage in emergency systems can effectively increase human safety in low or poor visibility conditions such as in smoke-filled situations. However, reflections of sound through walls, floor surfaces, and ceilings will affect clarity of speech. Unfortunately, because of the characteristics of sound reproduction systems, a single loudspeaker propagates sound waves omni-directionally at low frequencies. This paper proposes a simple multiple-loudspeaker system for reproducing sound with uni-directional characteristics. The proposed system consists mainly of a primary loudspeaker for introducing sound in the desired beam, a secondary loudspeaker for reducing gain in the undesired direction, and digital filters. An adaptive finite-impulse-response (FIR) filter is used to produce the controlling sound by implementing a filtered-x least-mean-square algorithm, and a delay filter for adjusting the time alignment of sound propagation between primary and secondary sources at the control point. Several operational conditions for illustrating real situations and reflections were considered in an anechoic chamber. Experimental results show the directivity patterns of the proposed multiple-loudspeaker system for the required conditions. In a low frequency range, the system is able to control unidirectional propagation; there is a sound beam in the desired direction and, conversely, reduction of gain in the undesired direction around the control point.

Interior and exterior sound field control using two dimensional higher-order variable-directivity sources

Spatial sound reproduction systems aim to produce a desired sound field over a volume of space. At high frequencies, the number of loudspeakers required is prohibitive. This paper shows that the use of loudspeakers with up to Nth order directivity allows reproduction over N times the bandwidth and produces a significantly attenuated exterior sound field. If the constraint on exterior cancellation of the field is removed, reproduction is possible over approximately 2N times the bandwidth. The use of higher order loudspeakers thus allows a significant reduction in the number of loudspeaker units, at the expense of increased complexity in each unit. For completeness, results are included for the generation of an exterior field with or without cancellation of the interior field.

The Road to Immersive Communication

Communication has seen enormous advances over the past 100 years including radio, television, mobile phones, video conferencing, and Internet-based voice and video calling. Still, remote communication remains less natural and more fatiguing than face-to-face. The vision of immersive communication is to enable natural experiences and interactions with remote people and environments in ways that suspend disbelief in being there. This paper briefly describes the current state-of-the-art of immersive communication, provides a vision of the future and the associated benefits, and considers the technical challenges in achieving that vision. The attributes of immersive communication are described, together with the frontiers of video and audio for achieving them. We emphasize that the success of these systems must be judged by their impact on the people who use them. Recent high-quality video conferencing systems are beginning to deliver a natural experience-when all participants are in custom-designed studios. Ongoing research aims to extend the experience to a broader range of environments. Augmented reality has the potential to make remote communication even better than being physically present. Future natural and effective immersive experiences will be created by drawing upon intertwined research areas including multimedia signal processing, computer vision, graphics, networking, sensors, displays and sound reproduction systems, haptics, and perceptual modeling and psychophysics.

A study of beamforming in FDTD method to synthesize directional sound for sound field reproduction

Sound field reproduction is useful to represent sound contents with high-realistic sensation. We have proposed a sound field reproduction system to control the perceived angles of virtual sound sources. The system synthesizes the propagated sounds by using sound field simulation and multi-directionally represents them with head-enclosed loudspeakers. The multi-directional sound representation requires the sound field simulation to synthesize directional sounds. We therefore focus on beamforming by array processing in finite-difference time-domain (FDTD) method. FDTD is an effective method to simulate sound field. It discretizes the time-space with meshes and defines the distribution of sound pressure level (SPL) by calculation result of the SPL propagation between the each mesh. We accordingly propose a new approach for sound field simulation to synthesize directional sound. In the proposed approach, the beamforming is applied to the SPL propagation between FDTD meshes. The beamforming with FDTD meshes achieves to control the directional characteristics at each mesh for SPL propagation. With the directional characteristics controlled by beamforming, the directional sound is synthesized. According to the evaluation conducted to verify the performance, it was confirmed that the proposed approach enabled FDTD to control the directional characteristics for directional sound synthesis.

Loudspeaker compensation using mixed phase technology

In a sound reproduction system loudspeakers always introduce distortions. The compensation of loudspeaker responses using digital signal technology is becoming an important part of improving sound reproduction quality. Several FIR and IIR filter design methods have been proposed to equalize the response of loudspeaker systems. However, high order filters are needed to obtain excellent resolution at low frequencies. From a psychoacoustic point of view, warped filters have been employed to improve the resolution at low frequencies, but at the expense of poor resolution at high frequencies. On the other hand, the use of warped filters increases the complexity of the filter structure. In this paper, a mixed phase technology is proposed to equalize the response of loudspeaker systems. Loudspeaker response can be decomposed into minimum and excess phase components, which are inverted respectively to construct the equalization filter. An all pass filter based on position-independent excess phase zeros is cascaded with a minimum phase filter to improve the phase response in the region. The experimental results demonstrate that the time-domain response of the loudspeaker systems is improved by using the presented mixed phase technology.

Influence of the presence of a human head in the controlled area in the three-dimensional sound field recording and reproduction system based on the boundary surface control principle: Objective examination

Influence of the presence of a human head in the controlled area in the three-dimensional sound field recording and reproduction system based on the boundary surface control principle: Objective examination

METHOD AND SYSTEM FOR REPRODUCING AN AUDIO SIGNAL

A system and method of reproducing an audio signal produced by an audio system which includes an earphone is described. The method including the steps of: receiving an audio signal; estimating short-term characteristics of the acoustic exposure of a listener; recording the short-term characteristics; controlling the audio signal and; outputting the controlled audio signal for reproduction. The system or method of the invention may be applied to any sound reproduction system that reproduces sounds by way of an earphone such as telephone headsets or handsets, personal music players, mobile telephones, and two way radios.

A Sounding Body in a Sounding Space: the Building of Space in Choreography – Focus on Auditory-motor Interactions

In the last 4 years, we have developed a partnership between dance and neuroscience to study the relationships between body space in dance and the surrounding space, and the link between movement and audition as experienced by the dancer. The opportunity to work with a dancer/choreographer, an expert in movement, gives neuroscientists better access to the significance of the auditory-motor loop and its role in perception of the surrounding space. Given that a dancer has a very strong sense of body ownership (probably through a very accurate dynamic body schema) ( Walsh et al. 2011 ), she is an ideal subject to investigate the feeling of controlling one's own body movements, and, through them, events in the external environment ( Moore et al. 2009 , Jola et al in press). We conducted several work sessions, which brought together a choreographer/dancer, a neuroscientist, a composer, and two researchers in acoustics and audio signal processing. These sessions were held at IRCAM (Institute for Research and Coordination Acoustic/Music, Paris) in a variable-acoustics concert hall equipped with a Wave Field Synthesis (WFS) sound reproduction system and infrared cameras for motion capture. During these work sessions, we concentrated on two specific questions: 1) is it possible to extend the body space of the dancer through auditory feedback ( Maravita and Iriki 2004 )? and 2) can we alter the dancer's perception of space by altering perceptions associated with movements? We used an interactive setup in which a collection of pre-composed sound events (individual sounds or musical sentences) could be transformed and rendered in real time according to the movements and the position of the dancer, that were sensed by markers on her body and detected by a motion tracking system. The transformations applied to the different sound components through the dancer's movement and position concerned not only musical parameters such as intensity, timbre, etc. but also the spatial parameters of the sounds. The technology we used allowed us to control their trajectory in space, apparent distance and the sound reverberation ambiance. We elaborated a catalogue of interaction modes with auditory settings that changed according to the dancer's movements. An interaction mode is defined by different mappings of position, posture or gesture of the dancer to musical and spatial parameters. For instance, a sound event may be triggered if the dancer is within a certain region or if she performs a predefined gesture. More elaborated modes involved the modulation of musical parameters by continuous movements of the dancer. The pertinence at a perceptive and cognitive level of the catalogue of interactions has been tested throughout the sessions. We observed that the detachable markers could be used to create a perception of extended body space, and that the performer perceived the stage space differently according to the auditory feedback of her action. The dancer reported that each experience with the technology shed light on her need for greater awareness and exploration of her relationships with space. Real-time interactivity with sound heightened her physical awareness – as though the stage itself took on a role and became another character.

Overview of an indoor sonic boom simulator at NASA Langley Research Center.

A facility has been constructed at NASA Langley Research Center to simulate the soundscape inside residential houses that are ensonified by environmental noise from aircraft. The purpose of this facility, the interior effect room, is to examine parameters that affect psychoacoustic response in a controllable indoor listening environment. The single room facility, built using typical residential construction methods and materials, is surrounded on two sides by arrays of loudspeakers. These exterior arrays are used to simulate aircraft noise sources that transmit into a room of a typical house. The exterior sound reproduction system, which consists of 52 subwoofers and 52 mid-ranges in close proximity to the walls of the room, has been designed to enable study of sonic booms transmitted into residential structures and has a usable bandwidth of 3 Hz–6 kHz. In addition to these exterior arrays, satellite speakers placed inside the room are used to simulate rattle and other audible contact-induced noise that can result from low frequency excitation of a residential house. The layout of the facility, operational characteristics, acoustical characteristics, and equalization approaches are summarized. Current research efforts utilizing the facility are described in two companion papers.

Suitable Truncation of Room Impulse Response for Inverse Filter Design of Sound Reproduction System

This paper introduces an automatic decision method for designing parameters of inverse filters to simplify realization of a high-performance sound reproduction system. The reproduced performance depends on several design parameters of the inverse filters that cancel the effect of room transfer functions (RTFs). Therefore, a method of determining the sample lengths of impulse responses of RTFs is proposed. In the proposed method, a suitable sample length of the impulse response is determined based on autocorrelation function (ACF) . The results of numerical simulations using real data reveal that the proposed method can determine suitable sample lengths while maintaining reproduction performance.