Loudspeaker Configurations Research Articles

Comparison of auditory localization performance with various loudspeaker rendering systems

Sound-field rendering systems based on multiple loudspeakers provide significant benefits as auditory displays for many applications in virtual audio, multimedia, teleconferencing, and auralization. In contrast to headphone-based binaural reproduction, the performance of loudspeaker rendering systems is independent of the HRTFs of the listener, and the listener is physically decoupled from the rendering system. In addition, many rendering techniques such as wave-field synthesis (WFS) are capable of simultaneously presenting an accurate perceptual experience to multiple listeners. However, the sound-field rendering technique, loudspeaker configuration, and number of sources play an important role in both the physical behavior of the rendering system and the associated localization performance of listeners. In this study, we examine the in situ localization performance of listeners exposed to various loudspeaker rendering systems using virtual sources. Specific reproduction methods investigated are WFS, first- and second-order Ambisonics (including a periphonic implementation), and stereophonic rendering techniques. In addition to virtual sources in the simulated free field, the effect of adding spatialized reverberation is also reviewed. The results are compared with a study of baseline auditory-system localization performance with real sources. [Work supported by the National Science Foundation and Rensselaer Polytechnic Institute.]

Numerical evaluation of the omnidirectional behavior of regular polyhedron loudspeakers

A regular polyhedron loudspeaker (RPL) consists of a rigid enclosure in the shape of a regular polyhedron with loudspeaker drivers mounted within each face. Room acoustics measurements often incorporate dodecahedron loudspeakers presumably as omnidirectional sources of sound. This research is intended to support experimental work to determine which of the five regular polyhedron loudspeaker configurations actually produces the most omnidirectional field over a wide frequency range. Loudspeaker models based on the boundary element method were created to assess frequency-dependent radiation patterns. These models assume that the loudspeaker drivers radiate as plane circular pistons. Far-field sound pressures were generated for several field points around the models (5-deg polar and azimuthal angle increments). Results are presented as directivity balloon plots and compared with experimental measurements. Other numerical results are shown as variations on the experimental setup. These involve dimensional scaling of an entire loudspeaker and dimensional scaling of driver diameters while keeping enclosure dimensions constant. They also involve generation of data at more closely spaced field points (1-deg polar and azimuthal angle increments). Results from a spherical enclosure with radiating pistons centered on the angular coordinates of dodecahedron facial centers are also compared to those produced by a dodecahedron loudspeaker model.

The creation and projection of ambiophonic and geometrical sonic spaces with reference to Denis Smalley's Base Metals

This article suggests a framework for the articulation of ambiophonic and geometrical spaces in electroacoustic composition and performance. Space-ambiophony explores the global perception of space, which is derived from the archetypal perception of surrounding environments. The term applies to usually large-scale observation but it can also include shifts in the listener's attention from gestalt perception to micro-structural observation. A spatial analysis of Smalley's Base Metals demonstrates the methods by which space-ambiophony is integrated into the composition. In space-geometry, relations and analogies are established between composed sonic events and principles of geometry and stereometry. Three primordial geometrical elements, drawn from Wassily Kandinsky's theoretical work on painting, serve as metaphorical cells for the construction and projection of this type of space: the point, the line and the plane.The interaction between the acoustic qualities of listening spaces, the configuration of loudspeakers, the composed space (sonic trajectories, background, foreground) and its projection by the interpreter in a concert, are all issues that occupy parts of the article.

Real-time control of sound diffusion parameters

Much electronic and computer music relies extensively on real-time diffusion of electronic sound in surround loudspeaker configurations. The most common method of sound diffusion in practice today is to use standard sound-reinforcement mixers whereby each fader controls the playback volume of a corresponding loudspeaker in a concert hall. Using the mixer this way, however, presents problems when one attempts to create sound trajectories, because complex, precise, and repeatable control of the individual faders is required. To address these interface issues, two different handheld controllers were created for real-time sound diffusion. The first controller is equipped accelerometers, force-sensing resistors, and joysticks and maps using input into diffusion parameters. The second controller mimics the operation of a standard mixer but allows more rapid movement of fader positions by replacing each fader with a bend sensor. To test the validity of each controller, twenty undergraduate music engineering students were asked to repeatedly perform various diffusion tasks (such as moving a monaural sound in a circle around the audience) using a standard mixer and each of the controllers. The accuracy and speed of their performances were tracked. The study concludes with lessons learned from the statistics gathered. [Research supported by the University of Miami.]

Method and device for projecting sound sources onto loudspeakers

For the purpose of spatial reproduction of an audio signal, the latter must be projected onto the positions of the existing loudspeakers. It is desirable in this case not to have to be fixed on a specific loudspeaker configuration for transmitting the audio signal. However, a problem here is that a multiplicity of possible combinations exists. In the method according to the invention, the sound sources (3) are interpreted as acoustic objects for the purpose of projecting them onto an arbitrary loudspeaker configuration (2). Here, an acoustic object consists in that in addition to the audio signal a sound source is assigned an item of spatial information which specifies a virtual, spatial position of the sound source. In order to reproduce an acoustic object, the spatial information of the sound source and the actual position of a loudspeaker are used to calculate the virtual distance from the sound source via the loudspeaker to the hearer (1). Before reproduction, separate processing (7, 8, 9) of the audio signal for each loudspeaker is then performed for each acoustic object.

Spectral contributions to the benefit from spatial separation of speech and noise.

Speech recognition in noise improves when speech and noise sources are separated in space. This benefit has two components whose effects are strongest in different frequency regions: (1) interaural level differences (e.g., head shadow), which are largest at higher frequencies, and (2) interaural time differences, which have their greatest contribution at lower frequencies. Binaural interactions enhance the separation of signals from noise through the use of these interaural differences. Here, the benefit attributable to spatial separation was measured as a function of the low- and high-pass cutoff frequency of speech and noise. Listeners were younger adults with normal hearing, older adults with normal hearing, and older adults with hearing loss. Binaural thresholds for narrowband noises were measured in quiet and in a speech-shaped masker as a function of masker low-pass cutoff frequency. Speech levels corresponding to 50% correct recognition of sentences from the Hearing in Noise Test (HINT) were measured in a 65-dB SPL speech-shaped noise. Thresholds for narrowband noises and for speech were measured with two loudspeaker configurations: (1) signals and speech-shaped noise at 0 degrees azimuth (in front of the listener) and (2) signals at 0 degrees azimuth and speech-shaped noise at 90 degrees azimuth (at the listener's side). The criterion measure was spatial separation benefit, or the difference in thresholds for the two conditions. Benefit of spatial separation for unfiltered speech averaged 6.1 dB for younger listeners with normal hearing, 4.9 dB for older listeners with normal hearing, and 2.7 dB for older listeners with hearing loss. Benefit was differentially affected by low-pass and high-pass filtering, suggesting a trade-off of the contributions of higher frequency interaural level differences and lower frequency interaural timing cues. As expected, older listeners with hearing loss benefited little from the improved signal-to-noise ratios in the higher frequencies resulting from head shadow, but showed some benefit from lower frequency cues. Spatial benefit for older listeners with normal hearing was reduced relative to benefit for younger listeners. This result may be related to older listeners' elevated thresholds at frequencies above 6.0 kHz.

An investigation of platonic polyhedron loudspeaker systems as omnidirectional sources of sound

For reasons of consistency, many room acoustics measurements (e.g., ISO 140-4 and ISO 3382) require the excitation of sound fields via omnidirectional sources. For years, acousticians have used dodecahedron loudspeaker enclosures with individual loudspeakers mounted on each face as conventional ‘‘omnidirectional’’ sources. However, frequency-dependent interference between loudspeakers, diffraction effects, and inherent directivities of individual loudspeakers must contribute to a departure from the omnidirectional ideal. As a result, criteria have been established to limit the maximum allowable deviations from omnidirectional radiation for qualified measurements. Despite such concessions, acousticians should consider an important question: is anything extraordinary about the dodecahedron loudspeaker configuration? The dodecahedron is merely one member of a family of five platonic polyhedrons. Other members of the family include the tetrahedron, hexahedron, octahedron, and icosahedron. How do the omnidirectional characteristics of loudspeaker systems based on these latter geometries compare to those based on the dodecahedron? This paper discusses several theoretical, numerical, and experimental results that provide answers to this question.

Evaluation of an adaptive, directional-microphone hearing aid: Evaluación de un auxiliar auditivo de micrófono direccional adaptable

The effectiveness of adaptive directional processing for improvement of speech recognition in comparison to non-adaptive directional and omnidirectional processing was examined across four listening environments intended to simulate those found in the real world. The test environment was a single, moderately reverberant room with four loudspeaker configurations: three with fixed discrete noise source positions and one with a single panning noise source. Sentence materials from the Hearing in Noise Test (HINT) and Connected Speech Test (CST) were selected as test materials. Speech recognition across all listening conditions was evaluated for 20 listeners fitted binaurally with Phonak Claro behind-the-ear (BTE) style hearing aids. Results indicated improved speech recognition performance with adaptive and non-adaptive directional processing over that measured with the omnidirectional processing across all four listening conditions. While the magnitudes of directional benefit provided to subjects listening in adaptive and fixed directional modes were similar in some listening environments, a significant speech recognition advantage was measured for the adaptive mode in specific conditions. The advantage for adaptive over fixed directional processing was most prominent when a competing noise was presented from the listener's sides (both fixed and panning noise conditions), and was partially predictable from electroacoustically measured directional pattern data.SumarioLa efectividad del procesamiento direccional adaptable para mejorar el reconocimiento del lenguaje en comparación con el procesamiento omnidireccional o el direccional no adaptable, fue examinada en cuatro ambientes diferentes, tratando de simular aquellos encontrados en el mundo real. El ambiente de evaluación fue una habitación moderadamente reverberante con una configuratión de cuatro parlantes: tres con posiciones discretas y fijas de la fuente de ruido y uno con una fuente única de ruido variable. Se seleccionó material de oraciones de la Prueba de Auditión en Ruido (HINT) y de la Prueba de Lenguaje Conectado (CST) como material de evaluatión. El reconocimiento del lenguaje en todas las diferentes condiciones auditivas fue evaluado en 20 sujetos adaptados binauralmente con audifonos retroauriculares (BTE) del tipo Phonak Claro. Los resultados indicaron mejoria en el rendimiento de la función de reconocimiento del lenguaje con procesamiento direccional adaptable o no adaptable, comparado con el medido a través de procesamiento omnidireccional en los cuatro ambientes. En tanto la magnitud del beneficio direccional resultanle fue similar en algunos ambientes de audition para sujetos que escuchan en modo direccional adaptable y fijo, una ventaja significativa en el reconocimiento del lenguaje fue obtenida para el modo adaptable, en condiciones especificas. La ventaja del procesamiento direccional adaptable sobre el fijo fue más prominente cuando se presentaba un ruido de competencia a los lados del sujeto (tanto en condiciones de ruido fijo y variable), y fue parcialmente predecible con base en la información sobre el patrón direccional electroacústicamente medido.

THE SPEECH INTELLIGIBILITY OF THE PUBLIC ADDRESS SYSTEMS AT 14 DUTCH RAILWAY STATIONS

The speech transmission quality of the complete public address system at 14 Dutch railway stations is determined. The listener positions, at which the speech intelligibility is measured, are selected at the platforms, halls and interconnections according to a specially developed measuring procedure. The 14 stations selected are representative of the total of about 400 stations in the Netherlands and are spread over the whole country. The speech intelligibility determined with the objective STI method was found to be “poor” to “fair”. In order to improve the quality, further investigations have begun. Different loudspeaker configurations are optimized by the help of a “ray tracing” computer program. Special attention is given to minimum costs, minimum annoyance in the environment and maximum speech intelligibility at the different platforms of railway stations.

Directivity of the human vocal source

The directivity affects of the voices of one male and one female talker were observed in several environments including an anechoic room. Measurements were made at all frequencies between about 200 Hz and 10 kHz at 45°, 90°, 135°, 180°, and 270° azimuths. All measurements were made in the horizontal plane at the level of the mouth opening and at one meter from the center of the head. The results agreed well with the only other known comparable studies [Dunn and Farnsworth, 1939; Moreno and Pfretzschner, 1979] and also agree well with results obtained by Olson (1972) who designed and used a simplified manikin source. Some loudspeaker types produce results very different from those of human talkers. A search is underway to determine whether there are any widely available or easily created loudspeaker configurations that reasonably closely replicate the observed directivity of human sources. [Work supported by NINCDS.]

Demonstration of binaural advantage in audiometric test rooms.

Binaural advantage was measured for 12 normally hearing subjects in a typical rectangular audiometric test room with a loudspeaker located in each corner. Four different loudspeaker configurations for presentation of signal and competition were evaluated. The results indicated that a configuration in which uncorrelated competition was delivered from both sides of the subject while the signal was presented from a 0 degree azimuth was the most resistant to interaural asymmetries resulting from the room geometry and produced the most consistent binaural advantages. Binaural advantage was then measured using this loudspeaker configuration for 15 hearing-impaired individuals wearing hearing aids. Although the group results indicate a mean unaided binaural advantage only slightly smaller than seen in the normal hearers, when hearing aids were worn an interaural asymmetry in a signal-to-competition ratio developed that reduced the clinical usefulness of the data for individuals. This outcome emphasizes that a valid clinical demonstration of binaural advantage is critically dependent on interaural symmetry in signal-to-competition ratios for both aided and unaided tests. Such symmetry may be difficult to achieve in a typical audiometric test room.