Sound Diffusion Research Articles

BoSSA: The Deconstructed Violin Reconstructed

Traditional musical instruments provide compelling metaphors for human-computer interfacing, both in terms of input (physical, gestural performance activities) and output (sound diffusion). The violin, one of the most refined and expressive of traditional instruments, combines a peculiar physical interface with a rich acoustic diffuser. We have built a new instrument that includes elements of both the violin’s physical performance interface and its spatial filtering audio diffuser, yet eliminates both the resonating body and the strings. The instrument, BoSSA (Bowed-Sensor-Speaker-Array), is an amalgamation and extension of our previous work with violin interfaces, physical models, and directional tonal radiation studies. In addition to describing the various physical and software elements that make up BoSSA, we discuss some of its musical features and potentials; we are particularly impressed by the sense of presence and intimacy it provides, and by its potential for creating a new kind of electronic chamber music.

Difference in acoustic effect of sound diffusers due to room shapes.

Difference in acoustic effect of sound diffusers due to room shapes.

RPG diffusers used for noise screening applications

The paper deals with the performances of noise barriers designed using the reflecting phase grating diffuser theory, which is based on the interference produced by slots of different depths. Usually such structures are used to improve sound diffusion in recording rooms, but they can be suitable also to reduce highway and railway noise for their capability of scattering sounds. A theoretical approach has been used to project their shape using a self-developed VB application, able to predict the scattered sound distribution as well. The theoretical results have been verified with a physical scale model in an anechoic room: insertion losses in several configurations have been measured, together with intensity measurements of the scattered acoustic field. Experimental results seem to match quite well those obtained using the simulation program.

The origin of the Vogel–Fulcher law near the liquid–glass transition

Taking into account the scattering processes due to random eigenfrequencies and random hopping matrices, we calculate the correlation functions of density fluctuations associated with the particle--hole pairs in the intraband and interband. The correlation functions for the intraband yield sound velocity (proportional to the mean atomic velocity) and diffusion (equal to the relaxation time of atoms multiplied by square of the sound velocity). Those for the interband yield phonons and viscosity (equal to the Maxwell relaxation time multiplied by square of the phonon velocity). The relaxation times and the transport coefficients are governed by the Vogel–Fulcher law through the hopping matrices. Phonons exist in both phases, but sound disappears below the freezing point. The Stokes’ law between diffusion and viscosity holds at higher temperatures, but breaks at lower temperatures.

Characteristics of the Structural Acoustic Loads and Transmission (SALT) facility at NASA Langley Research Center

The Structural Acoustic Loads and Transmission (SALT) facility at NASA Langley Research Center consists of a reverberant chamber, an anechoic chamber, and a common window. The 267-m3 reverberant chamber is structurally isolated from the rest of the building and is the source room in a transmission loss suite configuration. The receiving anechoic chamber is 4.57 m high, 9.63 m long, and 7.65 m wide, measured wedge tip to wedge tip. The window between the two rooms can accommodate 141×141-cm2 test structures for which sound transmission loss may be measured. Calibration of the transmission loss suite is discussed. The acoustic and structural flanking paths were evaluated by acoustic intensity and cross-spectral accelerometer measurements. Acoustic measurements in the reverberant room are accommodated by covering the window with a stiff, heavy insert. Measured ambient levels, reverberation times, sound field diffusivity, lowest usable frequency, and preferred test object dimensions are discussed. A transportable partition with foam wedges can be placed in front of the covered window in the anechoic chamber to facilitate acoustic free-field measurements. Anechoic room characteristics are presented including acoustic ambient levels, inverse square-law curves, cutoff frequency, and test object versus room size dimensions.

Sound, space, sculpture: some thoughts on the ‘what’, ‘how’ and ‘why’ of sound diffusion

Sound diffusion – the realtime (usually manual) control of the relative levels and spatial deployment during performance – is one of the most contentious issues in the field of electroacoustic music. There are parts of the world where the practice is virtually unknown; in other places it is the norm and appropriate facilities would be provided as a matter of course for any visiting composer or performer. These ‘local variations’ are not merely ripples on the surface of a standardised performance practice but stem from underlying attitudes to what composition and performance in this medium are about and, ultimately, to a definition of music itself. What follows summarises observations drawn from fifteen years of working with the BEAST concert diffusion system in numerous performance spaces in the UK and Europe, as well as experiencing, both as listener and performer, other systems in Europe and North America. Scientific rigour, in the normally accepted sense of tables of measurements etc., is not my goal – my portable measuring equipment has been my ears, and my conclusions are based on what I have heard.

Hydration and transport properties of aqueous solutions of α-α-trehalose

We report measurements of the sound velocity diffusivity and viscosity of aqueous solutions of α-α-trehalose at temperatures between 20 and 85 °C for volume fractions from 0.041 to 0.705. The ultrasonic data show that the mixing process is not ideal and that the trehalose-water interaction strength, because of the saturation of H-bond sites, decreases with increasing concentration. Photon correlation spectroscopy reveals marked changes in the effective diffusion coefficient in the dilute region over a limited temperature range. These measurements, interpreted in conjunction with viscosity data on the basis of a model by Mooney and Padova, quantify the hydration properties of α-α-trehalose. The dependence on volume fraction and the sensitivity to temperature changes characterize the “fragility” of this disaccharide-water system.

On the Vogel-Fulcher law near the liquid-glass transition

Abstract The correlation functions of density fluctuations associated with the particle-hole pairs in the intraband and interband are calculated. The correlation functions for the intraband yield the sound velocity (proportional to the mean atomic velocity) and diffusion (equal to the relaxation time of atoms multiplied by the square of the sound velocity). Those for the interband yield phonons and viscosity (equal to the Maxwell relaxation time multiplied by the square of the phonon velocity). Diffusion, viscosity, sound velocity, the mean atomic velocity and relaxation times obey the Vogel-Fulcher law. Phonons exist in both phases, but sound disappears below the freezing point.

Study on experimental equations for on-stage acoustics design

The relationship between the configuration of an orchestra shell and the acoustics inside have been studied based on the results obtained from the impulse response analysis using scale models of a series of 27 different conditions. Three points on a time profile curve were chosen as the acoustic factors in order to represent the onset process, the stationary state, and the decay process of the reflecting sound field, respectively. The averaged values adopted for discussion have been calculated using the data of three 1/1 octave bands around 1 kHz measured at three different positions in the main part of a stage floor. A remarkable difference in acoustics is found in the onset process between the cases with and without sound diffusers on the inner surface of a stage enclosure, and in the decay process as well. A faster rising in the onset process introduced by sound diffusers is followed by a faster decaying. They have a close connection. Finally, it is found to be possible to derive the experimental equations which relate these factors to the size and the shape of an orchestra shell, considering also the effect of reflections from the audience side of a hall.

Modelization of Kirchhoff scattering by a sound ray algorithm

The problem of the modelization of sound scattering by rough surfaces arises in room acoustics computer simulations, when sound diffusion is taken into account, as well as in other acoustical fields of interest. It is shown here how a sound ray algorithm can be applied to simulate a scattering process obeying the Kirchhoff tangent plane approximation. The Kirchhoff formulation for a random rough surface is briefly recalled, with the shadowing function proposed by Bass and Fuks. The scattered intensity is directly proportional to the statistical distribution of the surface slopes, which here is kept as general as possible. Then, it is established that this formulation is strictly equivalent to the result of a suitable sound ray algorithm, when the wavelength approaches zero in the Kirchhoff formulation. This is demonstrated in theory, and then applied to several Gaussian rough surfaces. Moreover, hints are given to extend the mathematical analysis of the sound ray technique to the second-order reflections on the rough surface. This is viewed as a way to take into account multiple scattering, which is neglected by the Kirchhoff approximation. [Work supported by FNRS, Natl. Fund for Scientific Research.]

Acoustical design of the Tokyo Opera City (TOC) Concert Hall

The TOC Concert Hall, called ‘‘Takemitsu Memorial’’ in honor of the late composer Toru Takemitsu, was opened September 10, 1997. With a seating capacity of 1636 and a volume of 15 300 m3, the hall is sized to cover the musical range from recitals to orchestral concerts. The plan is rectangular in shape but, by request of the architect Takahiko Yanagisawa, the ceiling is a distorted pyramid, with its peak nearer the stage than the rear of the wall. This unique shape had to be analyzed using a CAD model and a 1:10 scale model so that all interior surfaces would be adjusted in shape and absorption to yield optimum values for RT, EDT, IACCE3, surface diffusion, initial time delay gap, and loudness [Beranek, Concert and Opera Halls (ASA, New York, 1996)]. To provide a better ensemble condition for the musicians on stage and to provide early reflections to several other regions, a square canopy, almost 10 m on a side, is suspended above the stage. The pyramidal ceiling has diffusing elements added to simulate coffers. Schroeder QRDs on the ceiling surface facing the orchestra are used to control echo and to add sound diffusion. With audience, RT=1.95 s, G=6.4 dB, and [1−IACCE3]=0.72.

Acoustical design of the Tokyo Opera City (TOC) concert hall, Japan

The Tokyo Opera City concert hall seats 1632, volume 15 300 m3, and reverberation time, with audience and orchestra, 1.95 s. As part of the design process, measurements on CAD computer and 1:10 wooden models of the hall and full-sized materials samples were conducted over a 5-yr. period. The hall in plan is rectangular. The ceiling is a distorted pyramid, with its peak 28 m above the main floor and nearer the stage than the rear of the hall. This unique shape was analyzed on the models so that all interior surfaces combine to distribute sources on the stage uniformly over the seating areas and to yield optimum values for reverberation time (RT), early decay time (EDT), interaural cross-correlation coefficient (IACCE3), bass ratio (BR), initial-time-delay gap (ITDG), strength (G), and sound diffusion index (SDI) [for definitions see L. Beranek, Concert and Opera Halls: How They Sound (Acoustical Society of America, Woodbury, NY, 1996)]. On the long ceiling facing the stage, Schroeder QRD diffusers provide diffusion, eliminate a possible echo, and strengthen lateral reflections. Performers and critics judge the acoustics excellent.

Diffuseness of sound field and diffusivity of walls

Diffuseness of sound field and diffusivity of walls

ON THE TRAIL OF SHORT u

This article attempts a detailed reconstruction of recent developments in the history of English short u, the category that in southern English and its descendants shows up as a high vowel in PUT and a lowered vowel in CUT. Combining the comparative method with the interpretation of the historical documentary record, the exercise sets out to answer questions such as the following. At what stage did lowering result in a full-blown split between CUT and PUT? At what point did unrounding set in? Did lowering follow a peripheral or a central trajectory in vowel space? What mechanisms of change were involved — classically regular neogrammarian sound change or irregular lexical diffusion? The comparative aspect of the reconstruction draws heavily on vernacular Englishes which have emerged relatively recently in circumstances of large-scale language contact and shift, particularly those spoken in Ireland, West Africa and the Caribbean. The immediate significance of these varieties is that they emerged during a period when short u was in a state of considerable flux in the metropolitan language. The phonetic realisation and systemic organisation of the PUT and CUT vowels in these varieties offer certain direct insights into the history of short u that are no longer available in other dialects.

Mass distribution in heterogeneous structures

In order to define a statistical method of the analysis of mass heterogeneous structures, we have formulated stochastic and dynamic mass distribution in these structures. The expressions derived were used to calculate some of the basic characteristics of the heterogeneous structures at room and higher temperatures. The results for sound velocity, diffusion coefficient and thermal conductivity coefficient lie within the boundaries of physically expected values.

Performance Practice in the Presentation of Electroacoustic Music

In something as rich and diverse as electroacoustic music, the basic of musical may be ambiguous and difficult to identify, leading to a lack of comprehension on the listeners' part. As with any music, we need to know what aspect of the material defines structure; such a basic understanding is absolutely necessary to its effective communication. I would like to propose that the gentle art of sound diffusion over a carefully designed and installed array of loudspeakers should be recognized as a necessity rather than an option in the public presentation of electroacoustic music, as it is only through careful performance that such carriers of meaning can be effectively communicated. One reason for the limited appeal of electroacoustic music is cited by Jeff Pressing (1994 p. 27),

On measures to increase sound-field diffuseness and the applicability of diffuse-field theory

This letter discusses the definition of a diffuse sound field, two measures (diffuse surface reflection and volume scatterers) proposed to increase sound field diffuseness, and the applicability of diffuse-field theory. It is shown that the two proposed measures increase diffuseness, and the applicability of diffuse-field theory, with respect to sound decay/reverberation time. However, they decrease diffuseness, and the applicability of diffuse-field theory, with respect to steady-state sound-pressure level. The implications of these results for the definition of a diffuse sound field are discussed.

Temperature distribution and noninvasive monitoring during ultrasonic hyperthermia

In the ultrasonic hyperthermia for cancer therapy, for keeping the heating temperature in a certain range and avoiding problems from needle insertion, noninvasive monitoring of temperature is needed and has been developed. Using the bioheat transfer equation including thermal source, the temperature distribution at times has been calculated by the finite element method under certain boundary conditions. The influence of the focusing, tumor size, blood perfusion, and temperature of skin, etc., on the temperature field inside the human body, has been investigated. It is found that good control of the power emission can be made by measuring the skin surface temperature which has a definite relation with that at the focus under a certain group of parameters. It has also been found that the temperature at the equilibrium state due to the balance between sound power deposition and heat diffusion by blood perfusion can be calculated. This law can also be used to control the ultrasonic power emission for hyperthermia. The change of the temperature distribution corresponding to a change in the depth of focus has been investigated in detail. This can help to make the effective heating area enough to cover the whole cancer, so as to improve the efficacy of the therapy.

Two dimensional sound diffusor

A two-dimensional sound diffusor is composed of a plurality of wells defined by a matrix of projecting elements. The wells, which have different depths and widths, are arranged in a repeating pattern. The boundaries of the wells and of the repeating pattern are defined by projections arranged on a base. The ends of the projections extend away from the base, terminating in an inclined face which is inclined relative to the base by an angle of 10°. The incline may be rotated from one projection to the next, on a plane parallel to the base of the unit by 90° or 180°. This arrangement produces two dimensional sound diffusion.

Sound Field Diffusivity and Reverberation Effects on the Real-Ear Attenuation of Hearing Protectors with Implications for Test Standards

Sound Field Diffusivity and Reverberation Effects on the Real-Ear Attenuation of Hearing Protectors with Implications for Test Standards