Sound Reverberation Research Articles

Device for producing reverberation sound

Early reflection sounds and subsequent reverberation sounds are processed in different modes by separate processing devices in order to obtain reverberation effects close to those of natural sound as well as to freely produce reverberation effects that do not exist in natural sound. When the early reflection sound overlaps the subsequent reverberation sound in time, the early reflection sound and the subsequent reverberation sound are produced without noise. There is no need to omit either one of them. Besides, complex envelope control is executed for the early reflection sound, and the envelope levels are weighted and fluctuated. Therefore, it is possible to establish a highly sophisticated sound field.

Hand-held analyzer systems for building acoustics and sound intensity/sound power

Two new applications have been developed for a hand-held analyzer: Building acoustics and sound intensity/sound power. The building acoustics application is designed for measurements of airborne and impact sound insulation and reverberation time. The sound intensity application is used for sound power measurements, noise source location, noise mapping, and building acoustics. Both applications we used with complete systems consisting of all the necessary parts to simplify the measurement task and provide the user with all results immediately at the measurement site. There is no need for postprocessing. The measurements can be done according to a wide selection of international and national standards. The paper will describe the use of both applications in solving a problem in building acoustics. The building acoustic application will be used to detect a problem with poor sound insulation of a wall. Then, the intensity technique is used to determine the cause of the problem. Both applications use a built-in noise generator in the hand-held analyser with wireless transmission to an amplifier/loudspeaker. The paper will focus on the various design features that have been incorporated to ensure easy, secure, and flexible use.

Sound image enhancement apparatus

A sound image enhancement apparatus for reproducing two-channel stereo signals with speakers, includes for each channel a first phase shifter and a second phase shifter for introducing different amounts of phase shift to the signals. These phase shifters may be connected in parallel or in series. This arrangement enables virtual speakers to be located at the back of a listener. An inexpensive DSP is usable, and the number of processing steps is reduced to about one third of the number when an FIR filter is used. Moreover, it is possible to reproduce reverberation sounds from the front, back and sides, thereby simulating sound fields at a live performance.

Microphone actuation control system

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Relative auditory distance perception of synthetic reflections and reverberation presented over headphones

Relative auditory distance perception of a direct path signal by itself, with synthetic reflection(s), and with reverberation presented over headphones was measured using a 2AFC task. The stimulus, either a 500-ms pink noise burst or a 3-s phrase of male speech, was presented twice, first at a reference distance and second at an incremental distance from the reference. Reference distances included 5, 14, and 22 ft, and the incremental distances included multiples of 0.125, 0.25, and 0.5 ft, respectively. Stimuli pairs at each of the three distances were presented from four directions: front, back, left, and right. For each stimuli pair, the task of eight subjects was to indicate which of the two sounds appeared closer to himself/herself. The results of all locations indicated that the jnds for the direct path signal were 7%, jnds for the reflections were around 6%, and jnds for the reverberant sounds were about 12%. All of the sounds appeared out-of-head, however, almost all of the sounds presented from behind were perceived to be in front. Side sounds appeared to be biased towards the front when presented at the further distances.

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

A state estimation of mixed model type sound environment under the introduction of a wide sense digital filter and its application to sound reverberation measurement.

A state estimation of mixed model type sound environment under the introduction of a wide sense digital filter and its application to sound reverberation measurement.

Extended imaging split mode loudspeaker system

Direct field sound, represented by the sum of left and right stereo input signals, is projected in a narrow dispersion pattern from a front radiating speaker (28, 32) and reverberant field sounds, represented by difference between left and right stereo input signals, is projected from speakers (26, 30) having a wide dispersion pattern. Direct field and reverberant field sounds are acoustically combined in space to create an improved representation of stereo sound.

Effect of transient signal length on cross‐correlation functions in a room

An investigation was made of cross‐correlation functions with transient signals between two points, which correspond to both ears of a listener in a room. The interaural cross correlation is closely related to the subjective impressions of sound fields. The study attempted to account in a comprehensive way for the combined effects that initial reflected and reverberation sounds from music or other transient signals have on such impressions. To this end, cross‐correlation functions of the rise and fall of the sound field from transient signals were derived from the impulse responses at two points in the hall. These results were combined with image‐sources distribution patterns derived by the closely located four‐point‐microphone method; then, a comparative explanation was made of the changes with transient time duration of the cross‐correlation functions. Good agreement was found between changes with time in experimentally derived maximal cross‐correlation function values and the changes with time in image‐sources distribution of the sound field.

Appearance of gas-containing gallstones on sonography and computed tomography.

The diagnostic features of gas-containing gallstones on sonography and CT in 6 patients and the in vitro findings in 30 gas-containing gallstones are analyzed. On plain abdominal radiography, the stellate appearance of gas collections, though infrequent, is quite characteristic. On real-time sonography, gas-containing calculi can be observed to float within bile. Furthermore, larger gas collections within gallstones can be identified since they produce high-level echoes in the acoustic shadow of the stone, probably due to sound reverberation. These phenomena, although interesting, do not interfere with the high accuracy of sonography in the detection of gallstones. CT detects gallstones when their density differs from that of bile. Due to high-density resolution, even minute gas collections are displayed and can reveal gallstones with an isodense matrix. However, under routine abdominal scanning conditions (8 mm collimation), the gas collections often appear round or ovoid, because spatial resolution is inferior to that on plain radiography. This fact should be considered in the differential diagnosis of gas collections in the gallbladder region found on CT.

Musical instrument including electronic sound reverberation

An electronic reverberation system for use in an electronic musical instrument comprises a random access memory wherein two or more time delay channels are defined by address allocation in a controller circuit. An input analog signal is converted to digital signals by an analog-to-digital converter and the digital signals are processed by the controller into the time delay channels. The channels defined in the random access memory are of differing lengths which can be changed by switch settings. The controller sequentially retrieves stored digital data words from the random access memory channels in seriatum and couples each data word to a digital-to-analog converter. The analog output signal from the digital-to-analog converter is delayed in time by varying amounts due to the length of the channels in the random access memory. A portion of the delayed analog output signal contained in each channel is mixed with the input analog signal to produce a combined signal. The combined signal is converted to a digital data word which is stored back into the random access memory location from which the last digital data word was read. An enhanced reverberation effect is selectively achieved by switchably connecting a low frequency signal on the order of two hertz as an auxiliary input to be mixed with the input analog and delayed analog signals.

Acoustical Factors Affecting Hearing Aid Performance

This book is a compilation of papers presented at a conference organized by the editors in June 1978. Twentyseven persons participated in the preparation of 17 chapters designed bring to a wider audience a progress report on the 'state of the art' in the acoustic areas of hearing aid performance. The first of four sections reviews physical factors governing sound reverberation and speech perception by normal and hearing-impaired listeners in closed space. This is followed with reports of data showing variations in acoustic pressures recorded from manikin-worn aids as a function of (1) signal azimuths, (2) directional characteristics and location of receiving microphones, and (3) acoustic characteristics of the test environment. The second section focuses on the acoustic shaping characteristics of the normal and simulated external ear and on earmolds and microphones. The historic development and physical description of the Zwislocki coupler is outlined, followed by a report on

Theoretical Study on a Method of Estimation of the Reverberant Sound Absorption Coefficient of Plane Porous Material under any Mounting Conditions

Theoretical Study on a Method of Estimation of the Reverberant Sound Absorption Coefficient of Plane Porous Material under any Mounting Conditions

Reverberation and noise levels in sports areas

Seven indoor sports spaces at Washington State University were measured for sound reverberation and noise levels. The areas included two gynmasia, three aquatics areas, handball–racquetball courts, and a fieldhouse. Reverberation rates ranged from 2.0 to 8.5 sec. Sounds levels generated during typical classes averaged between 52 and 90 dB and frequently exceeded 100 dB.

Effective Modal Density in a Reverberant Sound Field for Finite Sized Sources

Much of the theory concerning the formation of sound fields in reverberant rooms and the measurement of the sound levels produced by these fields has emphasized the statistical aspects. A previous paper [K. M. Eldred, B. H. Sharp, and F. M. Murray, “The Coupling of Finite Sized Sources to a Modal Reverberant Sound Field,” presented at the 76th Meeting of the Acoustical Society of America (Nov. 1968), J. Acoust. Soc. Amer. 45, 338 (A) (1969)] discussed the coupling of finite sized sources to a reverberant sound field and showed that there is a strong dependence between sound level and source configuration in certain frequency ranges. This paper will briefly review these findings and extend the work to examine the relationship between the effective modal density and the calculated modal density as a function of source configuration. On the basis of this relationship, the relevance of statistical methods as applied to reverberant sound fields with finite sized sources will be discussed.

Discrete versus Continuous Space Averaging in a Reverberant Sound Field

Continuous averaging along a straight line does not always give better results than averaging at discrete points, uniformly spaced at half a wavelength apart along the same path. The continuous average is often a poorer estimate of the true mean than this discrete average. An explanation of this surprising fact is given, in terms of the cross-correlation curve for the sound field, and it is shown that a discrete average can be found that is always better than the continuous average. Averaging in two or three space dimensions is also considered, and the conclusion is reached that a discrete average, being more accurate and easier to obtain than a continuous average, is preferable. Curves are given for the percent probability of the sample mean lying within prescribed bounds of the true mean, for discrete sampling in a limited region in one, two, and three dimensions.

Coupling of Finite Sized Sources to a Modal Reverberant Sound Field

Much effort has been devoted to the development of statistical methods for the measurement of acoustic power levels and transmission loss in reverberant rooms. However, history is replete with unexplained interlaboratory variations in these measurements, particularly at low frequencies and when large specimens are involved. This paper examines some of the deterministic factors that govern the excitation of reverberant sound fields by finite sources. Such sound fields are investigated and compared with those produced by ideal point sources. Both analytical and experimental results show that the sound fields produced depend not only on the source position but on the source dimension. The relative amount of acoustic source power that is actually transferred to the modes is determined and the sound levels produced are compared with those that would exist under the assumption of diffuse conditions.

Underwater Sound Reverberation in the Arctic Ocean

Results of experimental studies of sound reverberation from the ice in the Arctic are presented and interpreted. The ice causes reverberation levels as much as 40 dB greater than those encountered from the icefree sea surface. An rms roughness of 3 m is indicated.

Size and Growth of Cavitation Bubble Nuclei

SOME years ago, one of us (K. S. I.), working in the laboratory of the late Prof. E. G. Richardson (King's College, Newcastle upon Tyne), made use of sound reverberation and optical scattering methods1 in an attempt to detect the presence and determine the size-distribution of nuclei responsible for the low tensile strength of liquids. During the course of the experiments it became evident that the nuclei existed in two forms in water—as stable air bubbles and as solid suspensions. The bubble nuclei, apart from possessing other unique features, were characterized by measurements of a consistent and reproducible nature when water containing them was subjected to ultrasonic and hydrostatic pressures. The measurements associated with the solid nuclei were erratic and showed considerable scatter.

Sound Reverberation from Smooth Ocean Floors

Recently both Mackenzie [J. Acoust. Soc. Am. 34, 66 (1962)] and Urick [J. Acoust. Soc. Am. 34, 1721 (1962)] have reported experiments measuring reverberation over deep, flat ocean floors. Both give data that may be empirically described by Lambert's law, at least over certain ranges of time. These results seem somewhat surprising since Lambert's law scattering is usually associated with very rough surfaces (compared to wavelength), quite unlike the deep ocean floors. In an effort to find a mechanism for reverberation, calculations have been made for a source located above a plane boundary separating two fluids. No roughness on the boundary was assumed. A reverberation “tail” was found to follow the specularly reflected signal. Computations show, however, that this “tail” is many orders of magnitude too small to account for the results of Mackenzie and Urick. Reasons for this discrepancy are considered. The possible interpretation of reverberation measurements for oceanographic data taking is discussed.