Relative Sound Pressure Research Articles

Evaluations of output from room acoustic computer modeling and auralization due to different sound source directionalities

Evaluations of the predictions and auralizations from the room acoustic modeling program, ODEON, have been run using three directional source types with the same sound power: (a) an omni-directional source; (b) three sources with realistically-directional characteristics based on measurements from real instruments (grand piano, violin, and singing voice); and (c) an artificial, extremely directional beaming source. Objective analyses have been run for nine source/receiver combinations in a simple hall on three acoustic parameters: relative sound pressure level (SPL), reverberation time (T30), and clarity index (C80). Auralizations were subsequently created for two source/receiver combinations and used in subjective testing with 28 subjects. Results show that, objectively, differences in SPL were negligible for the majority of cases. Some differences in T30 and C80 were found between the omni-directional and realistically-directional sources; however, subjects did not perceive any corresponding differences when comparing the auralizations, possibly due to the limited directional octave band data available. Subjects did significantly differentiate between auralizations from the omni-directional source and the extreme beaming source. Subjective results from comparing these two sources in terms of reverberation, clarity and realism were generally consistent with objective data, although source/receiver combination and musical track had some influence on the outcomes.

Room volume estimation from diffuse field theory

Among the parameters relevant in room acoustics, the room volume is one of the most important. The general course in room acoustics research is to use the room volume in the prediction of room acoustic parameters such as reverberation time or total relative sound pressure level. Contrary to this, it has been investigated to what extent the room volume can be retrieved from a measured room impulse response. The approach followed is based on room acoustic diffuse field theory and requires correctly measured room impulse responses with the initial time delay corresponding to the source to receiver distance. A total of ten rooms of varying size and acoustic characteristics have been included. The results in three rooms were unreliable, which was explained by the particular acoustic characteristics. In the remaining rooms the results were numerically useful and consistent between different positions within the same room (relative standard deviation around 20%). The influence of source and receiver directivity is also considered.

Method of controlling the auditory response of wireless devices

Cellular telephones, pagers, PDAs, and other wireless devices, are configured to network together when in close proximity with each other, measure the relative sound pressure level of their environment, and modify the auditory response of the wireless device based on established parameters. In this way, a wireless device may detect when it is in a quiet room with multiple other devices, which is indicative of a meeting that should not be disturbed, and thus defeat or modify its behavior to reduce interruptions of group events.

Reflection of sound from random distributions of semi-cylinders on a hard plane: models and data

A new analytical theory for multiple scattering of cylindrical acoustic waves by an array of finite impedance semi-cylinders embedded in a smooth acoustically hard surface is derived by extending previous results for plane waves (Linton and Martin 2005 J. Acoust. Soc. Am. 117 3413–23). Although the computational demands of the new theory increase as the number of the semi-cylinders in the arrays and/or the frequency increase, the theory offers an improvement on analytical boss theories since the latter (i) are restricted to non-deterministic (infinite) random distributions of semi-cylinders with spacing/radii small compared to the incident wavelength and (ii) are derived only for plane waves. The influence on prediction accuracy of truncation of the infinite system of equations introduced by the new theory is explored empirically. Laboratory measurements have been made over deterministic random arrays of identical varnished wooden semi-cylinders on a glass plate. The agreement between predictions and measured relative sound pressure level spectra is good both for single deterministic random distributions and for averages representing non-deterministic random distributions. The analytical theory is found to give identical results to those of a boundary element calculation but is much faster to compute.

The acoustic attenuation and hydraulic roughness in a large section sewer pipe with periodical obstacles

The acoustic attenuation, relative sound pressure levels and the equivalent Nikuradse wall roughness under variable flow conditions in a 600 mm concrete sewer pipe are experimentally investigated. The values of the acoustic attenuation are obtained in the case of airborne sound propagation in the dry pipe. A range of values of the equivalent wall roughness is artificially generated by deploying a periodical array of engineering bricks. A novel method of rapid evaluation of the acoustic attenuation is proposed. The method relies upon sound reflections from the adjacent manholes. The results demonstrate that the acoustic attenuation depends strongly on the value of the equivalent wall roughness. This work can pave the way to the efficient methodology for the in-situ, physical evaluation of the equivalent hydraulic roughness of new and existing sewer networks.

The acoustic attenuation and hydraulic roughness in a large section sewer pipe with periodical obstacles

The acoustic attenuation, relative sound pressure levels and the equivalent Nikuradse wall roughness under variable flow conditions in a 600 mm concrete sewer pipe are experimentally investigated. The values of the acoustic attenuation are obtained in the case of airborne sound propagation in the dry pipe. A range of values of the equivalent wall roughness is artificially generated by deploying a periodical array of engineering bricks. A novel method of rapid evaluation of the acoustic attenuation is proposed. The method relies upon sound reflections from the adjacent manholes. The results demonstrate that the acoustic attenuation depends strongly on the value of the equivalent wall roughness. This work can pave the way to the efficient methodology for the in-situ, physical evaluation of the equivalent hydraulic roughness of new and existing sewer networks.

Singer’s preferred acoustic condition in performance in an opera house and self-perception of the singer’s voice

Solo singers have been shown to over estimate the relative sound pressure level of a delayed, external reproduction of their own voice, singing single syllables, which, in turn, appears to influence the preferred delay of simulated stage reflections [Noson, Ph.D. thesis, Kobe University, 2003]. Bone conduction is thought to be one factor separating singer versus instrumental performer judgments of stage acoustics. Using a parameter derived from the vocal signal autocorrelation function (ACF envelope), the changes in singer preference for delayed reflections is primarily explained by the ACF parameter, rather than internal bone conduction. An auditory model of a singer’s preferred reflection delay is proposed, combining the effects of acoustical environment (reflection amplitude), bone conduction, and performer vocal overestimate, which may be applied to the acoustic design of reflecting elements in both upstage and forestage environments of opera stages. For example, soloists who characteristically underestimate external voice levels (or overestimate their own voice) should be provided shorter distances to reflective panels—irrespective of their singing style. Adjustable elements can be deployed to adapt opera houses intended for bel canto style performances to other styles. Additional examples will also be discussed. a)Now at Kumamoto Univ., Kumamoto, Japan. b)Now at: 1-10-27 Yamano Kami, Kumamoto, Japan.

The Acoustics Associated With A Long Rectangular CavityOf Constant Cross-section Immersed In A Thick Boundary Layer

The flows over cavities are of interest in many different areas of engineering from thermal equipment to engines and machinery and can be found in landinggear wells, surface-mounted instrumentation on aircraft, cut-outs on marine vehicles, printed circuit boards and land vehicles. The very nature of these flows can cause large changes in pressure, velocity, and density fluctuations as well as generate strong propagating acoustic waves. These are typical cavity applications where reductions in pressure fluctuation levels, heat transfer, vibration, noise, and structural fatigue are still of considerable interest. This experimental study was undertaken to examine the effect of cavity length on flow oscillations produced by an open cavity placed within a subsonic turbulent boundary layer. A narrow rectangular cavity with a constant width-to-depth ratio was immersed within such a boundary layer. Microphone-type pressure transducers were used to record the pressure time histories for six separate cavity lengths (or L/D values) and the spectral character of these signals was analyzed in terms of their magnitude and frequency content. A state of acoustic resonance was only observed at L/D = 1.47, while fluid-acoustic resonance occurred at LID between 1.47 and 8.73. Relative sound pressure level (RSPL) calculations indicate that energy within the cavity was increased by approximately 60% over this L/D range. It is also suggested that this increase in the RSPL was a result of vortical structure shedding and growth, with the location of maximum unsteadiness coinciding with the location of vortical structure saturation. Transactions on the Built Environment vol 71, © 2004 WIT Press, www.witpress.com, ISSN 1743-3509

Proposed SMPTE Recommended Practices: Relative and Absolute Sound Pressure Levels for Motion-Picture Multichannel Sound Systems — Applicable for Analog Photographic Film Audio, Digital Photographic Film Audio and D-Cinema

Proposed SMPTE Recommended Practices: Relative and Absolute Sound Pressure Levels for Motion-Picture Multichannel Sound Systems — Applicable for Analog Photographic Film Audio, Digital Photographic Film Audio and D-Cinema

Auditory behaviour of a parasitoid fly (Emblemasoma auditrix, Sarcophagidae, Diptera).

Females of the parasitoid fly Emblemasoma auditrix find their host cicada (Okanagana rimosa) by its acoustic signals. In laboratory experiments, fly phonotaxis had a mean threshold of about 66 dB SPL when tested with the cicada calling song. Flies exhibited a frequency dependent phonotaxis when testing to song models with different carrier frequencies (pulses of 6 ms duration and a repetition rate of 80 pulses s(-1)). However, the phonotactic threshold was rather broadly tuned in the range from 5 kHz to 11 kHz. Phonotaxis was also dependent on the temporal parameters of the song models: repetition rates of 60 pulses s(-1) and 80 pulses s and pulse durations of 5-7 ms resulted in the highest percentages of phonotaxis performing animals coupled with the lowest threshold values. Thus, parasitoid phonotaxis is adapted especially to the temporal parameters of the calling song of the host. Choice experiments revealed a preference of a song model with 9 kHz carrier frequency (peak energy of the host song) compared with 5 kHz carrier frequency (electrophysiologically determined best hearing frequency). However, this preference changed with the relative sound pressure level of both signals. When presented simultaneously, E. auditrix preferred 5-kHz signals, if they were 5 dB SPL louder than the 9-kHz signal.

Effect of Planform Aspect Ratio on Flow Oscillations in Rectangular Cavities

An experimental investigation was undertaken to examine the effect of cavity lateral width on the flow oscillations that occur in an open cavity placed within a turbulent subsonic boundary layer. A rectangular cavity with a length to depth ratio L/D=1 and planform aspect ratio L/W=0.115 was placed within a thick turbulent boundary layer with a corresponding Reθ=10.5×103. Pressure time histories were acquired at six separate cavity widths (or L/W values) using microphone-type pressure transducers. The spectral character of these signals was analyzed and the pressure levels and dominant frequencies determined. This study indicates that large changes in the pressure level occur as L/W varies from 0.115 to 0.682. A state of fluid dynamic resonance was observed at L/W=0.137 and fluid–acoustic resonance at L/W=0.682, the smallest cavity width. Relative sound pressure level calculations indicate that the energy within the cavity compared with that of the boundary layer, was observed to increase by approximately 40 percent at L/W=0.137. [S0098-2202(00)00601-5]

Quantitative diagnosis of hypernasality in cleft lip and palate patients by computerized nasal quality assessment

In patients with cleft lip and palate (CLP), the assessment of velopharyngeal morphology and function and the quantitative analysis of perceptual consequences of velopharyngeal insufficiency are of major importance regarding the effective planning of velopharyngoplasties for speech improvement. The NasalView, a new instrument for the objective assessment of rhinophonia, is presented. The NasalView measures nasalance, the relative sound pressure level of the nasal signal in speech, expressed as a percentage. In order to evaluate the effectiveness of the computerised measurement of nasalance, 156 patients with surgically treated CLP were examined. The NasalView differentiated with high sensitivity and specificity between patients with normal nasal resonance and patients with varying degrees of hypernasality. To illustrate the importance of the NasalView for making the decision for a velopharyngoplasty, a single case is presented.

Ground effect over hard rough surfaces

Laboratory and outdoor measurements are reported of the relative sound pressure level spectrum over hard surfaces containing either random or periodically spaced arrays of 2-D roughnesses. The resulting data have been compared with predictions obtained analytically and with numerical predictions of a boundary element code. Effective impedances of the rough surfaces have been calculated from the boss theory developed by Twersky. A classical asymptotic approximation for propagation near grazing incidence from a point source over an impedance boundary has been modified, heuristically, to allow for diffraction grating effects. The resulting predictions are found to be in tolerable agreement with the data except for close and random packing. The boundary element code is found to give superior results for larger roughnesses, but computational restrictions on element size reduce its usefulness for roughnesses with small width or height.

Pressure Oscillations in a Subsonic Cavity at Yaw

An experimental investigation was undertaken to examine the effect of yaw angle on flow oscillations that occur in an open cavity placed within a subsonic boundary layer. A rectangular cavity with a length-to-depth ratio of unity and a planform aspect ratio of 8.7 was placed within a thick turbulent boundary layer with a corresponding Reynolds number based on the momentum thickness of 10.5 × 10 3 . Pressure time histories were acquired at 15 separate yaw angles using microphone-type pressure transducers. The spectral character of these signals was analyzed, and the pressure levels and dominant frequencies were determined. This study indicates that large changes in the pressure level occur as the yaw angle is changed from 0 to 70 deg. A state of resonance was observed at an angle of 60 deg. Relative sound pressure level calculations indicate that the energy within the cavity increased more than seven times at this orientation. Evidence suggesting a critical angle of approximately 60 deg, as well as mode switching from a fluid dynamic mode to a fluid acoustic mode, is also presented.

Influence of the weight of mutes on tones of a violin family

The phrase ‘‘con sordino’’ is used for the score of a violin family to indicate the use of a mute. The mute is used to reduce the volume of the violin tones and change their tone quality. This paper examines the influence of the weight of mutes on tones of a violin using the spectral envelopes of the violin tones. Violins with and without mutes were played by a skilled player in an anechoic chamber to produce tone samples which were then recorded on a DAT recorder. Using the tone samples, the time variances of the fundamentals and spectral envelopes obtained by FFT analyses were examined. The force transfer function of a cello bridge with mutes installed, which is used for convenience, was measured. From these examinations and analyses, we made the following observations: (1) the higher the order of harmonics, the lower their relative sound pressure levels compared with that of the fundamental and (2) the level differences between the peaks and dips of the spectral envelopes are reduced as the weight of a mute is increased.

Comparisons of experimental measurements of sound propagation over a hill and the polar parabolic equation method

The polar parabolic equation (POPE) method, which introduces the boundary fitting coordinates into the parabolic equation (PE) method, was developed to solve for sound propagation over a curved surface and over irregular terrain (hills) [X. Di et al., J. Acoust. Soc. Am. 92, 2431 (A) (1992)]. POPE can include realistic sound‐speed profiles and ground impedance. Predictions based upon the POPE have been compared to measurements at the JAPE 91 (Joint Acoustic Propagation Experiment) terrain masking experiment at White Sands Missile Range, New Mexico during the period 27–28 July 1991. The sound sources were hovering helicopters at the base of a hill and far away from the hill. In the JAPE data, the relative sound pressure level decreases rapidly from the top of the hill and becomes nearly constant along the base of the hill. This characteristic feature is well predicted by the polar parabolic equation calculations. POPE method appears to be an accurate means for predicting sound propagation over realistic terrain.

Sound propagation in the atmospheric surface layer: Comparison of experiment with FFP predictions

This paper presents a set of acoustical and meteorological data from an outdoor sound propagation experiment. This experiment was done in a farm field near Rock Springs, Pennsylvania, on 7 July 1990. Meteorological and acoustical measurements were recorded simultaneously during six different times in the day. The meteorological measurements permitted determination of the sound speed profiles during each of the measurement sessions, using a method based on surface-layer similarity scaling. The acoustical measurements allowed precise determination of the relative sound pressure levels for a frequency range up to 3150 Hz at six different distances (66, 88, 125, 175, 250 and 350 m). The results show atmospheric conditions have an important effect on sound propagation. At medium and high frequencies, variations of the relative SPL have been measured at distances as short as 62 m. These effects increased with the distances so that variations as great as 30 dB have been measured during that day. Comparisons with the fast field program predictions are also presented, and amply demonstrate the accuracies of this model, especially for the downward refraction cases.

Regional song dialects of the Ortolan Bunting Emberiza hortulana L. in Sweden

During the period 1966—1990 we studied the occurrence of different song dialects of the Ortolan Bunting in Sweden. Song dialects were identified for more than 420 males from about 150 different localities. We found that two regional dialects, one Northern Swedish and one Central Swedish, were prevailing. The characteristics of these two dialects are shown on melograms with one curve for fundamental frequency and one curve for relative sound pressure. The dialects can be identified and the differences clearly heard in the field without technical means. The Northern Swedish dialect is predominant north of the province of Hälsingland and the Central Swedish dialect south of that province. The two dialects meet and “overlap” in Hälsingland. The picture is supplemented by the occurrence of individuals with the foreign dialect, both dialects or a mixed dialect.

Song Features Essential for Species Discrimination and Behaviour Assessment By Male Blackbirds (Turdus Merula)

The present study tested the signal value of different parameters of the blackbird song by comparing territory owner's responses to unmodified motif parts. Parameters were modified with reference to their natural limits of variation which were known a priori for some of the parameters. Those for the frequency of occurrence of the three types of motif sound figures (unmodulated and/or complex toned FM-figures, and compound MIX-figures composed of pieces of both the CF- and the FM-type) and their modulations, and the relative sound pressure (SP) of their harmonics, were determined in this study. The following results were obtained: The frequency of occurrence of the sound figure types is essential for species discrimination in the sense that motif parts must contain CF-pieces with a relatively constant frequency (either as CF-figures or as parts of MIX-figures), and it communicates additional information: a high proportion of FM-figures giving a gurgling sound character communicates a high arousal and vice versa. The ratio of SP of the fundamental to that of the 1 st and the 2nd overtone is also essential for species discrimination. The ratio must be greater than about 1:0.2:0.2 making the motif parts relatively pure toned. Above this value the SP ratio may communicate additional information: a relatively low ratio giving a hoarse sound character seems to represent a high arousal and vice versa. Also, a high sound pressure level of the motif parts communicates a high arousal and vice versa. Neither the order of sound figures, nor the specific variation across the motif part of the sound figures' frequency level, duration and amplitude is essential for species discrimination. So is, however, a certain variation per se of each of the three features across the motif part. The results fit in with the 'room for variation hypothesis' on the principles of coding information into bird song. Thus the species-essential parameters seem to be 'tuned' to their natural limits of variation in the sense that species discrimination ceases when they are changed beyond these limits; within these limits some of them convey additional behavioural information; and they include all sorts of parameters, e.g. basic as well as higher order syntactical and sound type parameters, and invariant as well as variable ones.

Turbulent scattering in an upward-refracting atmosphere

Weiner and Keast observed that in an upward-refracting atmosphere the relative sound pressure level versus range follows a characteristic “step” function that depends strongly on the sound-speed gradient but weakly on frequency [J. Acoust. Soc. Am. 31, 724–733 (1959)]. The observed step function has recently been predicted qualitatively and quantitatively by including the effects of small-scale turbulence in a parabolic equation (PE) calculation [Gilbert, Raspet, and Di, J. Acoust. Soc. Am. Suppl. 1 80, S209 (1988); J. Acoust. Soc. Am. (to be published)]. The present paper presents results from a simpler calculation based on a single scattering approximation. The purpose of the calculation is to obtain a better understanding of the physical mechanisms that produce the step function. As an initial test, an analytic single scattering calculation is compared to the PE calculation for a nonrefracting atmosphere. For upward-refracting atmospheres, the unscattered upward-refracted field is numerically integrated in a distorted-wave single scattering calculation. The results are compared to the PE calculation and to the data of Weiner and Keast. [Work supported by ONR.]