June 2016 - June 2017

Lee, J. S.; Violato, D.; Polifke, W. Acoustical characteristics of two-phase horizontal intermittent flow through an orifice

Acta Acust united Ac. Vol. 102, No. 5 (2016), pp. 804-812(9)
DOI: 10.3813/AAA.918995

Abstract: This study addresses acoustical characteristics, in particular, sound generation of intermittent flow regime in a horizontal pipe through an orifice, based on recorded pressure fluctuations and videos of upstream and downstream flow of the orifice. The flow regimes of interest are plug flow and slug flow, respectively, where sharpedged and rounded entrance orifice are tested. In principle, the noise generated in the intermittent flow regime through an orifice increases with a higher gas flow rate. The pressure fluctuation spectra show a "haystack" configuration with a peak at a low frequency associated with a sequence of elongated gas bubbles. It demonstrates that the sound generation is predominately governed by dynamic of elongated gas bubbles in intermittent flow through the orifice. Particularly, in plug flow, an additional small hump is detected close to St = 0.2, i.e., vortexshedding at the orifice exit contributes the sound generation in addition to the bubble dynamic. Furthermore, non-dimensional power of the downstream intermittent flow decays with St α . The value of α increases with a higher liquid rate, and the "haystack"-like shape at the peak frequency widens as the gas rate increases. In plug flow, the rounded entrance orifice generates less noise by resulting in a smaller pressure drop compared to the sharp-edged orifice in general; however, it generates noise in high frequency.

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Garai M, Schoen E, Behler G, Bragado B, Chudalla M, Conter M, Defrance J, Demizieux P, Glorieux C, Guidorzi P. Repeatability and Reproducibility of In Situ Measurements of Sound Reflection and Airborne Sound Insulation Index of Noise Barriers

Acta Acust united Ac. Vol. 100, No. 6 (2014), pp. 1186-1201(16)
DOI: 10.3813/AAA.918797

Abstract: In Europe, in situ measurements of sound reflection and airborne sound insulation of noise barriers are usually done according to CEN/TS 1793-5. This method has been improved substantially during the EU funded QUIESST collaborative project. Within the same framework, an inter-laboratory test has been carried out to assess the repeatability and reproducibility of the newly developed method when applied to real-life samples, including the effect of outdoor weather variability and sample ageing. This article presents the statistical analysis of the inter-laboratory test results, and the values of the repeatability and the reproducibility, both in one-third octave bands and for the single-No. ratings. The estimated reproducibility values can be used as the extended measure of uncertainty at the 95% credibility level in compliance with the ISO GUM. The repeatability and reproducibility values associated with airborne sound insulation are also compared with the corresponding values for laboratory measurements in building acoustics and an acceptable agreement is found.

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Lindau, Alexander; Erbes, Vera; Lepa, Steffen; Maempel, Hans-Joachim; Brinkman, Fabian; Weinzierl, Stefan. A Spatial Audio Quality Inventory (SAQI)

Acta Acust united Ac. Vol. 100, No. 5 (2014), pp. 984-994(11)
DOI: 10.3813/AAA.918778

Abstract: The perceptual evaluation of spatial audio systems may be based on singular auditory qualities such as the localization accuracy or the perception of coloration, on overall criteria of perceptual accuracy such as plausibility and authenticity or on detailed catalogues of auditory qualities. However, only the latter will be suited for the perceptual characterization of a simulation's technical shortcomings and allow for its focused improvement. Therefore, a common vocabulary containing all perceptual attributes which are relevant in this context appears desirable. Existing vocabularies for the evaluation of sound field synthesis, spatialization technologies and virtual acoustic environments were often generated ad hoc by authors or were focused on specific perceptual aspects or on specific spatialization techniques only. To overcome limitations with respect to the relevance and completeness of these vocabularies we have developed a Spatial Audio Quality Inventory (SAQI) for the perceptual evaluation of all spatial audio technologies used for the (re)synthesis of acoustic environments. It is a consensus vocabulary comprising 48 verbal descriptors of auditive qualities assumed to be of practical relevance when comparing (re)synthesized sound fields to real or imagined references or amongst each other. The vocabulary was generated by a Focus Group of 21 German speaking experts for virtual acoustics. Five additional experts helped verifying the unambiguity of all descriptors and the related explanations. Moreover, an English translation was generated and verified by eight bilingual experts. This article describes the applied methodology and presents the English version of the final vocabulary.

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Hornikx, Maarten; Forssén, Jens; Botteldooren, Dick; van Renterghem, Timothy; Wei, Weigang; Ögren, Mikael; Salomons, Erik. Urban Background Noise Mapping: The Multiple-Reflection Correction Term

Acta Acust united Ac. Vol. 100, No. 2 (2014), pp. 293-305(13)
DOI:
10.3813/AAA.918709

Abstract: Mapping of road traffic noise in urban areas according to standardized engineering calculation methods systematically results in an underestimation of noise levels at areas shielded from direct exposure to noise, such as inner yards. In most engineering methods, road traffic lanes are represented by point sources and noise levels are computed utilizing point-to-point propagation paths. For a better prediction of noise levels in shielded urban areas, an extension of engineering methods by an attenuation term A can has been proposed, including multiple reflections of the urban environment both in the source and in the receiver area. The present work has two main contributions for the ease of computing A can. Firstly, it is shown by numerical calculations that A can may be divided into independent source and receiver environment terms, A s and A r. Based on an equivalent free field analogy, the distance dependence of these terms may moreover be expressed analytically. Secondly, an analytical expression is proposed to compute A s and A r for 3D configurations from using 2D configurations only. The expression includes dependence of the street width-to-height ratio, the difference in building heights and the percentage of façade openings in the horizontal plane. For the expression to be valid, the source should be separated from the receiver environment by at least four times the street width.

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Lindau, Alexander; Weinzierl, Stefan. Assessing the Plausibility of Virtual Acoustic Environments

Acta Acust united Ac. Vol. 98, No. 5 (2012), pp. 804-810(7)
DOI:
10.3813/AAA.918562

Abstract: Aiming at the perceptual evaluation of virtual acoustic environments (VAEs), 'plausibility' is introduced as a quality criterion that can be of value for many applications in virtual acoustics. We suggest a definition as well as an experimental operationalization for plausibility, referring to the perceived agreement with the listener's expectation towards a corresponding real acoustic event. The measurement model includes the criterion-free assessment of the deviation from this non-explicit, inner reference by rating corresponding real and simulated stimuli in a Yes/No test paradigm and analyzing the results according to signal detection theory. The specification of a minimum effect hypothesis allows testing of plausibility with any desired strictness. The approach is demonstrated with the perceptual evaluation of a system for dynamic binaural synthesis in two different development stages.

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Rajabi, Majid; Mojahed, Alireza. Acoustic Manipulation of a Liquid-filled Spherical Shell Activated with an Internal Spherical Oscillator

Acta Acust united Ac. Vol. 103, No. 2 (2017), pp. 210-218(9)
DOI: 10.3813/AAA.919049

Abstract: Following the advent of acoustic manipulation techniques and micro-scale delivery systems, especially in engineering and medical applications, a novel configuration of spherical carriers activated with an internally oscillating radiator is proposed in order to achieve complete handling. The theory of acoustic plane harmonic wave scattering and the exerted radiation force are developed for a spherical thin-shell filled with ideal fluid and activated with an internal dipole rigid spherical oscillator, in an exact manner. It is shown that the non-intuitive phenomenon of acoustic radiation force cancellation is viable for oscillation properties belong to a frequency dependant straight line equation in a real–imaginary plane of oscillating characteristics. This characteristic line divides the real–imaginary plane into two distinct regions: "the positive radiation force or pushing effects and the negative radiation force or pulling effects". This capability of producing both pushing and pulling effects leads to possibility of complete acoustic handling. This investigation introduces a new branch in acoustic manipulation techniques and carriers with great application in modern medicine and engineering.

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Grothe, Timo; Baumgart, Johannes. Assessment of Bassoon Tuning Quality from Measurements under Playing Conditions

Acta Acust united Ac. Vol. 101, No. 2, 2015, pp. 238-245(8)
DOI: 10.3813/AAA.918822

Abstract: In reed woodwinds, the pitch of a sound is the result of an interaction between the air column, the reed, and the player. The air column is well described by its resonance frequencies and their damping. The reed is a pressure-controlled valve, which drives a coupled oscillation that settles with a fundamental frequency near a resonance frequency of the air column. The musician provides the blowing pressure and can alter the dynamical properties of the reed with his embouchure. An experimental study is presented that investigates from the player's perspective the tuning quality of the whole system under playing conditions for the case of the bassoon. A strong influence on tuning is reported for the bocal or crook, which is the interchangeable part of the resonator's top end. Here we focus on the lip force a musician has to exert for the instrument to play in tune. For normal playing regimes, the relation between lip force and pitch is roughly linear: higher lip force at constant blowing pressure increases the pitch. However, as each fingering requires a different lip force, playing a succession of notes may require considerable lip force changes that are tedious: the instrument appears to be badly tuned. Covering the full tonal and dynamical range on three modern German bassoons, this study investigates the tuning properties in two ways. Firstly, a professional musician has been asked to play notes without embouchure corrections on three bassoons. Secondly, the lip force and blowing pressure to play notes in tune were measured on these bassoons with an artificial mouth. A linear fit explains a half of the observed relation of the tuning discrepancy in uncorrected playing to the measured lip force when playing in tune. This link between objective and subjective tuning measurements justifies the method of measuring lip forces during playing with an artificial mouth to assess tuning quality. The results point to a common tuning trend of bassoons of the modern German type independent of the bocal and reed.

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Kuusinen, Antti; Lokki, Tapio. Wheel of Concert Hall Acoustics

Acta Acust united Ac. Vol. 103, No. 2 (2017), pp. 185-188(4)
DOI: 10.3813/AAA.919046

Abstract: More than a hundred years of research on concert hall acoustics has provided an extensive list of attributes to describe and evaluate the perceptual aspects of sound in concert halls. This brief overview discusses the current knowledge, and presents a "wheel of concert hall acoustics" in which the main aspects are gathered together with the descriptive attributes that are commonly encountered in the research literature.

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Brücker, Ch.; Kirmse, C.; Triep, M. Feedback of the Glottal Jet Flow with Supraglottal Wall Oscillations

Acta Acust united Ac. Vol. 102, No. 2 (2016), pp. 240-243(4)
DOI: 10.3813/AAA.918940

Abstract: Within this study the influence of wall oscillations in the supraglottal space on the evolution of the glottal jet is investigated. Special focus is laid on the modification of the jet evolution in space and time when small varicose vibrations are excited externally on the walls of the second constriction (ventricular folds) in the supraglottal space. The experiments are carried out in a water flow channel representing a 3:1 upscaled model of the glottal region. Instead of fixed walls in the second constriction we use silicone membranes with an internal air cushion. Sinusoidal pressure oscillations of various frequencies are excited from outside pressure lines. Flow studies show that the glottal deflection in the supraglottal space is highly sensitive to these weak oscillations, hinting on the non-linear interaction of the oscillatory waves with the shear-layer roll-up of the jet. This is known as modelocking in jet dynamics and is expected to have consequences on the sound spectrum in phonation, too.

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Postma, Barteld N. J.; Demontis, Hugo; Katz, Brian F. G. Subjective Evaluation of Dynamic Voice Directivity for Auralizations

Acta Acust united Ac. Vol. 103, No. 2 (2017), pp. 181-184(4)
DOI: 10.3813/AAA.919045

Abstract: It is possible to include static directivity patterns into auralizations to better represent the way in which real sources radiate sound and subsequently excite the room. Sources such as the voice have directivity patterns which vary with frequency and also due to dynamic movements of the performer. This study presents an investigation of the inclusion of dynamic voice directivity into room acoustic auralizations based on geometrical acoustics (GA) software. Previous studies have performed this using multi-channel anechoic recordings. In contrast, this study employs single channel anechoic stimuli. Focus is on the incorporation of dynamic orientation presenting the means by which it is included into the GA software as well as the results of a subjective listening test. Results indicate that dynamic voice directivity orientation auralizations are perceived as more plausible, more enveloping, and exhibiting greater apparent source width than auralizations with a static voice directivity and omnidirectional sources.

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