Peter Juhl - Academia.edu (original) (raw)

Papers by Peter Juhl

Sound intensity probes are often used with windscreens to minimise the effect of turbulence noise... more Sound intensity probes are often used with windscreens to minimise the effect of turbulence noise caused by mean flow. A theoretical and experimental study published ten years ago concluded that the use of a windscreen results in underestimation of the radiated sound power at low frequencies in strongly reactive sound fields. The theoretical part of this study was based on a windscreen of infinite extent. In this paper windscreens of realistic size and shape are dealt with by means of a coupled boundary element model for the windscreen and the surrounding air. The error of the estimated intensity caused by the windscreen is calculated under a number of sound field conditions of varying reactivity.

Annals of Occupational Hygiene, 2011

The effect of scattering and diffraction on measurement of sound pressure with 'two-microphon... more The effect of scattering and diffraction on measurement of sound pressure with 'two-microphone' intensity probes is examined numerically. Whereas it has been demonstrated recently that the sound intensity estimated with a two-microphone probe with half-inch microphones separated by a 12-mm spacer is reliable up to 10 kHz, the sound pressure will typically be underestimated at high frequencies. It is shown in this paper that a non-equal weighting of the pressure signals of the two microphones leads to an improved estimate of the sound pressure under a variety of realistic sound field conditions. The improved intensity probe can measure the sound pressure more accurately at high frequencies than an ordinary sound intensity probe or an ordinary sound level meter.

Small Bubble Curtains are an effective technique to reduce the underwater noise being emitted dur... more Small Bubble Curtains are an effective technique to reduce the underwater noise being emitted during offshore pile driving. In order to protect the marine fauna, noise reduction becomes even more important, since the increasing contribution of offshore wind energy leads to a rising number of offshore construction sites in order to cover the need for clean energy. Within the Bubble Curtain air bubbles are injected into the water surrounding the pile. When these are driven by the pressure wave being emitted from the pile, reflection, scattering and absorption effects occur. Within this paper, a method is presented in order to predict the rate of noise attenuation achieved by a Small Bubble Curtain. For this purpose, the bubble distribution is determined with Computational Fluid Dynamics. The noise radiation during pile driving is simulated by Finite Element Analysis and an Effective Medium Approach considers the acoustic effects within the Bubble Curtain. The pressure level at an arbi...

For many decades, models that can explain the behaviour of measurement condenser microphones have... more For many decades, models that can explain the behaviour of measurement condenser microphones have been proposed in the literature. These devices have an apparently simple working principle, a charged capacitor whose charge varies when one of its electrodes, the diaphragm, moves as a result of sound waves. However, measurement microphones must be manufactured very carefully due to their sensitivity to small changes of their physical parameters. There are different elements in a microphone, the diaphragm, the gap behind it, a back cavity, a vent for pressure equalization and an external medium. All these subsystems form a strongly coupled device that cannot be modelled properly as a superposition of submodels, but rather as a whole. For this reason, the challenge of microphone modelling is still an ongoing area of research. In this work, a newly developed Boundary Element Method implementation that includes visco-thermal losses is used to model measurement condenser microphones. The models presented are fully coupled and include a FEM model of the diaphragm. The behaviour of the acoustic variables in the gap and the effect of the pressure equalization vent are discussed, as well as the practical difficulty due to the production variability among single units of the same microphone model.

Many transducers (e.g. microphones) consist of a moving part facing the exterior on one side and ... more Many transducers (e.g. microphones) consist of a moving part facing the exterior on one side and facing a closed cavity on the other. In order to obtain and solve a model of such transducers, a fully coupled model can be used and the performance of this model will rely of the performance of the sub-models being coupled. Previous work has revealed that the performance of an interior lossless BEM formulation concerning a cavity with rigid walls can pose a limit on the accuracy of a fully coupled model of the transducer – in particular when including viscous and thermal losses in the cavity. This paper investigates the accuracy of a lossless acoustic BEM formulation for cavities with rigid walls at low frequencies and addresses possible solutions for restoring accuracy.

The concept of reciprocity is widely used in both theoretical and experimental work. In Boundary ... more The concept of reciprocity is widely used in both theoretical and experimental work. In Boundary Element calculations reciprocity is sometimes employed in the solution of computationally expensive scattering problems, which sometimes can be more efficiently dealt with when formulated as the reciprocal radiation problem. The present paper concerns the situation of having a point source (which is reciprocal to a point receiver) at or near a discretized boundary element surface. The accuracy of the original and the reciprocal problem is compared in a test case for which an analytical solution exists.

Numerical modeling of condenser microphones is a challenging task. In these devices, there is a s... more Numerical modeling of condenser microphones is a challenging task. In these devices, there is a strong coupling between the exterior medium, the metallic stretched membrane, and the interior domain. Viscous and thermal losses in the narrow gap between membrane and back plate play a central role in the precise damping of the membrane's first resonance and the definition of the sensitivity at high frequencies. The inclusion of losses means a drastic increase in the computational load and makes the modeling of the most complicated units very cumbersome. The difficulty is even higher when whole calibration systems, such as primary reciprocity setups, need to be modeled. There is a need for such models from the metrological community. In previous publications, the Boundary Element Method (BEM) has shown to be able to model several measurement condenser microphones, some of them containing many holes in the backplate. There is, however, a difficulty when low frequencies are modeled. The limit for "low" frequency depends on the unit, but it is generally below the membrane resonance. This issue is the consequence of the instability of the BEM at low frequencies for interior domains, where the pressure in the cavity is almost uniform. Some solutions have been found for microphone models that minimize this effect, but a complete removal would be more desirable. In this paper, the issue will be examined from the practical point of view. Some new remedies will be proposed, including numerical approaches that preserve the advantages of the BEM and can become more stable in the referred cases.

Journal of speech, language, and hearing research : JSLHR, Jan 20, 2017

The aim of this study was to add further knowledge about the usefulness of the Voice Range Profil... more The aim of this study was to add further knowledge about the usefulness of the Voice Range Profile (VRP) assessment in clinical settings and research by analyzing VRP dual-microphone equipment precision, reliability, and room effect. Test-retest studies were conducted in an anechoic chamber and an office: (a) comparing sound pressure levels (SPLs) from a dual-microphone VRP device, the Voice Profiler, when given the same input repeatedly (test-retest reliability); (b) comparing SPLs from 3 devices when given the same input repeatedly (intervariation); and (c) assessing the room effect. (a) The mean standard deviation across 17 measurement points was 0.7 dB for 1 device. (b) One device was less precise than the other 2 devices. All devices presented high SPLs at low frequencies compared with the reference. (c) Mean SPLs were almost equal in the anechoic chamber and the office. The high test-retest reliability of the dual-microphone VRP equipment, especially in general office surround...

Journal of speech, language, and hearing research : JSLHR, 2017

Critical differences state by how much 2 test results have to differ in order to be significantly... more Critical differences state by how much 2 test results have to differ in order to be significantly different. Critical differences for discrimination scores have been available for several decades, but they do not exist for speech reception thresholds (SRTs). This study presents and discusses how critical differences for SRTs can be estimated by Monte Carlo simulations. As an application of this method, critical differences are proposed for a 5-word sentences test (a matrix test) using 2 widely implemented adaptive test procedures. For each procedure, simulations were performed for different parameters: the number of test sentences, the j factor, the distribution of the subjects' true SRTs, and the slope of the discrimination function. For 1 procedure and 1 parameter setting, simulation data are compared with results found by listening tests (experimental data). The critical differences were found to depend on the parameters tested, including interactive effects. The critical dif...

International Journal of Audiology, 2016

Examination of Danish data for medico-legal compensations regarding hearing disabilities. The stu... more Examination of Danish data for medico-legal compensations regarding hearing disabilities. The study purposes are: (1) to investigate whether discrimination scores (DSs) relate to patients&amp;amp;amp;#39; subjective experience of their hearing and communication ability (the latter referring to audio-visual perception), (2) to compare DSs from different discrimination tests (auditory/audio-visual perception and without/with noise), and (3) to relate different handicap measures in the scaling used for compensation purposes in Denmark. Data from a 15 year period (1999-2014) were collected and analysed. The data set includes 466 patients, from which 50 were omitted due to suspicion of having exaggerated their hearing disabilities. The DSs relate well to the patients&amp;amp;amp;#39; subjective experience of their speech perception ability. By comparing DSs for different test setups it was found that adding noise entails a relatively more difficult listening condition than removing visual cues. The hearing and communication handicap degrees were found to agree, whereas the measured handicap degrees tended to be higher than the self-assessed handicap degrees. The DSs can be used to assess patients&amp;amp;amp;#39; hearing and communication abilities. The difference in the obtained handicap degrees emphasizes the importance of collecting self-assessed as well as measured handicap degrees.

Journal of the Audio Engineering Society, Mar 1, 1993

The spectral stereo theory, which was developed by Cooper and Bauck in order to determine the the... more The spectral stereo theory, which was developed by Cooper and Bauck in order to determine the theoretical relationship between stereo loudspeaker signals and localization, makes use of a spherical head model. In the present work the theory is combined with ...

Acoustical Society of America Journal, May 1, 2001

Boundary element method (BEM) calculations are used for the purpose of predicting the acoustic in... more Boundary element method (BEM) calculations are used for the purpose of predicting the acoustic influence of the human head in two cases. In the first case the sound source is the mouth and in the second case the sound is plane waves arriving from different directions in the horizontal plane. In both cases the sound field is studied in relation to two positions above the right ear being representative of hearing aid microphone positions. Both cases are relevant for hearing aid development. The calculations are based upon a direct BEM implementation in Matlab. The meshing is based on the original geometrical data files describing the B&K Head and Torso Simulator 4128 combined with a 3D scan of the pinna.

Acta Acustica United With Acustica, Jun 30, 2001