In this paper, with the aim of assessing the deterioration of speech intelligibility caused by a speaker wearing a mask, different face masks (surgical masks, FFP2 mask, homemade textile-based protection and two kinds of plastic shields) are compared in terms of their acoustic filtering effect, measured by placing the mask on an artificial head/mouth simulator. For investigating the additional effects on the speaker’s vocal output, speech was also recorded while people were reading a text when wearing a mask, and without a mask. In order to discriminate between effects of acoustic filtering by the mask and mask-induced effects of vocal output changes, the latter was monitored by measuring vibrations at the suprasternal notch, using an attached accelerometer. It was found that when wearing a mask, people tend to slightly increase their voice level, while when wearing plastic face shield, they reduce their vocal power. Unlike the Lombard effect, no significant change was found in the spectral content. All face mask and face shields attenuate frequencies above 1–2 kHz. In addition, plastic shields also increase frequency components to around 800 Hz, due to resonances occurring between the face and the shield. Finally, special attention was given to the Slavic languages, in particular Slovak, which contain a large variety of sibilants. Male and female speech, as well as texts with and without sibilants, was compared.
In acoustical spaces, room acoustics parameters are often predicted using energybased geometrical acoustics. For smaller rooms, interference among coherent reflections is taken into account by phased geometrical acoustics, which improves results for lower frequencies. The use of a spherical wave reflection coefficient improves the results further, yet the impact on room acoustics parameters is not fully known. This work focuses on the differences in predicted reverberation time when using plane or spherical wave reflection coefficients. The differences are analyzed for a variety of boundary conditions, including nonuniform distributions of absorption, in medium-sized rooms using a phased image source model. Since calculated differences are greater than the conventional just-noticeable-difference of 5% for reverberation time, a laboratory listening test is performed to confirm audibility of the modeled differences. Two narrow band noise stimuli (octave bands with central frequency 125 and 250 Hz) with a duration of 1 s were used for comparisons of 18 acoustic scenarios by means of a three-alternative forced choice method (3AFC). More than half of the listeners could hear the differences in all 36 cases. Statistically significant results (chi-squared test was used) were found in two thirds of the cases, corresponding to those with longer reverberation times.
The development and validation of single number quantities that are meant to serve for straightforward assessment and comparison of airborne sound insulation properties of partition walls are typically challenged by the necessity to perform large numbers of laboratory listening tests with human subjects. This is because a reliable validation of a single number quantity requires testing for many different wall types with multiple real-life stimuli that are representative for daily life soundscapes. In this article, an alternative approach is presented that allows to test a large number of “partition wall – real-life sound stimuli” combinations. This approach uses the well-established and nowadays generally accepted Zwicker’s Loudness for quantifying the subjective loudness of sound passing through a wall, and derive from that the subjectively perceived sound insulation. Using the proposed assessment method, the adequacy of single number quantities that are currently in use, and a number of newly proposed single number quantities, are compared.
Evaluating the adequacy of single number quantities that are used to assess the sound insulation performance of walls by listening tests is hampered by the difficulty to perform large numbers of subjective tests, due to the need for combining many stimuli, each representing different source/wall combinations. In this article, this problem is tackled by an alternative approach that makes use of Loudness based validation of proposed single number quantities. The adequacy of the newly proposed method was assessed by comparing wall rankings based on Loudness on one hand, and on laboratory listening tests on the other hand. Perceptual comparison of sounds passing through different types of walls between dwellings was performed by a listening test procedure that focused on differences in perception of sound insulation of a set of real-life heavy weight (HW) and light weight walls (LW), and synthetic variants of those. The latter were upshifted or downshifted versions of real wall insulation spectra. The listening tests were based on a three-alternative forced-choice testing method. Altogether, 40 test subjects with normal hearing ability were asked to rate the loudness of sounds transmitted through different walls, which were simulated by filtering a set of real-life sound stimuli. The resulting ranking of walls in order of isolation performance was compared with rankings based on the Loudness of the transmitted sound, and on the value of single-number quantities, that are commonly used for objective evaluation of the sound insulation i.e., Rw and Rw+C50-5000. Special attention was given to the weight of low frequency isolation values in the subjective assessment and in the calculation of the single number quantities. Two new single-number quantities, Rmod and Rmod,2 are proposed, which are found to fit better to subjective perception of sound insulation than the investigated existing quantities.
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