SummaryThis article presents a perceptual comparison of the loudness of a large range of 64 different typical "living room" sounds transmitted through two different walls: (1) a light-weight wall, composed of gypsum boards mounted on metal "C" studs and (2) a heavy-weight wall, built out of lime sand bricks plastered on one side. The two walls had different (laboratory measured) sound insulation spectra, but their Rw + C50−5000 rating was the same: 52 dB. Compared to the heavy-weight wall, the massspring-mass-type light-weight wall had better sound insulation properties in the middle frequency range and worse at low frequencies below 100 Hz and above 3150 Hz. Listening subjects had to choose the loudest stimuli between a pair of sounds (as transmitted through the lightweight and the masonry wall) presented through headphones in random order with one repetition, following a two-alternative forced choice (2AFC) procedure. Two sets of listening tests were conducted in this study, playing stimuli at realistic sound level and on artificially overall increased level. The listening experiments revealed significant differences in subjective assessment between the two types of acoustic insulation. The results also infer that the discussed single number rating does not adequately correspond with people's perception.

Featured Application: The work aims to give more insights into the relation between the sensitivity of the simulated objective parameters and the software input parameters for open-air ancient theatres. It is meant to raise awareness on the use of predictive acoustic software for unconventional outdoor environments in order to validate the possibility of re-using them as performance spaces. Abstract:Nowadays, ancient open-air theatres are often re-adapted as performance spaces for the additional historical value they can offer to the spectators' experience. Therefore, there has been an increasing interest in the modelling and simulation of the acoustics of such spaces. These open-air performance facilities pose several methodological challenges to researchers and practitioners when it comes to precisely measure and predict acoustical parameters. Therefore this work investigates the accuracy of predicted acoustical parameters, that is, the Reverberation Time (T 20 ), Clarity (C 80 ) and Sound Strength (G), taking the ancient Syracusae open-air theatre in Italy as a case study. These parameters were derived from both measured and simulated Impulse Responses (IR). The accuracy of the acoustic parameters predicted with two different types of acoustic software, due to the input variability of the absorption and scattering coefficients, was assessed. All simulated and measured parameters were in good agreement, within the range of one "just noticeable difference" (JND), for the tested coefficient combinations.

Most European countries have regulatory requirements or guidelines for reverberation time in classrooms which have the goal of enhancing speech intelligibility and reducing noise levels in schools. At the same time, school teachers suer frequently from voice problems due to high vocal load experienced at work. With the aim of improving working conditions for teachers, this article presents guidelines for classroom acoustics design that meet simultaneously criteria of vocal comfort and speech intelligibility, which may be of use in future discussions for updating regulatory requirements in classroom acoustics. Two room acoustic parameters are shown relevant for a speaker: the voice support ST V , linked to vocal effort, and the decay time DT 40,ME derived from an oral-binaural impulse response, linked to vocal comfort. Theoretical prediction models for room-averaged values of these parameters are combined with a model of speech intelligibility based on the useful-to-detrimental ratio U 50 and empirical models of signal-to-noise ratio in classrooms in order to derive classroom acoustic guidelines, taking into account physical volume restrictions linked to the number of students present in a classroom. The recommended values of reverberation time in fully occupied classrooms for exible teaching methods are between 0.45 s and 0.6 s (between 0.6 and 0.7 s in an unoccupied but furnished condition) for classrooms with less than 40 students and volumes below 210 m 3 . When designing larger classrooms, a dedicated acoustic study taking into account considerations about geometry, material and speaker/audience placements should be made, which can help to increase the voice support and reduce the vocal eort.

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