Nicola Prodi

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.

REACTIVE ACOUSTIC INTENSITY FOR GENERAL FIELDS AND ENERGY POLARIZATION

A kind of energy polarization is shown to occur in certain acoustic fields, because of energy oscillations due to the instantaneous reactive intensity. The time‐averaged behavior of such oscillations is described by a second degree symmetric tensor, which is identified with the time‐independent reactive intensity, whose conventional vectorial definition is obtained for particular fields, including monochromatic and spherical ones.

The evaluation of binaural playback systems for virtual sound fields

By means of virtual acoustics technologies the impulse response in a location of a real enclosure can be used to create a virtual room. Also in this virtual space, typically implemented in a dead room, an impulse response can be measured. From both ‘‘real’’ and respective ‘‘virtual’’ impulse response a group of room-acoustical parameters can be calculated. The match of the two groups of indicators mostly depends on the layout of the playback system and on the implemented processing. In this paper a procedure of virtual measurement in a dead room is developed and some typical layouts of playback systems employing two loudspeakers are compared. Based on the consistency of the room-acoustical indicators derived from ‘‘real’’ and ‘‘virtual’’ impulse responses can be investigated. It is shown how the performance depends on the angular separation of loudspeakers and the efficiency of the cross-talk is also tested and discussed. Finally, a set-up which is suitable for psychoacoustics tests is indicated. # 2002 Elsevier Science Ltd. All rights reserved.

An Italian matrix sentence test for the evaluation of speech intelligibility in noise.

Objective: Development of an Italian matrix sentence test for the assessment of speech intelligibility in noise. Design: The development of the test included the selection, recording, optimization with level adjustment, and evaluation of speech material. The training effect was assessed adaptively during the evaluation measurements with six lists of 20 sentences, using open- and closed-set response formats. Reference data were established for normal-hearing listeners with adaptive measurements. Equivalence of the test lists was investigated using the open-set response format at three signal-to-noise ratios (SNRs). Study sample: A total of 55 normal-hearing Italian mother-tongue listeners. Results: The evaluation measurements at fixed SNRs resulted in a mean speech reception threshold (SRT) of − 7.3 ± 0.2 dB SNR and slope of 13.3 ± 1.2 %/dB. The major training effect of 1.5 dB was observed for the first two consecutive measurements. Mean SRTs of − 6.7 ± 0.7 dB SNR and − 7.4 ± 0.7 dB SNR were found from the third to the sixth adaptive measurement for open- and closed-set test response formats, respectively. Conclusions: A good agreement has been found between the SRTs and slope and those of other matrix tests. Since sentences are difficult to memorize, the Italian matrix test is suitable for repeated measurements.

On the Subjective Evaluation of the Perceived Balance Between a Singer and a Piano Inside Different Theatres

In order to clarify the significant acoustical parameters affecting the subjective judgment of the balance between a singer and instruments inside opera theatres, acoustical measurements, virtual reproductions and listening tests were accomplished and analysed. With impulse responses measured inside several theatres of different design and with an anechoic source consisting of a soprano singer and a piano keyboard, several virtual sound fields with particular objective parameters were reproduced under controlled conditions. The sound level difference between the stage and the pit (or orchestra) sources was fixed in the virtual sound fields and paired-comparison tests were conducted to obtain scale values of the balance. A relationship between the scale value of the balance and a group of parameters used in the acoustical qualification of rooms is then achieved by using multiple regression analysis. A relevant finding is that the early decay time (EDT) for the stage source has a major effect on the scale values of balance. The contribution of the stage parameters to the scale value is greater than that of the pit/orchestra parameters.

On the Effect of Domed Ceiling in Worship Spaces: A Scale Model Study of a Mosque

Though the importance of domes in worship buildings has been recognised since ancient times, their acoustic effects have not been entirely addressed by acoustics researchers. In addition to the known detrimental effects of late reflections and echoes, more complicated behaviour can be expected as a result of the coupling of the dome volume to the rest of the room. This investigation is focused on the impact of a dome on reverberation time. This is done using a scale model study of a typical mosque. The results show how the parameter is affected and indicate how the phenomenon might be quantified.

Permutation Approaches for Stochastic Ordering

In many application problems, when dealing with comparisons between two or more groups, the classical parametric inferential statistical methods are used, although in real problems the quite stringent assumptions required by such methods are rarely satisfied. In particular a parametric approach to the test on ordering of C > 2 populations is very difficult. In order to tackle this problem two alternative methods are proposed in the present paper. Both the methods consist in permutation combination based tests: the first is supposed to be more powerful and it is suitable when the main goal of the study is related to the global ordering of the populations; the second is useful when the interest is in the pairwise comparisons between the populations.

MEASUREMENTS OF NEWLY DEFINED INTENSIMETRIC QUANTITIES AND THEIR PHYSICAL INTERPRETATION

This paper deals with the measurement and physical interpretation of the quantities a and r introduced in a previous paper [D. Stanzial, N. Prodi, and G. Schiffrer, “Reactive intensity for general fields and energy polarization,” J. Acoust. Soc. Am. 99, 1868–1876 (1996)]. The quantity a, which has the same time dependence as the squared acoustic pressure and the same direction as the time averaged sound intensity 〈j〉, will be called here “radiating” intensity, while r which has zero average, will be called “oscillating” intensity. A coherent picture of the energy transfer process in steady sound fields based on the decomposition j=a+r of the instantaneous sound intensity will be sketched and discussed. Furthermore, a direct experimental comparison between a and r and the real and imaginary parts of the complex intensity is presented for some field conditions.

Acoustics of Italian Historical Opera Houses

Opera houses represent a large group of performance spaces characterized by great complexity and, at the same time, versatility with respect to different usage (from opera to symphonic music and ballet). This kind of building originated in Italy during the 17th century and later spread across the country and then Europe and the rest of the world, slowly evolving into modern theatre shapes. As a consequence of the changes undergone by the interior space, the original acoustic features, which likely influenced many composers, experienced important variations. Thanks to acoustic measurement campaigns inside Italian Historical Opera Houses, promoted by National and Regional Projects, the distinctive features of these spaces were investigated in comparison to modern spaces. In this work, the newly acquired data are merged with data in the literature in order to present and discuss some of the distinctive acoustic features of historical spaces as regards their original function. Moreover, specific issues such as listening in stalls and boxes and the criteria governing the preference judgment of listeners are considered. The concept and the crucial role of the balance between stage and pit sources are also discussed by means of previous literature studies.

Acoustics of opera houses: A cultural heritage

An important part of contemporary Italian musical culture has developed inside historical opera houses. An outstanding opera repertory was especially conceived to match these places, both from the architectural and the acoustical points of view. But, while extensive attention is devoted to architectural and historical aspects, the acoustical characteristics of an opera house, that is, the set of listening attributes which make such a place unique among all spaces for music, are still nowadays hardly recognized as being paramount. In fact they can be rightly considered a relevant cultural heritage in Italy and can thus be called acoustical heritage. This new kind of heritage calls for accurate study and attention, both from the scientific and social points of view. To preserve the heritage for future generations, it is necessary to know it precisely and to elaborate means of accurate description. A project with the participation of international specialists has been established to agree on a standardized p...