Francesco Martellotta

An experimental study on noise indices in air conditioned offices

Abstract An acoustical environment survey was carried out in an air-conditioned office building. A total of 52 rooms occupied by one or more workers were analysed. In this survey, we used questionnaires and physical noise measurements. The offices characteristics lead us to belive that the noise sources to be considered were only those inside each room; this means that when a room is occupied by only one person the noise of the air conditioning system prevails. Instead, when a room is occupied by more than one person, the noise generated by the office activity prevails. Our results show that some noise indices are well correlated with subjective sensations of loudness and annoyance; we found the strongest correlation for the percentile level L A90 , and the equivalent sound pressure level.

Identifying acoustical coupling by measurements and prediction-models for St. Peter's Basilica in Rome.

St. Peters Basilica is one of the largest buildings in the world, having a huge volume resulting from the addition of different parts. Consequently, sound propagation cannot be interpreted using a conventional approach and requires experimental measures to be compared with statistical-acoustics and geometrical predictions in order to explain the interplay between shape, materials, and sound waves better. In previous research one of the most evident effects, the surprisingly low reverberation time, was believed to result from acoustical coupling phenomena. Taking advantage of more refined measuring techniques available today an acoustic survey was carried out and the results were analyzed using different methods, including Bayesian parameter estimation of multiple slope decays and directional energy plots, which showed that coupling effects actually take place, even though measured reverberation times were longer than those given in previous studies. In addition, experimental results were compared with geometrical- and statistical-acoustic models of the basilica, which showed that careful selection of input data and, in statistical models, the inclusion of phenomena such as direct sound radiation and non-diffuse energy transfer, allow obtaining accurate results. Finally, both models demonstrated that reduced reverberation depends more on increased absorption of decorated surfaces than on coupling effects.

Sound propagation and energy relations in churches

The results of an acoustic survey carried out in a group of Italian churches differing in style, typology, and location were used in order to study how the acoustic energy varies inside this kind of space. The effect of different architectural elements on sound propagation was investigated by means of three-dimensional impulse responses measured using a B-format microphone with sweep signals. Side chapels, columns, and trussed roofs appeared to scatter the reflections, so that the purely diffuse exponential sound decay begins after a time interval which grows with the source-receiver distance and with the complexity of the church. The results of the measurements were then compared with predictions given by existing theoretical models to check their accuracy. In particular a model previously proposed by the authors for a specific type of Romanesque churches was further refined taking into account the new findings and making some simplifications. Its application to the wider sample of churches under analysis showed that strength, clarity, and center time can be predicted with reasonable accuracy.

A new approach to assessing the performance of noise indices in buildings

Abstract The results of a wide acoustic environment survey are presented. Sound pressure measurements were carried out in a group of offices. These measurements lasted for five minutes and the resulting noise spectra were used to calculate the most significant acoustic parameters. During each measurement a questionnaire was administered to workers near each measuring position. The questionnaire asked them to indicate their subjective judgement about noise annoyance, noise loudness and dissatisfaction induced by noise present in the environment. The aim of the research was to investigate the performance of the measured noise indices in describing subjective responses to noise. A new method to calculate the average subjective responses is proposed. The performance of the noise indices was studied by means of linear regression analysis. Finally the A-weighted equivalent sound pressure level proved to be the best index among those analysed in describing subjective auditory sensations.

An improved model to predict energy-based acoustic parameters in Apulian-Romanesque churches

In this paper an improved model to predict energy relations in churches is proposed. A detailed acoustic survey was carried out of nine Romanesque churches having volumes ranging from 33 000 to 1500 m 3 . The measured sound level and early/late ratio showed significant correlation with the source–receiver distance, but the comparison with values predicted using theoretical models initially gave unsatisfactory results. The main difference was due to the early energy which was underestimated at points near the source and overestimated at distant points. Barron’s revised theory proved to be the most reliable among the analysed models, so, in order to improve its prediction accuracy, a modified early reflected energy component was added to the direct and reverberant sound. The improved model was finally validated and the comparison between predicted and measured values gave good results. # 2002 Elsevier Science Ltd. All rights reserved.

Acoustics of Apulian-Romanesque Churches: Correlations Between Architectural and Acoustic Parameters

This paper concludes the analysis of the results of an acoustic survey carried out on nine Romanesque churches in Apulia (Southern Italy), described in detail in a previous paper. The study was performed taking into account both room-average values and individual position values of monaural and binaural acoustic parameters, measured according to ISO 3382. First the effect of architectural parameters on reverberation time was investigated, showing that volume and materials play an important role. Then room-average values of the other acoustic parameters were investigated, showing that some are mostly correlated with reverberation time and others with total acoustic absorption. Analysis of individual location values showed that monaural parameters can be expressed as functions of the source-receiver distance, and one or two of the following parameters: room volume, total absorbing area, mean absorption coefficient, total length and reverberation time. Furthermore, it was demonstrated that individual position values of acoustic parameters describing clarity, are significantly correlated to each other.

Acoustics of Apulian-Romanesque churches: an experimental survey

A detailed acoustic survey was carried out of nine Romanesque churches built in Apulia, in Southern Italy. Despite the common architectural style the churches show specific features and have volumes ranging from 1500 m3 to 32000 m3. In each church both monaural and binaural acoustic parameters were measured according to the ISO 3382 standard. The results of the measurements are discussed in this paper, analysing both the distribution of the acoustic parameters inside each church, and how that distribution depends on specific characteristics. Finally, a discussion of the results as a whole is given. In a later paper the whole set of data will be used in order to investigate the correlations between architectural features, such as dimensions and materials, and acoustic characteristics.

Interference effects in field measurements of airborne sound insulation of building facades

The limits of the procedure for the measurement of the sound insulation of building facades represent the main subject of this paper.To calculate the facade insulation, standard ISO 140-5 requires that the difference between outdoor and indoor sound pressure levels is determined. However, the measurement of outdoor pressure levels presents several critical challenges, not fully considered in the standard. In fact, the placement of an external source and receiver according to ISO 140-5 is flexible to permit adapting the measurement configuration to specific building characteristics. Unfortunately, according to the relative external source and receiver positions, destructive interferences among waves may occur in different frequency bands. Comparisons between different source-receiver combinations are hence investigated theoretically, before being compared with field measurements. The paper investigates circumstances which might lead to destructive interferences in the external final sound field. The increasing attention of reproducibility in building acoustics suggests an investigation of possible measurement errors that may occur. The influence of interference effects on the single number rating of the sound insulation is finally given.

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.

Optimizing stepwise rotation of dodecahedron sound source to improve the accuracy of room acoustic measures

Dodecahedron sound sources are widely used for acoustical measurement purposes as they produce a good approximation of omnidirectional radiation. Evidence shows that such an assumption is acceptable only in the low-frequency range (namely below 1 kHz), while at higher frequencies sound radiation is far from being uniform. In order to improve the accuracy of acoustical measurements obtained from dodecahedron sources, international standard ISO 3382 suggests an averaging of results after a source rotation. This paper investigates the effects of such rotations, both in terms of variations in acoustical parameters and spatial distribution of sound reflections. Taking advantage of a spherical microphone array, the different reflection patterns were mapped as a function of source rotation, showing that some reflections may be considerably attenuated for different aiming directions. This paper investigates the concept of averaging results while changing rotation angles and the minimum number of rotations required to improve the accuracy of the average value. Results show that averages of three measurements carried out at 30° angular steps are closer to actual values and show much less fluctuation. In addition, an averaging of the directional intensity components of the selected responses stabilizes the spatial distribution of the reflections.