Carmine Ianniello

Measurement of the resistivity of porous materials with an alternating air-flow method

Air-flow resistivity is a main parameter governing the acoustic behavior of porous materials for sound absorption. The international standard ISO 9053 specifies two different methods to measure the air-flow resistivity, namely a steady-state air-flow method and an alternating air-flow method. The latter is realized by the measurement of the sound pressure at 2 Hz in a small rigid volume closed partially by the test sample. This cavity is excited with a known volume-velocity sound source implemented often with a motor-driven piston oscillating with prescribed area and displacement magnitude. Measurements at 2 Hz require special instrumentation and care. The authors suggest an alternating air-flow method based on the ratio of sound pressures measured at frequencies higher than 2 Hz inside two cavities coupled through a conventional loudspeaker. The basic method showed that the imaginary part of the sound pressure ratio is useful for the evaluation of the air-flow resistance. Criteria are discussed about the choice of a frequency range suitable to perform simplified calculations with respect to the basic method. These criteria depend on the sample thickness, its nonacoustic parameters, and the measurement apparatus as well. The proposed measurement method was tested successfully with various types of acoustic materials.

Steady-state air-flow and acoustic measurement of the resistivity of loose granular materials

In the course of a study for characterizing the acoustic properties of some loose granulates made of limestone chips, the authors have measured their resistivity in a very simple way by a steady-state air-flow technique. The results of these tests are compared with the corresponding values obtained by an acoustic technique. The latter relies on the assumption that at very low frequencies the real part of the normal-incidence flow impedance of a thin porous layer is very close to its steady-state air-flow resistance. The measurements results confirmed the above mentioned assumption to a certain degree. To the knowledge of the authors, no previous comparison of steady-state air-flow versus oscillating air-flow measurement of the resistivity of the considered granulates has been published yet.

A lumped parameter model for the iterative analysis of cylinderlike antivibration mounts

It is known that wave effects in antivibration mounts result in differences between the force transmissibility, calculated for a one‐degree‐of‐freedom system having constant spring and dashpot parameters, and the experimentally measured one. An evaluation method which allows one to obtain the above mentioned parameters as functions of the frequency for simple rubber systems is presented. The method takes into account the high‐frequency interaction between the distributed mass and elasticity which is responsible for the wave effects in the mount. Some experimental evidence about the validity of the method is given.

Calculation of the sound pressure reflection coefficient of sound-absorbing fibrous terminations for tubes based on a gradual transition of resistivity

Abstract Broadband anechoic terminations for tubes are usually obtained by inserting into the final tract of a tube, a sound-absorbing material which changes gradually along the tube axis. Among others, a possible change is a gradual increase of the resistivity of a fibrous material from the air-material interface onwards. In this paper two theoretical approaches are used for the prediction of the magnitude of the plane wave sound pressure reflection coefficient of tube terminations of the above-mentioned type. Simple laws are used to describe the intrinsic acoustical properties of the fibrous sound-absorbing material. Experimental results for some practical terminations are compared to predicted values, in order to indicate the accuracy that is likely to be achieved when using each theoretical approach associated with the above-mentioned simple laws.

A computer-aided procedure for selecting the optimal corrective absorption in rooms

Abstract This paper describes a simple, flexible computer procedure which can aid the acoustic designer in selecting the absorbing treatments needed to fit the reverberation time/frequency curve of an enclosure between assigned limits. For normal real life situations the procedure can be implemented on a personal computer. A program list in BASIC for an APPLE II computer is given.

The acoustics of the Italian opera house, ‘‘Teatro di San Carlo’’ in Naples, Italy

Teatro di San Carlo is reported to be the oldest existing European opera house. This horseshoe‐shaped theater was opened on the 4th of November 1737, 41 years before the opening of La Scala in Milan and 51 years before the opening of La Fenice in Venice. Surprisingly, no objective acoustical data were found in the open literature for San Carlo. Therefore, the authors were stimulated in carrying out measurements of modern objective criteria in the above‐mentioned opera house. As the theater hosts both symphonic/classical and opera concerts, two sets of measurements were carried out. The first one with the stage fitted for performing symphonic and classical music, and the second one with fitted scenery and the orchestra pit open, for performing opera concerts. Measurements in the unoccupied hall, yielded now classical, objective criteria (RT, EDT, C80, G, LE, and LF) at specific locations both on the main floor and in the boxes. The sound source was located along the longitudinal axis of the stage under the...

Measurement of objective criteria for performers in the ‘‘Teatro di San Carlo’’ opera house

In the last two decades some attention has been paid to the acoustics for performers in concert halls. The findings of these studies have shed some light on the structure of the sound field preferred for the ensemble. With respect to a concert hall, the performing condition is quite different in an opera house. Usually, the problems are related to: (a) the balance between singer(s) and the orchestra in the pit; (b) the ease of singing; (c) the ensemble of singers; (d) the ensemble of instrumentalists. To the knowledge of the authors no objective criterion has been suggested yet for (a). Some criteria are reported for the ensemble of instrumentalists (d). Useful information for (b) and (c) is reported in [A. H. Marshall and J. Meyer, Acustica 58, 130–140 (1985)]. Although well aware of the lack of accepted objective criteria, which should be well correlated with subjective criteria for the above‐mentioned topics, these authors report the results of measurements carried out in the ‘‘Teatro di San Carlo’’ in...