Gino Iannace

Acoustic properties of nanofibers

In recent years nanofibers have been used in the field of applied acoustics to improve the acoustic characteristics of traditional materials without increasing their weight and size. In this paper acoustic measurements are reported of the absorption coefficient of porous materials coated with a layer of nanofibers carried out with the impedance tube (“Kundt” tube) in the frequency range of 200 Hz – 6.3 kHz. The layers of nanofibers are obtained by NY6 (nylon) based on needle - free electro-spinning process available at “Next Technology Tecnotessile r.l.” (Prato, Italy). The layer of nanofibers is glued on different types of porous materials with different thicknesses. The values of the absorption coefficient measured at normal incidence, were compared with the values carried out on porous materials with and without the layer of nanofibers.

Characterization of sheep wool panels for room acoustic applications

Given the good thermal and sound absorption properties, the lack of harmful effects on health, and the availability in large quantities, natural fibers are becoming a valid option for sound absorption panels in building applications. This paper investigates sheep wool fibers and panels. The absorption coefficient and the static flow resistivity for samples of different thickness are measured and discussed. Then, the possibility of using fabrics obtained with different kinds of woven wool as sound absorbing systems is investigated. For this scope, wool tapestries were mounted at a variable distance from the rigid back wall. The high absorption obtained in some frequency bands, depending on the back cavity depth, confirmed the possibility of using wool tapestries for ad-hoc customized acoustic interventions. Finally, this paper discusses the advantages of adopting sheep wool for room acoustic applications.

Acoustic Measurements and Correction of a Council Room

This paper presents the acoustic correction of a Council Room, with an original reverberation time of 1.0 kHz higher than 3.0 seconds and marble floors walls and ceiling in plaster smooth. The work was conducted in four phases: the first was the measurement of acoustic characteristics with the empty hall; the second phase was the identification of the soundproof material for the acoustic correction and the measurement of the absorption coefficients with the tube of “Kundt”; the third phase was the implementation of a numerical model with the software “Odeon” to choose the position of absorbent material and of the plaster surface to be coated; the latest phase, after the installation of soundproof panels, was the acoustic measurement to verify if the results of the acoustic measurements are equal to those one of the numerical model.

Sound Absorption of Materials Obtained from the Shredding of Worn Tyres

The current legislation forbids depositing tyres in landfill at the end of their useful life (European Directive 1999/31 on the landfill of waste). Thus a problem for the reuse of these waste materials arises. One possible use of worn tyres is in the field of applied acoustics. After being shredded, in appropriate particle sizes, it can be possible to reutilise tyres as sound absorbing material. The purpose of this paper is to provide a theoretical model for predicting the sound absorption coefficient of granular materials resulting from the shredding of worn tyres. Starting from the knowledge of the physical properties (such as resistivity, porosity and the structure factor) measured for each range of particle size, by the application of a theoretical model it is possible to obtain the coefficient of absorption of the tested material. Measurements of the absorption coefficient were made using a tube of Kundt, with the use of FFT techniques. Given the dimensions of the tube, the measurements of the absorption coefficient were valid in the range from 200 Hz to 2.0 kHz. Then the theoretical developments were compared with the experimental ones in function of the frequency.

The Large Theatre of Pompeii: Acoustic Evolution

This paper reports the acoustic evolution of the “Large Theatre” of Pompeii: during the Greek-Hellenistic and Roman period, and through to the present time. Initially the style of the theatre was Greek-Hellenistic with an elongated U shape and a cavea built into the top of a hill. During the Roman period the theatre shape was changed with a larger scene and a summa cavea added to accommodate about 5.000 spectators. After being recovered from under the Vesuvius lava it was partially reconstructed. Most recently the original grass-covered cavea has been paved with bricks and today the theatre provides a venue for a variety of types of performance. Its acoustic characteristics have been analysed using a virtual model for the Greek- Hellenistic and Roman period, and then, for the later configurations, when the cavea was grass-covered and then paved with bricks, with acoustic measurements.

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.

Acoustic correction of monumental churches with ceramic material: The case of the Cathedral of Benevento (Italy)

In this work, soundproof systems for the acoustic correction of large spaces, such as monumental churches, are studied. The Cathedral of Benevento is considered as a case study. Dated back to the seventh century, the church was destroyed during the Second World War and rebuilt in the mid-twentieth century, using marble for the floor and smooth plaster for the side walls. In the current state, the cathedral exhibits an excessive reverberation time (about 10 s) that causes poor understanding of speech and not good listening to musical performances. It is difficult to perform any form of acoustic correction inside the cathedral, since the walls and the ceiling cannot be covered with traditional sound-absorbing material due to architectural and aesthetic reasons. Therefore, the possibility of using ceramic material applied to the side walls for the acoustic correction of low-frequency components and transparent micro-perforated sheets placed under the ceiling for the acoustic correction of medium- and high-frequency components are considered. The work is divided into three phases: in the first phase, measurement of the current acoustic characteristics of the cathedral is performed. In the second phase, sound absorption material is investigated and in the third phase, the effects of insertion of soundproof systems on the acoustic characteristics of the cathedral are theoretically evaluated by means of a room acoustic software.

Noise exposure in school gymnasia and swimming pools

School gymnasia and swimming pools are generally environments affected by poor acoustic conditions due to absence of sound absorbing materials, noisy sport activities, presence of many students at the same time and intensive use of blowing whistles to enforce the communication. The consequence is that physical education teachers can not only show long term stress but they can also be exposed to noise risk to noise-induced hearing loss. Investigation has shown that the problem is quite large; as many as 20�25% of physical education teachers can be affected by a noise exposure higher than acceptable limits. It is then necessary to analyze in detail all factors that can influence the noise in these special school environments in order to develop simple acoustical guidelines useful for school officials for stress management and hearing conservation programs.

Effects of noise from wind turbines inside home

The inland areas of southern Italy were built with many wind farms which are often situated close to houses. This work reports the results of acoustic measurements made in a room inside a house located near a wind farm. The acoustic measurements were carried out during the autumn season; the values of LeqA and L95 have been measured for different wind speeds.

Ceramic Material for Sound Absorption

The acoustic correction of large places for low frequency components can be obtained by inserting acoustic resonators. This paper reports the realization and the experimental verification of acoustic resonators obtained with ceramic material. The sound absorption is obtained by drilling the specimens of ceramic material with a hole size of 2 mm and 5 mm and a thickness of 3.0 cm, 2.0 cm and 0.6 cm. The sound absorption of perforated plates is based on the principle of Helmholtz resonators, which, however, are effective only on narrow frequency bands; so to make the phenomenon of absorption more effective and to increase the range in absorption frequency perforated panels are made, mounted at a suitable distance from a rigid surface. The measurements of the sound absorption coefficient were performed with an impedance tube (Kundt tube) with an internal diameter of 10 cm and with the validity of the measurement of the absorption coefficient in the range of 100 Hz – 1.0 kHz. The measurements of the absorption coefficient were performed, for each specimen, creating a cavity of air between the sample and the behind rigid surface, with the following thicknesses: 25 cm, 20 cm, 15 cm, 10 cm and 5 cm. As expected, for the same specimen, the peak of the absorption coefficient shifts to higher frequencies on decreasing size of the cavity between the specimen and the rigid wall.