Volume 126, Issue 4, October 2009
Index of content:
- ARCHITECTURAL ACOUSTICS 
126(2009); http://dx.doi.org/10.1121/1.3205398View Description Hide Description
Different models to improve prediction of energy-based acoustic parameters in churches have been proposed by different researchers [E. Cirillo and F. Martellotta, J. Acoust. Soc. Am.118, 232–248 (2005); T. Zamarreño et al., J. Acoust. Soc. Am.121, 234–250 (2006)]. They all suggested variations to the “revised” theory proposed by Barron and Lee [J. Acoust. Soc. Am.84, 618–628 (1988)], starting from experimental observations. The present paper compares these models and attempts to generalize their use taking advantage of the measurements carried out in 24 Italian churches differing in style, typology, and location. The whole sample of churches was divided into two groups. The first was used to fine-tune existing models, with particular reference to the “ model,” which was originally tested only on Mudejar-Gothic churches. Correlations between model parameters and major typological and architectural factors were found, leading to a classification that greatly simplifies parameter choice. Finally, the reliability of each model was verified on the rest of the sample, showing that acoustic parameters can be predicted with reasonable accuracy provided that one of the specifically modified theories is used. The results show that the model requiring more input parameters performs slightly better than the other which, conversely, is simpler to apply.
126(2009); http://dx.doi.org/10.1121/1.3204087View Description Hide Description
A variety of new porous materials with unusually small pores have been manufactured in the past decades. To predict their acoustical properties, the conventional models need to be modified. When pore size becomes comparable to the molecular mean free path of a saturating fluid, the no-slip conditions on the pore surface are no longer accurate and hence the slip effects have to be taken into account. In this paper, sound propagation in microfibrous materials is modeled analytically, approximating the geometry by a regular array of rigid parallel cylinders. It has been shown that velocity and thermal slip on a cylinder surface significantly changes the model predictions leading to lower attenuation coefficient and higher sound speed values. The influence of material porosity, fiber orientation, and size on these effects is investigated. Finite element method is used to numerically solve the oscillatory flow and heat transfer problems in a square array of cylindrical fibres. Numerical results are compared with predictions of the analytical model and the range of its validity is identified.
126(2009); http://dx.doi.org/10.1121/1.3205399View Description Hide Description
A critical task in predicting and tailoring the acoustic absorptionproperties of porous media is the calculation of the frequency-dependent effective density and compressibility tensors, which are explicitly related to the micro-scale permeability properties. Although these two quantities exhibit strong sensitivity to physics occurring at complex micro-scale geometries, most of the existing literature focuses on employing very limited in-house and oftentimes multiple numerical analysis tools. In order to predict these parameters and acoustic absorption efficiently and conveniently, this article synthesizes multiple disparate approaches into a single unified formulation suitable for incorporation into a commercial analysis package. Numerical results computed herein for four close-packed porous media are compared to similar results available in the literature. These include simple cubic, body-centered cubic, and face-centered cubic structures, and also hexagonal close-packed, which has not appeared in the literature. Together with critical comparisons of a hybrid versus direct numerical approaches, the close agreement demonstrates the capabilities of the unified formulation to analyze and control the acoustic absorptionproperties at the microscopic level.
126(2009); http://dx.doi.org/10.1121/1.3206582View Description Hide Description
In his 1942 paper on the sound insulation of single leaf walls, Cremer [(Year: 1942). Akust. Z.7, 81–104] made a number of approximations in order to show the general trend of sound insulation above the critical frequency. Cremer realized that these approximations limited the application of his theory to frequencies greater than twice the critical frequency. This paper removes most of Cremer’s approximations so that the revised theory can be used down to the critical frequency. The revised theory is used as a correction to the diffuse field limp panel mass law below the critical frequency by setting the nonexistent coincidence angle to 90°. The diffuse field limp panel mass law for a finite size wall is derived without recourse to a limiting angle by following the average diffuse field single sided radiation efficiency approach. The shear wave correction derived by Heckl and Donner [(Year: 1985). Rundfunktech Mitt.29, 287–291] is applied to the revised theory in order to cover the case of thicker walls. The revised theory predicts the general trend of the experimental data, although the agreement is usually worse at low frequencies and depends on the value of damping loss factor used in the region of and above the critical frequency.