Paolo Guidorzi

European methodology for testing the airborne sound insulation characteristics of noise barriers in situ: Experimental verification and comparison with laboratory data

In the frame of the 1994-1997 Standard, Measurement and Testing program, the European Commission funded a research project, named Adrienne, to define new test methods for measuring the intrinsic characteristics of road traffic noise reducing devices in situ. The research team produced innovative methods for testing the sound reflection/absorption and the airborne sound insulation characteristics of noise barriers. These methods are now under consideration at CEN (European Committee for Standardization), to become European standards. The present work reports a detailed verification of the test method for airborne sound insulation over a selection of 17 noise barriers, representative of the Italian and European production. The samples were tested both outdoors, using the new Adrienne method, and in laboratory, following the European standard EN 1793-2. In both cases the single number rating for airborne sound insulation recommended by the European standard was calculated. The new method proved to be easy to use and reliable for all kinds of barriers. It has been found sensitive to quality of mounting, presence of seals, and other details typical of outdoor installations. The comparison between field and laboratory results shows a good correlation, while existing differences can be explained with the different sound fields and mounting conditions between the outdoor and laboratory tests. It is concluded that the Adrienne method is adequate for its intended use.

Repeatability and Reproducibility of In Situ Measurements of Sound Reflection and Airborne Sound Insulation Index of Noise Barriers

In Europe, in situ measurements of sound reflection and airborne sound insulation of noise barriers are usually done according to CEN/TS 1793-5. This method has been improved substantially during the EU funded QUIESST collaborative project. Within the same framework, an inter-laboratory test has been carried out to assess the repeatability and reproducibility of the newly developed method when applied to real-life samples, including the effect of outdoor weather variability and sample ageing. This article presents the statistical analysis of the inter-laboratory test results, and the values of the repeatability and the reproducibility, both in one-third octave bands and for the single-number ratings. The estimated reproducibility values can be used as the extended measure of uncertainty at the 95% credibility level in compliance with the ISO GUM. The repeatability and reproducibility values associated with airborne sound insulation are also compared with the corresponding values for laboratory measurements in building acoustics and an acceptable agreement is found.

In situ measurements of the intrinsic characteristics of the acoustic barriers installed along a new high speed railway line

In September 2005 the new high speed railway line Torino-Novara, Italy, was near completion and acoustic barriers had just been installed according to specifications. At this site, the authors conducted in situ verification of the intrinsic characteristics of the noise reducing devices. It is the first European experience of this kind on a large construction workplace. The conditions were extremely demanding and the time scheduled for the task very short. The challenging task was successfully completed applying CEN/TS 1793-5 and taking advantage of the logistic support of the customer. The paper reports the key points of this successful experience and shows some exemplary results. The values measured in situ are compared with the results obtained some years before on products of the same kind. Regarding sound reflection, the in situ method proved to be reliable and to give values more realistic than the laboratory method. Regarding sound insulation, the comparison with previous measurements indicates that, as long as the barriers are well installed, similar results can be expected and that their variance is comparable to that of laboratory tests. On the other hand, large differences (4-5 dB or more) indicate poor quality of construction and installation work, that can be confirmed by a careful inspection. This sensitivity of the in situ method to detect faults paves the way to establish minimum construction and installation criteria. It is concluded that the selected method is fully adequate to in situ verification and could be repeatedly applied to check the acoustic durability of noise reducing devices over time.

Signal analysis in the sound absorption measurement procedure: The importance of time subtraction and reference surface corrections

The sound absorption coefficient measurement (following ISO 13472‐1 normative) of highly absorbing materials, which are tipically employed in room acoustic correction, presents some inherent difficulties. These materials present highly sound absorption coefficient indeed, but usually low sound insulation index and are installed over highly reflective surfaces. This leads to some measurement problems, partially solved by means of the reference surface method. In this work some measurement examples on the same materials but with different contour conditions are analyzed and the improvements on the results, due to reference surface normalization and time domain subtraction of free field response, are discussed.

In-situ measurements of sound reflection and sound insulation of noise barriers: Validation by means of signal-to-noise ratio calculations

After some years from its first release, the CEN/TS 1793-5 European standard for in-situ measurement of sound reflection and airborne sound insulation characteristics of noise barriers has been significantly enhanced and validated in the frame of the EU funded QUIESST project. The procedure, based on impulse response measurements near the noise barrier and in the free field, is robust and easily applicable but much attention must be paid when: (i) applying the signal subtraction technique to get the reflected signal component and (ii) extracting the transmitted component, especially measuring highly insulating noise barriers. In both cases, it is essential to avoid a poor signal-to-noise ratio of the critical part of the impulse response. In the frame of the QUIESST project specific quality criteria, applicable on site, have been introduced in order to check and validate the result. These criteria are rigorously described here for the first time and illustrative examples are presented.

Realization of a measurement system for physical and acoustic measurements on brick walls

Aim of this study is the development of a system for the measurement of frequency values of some physical variables such as the damping factor, the thickness of a structural element, the structural reverberation time and the longitudinal wave speed propagation in light brick walls. Such variables are required by the UNI EN 12354-1 normative for the analytical estimation of the sound reduction index R of monolithic elements in the laboratory. The results of the calculation, as a function of frequency, will be shown and compared with the measured values of the sound reduction index R.