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

Abstract

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.

Advancements in Sound Reflection and Airborne Sound Insulation Measurement on Noise Barriers

“…These 3.5 ms wide data windows are allowed to obtain meaningful frequency data tave band centred on 400 Hz, so that the SNR is evaluated in the one-third octave bands from 400 Hz to 5 kHz: stages of the microphones when the free-field measurement is taken. If the impulse responses are measured using an MLS signal, the sequence length and number of averages can be increased in order to maximize the effective signal-to-noise ratio [8,10,12], remembering that this technique requires stationary conditions of the meas-ured acoustic system, so that a very long measurement time can have adverse effects when measuring in nonideal weather conditions (presence of wind and quick changes of temperature or humidity).…”

“…The total length of the Adrienne temporal window is , 7.9 W ADR T  ms. While this method had the great merit of opening the possibility of extensive checking of noise barriers on site just after their installation (see for example [7,8]), some points need to be further improved.…”

“…For in situ measurements, the European technical specification CEN/TS 1793-5 [1], based on the results of the former ADRIENNE project [5], has been a big step forward and it is currently used by several Member States [6][7][8][9][10][11][12], but some problems still remain to be addressed, especially for sound reflection (with the ADRI-ENNE procedure, sound reflection instead of sound absorption is measured, as of course the two are strictly correlated: the higher the sound absorption, the lower the…”

Finding optimal geometries for noise barrier tops using scaled experiments

“…Barriers are usually built with solid materials that should effectively block direct sound propagation. However, it is known that poorly fitted panels and other defects can lead to sound leaks that significantly reduce barrier performance in the field 1 . Such construction-related performance issues and the transmitted pathway are not considered in this paper.…”

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

“…The sound reflection and the airborne sound insulation of noise barriers can be measured in-situ according to CEN/TS 1793-5 1,2,3,4 . The procedure, based on impulse response measurements close to the noise barrier and in the free field, is robust and easily applicable; it allows to get the results in real-time just after the measurements, in situ or in laboratory, applying a well defined post-processing to the raw data.…”