The noise caused by road and railway traffic is increasing every day and it is commonly considered the main cause of noise pollution in urban environment. In order to limit this annoyance, many different typologies of barriers are realized in several different configurations. Following the European standards, these barriers can be characterized by two indices, i.e.: the Reflection Index for sound reflection and the insulation index for airborne sound insulation. Both of them can be measured following the method described in CEN/TS 1793-5 standard, based on impulse response measurements employing a pressure microphone. The method mandates for averaging results of measurements taken in different points in front of the device under test and/or for specific angles of incidence, employing the MLS signal for performing the measurements, which can cause severe artifacts due to nonlinearity and time-variance of the system, and is nowadays surclassed by other acoustic signals. Furthermore, the CEN/TS 1793-5 standard presents some geometric problems, which could arise if the barrier does not reach a minimum height or if it has a very rough (scattering) surface. As demonstrated in a similar article, during the reflection index measurement on a barrier of limited height, the reflected sound can be contaminated by the ground reflection, compromising the fairness of the whole result. On the other hand, the insulation index can be affected by the height of the noise barrier, since the sound passing above the device under test can become mixed with the sound passing through it. It has been noticed how these practical problems,jointly with the assumption of a surface reflecting specularly in the final formula, can significantly over/under estimate the laboratory values of both the indices. Results of in situ tests based on CEN/TS1793-5 will be shown in comparison with results obtained through a different approach and with the traditional tests performed in the laboratory.
On the acoustic efficiency of road barriers. The Sound Insulation Index
TRONCHIN, LAMBERTO
2013
Abstract
The noise caused by road and railway traffic is increasing every day and it is commonly considered the main cause of noise pollution in urban environment. In order to limit this annoyance, many different typologies of barriers are realized in several different configurations. Following the European standards, these barriers can be characterized by two indices, i.e.: the Reflection Index for sound reflection and the insulation index for airborne sound insulation. Both of them can be measured following the method described in CEN/TS 1793-5 standard, based on impulse response measurements employing a pressure microphone. The method mandates for averaging results of measurements taken in different points in front of the device under test and/or for specific angles of incidence, employing the MLS signal for performing the measurements, which can cause severe artifacts due to nonlinearity and time-variance of the system, and is nowadays surclassed by other acoustic signals. Furthermore, the CEN/TS 1793-5 standard presents some geometric problems, which could arise if the barrier does not reach a minimum height or if it has a very rough (scattering) surface. As demonstrated in a similar article, during the reflection index measurement on a barrier of limited height, the reflected sound can be contaminated by the ground reflection, compromising the fairness of the whole result. On the other hand, the insulation index can be affected by the height of the noise barrier, since the sound passing above the device under test can become mixed with the sound passing through it. It has been noticed how these practical problems,jointly with the assumption of a surface reflecting specularly in the final formula, can significantly over/under estimate the laboratory values of both the indices. Results of in situ tests based on CEN/TS1793-5 will be shown in comparison with results obtained through a different approach and with the traditional tests performed in the laboratory.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
