Road traffic noise reducing devices - Test method for determining the acoustic performance - Intrinsic characteristics - In situ values of sound reflection and airborne sound insulation
The present document describes a test method for measuring two quantities representative of the intrinsic characteristics of traffic noise reducing devices : the reflection index for sound reflection and the sound insulation index for airborne sound insulation.
The test method is intended for the following applications :
— determination of the intrinsic characteristics of sound reflection and airborne sound insulation of noise reducing devices to be installed along roads, to be measured either in situ or in laboratory conditions ;
— determination of the in situ intrinsic characteristics of sound reflection and airborne sound insulation of noise reducing devices in actual use ;
— comparison of design specifications with actual performance data after the completion of the construction work;
— verification of the long term performance of noise reducing devices (with a repeated application of the method).
The test method can be applied both in situ and on barriers purposely built to be tested using the method described here. In the second case the sample shall be built as follows (see Figure 1):
— a part, composed of acoustic elements, that extends 4 m and is 4 m high ;
— a post 4 m high (if applicable for the specific noise reducing device under test) ;
— a part, composed of acoustic elements, that extends at least 2 m and is 4 m high ;
NOTE For qualifying the reflection index only, it is only necessary to have acoustic elements that extend 4 m or more.
NOTE For qualifying the sound insulation index of posts only, it is only necessary to have acoustic elements that extend 2 m or more on either side of the post (see Figure 1).
Results are expressed as a function of frequency, in one-third octave bands between 100 Hz and 5 kHz. If it is not possible to get valid measurements results over the whole frequency range indicated, the results shall be given in the restricted frequency range and the reasons of the restriction(s) shall be clearly reported.