# Possibilities of Evaluating the Effectiveness of Noise Barriers in Slovakia
## 2 Materials and Methods
### Measurement of Sound Insulation of a Barrier by the Adrienne Method  
The purpose of this measurement is to demonstrate the value of the sound insulation of the noise barrier in situ by the Adrienne method in accordance with EN 1793-5 [27] and EN 1793-6 [29]. Noise reduction devices along roads must be soundproof so that the sound passing through the device is negligible in comparison with the sound bent over its top. This European Standard specifies a test method for assessing the intrinsic airborne sound insulation for the barriers designed for roads in non-reverberant conditions. This method uses the same principles and equipment used for measurement of sound reflection [27] and uses a direct sound field. The test method can be used for:  
* Determination of the intrinsic characteristics of the sound insulation index of in situ or laboratory noise abatement equipment [29];
* Determination of the in situ intrinsic characteristics of the sound insulation index of noise reduction devices [29];
* Determination of sound reflection characteristics for in situ noise reduction in real conditions [27];
* Comparison of design characteristics with the values of the actual design after the completion of construction work [27]. To calculate the sound insulation index \(SI\) as a function of the frequency in the one-third octave frequency band, the Adrienne method uses Equation (8):  
\[SI_{j}=-10\cdot log\left(\frac{1}{n}\sum_{k=1}^{n}\frac{\int_{\Delta f_{j}} \abs{F[h_{tk}(t)w_{tk}(t)]}^{2}df}{\int_{\Delta f_{j}}\abs{F[h_{tk}(t)w_{tk}(t) ]}^{2}df}\right) \tag{8}\]  
where:  
\(h_{ik}(t)\)--reference transmitted pulse response component of the free field in the \(k\)-th microphone position;  
\(h_{ik}(t)\)--transmitted pulse response component in the \(k\)-th microphone position;  
\(w_{ik}(t)\)--Adrienne temporal window for the transmitted component in the \(k\)-th microphone position;  
\(F\)--symbol of the Fourier transform;  
--index of the \(j\)-th one-third octave frequency band (between 100 Hz and 5 kHz);  
\(\Delta f_{j}\)--the width of the \(j\)-th one-third octave frequency band; and  
\(N=9\)--number of microphone positions. First, an in situ measurement is performed in order to calculate the impulse response of the barrier under investigation. For this purpose, a grid of nine microphones is placed behind the barrier to be tested. Using an adequate noise source located between the path and the barrier (Figure 2), a maximum sequence length is generated, long enough to overcome the ambient background noise. The impulse response thus obtained includes a direct component, a component reflected by the barrier, as well as other undesired reflected components caused by surrounding obstacles. Their effect can be eliminated by using a time window (Adrienne window) [29]. The measurement principle for the Adrienne method is as follows. The sound from the source propagates in the form of sound waves, which are partly reflected from the  
Figure 2: Diagram of the set-up for measurement of the sound insulation index [29]. barrier, partly bent over the barrier, and partly transmitted through the barrier material (Figure 1). A set of microphones located on the other side of the barrier receives a sound pressure wave from a sound source that has passed through the test device and that has bent over the upper edge of the barrier. Legend:  
\(M\)--measurement grid of nine microphones (Figure 3a);  
\(S\)--noise source front panel--loudspeaker (Figure 3b);  
\(d_{S}\)--horizontal distance (loudspeaker--noise source reference plane) at the height \(h_{S}\) (m);  
\(h_{S}\)--reference height--height of source position (m);  
\(t_{B}\)--thickness of the barrier at the height \(h_{S}\) (m);  
\(d_{M}\)--horizontal distance of the central microphone (no 5) from the barrier at the height \(h_{S}\) (m);  
\(h_{B}\)--height of the barrier (m); and  
\(d_{T}\)--horizontal distance between the loudspeaker and the central microphone at the height \(h_{S}\) (\(d_{T}=d_{s}+t_{B}+d_{M}\)).