*5.3.3 Hoover's expression*

Hoover's expression has been presented in section 2, Eq. (7). It depends on the thickness of the green barrier and the frequency of sound.

The IL calculated using Eq. (7) and the SPL expected at the receiver are presented in **Table 16**. In this case, as the main considered phenomenon is the attenuation by the leaves and canopy, attenuation at 63 Hz would not be considered [3].


**Table 15.**

*IL according to thick barrier approach and expected sound pressure levels at P1 (all values are in dB).*

*Evaluation of Industrial Noise Reduction Achieved with a Green Barrier: Case Study DOI: http://dx.doi.org/10.5772/intechopen.108835*


#### **Table 16.**

*IL according to Hoover's expression and expected sound pressure levels at P1 (all values are in dB).*

The only correction needed was that of background noise at 8000 Hz, in order to avoid a calculated value lower than the measured one.
