# Spectrum

We present here some comparisons in terms of LA,eq,1h spectrum between in situ measurements and DEUFRABASE calculations.

- Measurements have been carried by Ifsttar (formely LCPC) between 1990 and 1999, on 47 many different road pavements, with impedance discontinuity dense/grass or porous/grass (depending on the pavement type), for a receiver at 7m50 from the road and 1m20 above the ground. The road traffic consists of PC and HT, with a speed of 100 km/h and 80 km/h respectively.
- These measurements are compared to the DEUFRABASE calculation:
- using built-in road pavement (i.e. the mean road pavement spectrum for PC and HT that are included in the DEUFRABASE),
- using user spectrum (i.e. with the corresponding spectrum that have been measured in situ for PC and HT).

Because the DEUFRABASE considers only PC with a speed of 90 km/h, a correction factor must be considered either on the measurements or on the DEUFRABASE calculations, in order to compare results at 100 km/h. See this page for details.

Figures below present some comparisons between the DEUFRABASE and the measurements, for 4 different road pavements. Results for the other pavements are quite similar.

- In global value (in dBA), one can note a very good agreement. The deviation is closed to one or two dB. A detailed analysis of the deviation is given at this page.
- Studying the spectrum in details, one can remark that the DEUFRABASE calculations are well in agreement with measurements. Some differences occur mainly below 500 Hz.
- Considering the DEUFRABASE calculations using a mean road pavement spectrum, these differences can be explained by the fact the mean spectrum may be insufficiently representative of all pavements of the same type, depending of the number of different road pavement that have been used for calculating this mean spectrum.
- Some discrepancies can also be due to the fact that impedance values at each side of the discontinuity may slightly differ from the in situ configurations and the built-in DEUFRABASE parameters.