Installing noise barriers is the most common method for reducing the highway traffic noise to the
road side residential area. After the report about edge potential concept of a noise barrier, various
types of noise reducing devices(NRDs) called “noise reducers” have been suggested for getting more
shielding effect on the top of highway noise barriers. But, it has been doubtful about effect of the
NRDs in field because there was no appropriate and unified method to estimate the acoustic
performance by using field measurement of the NRDs in Korea. In this study, the authors have
considered to setup a practical method to test and estimate the acoustic performance of NRDs. For
eliminating the noise reduction effect of the NRDs height itself, the source and measuring points are
adjusted as highly as the NRDs height. For the frequency weighting in the estimation of the NRDs
effect, the highway noise spectra were measured at asphalt and concrete road side and then averaged
for a unit spectral parameter.