This paper is concerned with the comparison of two methods well-suited for the prediction of the wideband response of built-up stuctures subjected to high frequency vibrational excitation. The first method is sometimes called the {\it vibrational conductivity method} and the second one is rather known as the {\it radiosity method} in the field of acoustics, or the {\it radiative energy transfer method}. Both are based on quite similar physical assumptions {\it i.e.} uncorrelated sources, mean response and high frequency excitation. Both are based on analogies with some equations encountered in the field of heat transfer. However these models do not lead to similar results. This paper compares the two methods. Some numerical simulations on a pair of plates joined along one edge are provided to illustrate the discussion.