The use of time-reversal techniques has been shown to allow focusing energy in a spot about half a wavelength wide. The fact of being able to concentrate energy into a reduced volume of space implies higher power densities and, ultimately, higher field levels. The use of this feature for improving the ability of a reverberation chamber in converting energy into high-intensity fields is investigated here. Experimental results are compared to those predicted by a simple asymptotic model, revealing the role played by losses and frequency bandwidth and how the performance of time-reversal techniques depends on these parameters.