  We propose and experimentally demonstrate a novel mechanism of sound wave
concentration based on soft reflections in chirped sonic crystals. The reported
controlled field enhancement occurs at around particular (bright) planes in the
crystal, and is related to a progressive slowing down of the sound wave as it
propagates along the material. At these bright planes, a substantial
concentration of the energy (with a local increase up to 20 times) was obtained
for a linear chirp and for frequencies around the first band gap. A simple
couple mode theory is proposed, that interprets and estimates the observed
effects. The results are obtained for the case of sound waves and sonic
crystals, however they are extendable to other type of waves in modulated host
matter.
