Through measurements of acoustic power, we studied two types of regenerators experimentally; one is made of ceramic honeycomb catalyst and the other is comprised of stacked wire meshes. It is found that the thermoacoustic theory can explain acoustic power decrease and increase by the positive temperature difference for the ceramic honeycomb but not for the stacked wire meshes. We proposed an empirical equation of wire mesh resistance by using two dimensionless meters; acoustic Reynolds number and ωτ_v. The observed acoustic power increase is found to be the sum of square term and cubic term of velocity amplitude.