The acoustic design of rooms for listening to music or recording is a very difficult subject: in order to improve the acoustic performance of these confined rooms, it may be necessary to absorb noise energy; sometimes all audible frequencies of the spectrum, sometimes at some specific frequencies. The design is especially difficult at low frequencies, where both resonance modes and standing waves are present. For the correction of problems of this kind, a resonance cavity perforated panel can be used. In the technical literature, there are some theoretical models describing the behavior of such a panel, but the results given are scarcely informative. Here we try to develop a simple but accurate approach for the design of these devices. On the basis of a reference FEM simulation of a drilled panel which was discussed in a previous paper, an engineering analytical model, which can be simply implemented either in few lines of FORTRAN code or by means of free engineering software tools like OpenOffice.org, has been developed. The dependency of the panel's behavior on the design parameters is here discussed.