PART V Loudspeakers FIGURE 13.19 (a) On-axis frequency response of the same diaphragm and cabinet as in Figure 13.18(b) but with the rear of the cabinet against a rigid wall. Interference between the direct sound from the loudspeakers and that reflected from the wall produces a comb-filtered response, but the response level at low frequencies is restored to that for the infinite baffle case (Figure 13.18(a)); (b) As in (a), above, but with the rear of the cabinet 0.25 meters from the rigid wall. (a) 10 0 (b) 10 0 dB ­10 ­20 ­30 100 1000 dB ­10 ­20 ­30 100 1000 Frequency (Hz) Frequency (Hz) edge diffraction. In general, it is also important to keep the front surface of the loudspeaker system as smooth as possible by recessing the drivers and screw heads. FRONT GRILLES It is somewhat rare, these days, to see front grilles on loudspeakers for professional use. The fact is that there are no truly transparent grille materials, but in domestic use their use is strongly justified, not only for aesthetic reasons but also for protection against children and over-zealous cleaners. Fabric grilles usually require wooden frames, and these can become diffraction sources as they provide a step at the edge of the baffle. Foam grilles can avoid this problem, but self-supporting foams of sufficient thickness will exhibit different distances through which the sound must pass, dependent upon the