The compressor inlet casing incorporates webs to support the bearing housing if outboard bearings are used. These webs must be carefully designed to be far enough away from the impeller to avoid impeller vane excitation. The casing also houses a combined air filter and silencer on most larger turbochargers (Figure 2.10). Sound waves originating at the compressor intake are reflected and reduced in intensity by baffles lined with sound absorbing material.