1. Field of the Invention
This invention relates to improvements in a resonator type silencer having plural resonance chambers, and more particularly to such a silencer which is formed of a plastic and arranged to facilitate changing the sound attenuating characteristics without a considerable modification in its basic design.
2. Description of the Prior Art
Hitherto a variety of resonator type silencers have been proposed and put into practical use in the field of automotive internal combustion engines. The silencers are usually employed in an intake system of the engine to attenuate intake air noise. Of these silencers, there is a resonator type silencer having two resonance chambers which are communicated in series with each other in order to attenuate noise at two frequency ranges under resonance. In other words, such a silencer has a noise attenuation characteristics which has two frequency peaks to be attenuated thereby expanding a noise attenuating region of the silencer as compared with a resonance type silencer having a single resonance chamber. Such a resonance type silencer having two resonance chambers is usually installed to an intake air duct through which intake air is inducted into the engine cylinders of the engine. The silencer includes a main body which is formed thereinside with a chamber. A partition plate is provided in the chamber to divide the chamber into the two resonance chambers.
However, the partition plate of the silencer is generally flat and therefore fixed in noise attenuating characteristics. In other words, the silencer has a characteristics in which the two frequency peaks to be attenuated are fixedly set and not variable, so that the noise attenuating characteristics of the silencer is not variable without modifying a basic design thereof.