Some Super Trapp Quiet Muffler models for generators are 3S and 5S. The 3S model is smaller and is best for small space. The 5S model is quietest when use with an optional resonator, says Jack's Small Engine & Generator Service.
A muffler reduces the noise level of an engine, including a generator. Each muffler has a set of tubes inside. When the exhaust gases and sound waves enter a muffler, the tubes inside the muffler reflect the sound waves such that they cancel each other out. The remaining sound waves pass through some holes in the muffler into another chamber before they exit.