A plate silencer consists of an expansion chamber with two side-branch cavities covered by light but extremely stiff plates. It works effectively with a wide stopband from low-to-medium frequencies only if the plate is extremely stiff, to ensure a strong reflection of acoustic wave to the upstream in the duct. However, a plate with a slightly weak bending stiffness will result in non-uniform tr...

A perforated plate with stepwise apertures (PPSA) is proposed to improve sound absorption for low frequencies. In contrast an ordinary insufficient acoustic resistance and small mass, the stepped holes could match of air characteristic impedance also moderately increase mass especially at Prototypes made by 3D printing technology are tested in tube. The measured results agree well that predicti...