Which type of noise-cancelling device commonly uses absorbing material around a single pipe?

• A. Cross-flow
• B. Helmholtz resonator
• C. Straight-through
• D. Barrier

Answer: (C)

When reducing noise in piping, using absorbing material around a single pipe is all about damping sound energy as it travels in a straight path. The porous lining around the duct acts like a sponge for acoustic waves, converting sound energy into a small amount of heat through viscous losses as air moves through the material. This approach quiets the flow while keeping it moving straight, which is why it’s typical of a straight-through muffler.

Other designs don’t fit this description. A cross-flow setup relies on redirecting sound or flow through different paths to cancel or reduce noise, rather than simply absorbing along a single pipe. A Helmholtz resonator uses a specific cavity and neck to target particular frequencies, not broad absorption around a pipe. A barrier blocks sound with a physical wall rather than providing absorptive lining around the duct. So the one that matches absorbing material around a single pipe is the straight-through type.