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

• A. Cross-flow
• B. Resonator
• C. Muffler
• D. Straight-through

Answer: (D)

Absorbent silencers damp noise by lining the flow path with porous material that converts sound energy into heat. In a straight-through arrangement, the exhaust gas travels directly through a central pipe that is surrounded by this absorbing packing. This setup reduces a broad range of frequencies while keeping backpressure relatively low, which is why it’s described as using absorbing material around a single pipe. Cross-flow designs use multiple channels and interference patterns, resonators rely on a tuned cavity to cancel specific frequencies, and don’t match the single-pipe absorbing-material description.