Lining the walls of an auditorium with perforated materials reduces

Step 1: Analyze the question The question asks what effect lining auditorium walls with perforated (porous, hole-filled) materials has on sound.

Step 2: Explain the concept

• Reverberation is the persistence of sound in an enclosed space caused by repeated reflections from hard walls, ceiling, and floor. Too much reverberation makes speech sound muddy and hard to understand.
• Hard, smooth surfaces reflect sound well. Perforated or porous materials (acoustic tiles, perforated boards, curtains, carpets) absorb sound energy, because the sound enters the holes and is dissipated as heat through friction.
• Less reflected sound means a shorter reverberation time.

Step 3: Check the options

• A. Reverberation: Absorbing sound reduces repeated echoes, so reverberation falls. ✔
• B. Diffraction: This is the bending of waves around obstacles or through gaps. Perforated lining is not meant to control it.
• C. Refraction: This is the change in wave direction when the speed changes between media. It is not what the lining targets.
• D. Auditorium pulse: This is not a real physics term.

Step 4: Answer Perforated lining absorbs sound and reduces its reflection, so it reduces reverberation.

Exam tip: In acoustics questions, link "walls, halls, echo, and absorbing materials" to reverberation. Remember: hard surfaces reflect, soft or perforated surfaces absorb.