- 2078 Chaitra · 6 marks
Sound insulation versus sound absorption
Short answer
Sound insulation stops sound transmission between spaces using dense, airtight barriers; sound absorption reduces reflected sound within a room using porous materials. Common acoustic defects include echo, excessive reverberation, sound foci, dead spots, echelon effect, resonance, and sound shadow.
Critically differentiate sound insulation & sound absorption. Explain common acoustic defects.
| Point | Sound insulation | Sound absorption |
|---|---|---|
| Meaning | Stopping sound from passing from one space to another | Reduction of reflected sound within a room |
| Aim | Isolate spaces (privacy, noise exclusion) | Control echo and reverberation |
| Mechanism | Reflects sound back (barrier) | Converts sound energy to heat in porous material |
| Materials | Dense, heavy, airtight (brick, concrete, lead) | Light, porous, soft (mineral wool, acoustic tile, curtain) |
| Governing property | Mass and airtightness | Porosity, thickness, flexibility |
| Measured by | Sound reduction index (dB) | Absorption coefficient (0 to 1) |
| Location | Walls, floors, doors between rooms | Ceiling and wall surfaces in the room |
| Example | 230 mm brick wall | Perforated board with wool backing |
Common acoustic defects
- Echo: Reflected sound arrives more than about 0.1 s after the direct sound, giving a repeated sound. Cured by absorbing surfaces on the reflecting walls.
- Reverberation: Persistence of sound after the source stops because of repeated reflections. Too much reverberation lowers clarity. Cure: add absorbing materials to reduce reverberation time.
- Sound foci (concentration): Concave surfaces focus sound at one point, making dead spots elsewhere. Avoid concave domes; use convex or absorbing finishes.
- Dead spots: Areas with little sound. Use reflectors and avoid focusing.
- Echelon effect: Repeating reflections from regularly-spaced steps or railings, giving a musical tone.
- Resonance: Panels or air volumes vibrate at their natural frequency and amplify some tones. Use damping.
- Sound shadow: Balconies shade the sound behind them.
- Insufficient loudness and external noise.
✓ Answer checked by Claude Opus 5.5 (high effort)
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