---
title: "Acoustics, acoustic defects and remedies"
subject: "Building Technology"
chapter: 1
key: "semester_6/building_technology:acoustics-defects-remedial"
source: https://www.bctengineer.com/q/semester_6/building_technology/acoustics-defects-remedial
site: BCT Engineering
---

# Acoustics, acoustic defects and remedies

Building Technology · Chapter 1: Functional Requirements of Buildings

- Asked in: 2076 Bhadra, 2+6 marks
- Video: [Acoustics – Identifying issues and designing solutions](https://www.youtube.com/watch?v=Y583kT-vJfw) — UQ Architecture, Design and Planning
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/acoustics-defects-remedial
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1

## Question

Define the term acoustics and explain in brief general acoustic defects, and suggest remedial measures of each defect.

## Short answer

Acoustics is the science of sound, dealing with hearing conditions and noise control. Defects include echo (remedy: absorbent on reflecting wall), excess reverberation (add absorbers), sound foci (avoid concave surfaces), dead spots (reflectors), echelon effect (irregular spacing), resonance (damping), and sound shadow (limit balcony depth).

## Answer

**Acoustics** is the science of sound, covering its production, transmission, absorption and reception. In buildings, it deals with providing good hearing conditions and controlling noise.

#### Acoustic defects and remedies
| Defect | Cause | Remedy |
|---|---|---|
| Echo | Hard, distant, parallel reflecting walls; delay of reflected sound over about 0.1 s | Absorbing material (acoustic plaster, panels, curtains) on the reflecting wall; irregular wall shapes |
| Excess reverberation | Too little absorption, so sound persists | Add absorbers: carpets, curtains, perforated boards, upholstered seats; $T = 0.16V/A$ |
| Sound foci | Concave surfaces (domes, curved walls) focus sound | Avoid concave shapes; use absorbing or convex diffusing finishes |
| Dead spots | Areas not reached by sound because of focusing and shadow | Reflectors and correct hall shape; proper speaker placement |
| Echelon effect | Regular reflections from stairs, railings, ribs | Absorbent covering, irregular spacing |
| Resonance | Panel or air space vibrating at natural frequency | Damping materials, avoid resonant cavities |
| Sound shadow | Balcony or beam blocking sound | Limit balcony depth (depth not more than twice the height of opening); raked seating |
| External noise and poor insulation | Traffic and neighbours | Sound-insulating walls, windows and doors; site planning with buffers |

Design of the hall should give uniform loudness, right reverberation time, and freedom from echo and noise.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Acoustics is:
   A. The science of light
   B. The science of sound: production, transmission, absorption and reception
   C. Heat transfer
   D. Structural design
   Answer: B. In buildings it provides good hearing and noise control. (Key point: Acoustics)

2. Excess reverberation is caused by:
   A. Too little absorption
   B. Too much absorption
   C. Convex walls
   D. Thick walls
   Answer: A. Sound persists when surfaces absorb little. (Key point: Reverberation cause)

3. Sound shadow from a balcony is limited by:
   A. Making it deeper
   B. Depth not more than twice the height of opening
   C. Removing seats
   D. Adding domes
   Answer: B. Limit depth and use raked seating. (Key point: Sound shadow)

4. Echelon effect comes from:
   A. Regular reflections from stairs, railings, ribs
   B. Concave domes
   C. Resonant panels
   D. Traffic
   Answer: A. Regular spacing gives repeating reflections; cure with absorbent covering or irregular spacing. (Key point: Echelon)

## Related in Building Technology

- [Common acoustic defects](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aacoustic-defects) — Building Technology, chapter 1
- [Causes and remedies of cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-causes-remedial) — Building Technology, chapter 10, asked 2×
- [Painting on masonry; causes and remedies of cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-masonry-cracks) — Building Technology, chapter 9

## Related in other subjects

- [Remedial measures for slope failure](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aslope-remedial-measures) — Soil Mechanics, chapter 11
- [In-plane, out-of-plane failure and remedial measures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-remedial) — Concrete Technology and Masonry Structure, chapter 9
- [Remedial measures for sediment deposition in RoR](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-sediment-deposition-remedial-measures) — Hydropower Engineering, chapter 5
- [Good acoustic building, reverberation time](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aacoustic-measures-reverberation-decrease) — Engineering Physics, chapter 3