Acoustics

Question 1

Reverberation Time

Answer 1

Time for sound to decay by 60 dB after source stops.

Long RT = echoey (concert hall)

Short RT = clear (classroom)

Question 2

Flutter Echo:

Answer 2

Rapid, repetitive echo between two parallel hard surfaces.

Fix: angled surfaces, absorptive materials, or diffusers

Question 3

Absorption vs. Insulation:

Answer 3

bsorption: reduces echo inside a room (e.g., foam, carpet)

Insulation: blocks sound transmission between spaces (e.g., concrete, dense walls)

Question 4

Types of Sound

Answer 4

Airborne Sound:
Travels through air (e.g., speech, music)

Impact Sound:
Caused by physical contact (e.g., footsteps, dropped items)

Question 5

Acoustic Design Examples

Answer 5

Shoebox Hall (e.g., Vienna Musikverein):

Long, narrow with high ceiling

Great lateral reflections, long RT for rich sound

Fan-Shaped Halls:

Sound disperses poorly = weak clarity

Philharmonie de Paris:

Modular surfaces, vineyard seating

Prioritises acoustic intimacy and clarity

Question 6

Sound Insulation Methods

Answer 6

Masonry Wall:

High mass → good at blocking low frequencies

Fire resistant and durable

Lightweight Wall (Timber/Steel):

Double or staggered studs

Filled with insulation (e.g., mineral wool)

Needs air gap and separation for best performance

Question 7

Common Construction Materials

Answer 7

Insulation Absorption
Concrete, brick Acoustic foam, carpet
Heavy plasterboard Mineral wool panels

Question 8

Mass Law of Sound Insulation

Answer 8

Doubling mass of wall = ~+6 dB increase in sound insulation

Works best for mid/high frequencies, less effective for low frequency

Alternative: double-leaf wall systems (mass + air gap)

Question 9

Acoustic Failures & Case Studies

Answer 9

Reverse Sensitivity:
New housing near noise sources (e.g., airports) → complaints
⇒ Planning must protect both new and existing uses

Central Gardens Case:
Rejected due to poor acoustic design near a noise source