This project is intended to design a concert hall for CUHK. The location of site is besides Sir Run Run Shaw Hall in
central campus. Sir Run Run Shaw Hall is a multi-purpose cultural centre of The Chinese University of Hong Kong. It
provides venue and services for large-scale functions such as congregations, examinations, assemblies, meetings
and classes. However, acoustic property of concert hall is quite different from multi-purpose hall, sound intelligibility
and reverberation time requirement is different. Thus, in this paper I want to design a concert hall for functional
supplyment of Sir Run Run Shaw Hall in CUHK from acoustic point of study. I will further how research shape and
material affects acoustic quality of concert hall in this paper.
Keyword: Intelligibility, reverberation time, shape, material
Fig. 1 Location of proposed concert hall in CUHK
1. Review of basic acoustic definition in concert hall
Before starting to design of concert hall, the preparation work is to review some basic acoustic definition of concert
There are 3 categorizes of reflected sound: (1) early and middle-reflected sound; (2) reverberation (late-reflected
sound); (3) standing waves. In concert design, the liveness of a concert hall is decided by early reflections, which
contribute more to perception of reverberation. Early and middle reflection occurs within the 250msec after arrival of
the direct sound. Early sound is considered to be 40msec after arrival of the direct sound for speech while for music
80msec is more appropriate. The number and quantity of early and middle reflection delivered to any particular
listening location depends largely on the rooms shape. For this reason, geometric analysis, which involves the study
of reflected sound propagation paths modeled as rays radiating from the source of sound, is particularly useful for
tracing echo paths and for studying the uniformity of early reflected sound in medium and large size spaces.
Echoes are reflections that can be heard distinctly and separately from the early reflected and reverberant sound.
Design criteria for echo detection depend on the type of space being constructed. For most general purposes involving
speech communication, echoes are normally heard due to intense reflection arriving 40 msec and later after the direct
sound signal has reached the listener. In other words, the difference in path length between the direct sound and the
reflected sound is at least 13.8m, corresponding to a propagation time of 40 msc or greater. In concert hall, echoes
are most commonly detected in the front rows of an auditorium and on stage. This results from the front row being
farthest from the rear wall, thus generating the largest path length difference between direct sound and the sound
reflection from the rear wall or the combination of the ceiling and the rear wall.
Reverberation is directly proportional to room volume, inversely proportional to the surface area, and inversely
proportional to the amount of sound-absorbing material. Excess reverberation results in blurring of sounds and can
reduce speech intelligibility. It is possible to reduce reverberation by the following means: (1) adding sound-absorbing
material; (2) reducing room volume; (3) increasing surface area.
Reverberation time is measure used to quantify reverberation and is the time required for sound reflections to decay
Due to some obstruction, some space cant get first reflected sound. These area
calls acoustic shadow area (Refer to Fig.2). Acoustic shadow usually appears in
space underneath of terraced seating which needs to be avoided in concert hall
Fig. 2 Forming of acoustic shadow
The cardinal rule in the design of rooms is to avoid sound reflections that focus in the plane of listening. A focusing
surface concentrates sound energy, which may then be intense enough to be perceived as an echo. Surfaces such as
domes, barrel-vaulted ceilings, and concave rear walls can cause sound focusing and are notorious for generating
2. Define volume and area of concert hall
First I would need to define the volume and dimension of concert
hall. Fig. 3 depicts typical volume requirement for different types of
performance spaces. We can see from fig. 3 the volume of concert
hall is 10-11.4 times required no. of seats.
The proposed concert hall is supposed to accommodate 800 seats.
The volume of concert hall V=800*10=8000m
Ceiling height also plays an important role in delivering early
reflections in music halls. Typical ceiling heights yielding an adequate
density of early sound are: (1) 500 seats: 9-11m; (2)1500
seats:13.5-16m; (3)2500 seats:18-21m. (Source from: Architrectural
acoustics principles and practice, 1999)
Typically, the maximum ceiling height (h) can be determined from
h= [3(V/T500)] *0,85
We can get expected best reverberation time of 8000m at 500 Hz is 1.6s (from Fig.4). h=[3(8000/1.6)] *0,85,
So the maximum ceiling height of 800 seats is 14.1m
The minimum area of proposed concert hall S=V/h, S=8000/14.1=567m
So the minimum area of proposed concert hall for 800 seats is 567m.
3. Geometric analysis and form test
From the review part, we know that the liveness of a concert hall is decided by early
reflections. Early reflections for concert hall are 80msec after arrival of direct sound. The
shape and dimension decides the early reflections. So I want to have geometric test and
analysis. The geometric test and analysis below are several conventional concert hall
Option 1: 25m x 10m rectangular
The computer simulation shows distribution of first reflected sound, the auditorium gets first reflected sound from the
two side lateral wall. I also use hand sketch to show relationship between rectangular shape and first reflection basic
on computer simulation result.
Option 2: irregular polygon
The computer simulation shows distribution of first reflected sound, the auditorium gets first
reflected sound from the two side lateral wall. This shape can bring listeners closer to stage.
Hand sketch is summary of computer simulation. It shows that first reflected sound at the
back of auditorium is weaker than that at the front. It would be not easy for central part of
concert hall to get first reflected sound from two side lateral wall.
Option 3: sector
The computer simulation shows distribution of first reflected sound. Hand sketch is
summary of computer simulation. We can see both from computer simulation and hand sketch that the center of
auditorium is very difficult to get first reflected sound from lateral wall. With the angle of sector increases, it is more and
more difficult to get first reflected sound from lateral wall.
Option 4: irregular polygon
We can see from the simulation that the central part of concert hall is
also hard to get first reflected sound from lateral wall. Some
amelioration is to provide corrugated shape for lateral wall. So central
part can get first reflected sound from lateral wall because the
orientation of reflector has been changed.
Option 5: hexagon
We can see from the simulation below that the central and front part
of concert hall is also hard to get first reflected sound from lateral wall,
in hexagon shape. But if we can see if we adopt corrugated
arrangement of lateral wall, central and front part can get first
reflected sound from lateral wall because the orientation of reflector
has been changed.
Compare 5 options, with the wider of concert hall, the auditorium will be closer to stage but the front part will be more
difficult to receive early reflections. I need to make a balance between early reflections and distance. Option 1 the
concert hall is too narrow which makes auditorium far away from stage. Option 2 is appropriate. Option 3 the angle of
two lateral wall is too large which makes lateral wall difficult to provide early reflections. Option 4 the concert is too
wide for central part to receive early reflections from lateral wall. Option 5 the width, angle of lateral wall, distance
between stage and auditorium is appropriate.
Here I would like to use option 5 for concert hall plan design.
Option 5 has the problem of lack of first reflected sound for front parts. Ceiling design would be important for hexagon
shape concert hall because ceiling can also reflect sound from sources and provides early reflections for the front and
middle part of concert hall.
4. Geometric design of concert hall
I would use ray tracing method to design the shape and dimension of ceiling, the sound source S is located 2.5m
from the edge of stage, the height is 1.5m. The front part of concert hall is from A to B (A, B area both 1.1m from FFL).
Fig. 5 Ceiling shape design by ray tracing method
The stage height is 6m. I connect SA and AA and draw internal bisector AQ1, then I draw AA which is
perpendicular to AQ1. Then I mirror S to S1 by AA. After I get S1, I connect S1 and B. Finally I get the position of A
from the intersection of AA and S1B. And then I connect S and A, , I take B from the extensi