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ACOUSTIC DESIGN OF CONCERT HALL FOR CUHK. SENV 7700 _1155021643 ZHOU SHAO KANG 2012.12. 1. Design Background. Sir Run Run Shaw Hall is a multi-purpose cultural centre of The Chinese University of Hong Kong.

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ACOUSTIC DESIGN OF CONCERT HALL FOR CUHK

SENV 7700 _1155021643 ZHOU SHAO KANG 2012.12

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1. Design Background

Sir Run Run Shaw Hall is a multi-purpose cultural centre of The Chinese University of Hong Kong.

Acoustic property of concert hall is quite different from multi-purpose hall, sound intelligibility and reverberation time requirement is different

A concert hall for functional supplyment of Sir Run Run Shaw Hall

Location of proposed concert hall in CUHK

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2. Review Acoustic Definition of Concert Hall

Reflected Sound

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.

Echoes

Echoes are reflections that can be heard distinctly and separately from the early reflected and reverberant sound. Echoes are normally heard due to intense reflection arriving 40 msec and later after the direct sound signal has reached the listener.

Reverberation

Reverberation time is measure used to quantify reverberation and is the time required for sound reflections to decay 60 dB.

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2. Review Acoustic Definition of Concert Hall

Acoustic Shadow

Due to some obstruction, some space can’t 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 design.

Forming of acoustic shadow

Focusing

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 strong echoes

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3. Define Volume and Area of Concert Hall

The proposed concert hall is supposed to accommodate 800 seats. The volume of concert hall V=800*10=8000m³

Typically, the maximum ceiling height (h) can be determined from

h= [3√(V/T500)] *0,85

We can get expected best reverberation time of 8000m³ at 500 Hz is 1.6s (from Fig.4). h=[3√(8000/1.6)] *0,85, h=14.1.

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=567m²

So the minimum area of proposed concert hall for 800 seats is 567m².

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3. Geometric Analysis and Form Test

Option 1: 25m x 10m rectangular

Option 2: irregular polygon

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Option 3: sector

Option 4: irregular polygon

Option 5: hexagon

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3. Geometric Analysis and Form Test

3

1

2

the angle of two lateral wall is too large which makes lateral wall difficult to provide early reflections

appropriate

the concert hall is too narrow which makes auditorium far away from stage.

4

5

appropriate

concert is too wide for central part to receive early reflections from lateral wall

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4. Design Outcome

Here are hand sketch drawing of plan, section and interior perspective of concert hall I designed.

This plan is from basic hexagon. Length of side is 17m. This concert hall has 800 seats. The area of concert hall is 600 m2 (>567 m2)Ceiling height is from 3.5m to 11m (<14.1m).

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6. Average sound absorptive coefficient calculation, material use and reverberation time calculation

In this paper I would use EYring’s Formula to calculate reverberation time of concert hall.

T60=KV/-SLN(1-a)+4mV

“V” is the volume of room (m3)

“S” is the surface of all indoor surfaces (m2)

“a” is the sound absorption coefficient of all indoor surfaces

4m is the air sound absorption coefficient

We can get data from the table in Fig. 4 that the best reverberation time for 8000m3 concert hall is 1.6s. T60=1.6s, K=0.161, S=2765m2,. In the condition of frequency < 1000Hz, 4mV can be neglected.

1.6= 0.161* 8023/ -2765 ln(1-a), a=0.26.

“a” is the average sound absorptive coefficient including all concert hall material and human beings.

We are trying to get average sound absorptive coefficient “a1”

This concert hall can accommodate 800 people. The surface of one people is supposed to be 1m2, but when people are sitting its surface exposed to outside is 0.4 m2, sound absorptive coefficient of people is 0.33 under 500 Hz condition.

So, a*(S+S’)=a1*S+a2*S’,

“S” is the surface of all indoor surfaces (m2)

“S’ ” is the surface of all human beings (m2)

Because a=0.26, S=2765, S’=800, a2=0.49

0,26*(2765+800)=a1*2765+0.33*800, a1=0.24

So the average sound absorptive coefficient of all material in concert hall is 0.24

Sound absorptive coefficient of material I select for concert hall should be near 0.24 in 500Hz condition, because different sound absorptive coefficient of same material at different frequency. The table below is material I would choose for concert hall.

Here are different materials I select for floors, ceilings, lateral walls, rear wall and chairs of concert hall.

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After the calculation, we can get reverberation time T60 is 1.97s when concert hall is full in 500Hz condition. T60 is 2.08s when concert hall is empty when concert hall is empty in 500Hz condition.

We know the best reverberation time for concert hall in 500 Hz condition is 1.6s, in order to increase reverberation from 2.08 to 1.6s, we can change the material of concert hall.

EYring’s Formula “T60=KV/-SLN(1-a)+4mV”, if the “a” value is increased, T60 decreases. Here we try to apply carpet and concrete to floor respectively.

Change wooden floor to carpet surface:

The sound absorption of carpet is 0.57 in 500Hz condition. Because the surface area of floor is 600m2, sound absorption is 0.57*600=342. Total sound absorption is 342+30+102+144+132+198=816, average sound coefficient is 816/3550=0.230. So,–ln(1-a)=-ln(1-0.23)=0.2614. T60=0.161*8023/(3550*0.2614)=1.39s

Compare to T60=2.08s, 1.39s is more near to best reverberation time 1.6s. The calculation result shows the application of carpet is benefit the reverberation time.

The approach to achieve best reverberation 1.6s in 500Hz condition is most of floor area applies carpet but remains some part of floor area applies wooden floor.

Then I would like to calculate the area ratio of carpet area and wooden floor area.

In order to achieve T60=1.6s. 1.6s= 0.161* 8023/ -3550 ln(1-a), so ln(1-a)=0.2272, a=0.2. so the average sound absorption of all material(when concert hall is full) is 0.2.

Sound absorption of floor is 0.2*3550-30-102-144-132-198=236. We suppose the area of carpet is “x”, so the area of wooden floor is “600-x”, 0.57*x+0.1*(600-x)=236, x=374

So the area of carpet is 374 m2

The area of wooden floor is 600-374=226 m2

When we change 374 m2 wooden floor to carpet, we can achieve the best reverberation in 500Hz condition 1.6s

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7. Material Details

Materials for rear wall:

Materials for lateral wall:

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THANK YOU FOR ATTENDING!

SENV 7700 _1155021643 ZHOU SHAO KANG 2012.12