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10
Noise and Sound Insulation
噪声和隔声
Noise is unwanted sound.
Even if a sound consists of the finest music
it can be considered as noise
if it occurs in the middle of the night!
What are the effects of noise?
Hearing loss 听力损失 :
Quality of life 生活质量:
Interference干扰:
important sounds such as speech
Distraction分心: noisy can cause inefficiency
Expense 花费: the cost to control excessive noise are
expensive.
This chapter is concerned with
10.1 Measurement of noise 噪声的测量
10.2 Noise control 噪声的控制
10.3 Noise transfer 噪声的传播
10.4 Sound insulation 隔声
10.1 how to measure noise?
10.1.1 Sound level meter声级计

How does a sound level meter work?

variations in air pressure
variations of voltage
amplified and displayed on an electrical meter calibrated in
decibels.

these meters can be small enough to be hand-held and are
supplied in several grades of accuracy.
record many instantaneous瞬时的 readings of sound
level,
t1
L1
t2
L2
tn
LN
A typical sound level meter takes an RMS( root mean
square)均方根 value of the signal
10.1.2 Frequency components

Most practical noise contains different frequencies

The interpretation分析of these different frequencies needs
consideration in a sound level meter

the ear is most sensitive in the frequency range between
2~5kHz , and least sensitive at low frequencies or at
extremely high frequencies.

human hearing judges some frequencies to be more important
than other frequencies.

The method of dealing with different frequencies.
One method of dealing with the frequency content
of sound is
to emphasis or give “weight” to the frequencies that
human hearing emphasises.
The weighting networks加权网络
The response to low frequencies and to very high
frequencies is reduced in a specified manner
four different weightings have been developed
as the A,B,C and D scales.
The A scale is the most useful weighting network.
Many measurements of noise measured on the A
scale
dB(A)

A 对500Hz以下的声音有较大的衰减，以模拟人耳对低频不敏感
的特性。

C在整个可听范围内几乎不衰减，以模拟人耳100方纯音的响应；

B，介于两者之间，对低频有一定的衰减，

D，用来测量航空噪声；

用声级计的不同网络测得的声级，分别计作dBA、 dBB、dBC、
dBD 。
Figure 10.1 Construction of a sound level meter

If a noise contains single frequency
it is usually more annoying than
a noise with different frequencies.

industrial equipment such as high speed fans or other
machinery , and by electrical generators发电机 and
transformers变压器.
the result of noise measurement
Each
Frequency bands 频带
Has a each value
Some sound level meters
allow the use of filters,
which pass selected
frequencies only.
Noise spectrum of telephone buzzer
how to evaluate noise?
10.1.3 Noise limiting curve 噪声评价曲线
1）Noise Criterion 噪声评价曲线(NC) :
Table10.1
acceptable levels of
background noise from
services installations.
2）Preferred Noise Criterion 噪声评价曲线(PNC) :
a development of the NC curves.
PNC=3.5+NC
3）Noise Rating噪声评价曲线 (NR) :
NR＝NC+5
对低频的要求没有NC曲线苛刻
1）Noise Criterion 噪声评价曲线(NC) :
2）Preferred Noise Criterion 噪声评价曲线(PNC)
3）Noise Rating噪声评价曲线 (NR) :
The NC curves have been widely used for assessing the
noise made by heating and ventilating equipment
PNC curves are a development of the NC curves.
NR curves are commonly used for other industrial
measurements of noise.
10.1.4 Time components
（声级计的时间组成）
During a chosen period of time, such as 12 hours, it is possible
to record many instantaneous 瞬时的readings of sound level,
Figure 10.4 Time distribution of noise level
Vertical
coordinate
Horizontal coordinate 横坐标
The variations in these readings can be combined into one single
LA10 is a sound level, measured as A-weighted sound level,
exceed for 10% of a given measurement time.
for estimating maximum noise levels
LA90=48dB(A)
is used to estimate background noise
10.1.5
Traffic noise index 交通噪声指标
Traffic noise index LA10 is an average of the 18 hourly
L10 values taken between 0600 and 2400hours on a
normal weekday.
LA10，18h =70dB
18h
between 10% of that 18h ,the traffic noise is greater
than 70dB

The left 90% time, the traffic noise is less than 70dB

随时间起伏的随机噪声
10.1.6
Equivalent continuous sound level LAeq
等效连续A声级
for varying sound，how to evaluate its noise effect?
LAeq，8h=90 dB(A)
90 dB(A) for 8 hours
93 dB(A) for 4 hours
99 dB(A) for 1 hours
All give the same value of
An equivalent continuous sound level LAeq is being
used to assess
railway noise

in the UK.
It is difficult to directly compare road noise
and railway noise because of differences in
their nature, especially in duration and
regularity of the noise

LAeq ,T approximately equals LA10,T -3
10.1.7 Hearing risk 听力危胁

Because the risk of damage to hearing is
largely dependent on the total energy
reaching the ear in a given period ,


LAeq is the basis of safe exposure to noise.
Recommended levels are usually in the
range LAeq=80 to 90 dB.
One type of hearing risk index
Occupational noise index LA，EP,d
职业噪声指标



Daily personal noise exposure.
适用于每天在噪声中工作的情况
It measures the cumulative （累积的）noise
energy received by a person during a
standard 8-hour working day.
Has three levels
（1）First action level 第一级
LEP,d value = 85 dB(A) is possibly hazardous and is used as
an industrial action level when staff must be informed,
assessments 补偿must be made,

and hearing defenders听力保护made available.
（2） Second action level：
第二级
LEP,d value = 90 dB(A)
This exposure is a maximum which must not be
exceed and
hearing protectors must be used
（3） Peak action level：
极限值
Sound pressure level =200Pa （or 140 dB）
This peak level is a maximum which must not be
exceed and hearing protectors must be used
another type of hearing risk index
noise dose 噪声量


The noise dose index make 100% dose equal
to a fixed noise exposure such as 85 or 95
dB(A) for 8 hours.
Individual noise exposure can be assessed
by wearing a personal dosemeter (计量计 )
The third type of hearing risk index
peak 峰值
The peak is the highest pressure produced by an
explosive sound, such as those from cartridge 弹药
筒tools and gunshots.
Although the peak only lasts for a brief instant, its
pressure is high and damaging to hearing.
A peak of 200Pa ( equivalent to 140 dB) is used as an
industrial action level
At this level of sound, an 8 hour Leq exposure to
90dB(A) is reached in about 1/5th second
10.1.8 Construction site noise
施工工地噪声

The activities on a construction site often generate noise
that can
Causing hearing damage to people working on the
construction site
Cause annoyance to people near the construction site

A 12hour Leq value of 75dB(A) is a common limit

above 75dB(A) , site operations can be stopped by legal
action
10.1.9 Other noise measurements
其他噪声测量
(1)

Sound exposure level (SEL) ,LA,SEL, 爆发声级 is an
index of transient 瞬时的noise levels, such as those
produced by passing road vehicles or aircraft.
the sound level in dB is measured using A-scale
Sound exposure level is that constant sound level in dB
(A) which, during one second, provides the same total
sound energy as the measured noise.
(2) Perceived noise level (LPN)
感知噪声声级

Perceived noise level is an index of aircraft noise that
takes account of those higher frequencies in aircraft
engine noise which are known to cause annoyance.

An approximate value for perceived noise level is
obtained by adding 13 dB to the measured dB (A) noise
level.
(3) Noise and Number Index (NNI)
噪声和数值指数

NNI is an index of aircraft noise that includes the average
perceived noise level and the number of flyovers heard in a
given period.

This index has been used to predict and to measure annoyance
resulting from noise near airports.

It has also been used as the basis for the award of
compensation payments to householders for sound insulation.

flyover(阅兵时)飞机编队低空飞行
(4) Speech Interference level (SIL)
演讲干扰声级

SIL is a measure of the level of background noise at
which the noise will interfere with speech in a particular
situation.

The type of voices and distances involved are taken into
account.
10 .1 how to measure noise?
10 .2 Noise control 噪声控制

Noise control can be realized by three main aspects.

Source声源:

Path传播途径:

Receiver接收者:
10.2.1 Noise control actions噪声控制措施

The following actions are useful to control noise from
many industrial sources, including factories and
construction sites.
(1) Design and Elimination消除、排除:
Noise control is most effective when it is considered at
the design stage.
(2) Choice of equipment
Some types of equipment are quieter than other types
Try to use quieter machinery and tools at planning stage
Using a later model with improved noise insulation
Using electric motors instead of petrol/diesel motors 汽油/柴油发
动机
Fitting anti-vibration mountings between engines and other
structures
Using hydraulic液压system instead of pneumatic system气压
Use of tools with hush kits 消音组件（消声器）
（3）working planning


Some methods of working are quieter than
others and can be incorporated at the design
and working planning stage
Hydraulic piling 水压打桩rather than hammer
piling 锤子打桩
（4）work practices




The actions of people carrying out operations
have an important effect on noise control
Correctly using equipment such as wearing
their own hearing protectors
A skilled operator will use equipment with
high levels of sound for shorter periods of
time
Good training and education is effective
(5) Distance and location



A single machine
A point source
The noise level falls by between 3 to 6 dB
every time the separation distance is doubled
(6) Acoustic screen and barriers
隔声屏和隔声板


Devices to deflect and absorb sound waves
can be effective it they are placed close to
the source of sound,
or close to the recipient 接收者of the noise.
（7）personal protection
个人防护




If other methods fail to reduce the noise
energy reaching the ear
Hearing defenders
Ear plugs 耳塞
Ear muffs 耳套
10.3 how is Noise transferred？

Noise is transferred into buildings and between different parts
of buildings

by means of several different mechanisms.

Airborne sound 空气传播

Impact ( structure- borne) sound 冲击声（结构传播）
10.3.1 Airborne sound 空气传播

Airborne sound is sound which travels through the air
before reaching a partition.

typical sources of airborne sound include voices, radios,
musical instruments, traffic and aircraft noise.
Impact sound or structure-borne结构传播

Generated on a partition

typical sources of impact sound include footsteps, slammed
砰地关上doors and windows , noisy pipes and vibrating
machinery.
how to control the noise transfer?
10.4 sound Insulation
is the principal method of controlling both airborne and
impact sound in buildings.
Figure 10.7 Noise control by absorption
How to evaluate the effect of sound insulation?
10.4.1 Sound Reduction Index (SRI)
减噪指数

for airborne sound.
transmission coefficient 透射系数
transmitte d sound energy
T
incident sound energy
1
SRI  10log 10  
T
Figure 10.9 An insulation curve for double glazing
10.4.2 what are the Insulation principles

Good sound insulation depends upon the following
general principles

Heaviness 重量

Completeness 完整性

Flexibility 弹性

Isolation 独立性
1) Heaviness 重量

The Mass Law质量定律 :
the sound insulation of a single leaf partition is proportional to
its mass per unit area.

Sound insulation increase by about 5 dB whenever the
frequency is doubled.

Theory predicts : an insulation increase of 6 dB for each
doubling of mass
for practical : Sound insulation increases by 5 dB whenever the
mass is doubled
2） Completeness 完整性

small gaps in the construction of a wall have a far
greater effect on overall insulation

The completeness of a structure depends upon
airtightness气密性 and uniformity均匀性.
Airtightness 气密性

For example
If a brick wall contains a hole or crack which in size
represents only 0.1% of the total area of the wall, the
average SRI of that wall is reduced from 50dB to 30dB
In which parts air gaps often exist？
air gaps often exist because of poorly constructed seals
around partitions, particularly at the joins with floors,
ceilings, windows, doors, service pipes and ducts.
Uniformity 均匀性

The overall sound insulation of a construction is greatly
reduced by small areas of poor insulation.

For example

An unsealed door occupying 25% of the area of a half-
brick wall reduces the average SRI of that wall from
around 45dB to 23dB.
（3）Flexibility 弹性

High stiffness硬度 can cause loss of insulation at
certain frequencies where there are resonances
共振and coincidence effects重合效应.

Loss of insulation by resonance共振occurs if the
incident sound waves have the same frequency as
the natural frequency of the partition构件.
Loss of insulation by
coincidence重合 is caused
by the bending flexural
vibrations 弯曲振动which
can occur along the length
of a partition 构件.


When sound wave reach a partition at angles other than
90°, their transmission can be amplified by the flexing
inwards and outwards of the partition.
The sound –wave frequency and the blending-wave
frequency coincide at the critical frequency 临界频率
（4）Isolation 独立性


As the sound is converted to different wave
motions at the junction of different materials
energy is lost and a useful amount of
insulation is gained.
This is the principle behind the effectiveness
of air cavities in windows, of floating floors
（架空楼板）, of carpets and of resilient
mountings（弹性垫层） for vibrating
machines.
10.4.3 sound insulation regulations?
隔声规范

Building regulations give the minimum standards of
sound insulation dwelling walls and floors
10.4.4 some Insulated constructions
隔声结构

Walls
Figure 10.13 Timber frame wall for sound insulation
Floors
混凝土地板隔声
木地板隔声
Windows
tongue-and-groove 〈建〉舌榫
双层玻璃窗隔声
10.4.5 how to calculate sound insulation

A wall transmits 1 per cent of the sound energy
incident upon the wall at a given frequency. Calculate
the sound reduction index of the wall at this frequency.
Let incident sound energy =100
transmitted sound energy = 1
So T=1/100=0.01
1
 1 
SRI  10log 10    10log 
  10log(100)  20dB
T
 0.01 
for Composite partitions 组合构件

The overall transmission coefficient
(T1  A1 )  (T2  A 2 )  (T3  A 3 )  ...
T0 
A1  A 2  A 3  ...
Worked example 10.2

A wall of area 10m2 contains a window of area 2m2. the
SRIs are: 50dB for the brickwork and 18dB for the
window. Calculate the overall SRI for the wall.

For brickwork let: T1=? A1=10-2=8m2 SRI=50dB

For window

Using
1
SRI  10log 10  
T
let: T2=? A2=2m2
1
50  10log 10  
 T1 
1
18  10log 10  
 T2 
T0
=3.18X10-3
SRI=18dB
T1=10-5
T2=1.585x10-2
(T1  A1 )  (T2  A 2 )
T0 
A1  A 2
Today’s key words






electrical generator发电机
transformer变压器.
Horizontal coordinate 横坐标，水平坐标
Vertical coordinate 纵坐标，垂直坐标
Construction site 施工工地
hush kits 消音组件（消声器）
Today’s key sentences

During a chosen period of time 在给定的时间内

whenever the mass is doubled 当质量翻倍时
Exercises in class
1 The NC curves have been widely used for
assessing the noise made by heating and
ventilating equipment
A heating equipment
B ventilating equipment
C cooling equipment
D industrial equipment
2 NR curves are commonly used for
A heating equipment
B ventilating equipment
C cooling equipment
D industrial equipment
3 Theory predicts : an insulation increase
of (
A 3dB
B 5dB
C 6 dB
D 10dB
) for each doubling of mass
4 for practical : Sound insulation increases by
( ) whenever the mass is doubled
A 3dB
B 5dB
C 6 dB
D 10dB
5 typical sources of airborne sound include(
A voices
B radios, musical instruments
C traffic and aircraft noise
D footsteps
E slammed doors and windows
F noisy pipes and vibrating machinery
)
6 typical sources of impact sound include (
A voices
B radios, musical instruments
C traffic and aircraft noise
D footsteps
E slammed doors and windows
F noisy pipes and vibrating machinery
)
7 Good sound insulation depends upon the
following general principles
A Heaviness 重量
B Completeness 完整性
C Flexibility 弹性
D Isolation 独立性