ar2ae045-ra1 room acoustics 1
TRANSCRIPT
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Acoustics
Room AcousticsRoom Acoustics
Lecture AR2AE045-D1-1
Martin Tenpierikp
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 1
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Introduction Architectural Acoustics can be subdivided into
Room Acoustics / Spatial Acoustics
Traffic Noise and Urban Acoustics
Sound Insulation and Sound Proofing
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Content This lecture focuses on Room Acoustics.
Room Acoustics includes acoustics of concert halls, theaters and auditoria.
But also:- Noise reduction in noisy spaces- Speech intelligibility in rooms / offices / schoolsSpeech intelligibility in rooms / offices / schools- Sound propagation through “Coupled Rooms”
Concert halls only once per 10 year ??Restaurant nearly every day
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Room Acoustics
Sound Reflection in EnclosuresSound Reflection in Enclosures
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Thousands of Rays!
longer path
later arrival
“reverberation"
direct sound
microphone
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Measuring a Room
Past:- Use alarm pistol or clap your hands: “impulse”And listen or register on tapeAnd listen or register on tape
Nowadays:Use loudspeaker and microphone- Use loudspeaker and microphoneCalculate impulse response on computer
Different signals can be used:Different signals can be used:- Digital noise (white noise, pink noise)- Sweep signals
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Impulse Response
An Example direct
echoecho reverberation
100 ms time axis00 s time axis
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Our Ears + Brains
They are sensitive to Energy or Power
And are a logarithmic ‘device’And are a logarithmic device
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Energy ~Pressure SquaredSquared
linear
direct
scale
0.3 stime axis
echo
time axis
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Echogram
direct
echolog-
scale
0.6 stime axis
20 dB
time axis
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Often drawn as
80direct
ude
[dB
]“reverberation"
60
Am
plitu
400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4
time [s]
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Backward Integration:
Schröder
1 stime
20 dB
time
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Reverberation Time:
Sabine’s Definition (1900)
reverberation time T
(1900) 60 dB decreasedraw straight line
1 stimetime
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Example: Reverberation time
Reverberation in a room
T = 0 6 s in a small roomtime T = 0.6 s in a small room
T = 1.0 s in a small room
T = 2.0 s in a big room
T = 2.5 s in a big room
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Reverberation Time:
From the energy balance of a room, Sabine derived an equation for the reverberation time as:
Sabine’s Definition (1900) 0
55.3 0.1616
V V VTc A A A
(1900)
c0 = speed of sound wave in air (=340 m/s)
l f ( 3)V = volume of room (m3)A = total absorption in room (m2 sabin) = sound absorption coefficient of a surface (-)1
n
i ii
Sp ( )
S = area of a surface (m2)
This equation can be derived from the energy balance of the
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 15
This equation can be derived from the energy balance of the room in case of a diffuse sound field.
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Reverberation Time:
Energy balance equation of a room:
dEW V IA Derivation
W = power of sound source (W)
W V IAdt
V = volume of room (m3)E = energy density in room (J/m3)t ti ( )t = time (s)I = acoustic intensity in room (W/m2)A = total absorption in room (m2 Sabine)A total absorption in room (m Sabine)
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Reverberation Time:
Reverberation time is the decay of acoustic energy after a source is switched off (thus W =0 W):
dDerivation 0 dEV IAdt
Since and in a diffuse field,2
2effp
Ec
2
4effp
Ic
the equation becomes
0c 04 c
22 0( )
( )4
effeff
dp t c Ap tdt V
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Reverberation Time:
Assuming p2eff(t) = p2
eff(0) at t = 0, the solution to this equation becomes
Derivation 02 2 4( ) (0)
c AtV
eff effp t p e
or024
2
( )10 log 10log
(0)
c Ateff Vp t
e
which equals
2g g(0)effp
02 24
2 20 0
(0) ( )10log 10log 10log
c Ateff eff Vp p t
ep p
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0 0
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Reverberation Time:
Since T is defined for a decay of 60 dB, the term on the left hand side of the equation is 60 dB
Derivation 0460 10logc AT
Ve
or
6 55.3 55.34ln 10 V V VT 0 0 0
4 ln 10
tot
Tc A c A c S
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Reverberation Time:
Sabine’s definition however gives problems for high average absorption coefficient. Eyring therefore derived another reverberation time as:
Eyring’s Definition (1930)
derived another reverberation time as:
55.3
V VT(1930)
d f d i i ( 340 / )
0 ln 1 6 ln 1 tot totc S S
c0 = speed of sound wave in air (=340 m/s)
V = volume of room (m3)Stot = total surface area in room (m2)Stot o a su ace a ea oo ( ) = average absorption coefficient (-)
Th d i i ill b d h
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The derivation will not be presented here.
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Reverberation Time
Sabine versus Eyring
55 3 VSabine:
55 3 V0
55.3
tot
VTc S
Eyring: 0
55.3ln 1
tot
VTc S
- Note the minus sign in Eyring’s equation
- Differences are small if is small
- Differences become bigger if approaches 1
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gg pp
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Reverberation Time:
Sabine’s and Eyring’s reverberation time:
Example Room size: 13 x 10 x 6 m3
Average sound absorption coefficient: 0.21
Total Absorption: 0.21 x 536 = 113 m2 sabin
55 3 78055.3 780 1.1340 0.21 536sabT s
55.3 780 1.0340 536 ln(1 0.21)eyrT s
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4
Sabine vs.Eyring
A room with V/Stot = 3 m
2 5
3
3,5m
e, T
[s]
1,5
2
2,5
rber
atio
n tim
0
0,5
1
Reve
r
SabineEyring
00 0,2 0,4 0,6 0,8 1
average absorption coefficient [-]
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Reverberation Time:
60 dB??
Extrapolation only allowed if
1 stime
y
straight line!
time
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Reverberation Time:
Sometimes therefore other intervals are used for characterising a room:
T i t l f 30 dBOther definitions
- T30 uses an interval of 30 dB multiply the found value with 2
- T15 uses an interval of 15 dB 15
multiply the found value with 4- EDT (Early Decay Time) uses the first 10 dB decay
multiply the found value with 6multiply the found value with 6
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Reverberation Time
T is often used as a measure for acoustical quality
- 1.5 - 2.2 s for music- 0.8 - 1.0 s for speech- 0.8 s for an office (too high ??)( g )- 0.4 - 1.2 s in dwellings- 0.3 - 0.4 s maximum for the ‘hearing impaired’- 0.1 - 0.2 s is often disliked
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Reverberation Time
Problem however is that T depends on volume:
- 0.4 s for a living room
- is 1.8 s for a sports facility if scaled-up
Therefore a better measure is needed:Therefore a better measure is needed:- STI (Speech Transmission Index): from 0 to 1;- C50 , U50 (clarity): from -15 dB to +15 dB;- average (average absorption coefficient): 0 to 1
ll l dStill, T is most commonly used.
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Room Acoustics
Influence of Sound Absorbing MaterialsInfluence of Sound Absorbing Materials
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ROOM ACOUSTICS ROOM ACOUSTICS ROOM ACOUSTICS ROOMabsorbed + transmitted
Absorbing Surface absorbing material
sound sound
microphone
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Increasing Absorption
80 Multiple reflections:Direct sound not affected
Decrease of reverberation time ud
e [d
B]
Multiple reflections:
extra energy loss
time60
Am
plitu
400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4
time [s]
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Speech Intelligibility and Musical Clarity 80Musical Clarity
Boundary:50 ms: Speech ud
e [d
B]
50 ms: Speech80 ms: Music 60
Am
plitu
400 0 0 1 0 2 0 3 0 40.0 0.1 0.2 0.3 0.4
time [s]
early: energy increase late: disturbing noise
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Increasing Absorption
80However, total energy
ude
[dB
] Is reduced
60
Am
plitu
400 0 0 1 0 2 0 3 0 4
Ratio of early to late increases
0.0 0.1 0.2 0.3 0.4time [s]
early: energy increase late: disturbing noise
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Reverberation Time Revisited
Should we choose reverberation time as low as possible?
Revisited
Yes, reverberation decreases speech intelligibility
Maybe, but sound pressure level might get too low
No, people do not like anechoic music
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Reverberation Time Revisited
Yes Maybe or No
RevisitedAcoustic design is a compromise!
E.g., a theatre is not the same as a concert hall.
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Room Acoustics
Absorption MechanismAbsorption Mechanism
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Types of Absorption
Three types of sound absorption are distinguished:
- Friction of molecules in porous material;
- Panel resonance (mass-spring system)
- Perforated panels: Helmholtz resonance + panel resonance
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Types of Absorption:
transmissionFriction of Molecules
transmission
absorption
reflectionincident
abs. + transm. + refl. = incident
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Types of Absorption:
Hole size (or specific flow resistance) is essential.
Friction of Molecules
Too open hardly any friction
OKOK
Too dense hardly any entrance
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Types of Absorption:
Reflection at back wall reduces absorption…
Friction of Molecules
reflection at backsiderigid layer, like concrete
absorption material
reflectionincident reflectionincident
… but mostly needed as structure and for reducing
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y gsound transmission.
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Types of Absorption:
Absorption as a function of frequency
1.0laagdikte 4 cmLayer thickness 4 cm
Friction of Molecules
0 6
0.8ci
ent
g20 000 Ns/m4
Layer thickness 4 cmFlow resistance 20000 Ns/m4
0.4
0.6
sorp
tieco
effic
harmonics
0 0
0.2
abs
fundametalsspeech
harmonics
speech
0.050 100 200 400 800 1600 3150
frekwentie [Hz]
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1.0stromingsweerstand 20 000 Ns/m4
Types of Absorption:
Thickness of absorption layer is important as well
Flow resistance 20000 Ns/m4
0 6
0.8ci
ent
16
Friction of Molecules
Flow resistance 20000 Ns/m
0.4
0.6
sorp
tieco
effic
laagdikte 1 cm24
8
Layer thickness 1 cm
0 0
0.2
abs
Acoustic wall paper does not exist
Carpet needs to be thick
0.050 100 200 400 800 1600 3150
frekwentie [Hz]Modern plaster ??
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Types of Absorption:
Paint layers or thin protective films cause shielding of the material from acoustic waves above the following frequency:
Panel Resonance
following frequency:
0 0 4102 2shield
cft t
th ifi ti i d (k / 2/ )
2 2f f f ft t
0c0 the specific acoustic impedance (kg/m2/s)
ftf the mass of the film (kg/m2)
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Types of Absorption:
Absorption due to resonance of mass-spring system.
Panel Resonance
rigid layer, like concrete
thin panel(filled) cavitySPRING
MASS
reflectionincident
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Types of Absorption:
Absorption highest near resonance frequency:
'1 60sPanel Resonance
1 602 0.6
tres
plate cav
sfm m a b d
with m the mass of the system (kg/m2)
mplate the mass of the plate (kg/m2)
s’t the stiffness of the spring (air layer) (N/m3)
dcav the thickness of the cavity (m)
a, b the dimensions of the plate (m)
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Types of Absorption:
Absorption as a function of frequency
1.0laagdikte 4 cm
Panel Resonance
0 6
0.8ci
ent
g20 000 Ns/m4
0.4
0.6
sorp
tieco
effic
0 0
0.2
abs
0.050 100 200 400 800 1600 3150
frekwentie [Hz]
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Types of Absorption:
Absorption due to resonance of mass-spring system.
Perforated Panels
rigid layer, like concrete
perforated panelporous absorber
reflectionincident
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Types of Absorption:
Absorption highest near:
ePerforated Panels
54resplate cav
efd d
with e the degree of perforation (-)
dcav the thickness of the cavity (m)
dplate the thickness of the perforated plate (m)
e should be smaller than 30%
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Types of Absorption:
Absorption as a function of frequency
1.0laagdikte 4 cm
Perforated Panels
0 6
0.8ci
ent
g20 000 Ns/m4
0.4
0.6
sorp
tieco
effic
0 0
0.2
abs
0.050 100 200 400 800 1600 3150
frekwentie [Hz]
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Room Acoustics
Some Examples of Absorption MaterialsSome Examples of Absorption Materials
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Examples of Absorbers:
Standard Office
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© Lau Nijs
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Examples of Absorbers:
Integrated Ceiling
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© Lau Nijs
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Examples of Absorbers:
Absorbing Plasters
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© Lau Nijs
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Examples of Absorbers:
Perforated Panels
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© Lau Nijs
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Examples of Absorbers:
Carpets
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© Lau Nijs
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Examples of Absorbers:
Panels
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© D. Bankersen en L.M. Schaberg
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Examples of Absorbers:
Plants??
Yes but youYes, but you need a lot of them
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© Roby van Praag
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Examples of Absorbers:
Baffles
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© Lau Nijs
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Room Acoustics
Sound Power LevelSound Power Level
Sound Pressure Level
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Recapitulation from Previous Lectures
Several Sound Levels can be defined:
2p LecturesSound Pressure Level:
20
10 log effp
pL
p
W Sound Power Level:
0
10 logWWLW
and many more.
p0 = 2·10-5 Pa
W0 = 1·10-12 W
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0
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Recapitulation from Previous Lectures
Sound power is extremely low.
W WLLectures
0
10 logWWLW
100 10
W
W W
Example:
If the source has a sound power level of 80 dBre10-12
then the sound power equals 10-4 W.
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One Source in a Room
diffuse field
source
diffuse field
direct sound
microphone
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Direct Sound Only
2 0 0c Wp
source
; 24eff directpr
direct sound
microphone
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Diffuse Field
2 0 04 1c Wp ; 1eff diffusepA
microphonemicrophone
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Addition of Sound Pressures
2 0 0; 24eff direct
c Wpr
2 0 0;
4 1eff diffusec WpA
Pressures
2 2 2; ; ;eff total eff direct eff diffusep p p
thus (Sabine-Franklin-Jäger theory)
2
4 1110 log4p WL L
A
2g
4p W r A
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Addition of Sound Pressures
2 0 0 0 0; 2
4 14eff total
c W c Wpr A
Pressures
Divide by p02
2
; 0 0 0 02 2 2 20 0 0
4 14
eff totalp c W c Wp r p A p
Since p02 equals 0c0W0, this becomes
0 0 0
2
;2 20 0 0
4 14
eff totalp W Wp r W AW
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0 0 04p r W AW
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Addition of Sound Pressures
This can be rewritten as
2;
4 11ff t t lp W Pressures ;
2 20 0
14
eff totalp Wp W r A
Take the log on both side and multiply with 10
2 4 11p W ;
2 20 0
4 1110log 10log4
eff totalp Wp W r A
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Sound pressure level according to
If we rewrite, we get
2 4 11ff t t lp W according to Sabine-Franklin-Jäger theory
;2 20 0
110log 10log 10log4
eff totalp Wp W r A
theory
This equals
4 11 2
4 1110 log4p WL L
r A
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Reverberation Radius
The reverberation radius is defined as the distance from the source where both the direct and diffuse sound pressure are equal:sound pressure are equal:
2 2; ;eff direct eff diffusep p
and thus
16 1g
Ar
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Example(given earlier)
Ceiling
S (m2)
130
0.5
A (m2)
65
Floor
Side wall left
Side wall right
130
78
78
0.1
0.1
0 2
13
7.8
15 6Side wall right
Front
Back
78
60
60
0.2
0.1
0.1
15.6
6
6
Totals 536 113.4
113.4 0.21536
Room
13 10 6 m3
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85
90
ExampleSound Pressure
Lecture room of 13 x 10 x 6 m3 and LW = 86 dB
70
75
80
85
[dB]
Pressure Level 0.02
0.050.100.20
50
55
60
65
SPL,
Lp
[
0.50
1.00 4 11
40
45
50
0 2 4 6 8 10 12
2
110 log4p WL L
r A
distance from source [m]
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85
90
ExampleSound Pressure
Lecture room of 13 x 10 x 6 m3 and LW = 86 dB
70
75
80
85
[dB]
Pressure Level 0.02
0.050.100.20
50
55
60
65
SPL,
Lp
[
0.50
1.00 4 11
High value is not necessarily a good room
40
45
50
0 2 4 6 8 10 12
2
110 log4p WL L
r A
High level means a lot of reverberation
distance from source [m]So again: compromise must be found
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Sound Pressure Level with
According to Sab.-Fr.-Jäg. theory SPL reaches a constant level far from the sound source. However, SPL keeps decreasing with increasing distance fromLevel with
Michael Barron’s correction
SPL keeps decreasing with increasing distance from source. Therefore Barron made following correction
correction
2
1 4 0.04010 log exp4
p W
rL Lr A T
which can be written as
/ r mfp /
2
4 1110 log4
r mfp
p WL Lr A
4
tot
VmfpS
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85
90
ExampleSound Pressure
Lecture room of 13 x 10 x 6 m3 and LW = 86 dB
70
75
80
85
[dB]
Pressure Level: Sab-Fr-Jag
0.020.050.100.20
50
55
60
65
SPL,
Lp
[
0.50
1.00
40
45
50
0 2 4 6 8 10 12
distance from source [m]
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85
90
ExampleSound Pressure
Lecture room of 13 x 10 x 6 m3 and LW = 86 dB
70
75
80
85
[dB]
Pressure Level: Barron 0.02
0.050.100.20
50
55
60
65
SPL,
Lp
[
0.50
1.00
40
45
50
0 2 4 6 8 10 12
distance from source [m]
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Room Acoustics
SpeechSpeech
Noise in Rooms
Multi-Source Situations
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Wanted Speech + Noise
wanted speech receiver
wanted speech:Noise a ted speec
- heavily depends on direct sound,
- so room not very important
perceived noise:
noise source
- very often in diffuse field,
- so it depends on the room
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Example: Speech with Noise
Reverberation chamber speech + radio
“Ik sta hier in de nagalmkamer op 1 m afstand van deNoise Ik sta hier in de nagalmkamer op 1 m afstand van de mikrofoon. Op 5 meter afstand van de mikrofoon bevindt zich een spelend radiootje. Kunt U mij nog verstaan?”
… Music …………………….
Translation: I am standing here in a reverberation chamber at a distance of 1 m from a microphone At 5 m from thisdistance of 1 m from a microphone. At 5 m from this
microphone a radio is playing. Can you still understand me?
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Example: Speech with Noise
Anechoic room speech + radio
Noise“We bevinden ons in de dode kamer. Op 5 meter afstand van de mikrofoon staat een spelende radio; zelf sta ik op 1 m van de mikrofoon. U merkt wel dat de radio hier
i d hi d lijk i d i d l k ”minder hinderlijk is dan in de nagalmkamer.”
… Music …………………….
Translation: We are now in an anechoic room. At 5 m distance from the microphone a radio is playing; I myself am standing afrom the microphone a radio is playing; I myself am standing a 1 m distance from this microphone. You probably observe that the radio is less annoying than in the reverberation chamber.
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Example: Speech with Noise
Living room speech + radio
Noise“Dit is een stukje tekst opgenomen in een huiskamer die een tikkeltje galmt. De spreker bevindt zich op 1 m van de mikrofoon; op 5 m staat een spelend radiootje. U
kt d t i d t d ij t k t l tmerkt dat, voor iemand met goede oren, mijn tekst wel te volgen is, maar aangenaam is anders, zeker als mijn tekst ook nog veel langer zou duren.”
… Music …………………….
Translation: This is a piece of text recorded in a living roomTranslation: This is a piece of text recorded in a living room which is slightly reverberant. The speaker is distanced 1 m from the microphone; At 5 m from this microphone is a radio. You observe that for someone with good ears my text is intelligible
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 79
observe that, for someone with good ears, my text is intelligible, though not pleasantly, particularly if there would be more text.
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Example: Speech Levels
Vocal effort Measured at 1 m in front of mouth
Maximum .......................... 90 dB(A)Shouting ........................... 84Very Loud ......................... 78yLoud ................................. 72Raised Voice ...................... 66Normal .............................. 60Relaxed ............................. 54
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Some Noise Levels
Some Noise Levels
Damage to the ears ....................... >80 dB(A)Normal speech at 1 m ................... 60
Sleep disturbance ........................ 40Difficult tasks at school or office .... 35-45Traffic noise ................................ 55-75Restaurant .................................. 55-85
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Signal to Noise RatioS/N Wanted soundS/N
Noise
Difference between both levels is excellent first estimation
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Noisy space Signal strength (= direct sound)
110 logL L 210 log4p WL L
r
n ‘noise’ sources with equal sound strength
4 1
4 110 log 10 logp WL L n
A
4 110 logp W
nL L
A
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S/N ratio Signal
110 logL L 210 log4p WL L
r
Noise
4 110 l
nL L
10 logp WL LA
S/N= Signal – Noise
Th ll ti f L
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Thus a cancellation of LW
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S/N ratio Signal to noise ratio is then defined as
4 11 n 2
4 11/ 10 log 10 log4
nS N
r A
S/N depends on:- distance to wanted speaker r- distance to wanted speaker r- number of noise sources in the room n- total absorption (including guests) A- mean absorption coefficient
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Speech Intelligibility
Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6Good S/N +6
For a whole day at school, higher values required
Also for the hearing impaired S/N = +15 !!!!!
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Example of a Restaurant
r n gem lbh Signal Noise S/N
1 10 0 1 13 10 6 59 0 68 3 9 31 10 0.1 13106 59.0 68.3 -9.3
The person speaking here is inaudible.
Yet, such spaces are still designed and built.
l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6
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Ketelhuis BK-City
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© Pau Sarquella Fabregas
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Example of a Restaurant (1)
r n gem lbh Signal Noise S/N
1 10 0 1 13 10 6 59 0 68 3 9 31 10 0.1 13106 59.0 68.3 -9.3
0.5 10 0.1 13106 65.0 68.3 -3.3
0.25 10 0.1 13106 71.0 68.3 2.70.25 10 0.1 13106 71.0 68.3 2.7
Distance to source is an important factor.
l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6
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Example of a Restaurant (2)
r n gem lbh Signal Noise S/N
1 1 0 1 13 10 6 59 0 58 3 0 71 1 0.1 13106 59.0 58.3 0.7
1 5 0.1 13106 59.0 65.3 -6.3
1 25 0.1 13106 59.0 72.3 -13.21 25 0.1 13106 59.0 72.3 13.2
Number of unwanted sources is important.
l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6
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Example of a Restaurant (3)
r n gem lbh Signal Noise S/N
1 5 0 1 13 10 6 59 0 65 3 6 31 5 0.1 13106 59.0 65.3 -6.3
1 5 0.2 13106 59.0 61.3 -2.3
1 5 0.3 13106 59.0 59.4 -0.41 5 0.3 13106 59.0 59.4 0.4
Mean absorption coefficient is important.
l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6
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Example of a Restaurant (4)
r n gem lbh Signal Noise S/N
1 5 0 2 6 5 5 3 59 0 67 8 8 81 5 0.2 6.553 59.0 67.8 -8.8
1 5 0.2 13106 59.0 61.7 -2.7
1 5 0.2 262012 59.0 55.5 3.51 5 0.2 262012 59.0 55.5 3.5
Total area is important as well.
l l f d S/ 6Minimum level for good ears S/N = -6Fair S/N = 0Good S/N =+6
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S/N ratio Lombard effect (1911)
People tend to talk louder in a reverberant space.
And the more people are present, the louder they speak.
However,
this effect is not reflected in the S/N ratio.
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Room Acoustics
Auditorium Acoustics: Strength / LoudnessAuditorium Acoustics: Strength / Loudness
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Strength / Loudness (1)
One measure often used to characterise auditoriums for music is strength, G.
It is defined as the amount of energy at a certain iti i th l ti t th t fposition in the room relative to the amount of
energy at a distance of 10 m from the source in an anechoic room.
2 ( )t
effp t dt0
2,10
0
10 log( )
t
A m
Gp t dt
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0
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Strength / Loudness (2)
G (dB) characterises the influence of the room on sound pressure level relative to an anechoic situationsituation.
It b ittIt can be written as
1 4(1 ) 2
2
( )410 log 1
r AG
24 10
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Strength / Loudness (3)
At a large distance from the sound source (r >2rg) this can be approximated as
21 4(1 )
4(1 )410 log 10 log 31r AG
2
10 log 10 log 3114 10
GA
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30
ExampleLoudness / Strength
Concert Hall of 20 x 50 x 14 m3
15
20
25dB
]
Strength
0.02 0 05
too loud,headaches
5
10
15
Stre
ngth
, G [ 0.05
0.10 0.20
0 505.5 dB4 0 dB
-10
-5
00 10 20 30 40 50
S 0.50
1.00 too weak,inaudible
4.0 dB
10
distance from source [m]
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Strength / Loudness (4)
According to this classical theory, the strength/loudness becomes constant at large distance from the sourcedistance from the source.
I lit G k d i if iIn reality G keeps decreasing if r increases.
A i h Mi h l B ’ ti liAgain here Michael Barron’s correction applies.
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Concertgebouw Amsterdam
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© Stylos
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Room Acoustics
Auditorium AcousticsAuditorium Acoustics
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Auditorium Acoustics
More Information on Auditoriums can be found in
More Information
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© Lau Nijs
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Auditorium Acoustics
This book contains 100 concert halls from all over the world.
Among these halls are ‘het Concertgebouw’ in A t d d ‘d D l ’ i R tt dAmsterdam and ‘de Doelen’ in Rotterdam.
The book also contains questionnaires among musicians and audience.
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Concert Halls
Concertgebouw
More Information on Auditoriums can be found in
ConcertgebouwAmsterdam
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Concert Halls
Doelen
More Information on Auditoriums can be found in
Doelen Rotterdam
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Concert Halls
Doelen
Amsterdam versus Rotterdam
1888Doelen Rotterdam
year 1888
2037 seats
18780 318780 m3
year 1966
2242 seats
24070 m3
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Auditorium Acoustics
Beranek uses among others 4 measures for characterising concert halls:
Parameters - Reverberation time
- Bass ratio
- Strength / Loudness
- Degree of diffusivity
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Auditorium Acoustics
A concert hall does not contain much absorption from its own. Absorption mainly results from audience
Absorptionaudience.
K t ’ ti ti (‘D l ’)Kosten’s reveration equation (‘Doelen’):
VT 6 1.07
Tseated area
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Auditorium Acoustics
Bass ratio is defined as a ratio of reverberation times at different frequencies:
Bass Ratio125 250
500 1000
T TBRT T
People tend to like that T is longer at lower f
500 1000
frequencies.
1.1 < BR < 1.45 for ‘short’ T (chamber music)
1.1 < BR < 1.25 for ‘long’ T (auditorium)
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Auditorium Acoustics
Strength / Loudness has already been defined previously.
Strength / Loudness
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Auditorium Acoustics
In a completely diffuse sound field a listener in the audience feels completely enveloped by the sound.
DiffusivityTo increase diffusivity use scattering elements with th i f l th i dit i ( 50 ?)the size of wave lengths in auditorium (…50 cm?)
h l d h k f h ’ (fl h ’ )This also reduces the risk of echo’s (flutter echo’s)
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Auditorium Acoustics
Very often concert halls are built in a shoebox shape, like the ‘Musikverein’ in Vienna:
Shoebox Shape
- Reduces risk of errors
- More constant distribution of important parameters thacross the room
- Seats below a balcony often notorious for bad soundsound
- Risk of flutter echo’s between opposite walls
Other shapes are of course possible too.
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 113
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Auditorium Acoustics
Two of Beranek’s parameters:
- Reverberation time, T: between 2.0 – 2.3 s
ParametersRevisited
- Strength / Loudness, G: between 4.0 and 5.5 dB
A simple Excel sheet can now be used as a first estimate.
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 114
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Auditorium Acoustics
With pencil and paper a good estimate of a concert hall can be made (70% ???)
Modern simulation software is an important tool (80% ???)(80% ???)
l d ll h l d l dFor large auditoriums still physical models are made and tested (90% ???)
The remaining 10% is pure psychology, PR and luck.
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 115
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That’s it for today!End
More information on room acoustics can be found here
htt //bk ij t / b L Nij (D t h l )•http://bk.nijsnet.com/ by Lau Nijs (Dutch only)
•“Concert and Opera Houses – How they sound” by L.L. BeranekL.L. Beranek
•“Auditorium Acoustics and Architectural Design” by M. Barron
DR. IR. ARCH. MARTIN TENPIERIK / FACULTY OF ARCHITECTURE / BUILDING PHYSICS / AR2AE045 / 01 February 2012 / 116