声学基本概念
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BA 7666-11, 8 860504/1
Time
Sound Pressure
Pressure [Pa]
Atmospheric Pressure
100 000 Pascal
New York Mexico City
BA 7666-11, 9
Acoustic Pressure Variations
Range of Sound Pressure
31.7 20 ×10−6
= 20 log 1.58 × 10-6 = 124 dB
BA 7666-11, 13
Perception of dBs
Change in Sound Level (dB)
3 5 10 15 20
Change in Perceived Loudness
Just perceptible Noticeable difference Twice (or 1/2) as loud Large change Four times (or 1/4) as loud
Directivity Index
Source Location
Directivity Directivity
Factor
Index, dB
Free field
1
0
On a flat plane
2
3
At a junction of two
4
6
planes
At a junction of three
L+ dB 3
2
1.4 dB
1
Example:
L1 = 55 dB L2 = 51 dB ∆L = 4 dB L+ = 1.4 dB Lt = 55 + 1.4 = 56.4 dB
0
∆L
0
5
10
15
dB
4 dB
BA 7666-11, 27 860512/2
Subtraction of Noise Levels
BA 7666-11, 35
b
Example: b=1m λ = 0.344 m (≈ f = 1 kHz)
Diffusion of Sound b << λ
b >> λ
b
Example : b = 0.1 m λ = 0.344 m (≈ f = 1 kHz)
BA 7666-11, 36
b
Example: b = 0.5 m λ = 0.344 m (≈ f = 1 kHz)
Pressure Ratio
1.00 0.989 0.977 0.966 0.955 0.944 0.933 0.923 0.912 0.902
0.891 0.841 0.794 0.708 0.631 0.562
dB to Pressure Ratio
− db + Pressure Pressure
λ=c f
λ
λ
Wavelength, λ [m]
20
10
5
2
1
0.2
0.1
0.05
10
20
50
100 200
500
1k
2k
Frequency, f [Hz]
5 k 10 k
BA 7666-11, 34
Diffraction of Sound b << λ
b >> λ
b
Example : b = 0.1 m λ = 0.344 m (≈ f = 1 kHz)
dB – decibel
p
Lp = 20 log p0 dB re 20 µPa
(p0 = 20 µPa = 20 × 10-6
Pa)
Ex. 1: p = 1 Pa
Lp = 20 log
1 20 ×10−6
= 20 log 50 000 = 94 dB
Ex. 2: p = 31.7 Pa
Lp = 20 log
Examples: N = 2: LTotal = L1 + 3 dB N = 10: LTotal = L1 + 10 dB
10
15 N
BA 7666-11, 30
Frequency Range of Different Sound Sources
1
10
BA 7666-11, 31
Frequency
Compression
t = 1/2 T t = 3/4 T t=T
BA 7666-11, 7
Extension
Minimum compression
Maximum compression
No compression
Sound Pressure
Pressure [Pa]
100 000 Pascal
Range of Sound Pressure Levels
Sound Pressure, p [Pa]
100
10
1
0.1
0.01
0.001
0.000 1
0.000 01
Sound Pressure Level, Lp
140
[dB]
120
100
80
60
40
20
0
BA 7666-11, 12 860508/2
100
1000
10 000 [Hz]
Audible Range
1
10
BA 7666-11, 32
Frequency
100
1000
10 000 [Hz]
Wavelength
Wavelength, λ [m]
BA 7666-11, 33
Speed of sound, c = 344 m/s
Wavelength and Frequency
Terminology of Sound
RMS Peak
Fast Slow Impulse
Sound Pressure dB
Logarithmic scales
Percentile level Weighting
Pascal
RMS
Statistical analysis
Leq
L10
L90
1/1 and 1/3 Octave Analysis
1.5
1.189
0.0100
2.0
1.259
0.0032
3.0
1.413
10-3
4.0
1.585
10-4
5.0
1.778
10-5
− db +
6 7 7 9 10 12 14 16 18 20
30 40 50 60 80 100
Pressure Ratio
1.995 2.239 2.512 2.818 3.162 3.981 5.012 6.310 7.943 10.000
31.62 100
316.2 103 104 105
BA 7666-11, 16
Simple Rules for Conversion
Sound Pressure, p [Pa]
20
10
Sound Pressure Level, Lp dB re 20 µPa
114
× 100
2
1
× 10
0.3
× 4 × 3 × 2 0.2
LS+N [dB]
BA 7666-11, 28
LN [dB]
Subtraction of dB Levels
L− dB
Ex:
6
LS+N = 60 dB LN = 53 dB
5
∆L = 7 dB
4
L− = 1 dB LS = 60 − 1 = 59 dB
3
2
1
∆L
1 2 3 4 5 6 7 8 9 10
Basic Concepts of Sound
BA 7666-11, 1
Contents: Definitions dB Conversion Sound Fields dB ± dB
Sound
BA 7666-11, 2 860499/1
Sound and Noise
BA 7666-11, 3 860500/1
Point source
r: Lp 2r: Lp − 6 dB
BA 7666-11, 19 860510/1
r: Lp 2r: Lp − 3 dB
Line source Plane source
r: Lp 2r: Lp
Anechoic and Reverberant Enclosures
BA 7666-11, 20 860511/1
dB
☺
LS ~ LS+N
BA 7666-11, 29
Addition of many dB values
Addition of sound levels : L1 + L2 ..... + LN = ?
10 log N
12
10
8
6
4
2
0
0
5
For L1 = L2 = L3..... = LN LTotal = L1 + 10 logN
Ratio
Ratio
0.0
1.000
0.501
0.1
1.012
0.447
0.2
1.023
0.398
0.3
1.035
0.355
0.4
1.047
0.316
0.5
1.059
0.251
0.6
1.072
0.200
0.7
1.084
1.158
0.8
1.096
0.126
0.9
1.109
0.100
1.0
1.122
0.0316
Reflection of Sound
Source
Source
Source
Imaginary Source
BA 7666-11, 37
Sound Frequencies
Infra
Audio
Ultra
0.02 0.2
2
20
200 2000 20.000 200K
BA 7666-11, 5
Power P [W]
Electrical Heater
Basic Parameters of Sound
Under free-field conditions: P2
P
r1
→
The Sound Intensity vector, Ι, describes the amount and direction P2 of flow of acoustic energy at a
Pressure Field
BA 7666-11, 21
Loudspeaker Enclosure
Microphone
Sound Fields
Lp
Near
field
Far field Free field
Reverberant field
6 dB
A1
2 × A1
Distance, r
BA 7666-11, 22 860512/2
Pressure, p [Pa]
100 10 1 0.1 0.01 0.001 0.000 1 0.000 01
BA 7666-11, 10 860505/2
Basic Concepts of Sound
BA 7666-11, 11
Contents: Definitions dB Conversion Sound Fields dB ± dB
given position Ι2
Ι1
r2
P p2 Ι = wenku.baidu.comπr2 = ρc
Power: Intensity: Pressure:
P [W] Ι [J/s/m2] = W/m2 p [Pa = N/m2]
BA 7666-11, 6 861218/2
Propagation of Sound
t=0 t = 1/4 T
Constant percentage bandwidth Noise Dose
BA 7666-11, 4
Pressure vs. Power
Pressure p [N/m2 = Pa] Lp [dB]
Power P [W]
Analogy
Temperature t [°C]
Sound Source
BA 7666-11, 14
Conversion to dB using Charts
Lp
dB re 20 µPa
200
150
100
94 dB
50
0
0.0001
0.01 0.1 1 10 100 1000 10 000
p0 = 20 µPa
BA 7666-11, 15
Pressure [Pa]
Conversion to dB using Tables
0.1
40 dB 94
86
20 dB
84
80
12 dB 6 dB 10 dB
74
BA 7666-11, 17
Basic Concepts of Sound
BA 7666-11, 18
Contents: Definitions dB Conversion Sound Fields dB ± dB
Types of Sound Sources
BA 7666-11, 25
Contents: Definitions dB Conversion Sound Fields dB ± dB
Two Sound Sources
BA 7666-11, 26
Lp1 = X dB Lp2 = X dB Lp1 + Lp2 = X + 3 dB
Addition of dB Levels
8
9
planes
BA 7666-11, 23
L = Lp L = Lp + 3 dB L = Lp + 6 dB L = Lp + 9 dB
Pressure Increase at Walls
Lp L = Lp + 6 dB L = Lp + 3 dB
BA 7666-11, 24
Basic Concepts of Sound
Time
Sound Pressure
Pressure [Pa]
Atmospheric Pressure
100 000 Pascal
New York Mexico City
BA 7666-11, 9
Acoustic Pressure Variations
Range of Sound Pressure
31.7 20 ×10−6
= 20 log 1.58 × 10-6 = 124 dB
BA 7666-11, 13
Perception of dBs
Change in Sound Level (dB)
3 5 10 15 20
Change in Perceived Loudness
Just perceptible Noticeable difference Twice (or 1/2) as loud Large change Four times (or 1/4) as loud
Directivity Index
Source Location
Directivity Directivity
Factor
Index, dB
Free field
1
0
On a flat plane
2
3
At a junction of two
4
6
planes
At a junction of three
L+ dB 3
2
1.4 dB
1
Example:
L1 = 55 dB L2 = 51 dB ∆L = 4 dB L+ = 1.4 dB Lt = 55 + 1.4 = 56.4 dB
0
∆L
0
5
10
15
dB
4 dB
BA 7666-11, 27 860512/2
Subtraction of Noise Levels
BA 7666-11, 35
b
Example: b=1m λ = 0.344 m (≈ f = 1 kHz)
Diffusion of Sound b << λ
b >> λ
b
Example : b = 0.1 m λ = 0.344 m (≈ f = 1 kHz)
BA 7666-11, 36
b
Example: b = 0.5 m λ = 0.344 m (≈ f = 1 kHz)
Pressure Ratio
1.00 0.989 0.977 0.966 0.955 0.944 0.933 0.923 0.912 0.902
0.891 0.841 0.794 0.708 0.631 0.562
dB to Pressure Ratio
− db + Pressure Pressure
λ=c f
λ
λ
Wavelength, λ [m]
20
10
5
2
1
0.2
0.1
0.05
10
20
50
100 200
500
1k
2k
Frequency, f [Hz]
5 k 10 k
BA 7666-11, 34
Diffraction of Sound b << λ
b >> λ
b
Example : b = 0.1 m λ = 0.344 m (≈ f = 1 kHz)
dB – decibel
p
Lp = 20 log p0 dB re 20 µPa
(p0 = 20 µPa = 20 × 10-6
Pa)
Ex. 1: p = 1 Pa
Lp = 20 log
1 20 ×10−6
= 20 log 50 000 = 94 dB
Ex. 2: p = 31.7 Pa
Lp = 20 log
Examples: N = 2: LTotal = L1 + 3 dB N = 10: LTotal = L1 + 10 dB
10
15 N
BA 7666-11, 30
Frequency Range of Different Sound Sources
1
10
BA 7666-11, 31
Frequency
Compression
t = 1/2 T t = 3/4 T t=T
BA 7666-11, 7
Extension
Minimum compression
Maximum compression
No compression
Sound Pressure
Pressure [Pa]
100 000 Pascal
Range of Sound Pressure Levels
Sound Pressure, p [Pa]
100
10
1
0.1
0.01
0.001
0.000 1
0.000 01
Sound Pressure Level, Lp
140
[dB]
120
100
80
60
40
20
0
BA 7666-11, 12 860508/2
100
1000
10 000 [Hz]
Audible Range
1
10
BA 7666-11, 32
Frequency
100
1000
10 000 [Hz]
Wavelength
Wavelength, λ [m]
BA 7666-11, 33
Speed of sound, c = 344 m/s
Wavelength and Frequency
Terminology of Sound
RMS Peak
Fast Slow Impulse
Sound Pressure dB
Logarithmic scales
Percentile level Weighting
Pascal
RMS
Statistical analysis
Leq
L10
L90
1/1 and 1/3 Octave Analysis
1.5
1.189
0.0100
2.0
1.259
0.0032
3.0
1.413
10-3
4.0
1.585
10-4
5.0
1.778
10-5
− db +
6 7 7 9 10 12 14 16 18 20
30 40 50 60 80 100
Pressure Ratio
1.995 2.239 2.512 2.818 3.162 3.981 5.012 6.310 7.943 10.000
31.62 100
316.2 103 104 105
BA 7666-11, 16
Simple Rules for Conversion
Sound Pressure, p [Pa]
20
10
Sound Pressure Level, Lp dB re 20 µPa
114
× 100
2
1
× 10
0.3
× 4 × 3 × 2 0.2
LS+N [dB]
BA 7666-11, 28
LN [dB]
Subtraction of dB Levels
L− dB
Ex:
6
LS+N = 60 dB LN = 53 dB
5
∆L = 7 dB
4
L− = 1 dB LS = 60 − 1 = 59 dB
3
2
1
∆L
1 2 3 4 5 6 7 8 9 10
Basic Concepts of Sound
BA 7666-11, 1
Contents: Definitions dB Conversion Sound Fields dB ± dB
Sound
BA 7666-11, 2 860499/1
Sound and Noise
BA 7666-11, 3 860500/1
Point source
r: Lp 2r: Lp − 6 dB
BA 7666-11, 19 860510/1
r: Lp 2r: Lp − 3 dB
Line source Plane source
r: Lp 2r: Lp
Anechoic and Reverberant Enclosures
BA 7666-11, 20 860511/1
dB
☺
LS ~ LS+N
BA 7666-11, 29
Addition of many dB values
Addition of sound levels : L1 + L2 ..... + LN = ?
10 log N
12
10
8
6
4
2
0
0
5
For L1 = L2 = L3..... = LN LTotal = L1 + 10 logN
Ratio
Ratio
0.0
1.000
0.501
0.1
1.012
0.447
0.2
1.023
0.398
0.3
1.035
0.355
0.4
1.047
0.316
0.5
1.059
0.251
0.6
1.072
0.200
0.7
1.084
1.158
0.8
1.096
0.126
0.9
1.109
0.100
1.0
1.122
0.0316
Reflection of Sound
Source
Source
Source
Imaginary Source
BA 7666-11, 37
Sound Frequencies
Infra
Audio
Ultra
0.02 0.2
2
20
200 2000 20.000 200K
BA 7666-11, 5
Power P [W]
Electrical Heater
Basic Parameters of Sound
Under free-field conditions: P2
P
r1
→
The Sound Intensity vector, Ι, describes the amount and direction P2 of flow of acoustic energy at a
Pressure Field
BA 7666-11, 21
Loudspeaker Enclosure
Microphone
Sound Fields
Lp
Near
field
Far field Free field
Reverberant field
6 dB
A1
2 × A1
Distance, r
BA 7666-11, 22 860512/2
Pressure, p [Pa]
100 10 1 0.1 0.01 0.001 0.000 1 0.000 01
BA 7666-11, 10 860505/2
Basic Concepts of Sound
BA 7666-11, 11
Contents: Definitions dB Conversion Sound Fields dB ± dB
given position Ι2
Ι1
r2
P p2 Ι = wenku.baidu.comπr2 = ρc
Power: Intensity: Pressure:
P [W] Ι [J/s/m2] = W/m2 p [Pa = N/m2]
BA 7666-11, 6 861218/2
Propagation of Sound
t=0 t = 1/4 T
Constant percentage bandwidth Noise Dose
BA 7666-11, 4
Pressure vs. Power
Pressure p [N/m2 = Pa] Lp [dB]
Power P [W]
Analogy
Temperature t [°C]
Sound Source
BA 7666-11, 14
Conversion to dB using Charts
Lp
dB re 20 µPa
200
150
100
94 dB
50
0
0.0001
0.01 0.1 1 10 100 1000 10 000
p0 = 20 µPa
BA 7666-11, 15
Pressure [Pa]
Conversion to dB using Tables
0.1
40 dB 94
86
20 dB
84
80
12 dB 6 dB 10 dB
74
BA 7666-11, 17
Basic Concepts of Sound
BA 7666-11, 18
Contents: Definitions dB Conversion Sound Fields dB ± dB
Types of Sound Sources
BA 7666-11, 25
Contents: Definitions dB Conversion Sound Fields dB ± dB
Two Sound Sources
BA 7666-11, 26
Lp1 = X dB Lp2 = X dB Lp1 + Lp2 = X + 3 dB
Addition of dB Levels
8
9
planes
BA 7666-11, 23
L = Lp L = Lp + 3 dB L = Lp + 6 dB L = Lp + 9 dB
Pressure Increase at Walls
Lp L = Lp + 6 dB L = Lp + 3 dB
BA 7666-11, 24
Basic Concepts of Sound