声学基础课件(许肖梅)fundamentals of acoustics 07-9-26页精选文档
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VE0 120u212p0c22
The instantaneous particle speed and acoustic pressure are functions of both position and time, and consequently the instantaneous energy density is not constant throughout the fluid.
3.5 Pressure and Intensity Level
• The average power produced by a person talking in an ordinary conversational tone is about 10-5 watt, or 100 ergs per sec.
• The range of power that can be produced by the voice varies from about 1 erg per sec for very weak speech to about 104ergs per sec for loud speech.
3.4.1 Sound Energy Density
The energy transported by acoustic waves through a fluid medium is of two forms:
• The kinetic energy of the moving particles ; • The potential energy of the compressed
The total acoustic energy of the volume element is:
EEkEp1 20V0u21 2p 0c22V0
The instantaneous energy density is defined as the energy per unit volume, in Joules per Cubic meter (J/m3).
EK 12(0V0)u2
Where the mass of the element, 0 V 0 is
calculated using the density and volume of the undisturbed fluid.
The change in potential energy associated
Sound Power
Total sound power emitted by a source in all directions, measured in watts (joules/second)
Wa IdS ; or Wa cS s
The amount of power produced by sound generator is very small compared with usual electrical powers.
with a volume change from V0 to V is
V
V
Ep
PdV
V0
V0
p
dV
• Where the negative sign indicates that the potential energy will increase as work is done on the element when its volume is decreased by action of a positive acoustic pressure p.
1T
IT0 Re(p)Rபைடு நூலகம்(u)dt
Where the integration is taken over a time corresponding to the period of one complete cycle. For harmonic waves this yields:
I
1 2
pmumcos
fluid.
Consider a small fluid element that moves with the fluid and occupies volume V0 of the undisturbed fluid.
The kinetic energy of this element is:
• Its fundamental units are watts per square meter (W/m2).
• The sound intensity is the time average of sound energy flux density
1T r
I
T
0
pudt
It can be written in another form
vv
Sound energy flux density:
uvpdSdpdpuv
dSdt dt
3.4.3 Sound Intensity and Sound Power
• The acoustic intensity of a sound wave is defined as the average rate of flow of energy through a unit area normal to the direction of propagation.
3.4.2 Sound Energy Flux Density
Sound energy transmitted through a unit area and a unit time normal to the direction of sound transmission.
v
v
Sound energy : FdpdSd
• From conservation of mass we have
V 0V0
dV d 0V 0, Ppc2(0)
(the equation of state)
So we obtain:
E p 0c 2 (0 )dV 0 0 2 V 0 0c 2 (0 )2 2 p 0 2 c 2V 0
The instantaneous particle speed and acoustic pressure are functions of both position and time, and consequently the instantaneous energy density is not constant throughout the fluid.
3.5 Pressure and Intensity Level
• The average power produced by a person talking in an ordinary conversational tone is about 10-5 watt, or 100 ergs per sec.
• The range of power that can be produced by the voice varies from about 1 erg per sec for very weak speech to about 104ergs per sec for loud speech.
3.4.1 Sound Energy Density
The energy transported by acoustic waves through a fluid medium is of two forms:
• The kinetic energy of the moving particles ; • The potential energy of the compressed
The total acoustic energy of the volume element is:
EEkEp1 20V0u21 2p 0c22V0
The instantaneous energy density is defined as the energy per unit volume, in Joules per Cubic meter (J/m3).
EK 12(0V0)u2
Where the mass of the element, 0 V 0 is
calculated using the density and volume of the undisturbed fluid.
The change in potential energy associated
Sound Power
Total sound power emitted by a source in all directions, measured in watts (joules/second)
Wa IdS ; or Wa cS s
The amount of power produced by sound generator is very small compared with usual electrical powers.
with a volume change from V0 to V is
V
V
Ep
PdV
V0
V0
p
dV
• Where the negative sign indicates that the potential energy will increase as work is done on the element when its volume is decreased by action of a positive acoustic pressure p.
1T
IT0 Re(p)Rபைடு நூலகம்(u)dt
Where the integration is taken over a time corresponding to the period of one complete cycle. For harmonic waves this yields:
I
1 2
pmumcos
fluid.
Consider a small fluid element that moves with the fluid and occupies volume V0 of the undisturbed fluid.
The kinetic energy of this element is:
• Its fundamental units are watts per square meter (W/m2).
• The sound intensity is the time average of sound energy flux density
1T r
I
T
0
pudt
It can be written in another form
vv
Sound energy flux density:
uvpdSdpdpuv
dSdt dt
3.4.3 Sound Intensity and Sound Power
• The acoustic intensity of a sound wave is defined as the average rate of flow of energy through a unit area normal to the direction of propagation.
3.4.2 Sound Energy Flux Density
Sound energy transmitted through a unit area and a unit time normal to the direction of sound transmission.
v
v
Sound energy : FdpdSd
• From conservation of mass we have
V 0V0
dV d 0V 0, Ppc2(0)
(the equation of state)
So we obtain:
E p 0c 2 (0 )dV 0 0 2 V 0 0c 2 (0 )2 2 p 0 2 c 2V 0