FUNDAMENTALS OF ACOUSTICS 21

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FUNDAMENTALS OF ACOUSTICS (21)

• RECEPTION OF ACOUSTIC WAVES

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• A loudspeaker is an electronacoustic transducer
  which converts electrical energy to acoustical
  energy. ( Transmitter )
• A microphone is also an electroacoustic
  transducer, but it converts acoustical energy to
  electrical energy. ( Receiver )
• In general, loudspeakers are used to reproduce
  and amplify sound while microphones are used to
  record sound and to make acoustical measurements.

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The receiver must have high efficiency, good
power-handing capacity, uniform frequency
response, and minimum distortion
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The acoustic pressure of the receiver
When a sound wave crosses an interface between
two different media some of the acoustic energy
is usually reflected.
The incident, scattered velocity of the receiver
are
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The scattering of sound can be processed as the
radiation of sound which has radiation impedance
The force due to the medium reaction acting on
the radiator is
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The total force acting on the receiver is
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Where K is distortion coefficient
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For low frequency or small source, K1
Radiation impedance is
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0
0
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2
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4
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0
0.4
0.8
1.2
2.0
1.6
When
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The Distortion of the sound field
For Zs is the function of frequency, K is the
function of frequency
Incident pressure in free field is pi (t)
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The reception of pressure is
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The sensitivity and directivity index of the
receiver

• Sensitivity is the open-circuit voltage response
  for a sound pressure input of one receiver under
  a certain frequency.
• The actual sound field sensitivity is expressed as

Free sound field sensitivity
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Directivity index
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The variation of intensity level with angle is
the beam pattern
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The receiver of the simple line array

• Consider a line of N simpler sources with
  adjacent element spaced distance d apart, as
  shown in Fig.
• If all sources have the same source strength and
  radiate waves with the same phase.

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Homework

• P279 6-3
• 6-4