17.7
音の強さ
音源の大きさは、音源がどれだけエネルギー的に振動しているかに関係しており、その結果、伝播媒体の分子が振動します。 音源の音量を測定する場合、対象となる物理量は強度です。 これは、音波の伝播方向に垂直な単位面積あたり、単位時間あたりに放出されるエネルギーとして定義されます。 音源がより長い期間、より広…
音の大きさは、人間の耳に聞こえる知覚に関係しています。それは、音源がどれだけエネルギー的に振動しているかによります。
ラウドネスは、物理量、つまり強度によって表されます。ソースの強度は、伝搬方向に垂直な単位面積あたりのソースから放出される電力として定義されます。
一般的に、電力は時間とともに変動します。したがって、強度は、単位垂直領域あたりの平均電力として定義されます。
電力のSI単位はワットで、面積のSI単位はメートルの2乗です。したがって、強度のSI単位はワット/メートルの2乗です。
音源が音波を全方向に均一に放射する場合、伝搬に垂直な領域は音源を覆う球の領域になります。したがって、強度は距離の2乗として減衰します。
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Q1: What is sound intensity and how is it measured?
Sound intensity is the average power emitted by a sound source per unit area perpendicular to the direction of propagation. It is measured in watts per square meter, the SI unit derived from power in watts and area in square meters. Intensity quantifies the loudness of a sound source based on how energetically the source vibrates.
Q2: Why does sound intensity decrease with distance from the source?
When a sound source emits waves uniformly in all directions, the sound spreads over an increasingly larger spherical area. Since intensity is power divided by area, and the sphere's surface area increases with the square of the distance, intensity falls off as the square of the distance from the source.
Q3: How is sound intensity related to pressure amplitude?
Sound intensity is proportional to the square of the pressure amplitude creating oscillations in the medium. Since oscillation amplitude is proportional to pressure amplitude, and intensity increases with oscillation amplitude, the relationship between intensity and pressure amplitude is quadratic. This connection is explored in intensity and pressure of sound waves.
Q4: Why is average power used instead of instantaneous power in the intensity definition?
Sound sources oscillate hundreds or thousands of times per second, but the human ear perceives only the time average of these rapid oscillations. Using average power accounts for what humans actually hear rather than the fluctuating instantaneous values, making the intensity definition physically meaningful for perception.
Q5: What factors determine a sound source's intrinsic loudness?
A sound source's intrinsic loudness depends on how energetically it vibrates and the pressure amplitude it generates in the propagation medium. The intensity definition divides emitted energy by time and area to isolate the source's intrinsic loudness from factors like duration of vibration or size of the radiating surface.
Q6: How does the medium's particle vibration affect sound intensity?
Sound propagates through vibration of the medium's particles, so intensity increases with the pressure amplitude driving these oscillations. The greater the pressure amplitude, the larger the oscillation amplitude of medium constituents, and consequently the higher the sound intensity produced by the source.
Q7: What is the relationship between oscillation amplitude and sound intensity?
Sound intensity is proportional to the square of the oscillation amplitude of the medium's constituent particles. This quadratic relationship means that doubling the oscillation amplitude increases intensity by a factor of four, making amplitude a critical factor in determining how loud a sound appears.