Assertion: sound wave's propagation | /r/HasProperty | θ = 0°
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Source sentences:
text: For example, a sound at SPL = 85 dB or p = 0.356 Pa in air (ρ = 1.2 kg⋅m−3 and c = 343 m⋅s−1) through a surface of area A = 1 m2 normal to the direction of propagation (θ = 0°) has a sound energy flux P = 0.3 mW.