This question is incomplete, the complete question is;
When an auditorium has a solid wall, sound waves will tend to perfectly reflect off the wall (i.e. with a 180o phase change). If listening to music, as from an orchestra, the incoming and reflected waves will interfere with each other. For a listener sitting 0.5 m from the wall, what is the lowest frequency which gets suppressed by this interference? Use vsound=330 m/s.
Answer: f = 165 Hz
the lowest frequency which gets suppressed by this interference is 165 Hz
Explanation:
For a reflected wave (out of phase), the path difference between the incoming and reflected wave should be equal to the half integral multiple of wavelength.
r₂ - r₁ = ( m + 1/2) λ/2
r₂ is the distance from the source to observer via reflection
r₁ is distance from source to observer
here r₂ would travel an additional distance of 0.5 m due to reflection that straight approaching wave.
Therefor to have minimum/lowest possible frequency, we say m = 0
we substitute
0.5 = ( 0 + 1/2 ) λ/2
λ = 2m
The frequency would be
f = Vsound / λ
f = 330 / 2
f = 165 Hz
Therefore the lowest frequency which gets suppressed by this interference is 165 Hz
