Question

A manufacturing firm has hired your company, Acoustical Consulting, to help with a problem. Their employees are complaining about the annoying hum from a piece of machinery. Using a frequency meter, you quickly determine that the machine emits a rather loud sound at 1100 Hz. After investigating, you tell the owner that you cannot solve the problem entirely, but you can at least improve the situation by eliminating reflections of this sound from the walls. You propose to do this by installing mesh screens in front of the walls. A portion of the sound will reflect from the mesh; the rest will pass through the mesh and reflect from the wall.How far should the mesh be placed in front of the wall for this scheme to work?

Answer 1

Answer: 7.7cm

Step-by-step explanation:

If i want to set up destructive interference, meaning that the reflection will be half (½) of the wavelength out of phase, or the distance is ¼ of a wavelength.

v.s = Speed of sound = 340 m/s ( some books may use 343 m/s, this change varies due to change in temperature and humidity.)

f = 1100 hz

λ = v.s / f

λ = 340 m/s / 1400 Hz

λ = .3091 m

Recall that the distance is ¼ of the wavelength,

.3091/4 = 0.0773 m

Distance used would be = 7.7 cm