Question

# Loudspeakers can produce intense sounds with surprisingly small energy input in spite of their low efficiencies....

Loudspeakers can produce intense sounds with surprisingly small energy input in spite of their low efficiencies. Calculate the power input needed (in W) to produce a 92.1 dB sound intensity level for a 15.5 cm diameter speaker that has an efficiency of 1.06%. (This value is the sound intensity level right at the speaker.)

#### Homework Answers

Answer #1

Sound intensity level right at the speaker = = 92.1 dB

Sound intensity right at the speaker = I

I = 1.622 x 10-3 W/m2

Diameter of the speaker = D = 15.5 cm = 0.155 m

Area of the speaker = A

A = 1.887 x 10-2 m2

Power output of the speaker = Pout

Pout = IA

Pout = (1.622x10-3)(1.887x10-2)

Pout = 3.061 x 10-5 W

Power input to the speaker = Pin

Efficiency of the speaker = = 1.06% = 0.0106

Pin = 2.89 x 10-3 W

Power input needed by the speaker = 2.89 x 10-3 W

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