A dB meter registered 125 dB when it was placed 3.90 m in front of a speaker. (i)  Calculate the power output of the speaker, assuming uniform spherical spreading of the sound and negligible absorption by the air.

A guitar string made of steel has a length of 40cm and mass of 35gm.when used on a guitar ,a tension of 40N is applied and a section of the string 35cm long will cause a vibration with a bow.The generated sound will have an intensity level of 60 dB at a distance of one meter. (I)What is the sound intensity level(dB) at a distance of 30m?

(III) Two loudspeakers are placed 3.00 m apart, as shown in Fig. 12–37. They emit 474-Hz sounds, in phase. A micro- phone is placed 3.20 m distant from a point midway between the two speakers, where an intensity maximum is recorded. (a) How far must the microphone be moved to the right to find the first intensity minimum? (b) Suppose the speakers are reconnected so that the 474-Hz sounds they emit are exactly out of phase. At what positions are the intensity maximum and minimum now? H3.00 m- 3.20 m dɔ FIGURE 12-37 Problem 54.