Two loudspeakers are placed side by side a distance d = 4.00 m apart. a listener observes maximum constructive interference while standing in front of the loudspeakers, equidistant from both of them. the distance from the listener to the point halfway between the speakers is l = 5.00 m . one of the loudspeakers is then moved directly away from the other. once the speaker is moved a distance r = 60.0 cm from its original position, the listener, who is not moving, observes destructive interference for the first time. find the speed of sound v in the air if both speakers emit a tone of frequency 700 hz .