At a rock concert, a dB meter registered 130 dB when placed 2.5 m in front of a loudspeaker on the stage.

At a rock concert, a dB meter registered 130 dB when placed 2.5 m in front of a loudspeaker on the stage. (a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air? (b) How far away would the sound level be a reasonable 90 dB?