[填空题]
At a rock concert, a dB memj 6j)d w8zt2mter registerm7wg c)4;siye,bm 9fk c2i*dp 1nsr,ded 130 dB when placed 2.8 m in front of a loudspeaker on the stwsi 2*nfdd7 r mmkc1;s)eg, 4cip,yb9age.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$ $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB? $ \times10^{2}$m
