A small loudspeaker radiates sound power of 8 W uniformly in all directions. (a) Find the sound intensity at a distance of 4 m from the speaker. (b) Express this intensity level in decibels. Solution: (a) The power spreads over a sphere of area 4 pi r^2 = 4 pi (4)^2 = 64 pi = 201 m^2. Intensity I = P / A = 8 / 201 = 0.0398 W/m^2 (about 4.0 x 10^-2 W/m^2). (b) Sound level beta = 10 log10(I / I0) = 10 log10(0.0398 / 10^-12) = 10 log10(3.98 x 10^10) = 10 x 10.6 = 106 dB. This is extremely loud - comparable to a rock concert - so nobody should stand that close to such a powerful speaker.