Sound Power

Again in the case of the oscillating piston, we will consider the sound power radiated by the piston into the tube. The sound power radiated by the piston, W, is

(3.18)

But from Eqs. (3.10) and (3.14) the power is

(3.19)

and close to the piston, the rms particle velocity, u_rms, must be equal to the rms piston velocity. From Eq. (3.19), we can write

(3.20)

where r is the piston and duct radius, and v_rms is the rms velocity of the piston.