Question

Sound is often characterized by the decibel scale. 60 decibels is normal conversation and that corresponds to a sound pressure level of about 0.02 Pa. Consider the A-440 pure tone. This is a sine wave at 440 Hz with an amplitude of 0.02 Pa. If this wave travels through air at standard conditions, determine the wavelength of the wave, and variation of pressure, temperature, and density with time as one wave passes through a given receiving location. 4.

Answer 1

Sound is characterized by decibels 60 decibels being normal conversation and sound pressure level = 0.02 Pa. Consider the A-440 pure tone sine wave with through air at standard conditions speed of sound (c) = squareroot k_s/rho e is density c = squareroot partial differential Q/ partial differential e P is pressure hence partial differential P alpha partial differential E change in pressure is directly proportional to change in density C_air = 20.05 squareroot T/K m/s T rightarrow Temperature K = r middot P r = adiabatic index C_P = 20.05 squareroot T/r P \r\n V = r = 340/440 = 0.773 m Intensity of sound = PV V = velocity P = pressure therefore I = I_0 sin wt thus P varies as I_0/V sin wt therefore P(r) alpha 1/r and I(r) alpha 1/r^2 therefore sound pressure level alpha_11 = ln(P/P_0)N_P = 20 log(P/P_0)dB.