7.0 Characteristic of Sound waves

It is the charateristics of a wave by which sound wave appears shrill or grave. It depends upon the frequency of the wave.

Higher the frequency higher will be the pitch and vice versa.

It is the sensation received by the ear due to intensity of sound. $$L \propto \log I$$ Greater the amplitude of vibration, greater will be the intensity $I$ and so louder will be the sound.

Similarly, lesser the intensity, feeble will be the sound.

The unit of loudness in decible $(dB)$ is, $$L = 10{\log _{10}}\frac{I}{{{I_0}}}$$ Here, ${{I_0}}$ is constant i.e. minimum intensity ($ = {10^{ - 12}}W{m^{ - 2}}$) just audible at intermediate frequencies.

The loudness of normal talk is about 60 dB.

It is sensation received by the ear by which, we are able to differentiate two sounds ( even if they are of same pitch and loudness). The quality actually depends on the shape of waveform and the number of overtones.

Reverberation is the phenomenon of persistence of sound for sometime after the source stop producing sound.

The time for which the sound continues to be heard after the source has stopped producing sound is known as reverberation time.

According to Sabine's formula, the reverberation time of a hall is given by, $$T = \frac{{0.16V}}{{\sum {{a_i}{s_i}} }}$$

where,

$V$: Volume of the hall (in $m^3$)

$\sum {{a_i}{s_i}} = {a_1}{s_1} + {a_2}{s_2} + {a_3}{s_3} + ...=$ total absorption of the hall

${s_1},{s_2},{s_3}...$: are the surfaces (in $m^2$) which absorbs sound

${a_1},{a_2},{a_3}...$: are their respective absorption constants