The Decibel Scale: Mastering Physics of Sound Intensity

Sound intensity varies by a factor of 10^12 from the threshold to a sound that causes damage within seconds. This immense range makes it essential to understand how our ears process and perceive sound. In this article, we will delve into the fascinating world of sound intensity and explore its relationship with physics.

One of the most impressive aspects of sound intensity is its sensitivity. The ear can detect as little as a trillionth of a watt per meter squared, which is remarkable considering that the area of the eardrum is only about 1 cm^2. This means that at the threshold of hearing, only 10^-16 W falls on it.

Air molecules in a sound wave with this intensity vibrate over a distance of less than one molecular diameter, and the gauge pressures involved are less than 10^-9 atm. These tiny vibrations are what allow us to perceive sound waves as different frequencies and intensities.

Another impressive feature of sound intensity is its numerical range. The decibel level of a sound having an intensity of 10^-12 W/m^2 is beta = 0 dB, because the logarithm of 1 is zero. This means that most sounds have relatively low intensities in watts per meter squared.

The concept of sound intensity is not limited to audible sounds; it is a valid physical quantity that applies to all sounds, regardless of whether they are within our range of hearing or not. High noise exposure can be hazardous to hearing, and musicians are often susceptible to hearing loss due to prolonged exposure to loud sounds.

In cartoons depicting a screaming person or an animal making a loud noise, the cartoonist often shows an open mouth with a vibrating uvula, suggesting a loud sound coming from the throat. We are all familiar with the loudness of sounds and recognize that they are related to how energetically the source is vibrating.

The decibel scale provides a way to measure and compare the intensity of different sounds. Table 17.2 gives levels in decibels and intensities in watts per meter squared for some familiar sounds, including the threshold of hearing at 0 decibels. By understanding the physics behind sound intensity, we can better appreciate the world around us and the incredible range of sounds that we experience every day.

The decibel scale mastering physics