# Please explain what a negative sound level, such as -10 db, is.Objectives are to (1)demonstrate the properties that sound shares with other waves, (2)relate the physical properties of sound waves...

Please explain what a negative sound level, such as -10 db, is.

Objectives are to (1)demonstrate the properties that sound shares with other waves, (2)relate the physical properties of sound waves to our perception of sound, and (3)identify some applications of the Doppler effect.

valentin68 | Certified Educator

The decibel is by definition a dimensionless logarithmic quantity from a the intensity of sound reported to a standard reference intensity.

`dB =10*log(I/I_0)`

where `I_0 =10^-12 W/m^2`

The reference intensity is taken as the lowest sound intensity that in normal conditions is audible. Lower sound intensity levels than the reference intensity are usually inaudible.

The corresponding sound intensity for a -10 dB level is

`-10 =10*log(I/I_0)`

`-1 =log(I/I_0)`

`I =I_0*10^-1 =10^-12*10^-1 =10^-13 W/m^2`

Sound is just an oscillation of the air molecules and thus it is transmitted over large distances like a wave. The decibel scale was invented as a necessity to measure oscillations intensities spread over a very wide range (for example the highest audio sound intensity when all the air in one semi-plane of the oscillation is depleted, is about `10^20`  ` ` times the lowest audible sound). The human perception of sound (the ear) is working in a range of intensities of about `10^14` .