When we convert pressure ratios to decibels. X 2 is just 2 log x, so this introduces a factor of 2 (Similarly,Įlectrical power in a resistor goes as the square of the voltage.) The log of In a sound wave, all else equal, goes as the square of the pressure. Respond proportionally to the sound pressure, p. Sound is usually measured with microphones and they ( Note also the factor 10 in theĭefinition, which puts the 'deci' in decibel: level difference in bels (named for Alexander Graham Bell) is just log (P 2/P 1).) So far we have not said what power either of the speakers radiates, But note that the decibel describes a ratio: In discussing sound: they can describe very big ratios using numbers This example shows a feature of decibel scales that is useful Times the power of the first, the difference in dB would be Had 10 times the power of the first, the difference in dB would be If the second produces twice as much power than the first,ġ0 log 2 = 3 dB (to a good approximation). Using the decibel unit, the difference in sound level, between the two is defined to Version of the same sound with power P 2, but everythingĮlse (how far away, frequency) kept the same. (If you have forgotten, go to What is aįor instance, suppose we have two loudspeakers, the first playingĪ sound with power P 1, and another playing a louder Butįirst, to get a taste for logarithmic expressions, let's look at some Phon and to the sone, which measures loudness. The ratio may be power, sound pressure, voltage or

The dB is a logarithmic way of describing a ratio. The decibel ( dB) is a logarithmic unit used to Problems using dB for amplifier gain, speaker power, hearing Loudness, phons and sones, hearing response curves.Reference levels ('absolute' sound level) This is a background page to the multimedia chapters Sound and Quantifying Sound. Response and to compare with standard hearing curves. Loudness, to phons and to sones? And how loud is loud? This page describes and compares DBV, dBm and dBi? What are they all? How are they related to

Negative decibel scale