The dB Concept

The dB Concept CHAPTER OUTLINE dBdPower Ratio..................................................................................................................... 40 dBdAmplitude Ratio.............................................................................................................. 40 From dB to Power or Amplitude Ratio............................................................................ 41 Conversion Table ....................................................................................................................... 41 Reference Values ...................................................................................................................... 41 Other Relative Units ................................................................................................................43 Weighted Measurements ....................................................................................................... 44 Addition of dB ........................................................................................................................... 44

When sound levels have to be specified, it is practical to do so in a manner that

corresponds to the way in which the ear perceives them. Human hearing is

approximately logarithmic with respect to the perception of both level and

frequency. Logarithmic growth means that there is a constant proportion

between the individual steps on the scale. For example, if 1 W is first imparted

to a loudspeaker and then followed by 2 W, this will be experienced as a given

step in perceived level. In order to experience an equivalent change of level

again, not 3 W, but, rather, 4 W must be added e and 8 W for the next step.

Here, there is a ratio of 2 between the individual steps.