![]() Likewise our hearing does not have the same sensitivity at all frequencies. No microphone has the same sensitivity to all frequencies and no speaker reproduces all frequencies equally well, as we will see in Chapter 18 on electronics. A decibel level of 120 is nearly 1 million times greater in terms of sound. With every 6.02 dB, the sound pressure actually doubles or with a -6.02 dB, the sound pressure actually halves. This means that the intensity (amplitude) of a sound increases more quickly than the numbers along the decibel scale. Despite these challenges, the decibel scale is increasingly being used in sectors ranging from underwater navigation to virtual reality headsets and beyond. The decibel scale is a logarithmic scale. The above curves are very much like the frequency response curves of microphones and speakers. Accurately interpreting decibel readings is difficult due to environmental factors that affect measured values or confusion of relative values within different scales. Medium loudness doesn't change the perceived pitch very much. Low frequencies are perceived to be slightly lower than expected if they are very loud. High frequencies are perceived to be a slightly higher pitch than normal if they are very loud. Take the sound scale shown in pressure in Figure 1: Figure 1: Pressure scale of sound has a wide range of numbers ranging from many zeros after the decimal place to whole numbers. By using decibels, it can be easier to compare different values. It is also the case that intensity has an effect on perceived frequency the same laboratory frequency will appear to be a slightly different frequency if the intensity is different. The decibel is not a traditional unit of measure - it is a logarithmic ratio between two numbers. \( \newcommand\) is due to the tube resonance of the auditory canal (see chapter 12 for tube resonance and chapter 10 for a picture of the auditory canal).
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