Decibel Reference Scale: Understanding the Basics

The decibel (dB) is a widely used unit of measurement for sound intensity, but it's often misunderstood. In this article, we'll delve into the basics of the decibel reference scale and explore its applications in science and medicine.

A Graphical Representation of Loudness Contours

Here's a graph depicting the loudness contour for different dB HL (red is the current standard, while blue was the previous standard). The normalization of tones used for hearing tests is set by ISO 226:2003 standard converting dB SPL to 0 dB HL. A 10 dB change represents sound energy that is increased/decreased by a factor of 10. Specifically, 3 dB intervals were chosen as it represents a doubling or halving of sound energy.

Reference Tones and Sound Pressure Levels

Check out the following set of reference tones that vary based on different sound pressure levels, not hearing levels. This means that a given dB change which reflects different sound pressure levels in a strictly mathematical fashion does not necessarily equal the perceived loudness heard by a person. To compensate for this discrepancy, an adjustment has been made to all tested frequencies so we have a nice straight line at 0 dB HL rather than a curvy one.

The Decibel as a Ratio

The decibel (dB) is a ratio of two power values. It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 10^1/10 (approximately 1.26) or root-power ratio of 10^120 (approximately 1.12). In other words, a 3 dB increase in sound pressure level represents a doubling of the sound energy.

0 dB SPL: The Complete Absence of Sound

0 dB SPL is when there is absolute complete absence of sound, obviously. On the other hand, 0 dB on a hearing test is not the same as 0 dB SPL. This is because the human threshold to actually hear a sound is different depending on the frequency.

The Difference Between Scientific and Medical Decibel Scales

Scientifically, decibels are measured in sound pressure levels or dB SPL. In medicine, however, decibels are used to measure hearing levels (dB HL). This distinction is crucial when interpreting and applying decibel measurements in different contexts.

In conclusion, the decibel reference scale may seem complex at first, but understanding its underlying principles can help you better comprehend the nuances of sound measurement in various fields. Whether in science or medicine, a solid grasp of the decibel scale is essential for accurate interpretation and application of results.

Decibel reference scale