The decibel (dB) is a logarithmic unit of measurement used to quantify various phenomena such as sound intensity, electrical signals, or power ratios. The decibel scale expresses relative differences, allowing for simpler comparison of large differences.
What does decibel mean?
The dB expresses the ratio between two values on a logarithmic scale, based on the following general formula:
dB = 10 × log10 (P2 / P1)
P2: the measured value
P1: reference value
In the case of sound intensity, the reference value is often the threshold of human hearing (0 dB), which is approximately 20 μPa (micropascals).
Characteristics of the decibel
- Logarithmic scale: The dB scale is logarithmic, meaning that a 10 dB increase signifies a 10-fold increase in sound intensity, while 20 dB means a 100-fold increase.
- Relative unit: The decibel provides relative values, not absolute quantities. For example, 0 dB does not mean there is no sound, but that the sound intensity is equal to the given reference value.
- Sensitivity to human hearing: The human ear's sensitivity is logarithmic, so the decibel scale accurately reflects how we perceive loudness.
Noise reduction and insulation:
The effectiveness of noise-reducing materials or technologies is expressed in decibels.
Examples of values on the decibel scale
| dB value | Intensity | Example |
| 0 dB | Hearing threshold | Perception of a movement of air. |
| Quiet | Whisper in a quiet room. | |
| 60 dB | Normal | Average conversation. |
| 90 dB | Loud | Lawnmower or city traffic. |
| 120 dB | Pain threshold | Concert or siren up close. |
Why is the dB scale logarithmic?
- Covers a wide range: The logarithmic scale allows extremely small and large intensities to be compared easily.
- Matches the nature of human hearing: The human ear perceives sounds non-linearly: doubling the loudness is not equivalent to doubling the physical intensity.
- Simplification: Uses smaller, more manageable values instead of large numbers, e.g., 60 dB instead of 1,000,000.
Important notes
- Reference values: The dB scale always refers to a reference value. For example:
- In acoustics: 0 dB is the human hearing threshold.
- In electronics: 0 dB is typically 1 milliwatt (dBm).
- Non-linear perception: Human perception is non-linear, so a 10 dB increase might be perceived as twice as loud, even though the physical intensity has increased tenfold.
Summary
The decibel (dB) is a universal, logarithmic unit of measurement widely used to quantify sound intensity, electrical signals, and other ratios. The dB scale simplifies the handling of values across a large range and accurately reflects the nature of human perception. Its knowledge and correct application are fundamental in acoustics, electronics, and other technical fields.