Such large measurement ranges are conveniently expressed in logarithmic scale: the base-10 logarithm of 1012 is 12, which is expressed as a sound pressure level of 120 dB re 20 μPa. Since the human ear is not equally sensitive to all sound frequencies, noise levels at maximum human sensitivity, somewhere between 2 and 4 kHz, are factored more heavily into some measurements using frequency weighting.
Sound pressure level (SPL) is a measure of the amplitude or intensity of sound waves, measured in decibels (dB). It is a logarithmic scale that compares the pressure of a sound wave to a reference pressure of 20 microPascals (μPa).
SPL is measured using a device called a sound level meter. The meter has a microphone that captures the sound waves and converts them into an electrical signal. This signal is then amplified and displayed in decibels on the meter.
The "re 20 μPa" in the example refers to the reference pressure of 20 microPascals. This is the standard reference pressure used for measuring SPL and is equivalent to the lowest sound level that the human ear can detect.
The sound pressure level can have a significant impact on human hearing. Prolonged exposure to high levels of SPL can lead to permanent hearing loss, while short-term exposure to loud sounds can cause temporary hearing loss or ringing in the ears (tinnitus).
Some common examples of sound pressure levels include 60 dB for normal conversation, 85 dB for heavy traffic, and 120 dB for a rock concert. Exposure to sound levels above 85 dB for extended periods of time can be harmful to human hearing, so it is important to protect your ears in loud environments.