What Are Decibels and How Are They Assessed?

Decibels act as the global standard for quantifying sound intensity, covering the broad spectrum of sounds detectable by the human ear. From the soft rustling of leaves to the deafening roar of a jet engine, this logarithmic scale offers a detailed method for interpreting sound levels.

Beyond acoustics, decibels are also utilized to gauge various forms of energy, including electrical power, enabling comparisons across multiple technical fields.

Grasping decibels goes beyond theory. Prolonged exposure to loud noises can cause irreversible hearing damage, making it crucial to understand safe decibel thresholds to protect your hearing.

What Are Decibels?

Decibels (dB) are the units used to quantify the relative loudness of a sound. The decibel measurement is unique because the human ear is remarkably sensitive.

The human ear can detect everything from the faintest touch of your fingertip on your skin to the deafening sound of a jet engine. In terms of power, the jet engine’s sound is roughly 1,000,000,000,000 times more intense than the quietest sound. Quite a contrast!

A linear scale wouldn’t be practical for representing the wide range of sounds the human ear can hear, which is why the decibel scale is logarithmic. Some describe a decibel as the "just noticeable difference" in sound intensity, especially for quieter noises, but for louder sounds, the difference in sound pressure may be as small as half a decibel.

Decibels: More Than Just Sound Intensity

In technical terms, A-weighted decibels (dBA) are used to measure the human perception of a wide range of sounds.

Other variations of the decibel scale exist, such as decibel-milliwatts (dBM) for measuring electrical power with a reference level of one milliwatt, and decibel-volts (dBV) for assessing output voltage levels. While they use different units, all these scales are calculated similarly by comparing two signals logarithmically.

Since A-weighted decibels are the standard in most practical uses, the term "decibel" generally refers to sound level in everyday contexts.

The Decibel Measurement Scale

The decibel scale starts with 0 dB, representing the faintest sound audible to the human ear, which is almost complete silence. Because the scale is logarithmic, a sound that is 10 times stronger than this threshold measures 10 dB, 100 times stronger is 20 dB, and 1,000 times more powerful registers as 30 dB.

Below are some common sounds from everyday life and their corresponding decibel levels:

From personal experience, you're likely aware that the distance between you and the sound source impacts how loud it seems. The sound levels provided here are all based on being in close proximity to the source.

A person with average hearing ability can detect sounds around 10 dB, while someone with moderate hearing impairment might struggle to hear anything below 50 dB.

Noise-Induced Hearing Loss

As reported by the Centers for Disease Control and Prevention, 17 percent of adults suffer from irreversible hearing damage caused by exposure to loud noises.

Any noise above 85 dB can lead to hearing damage, with the extent of the damage depending on both the sound's intensity and the duration of exposure. If you find yourself raising your voice to be heard, you're likely experiencing a sound at 85 dB.

Exposure to a 90-dB sound for 8 hours can cause harm to your hearing. Any noise reaching 140 dB will inflict immediate damage to your ears, even causing pain.

The National Institute for Occupational Safety and Health (NIOSH) recommends that workers should not be exposed to noise levels above 85 dB for more than 8 hours. With every 3 dB increase in volume, the recommended exposure time is cut in half. For example, workers should only endure 88 dB for up to 4 hours, and a 100-dB sound for just 15 minutes.

To protect your hearing from loud sounds, NIOSH advises wearing hearing protection (such as earplugs or earmuffs), even for brief exposure to noises exceeding 85 dB. Unsure of the noise level around you? NIOSH offers an app that transforms your phone into a sound level meter.