Sound Level Converter
Convert Pascals (Pa) for sound pressure, Decibels SPL (dB SPL), Bels SPL, and Nepers (Np).
Result
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Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (Pascal).
Unit Information
What are Decibels SPL (dB SPL)?
Decibels Sound Pressure Level (dB SPL) is a logarithmic unit used to express the ratio of a sound pressure to a reference sound pressure. The standard reference pressure in air is 20 micropascals (µPa), which is considered the approximate threshold of human hearing. The dB SPL scale effectively compresses the vast range of sound pressures humans can perceive into a more manageable range of numbers.
What are Pascals (Sound Pressure)?
Pascal (Pa) is the SI unit of pressure. When measuring sound, it refers to the root mean square (RMS) of the sound pressure deviations from the ambient atmospheric pressure caused by a sound wave. While Pascals provide a direct physical measure of pressure, the range is enormous (from 20 µPa for hearing threshold to over 20 Pa for very loud sounds), which is why logarithmic scales like dB SPL are preferred.
What are Bels (B SPL)?
A Bel is a logarithmic unit named after Alexander Graham Bell. It represents a ratio of power, where 1 Bel is a tenfold increase in power. In terms of sound pressure level, 1 Bel equals 10 decibels. It is a larger, less commonly used unit than the decibel.
What are Nepers (Np)?
The Neper is a logarithmic unit used to express ratios, similar to the decibel, but it uses the natural logarithm instead of the base-10 logarithm. For pressure fields, 1 Neper is equivalent to approximately 8.686 dB. It is more common in theoretical physics and some telecommunications fields.
Formulas
dB SPL = 20 × log₁₀(P / P₀)
P is sound pressure, P₀ is reference pressure (20 µPa).
P = P₀ × 10^(dB SPL / 20)
Calculates sound pressure from a dB SPL value.
Bels = dB / 10
One Bel is equal to ten Decibels.
Nepers (Pressure) = ln(P / P₀)
Calculates sound pressure level in Nepers using the natural logarithm.
Key Reference Points
- Threshold of human hearing: ~0 dB SPL (20 µPa).
- Quiet library: ~30-40 dB SPL.
- Normal conversation (at 1m): ~60-70 dB SPL.
- City traffic: ~80-90 dB SPL.
- Rock concert / Jet engine (at 100m): ~110-130 dB SPL (risk of hearing damage).
- Threshold of pain: ~130-140 dB SPL.
- A quiet room might have a sound pressure of 0.0002 Pa (40 dB SPL).
- A loud shout at close range might be 1 Pa (94 dB SPL).
- Instant eardrum rupture: ~165 dB SPL.
- Loudest possible sound in Earth's atmosphere: ~194 dB SPL.
Did You Know?
The human ear perceives loudness logarithmically. A sound that is physically ten times more intense (10 times the power) is perceived as roughly twice as loud. A 3 dB increase represents a doubling of sound power, while a 10 dB increase is generally perceived as a doubling of loudness.
The reference pressure for dB SPL (20 µPa) is for sound in air. For sound in water, a different reference pressure (1 µPa) is typically used, so dB levels are not directly comparable without context.
While less common in acoustics, the Neper (Np) is sometimes used in telecommunications and electronics to express ratios of amplitudes or power, particularly when dealing with transmission lines and filters.
In a free field, the sound pressure level decreases by 6 dB for every doubling of distance from the source. This is a crucial principle in audio engineering and environmental noise control.
The 1883 eruption of the volcano Krakatoa is considered the loudest sound in recorded history. It was estimated to be around 172-180 dB SPL even 100 miles (160 km) away, and was reportedly heard thousands of miles away.
Anechoic chambers are rooms designed to completely absorb reflections of sound. The quietest one in the world has a background noise level of about -20 dB SPL, which is so low that you can hear your own heartbeat and other bodily sounds.
The Doppler effect causes a change in the perceived frequency of a sound wave when the source and observer are moving relative to each other. This is why a siren sounds higher in pitch as it approaches and lower as it moves away.
Sounds with frequencies below human hearing (< 20 Hz) are called infrasound, and those above (> 20 kHz) are ultrasound. Elephants and whales use infrasound for long-distance communication, while bats and dolphins use ultrasound for echolocation.
Sound travels much slower than light. This is why you see lightning before you hear the thunder. The speed of sound in air is approximately 343 meters per second, while light travels at about 300 million meters per second.
The phon is a unit of perceived loudness level for pure tones. By definition, the number of phons of a sound is the dB SPL of a 1 kHz tone that sounds equally loud.
This is a key acoustic parameter for rooms. It's the time required for the sound pressure level to fall by 60 dB after the sound source has stopped. It determines how 'live' or 'dead' a room sounds.
The Bel, and by extension the decibel, was named in honor of Alexander Graham Bell, an inventor and scientist credited with patenting the first practical telephone.
Prolonged exposure to sound levels above 85 dB SPL can cause permanent hearing damage. Shorter exposure to much louder sounds (e.g., 120 dB SPL) can cause immediate harm.
Materials are rated with a sound absorption coefficient, which ranges from 0 (perfectly reflective) to 1 (perfectly absorptive). Soft, porous materials like acoustic foam have high coefficients and are used to control echoes.
Sound travels much faster through solids than through air. For example, the speed of sound in steel is over 5,000 meters per second. This is why you can hear a distant train by putting your ear to the rail long before you can hear it through the air.
When two sound waves of slightly different frequencies are played together, they interfere to create a periodic variation in loudness called 'beats'. The beat frequency is equal to the difference between the two original frequencies.
A microphone's sensitivity is often specified in decibels relative to 1 Volt per Pascal (dBV/Pa). This indicates how much electrical voltage the microphone produces for a given sound pressure.
A whisper from a few feet away is only about 20-30 dB SPL. Because the decibel scale is logarithmic, this is thousands of times less intense in terms of power than a normal conversation at 60-70 dB SPL.