What Is Sound Pressure Level (SPL)?

Sound pressure level (SPL) is a measurement of the sound pressure of a sound relative to a reference value (https://pulsarinstruments.com/news/sound-pressure-level-and-spl-meters/). It is expressed on a decibel (dB) scale, which represents the ratio between a measured pressure level and a reference level. The reference sound pressure level used to compare other sound pressure levels against is 20 μPa (20 micropascals).

Decibels are used for sound measurements because they can capture the enormous range of sound intensities the human ear can detect, from the faintest whisper to a jet engine. The decibel scale is logarithmic, meaning that an increase of 10 dB corresponds to a tenfold increase in sound pressure. So 20 dB is 10 times more intense than 10 dB, and 30 dB is 100 times more intense. This allows the large range of audible sound pressures to be managed on a convenient scale (https://ec.europa.eu/health/opinions/en/hearing-loss-personal-music-player-mp3/l-3/2-sound-measurement-decibel.htm).

Measuring sound pressure levels serves several important purposes. It allows the loudness of different sound sources to be compared objectively. SPL measurements are used to monitor noise exposure and environmental noise pollution. They also help determine appropriate noise control measures and assess risks of hearing damage from excessive noise (https://svantek.com/academy/sound-pressure-level-spl/).

How Sound Pressure Level is Measured

Sound pressure level is measured in units called decibels (dB). Decibels provide a relative scale that compares the sound pressure to a reference pressure. The reference pressure for airborne sound is 20 micropascals, which is considered the threshold of human hearing. Any sound with a sound pressure less than 20 micropascals will not be audible to the human ear.

Sound level meters are used to measure sound pressure levels. These devices contain a microphone to detect the sound pressure and convert it into an electrical signal that can be analyzed. The signal is passed through filters and weighted scales to match the sensitivity of human hearing. The A-weighted scale is commonly used to measure environmental noise and mimic the human ear’s nonlinear sensitivity to different frequencies of sound.

The sound level meter processes the signal to calculate the decibel level. This value quantifies the sound pressure of the noise compared to the reference level. Typical conversational speech has a sound pressure level of 60 dB, while loud rock concerts can reach 120 dB. Knowing the decibel level helps assess the loudness of different sounds.

Decibel Scale

The decibel scale is used to measure the intensity or loudness of a sound. Decibels (dB) represent a logarithmic scale for sound intensity, with 0 dB corresponding to the threshold of human hearing and 120-140 dB corresponding to the threshold of pain (Source). The decibel scale is logarithmic, meaning that an increase of 10 dB corresponds to a 10-fold increase in sound intensity. For example, 20 dB is 10 times more intense than 10 dB, and 30 dB is 100 times more intense than 10 dB.

The specific formula for calculating sound intensity in decibels is:

dB = 10 x log10 (I/I0)

Where I is the sound intensity being measured and I0 is a reference intensity corresponding to the threshold of human hearing at 1000 Hz, which is defined as 0 dB. This reference pressure is equivalent to 20 micropascals. Using a logarithmic scale allows for a huge range of sound intensities to be represented in a manageable way, from the faintest audible sounds to noise levels that can cause immediate permanent hearing damage (Source).

On the decibel scale, common sounds range from 0 dB (near total silence) to over 120 dB (extremely loud rock concert). Sounds begin to become uncomfortable starting at around 85-90 dB and can cause immediate permanent hearing damage at around 130 dB (Source). The decibel scale allows us to quantify sound levels and assess potential hearing risks.

Sound Pressure Level Uses

Sound pressure level measurements have many important uses in various fields and industries. Some of the key uses and applications of SPL include:

Occupational Safety

Monitoring sound levels in work environments is critical for occupational safety and health.High noise exposure can lead to noise-induced hearing loss over time. Regulatory agencies like OSHA set legal limits on allowable noise exposure in the workplace. Companies must conduct noise assessments to identify hazardous noise levels in facilities and take precautions like hearing protection to prevent hearing damage.

Noise Ordinances

Cities and municipalities often have noise ordinances restricting noise pollution, especially at night. SPL measurements are used to enforce these ordinances. Police or inspectors may monitor and cite violations for noise above allowed decibel limits from construction, vehicles, parties, etc.

Product Testing

Manufacturers test and report sound levels for products like appliances, tools, vehicles, and electronics. This helps consumers compare noise levels and choose quieter options. It also verifies that sound emissions meet specifications and comply with regulations.

Environmental Assessments

SPL meters measure ambient noise levels in communities near potential noise pollution sources like airports, highways, and industrial sites. Environmental impact statements predict effects on residents. If noise thresholds are exceeded, mitigation like sound barriers may be required.

Safe Sound Levels

Prolonged exposure to loud noise above 70-80 decibels can cause gradual hearing loss over time. Recommended exposure limits have been established to help prevent noise-induced hearing loss.

The Occupational Safety and Health Administration (OSHA) has set legal limits on noise exposure in the workplace. The permissible exposure limit over an 8 hour day is 90 decibels. At this level, employers are required to make hearing protection available and conduct hearing tests (OSHA).

For every 3 decibel increase above 90 db, the permissible exposure time before possible damage is cut in half. So at 95 db, the limit is 4 hours, at 100 db it’s 2 hours, and so on. Exposure to sounds louder than 115 db is considered dangerous and requires immediate mitigation.

The National Institute for Occupational Safety and Health (NIOSH) recommends an even more conservative limit of 85 db over an 8 hour period to help prevent gradual hearing loss. Anything above this level poses a potential hazard (NIOSH).

Outside of work, noise from concerts, sporting events, nightclubs, personal audio devices, power tools, and other loud activities should be moderated. Brief, infrequent exposure is likely safe, but care should be taken to avoid chronic loud noise which can accumulate over time.

Common Sound Levels

The decibel scale is used to quantify sound levels for various noise sources. Here is a table showing examples of sound levels in decibels (dB) for common sounds:

Sound Source Sound Level (dB)
Whisper 30
Normal conversation 60-70
City traffic 80
Lawnmower 90
Motorcycle 95
Car horn 110
Jet takeoff 120
Gunshot blast 140-190

As the table shows, sound levels range greatly depending on the source. Quiet sounds like a whisper measure just 30 dB, while loud sounds like a gunshot can be as high as 190 dB. Comparing these decibel levels gives a sense of the wide spectrum of audible sound.

Knowing the sound level of common sources is useful for evaluating potential hearing damage risks. Sounds above 85 dB experienced over long periods can lead to permanent hearing loss. Loud impulsive sounds like gunshots at 140-190 dB can cause immediate damage. Being aware of these sound levels helps protect hearing.

Source: https://revisione-renault-twingo.futurespark.cfd/

Factors Affecting Perceived Loudness

Several factors play a role in determining how loud a sound is perceived to be by the human ear, including:

Frequency: Higher frequency sounds are perceived as louder than lower frequencies at the same sound intensity. This is because the ear is more sensitive to mid and high frequency sounds.

(Source: https://encyclopedia.arabpsychology.com/loudness/)

Distance: As the distance between the sound source and listener increases, the perceived loudness decreases. This is due to the dispersion of sound energy over a greater area.

Duration: Sounds that persist for longer durations tend to be perceived as louder than short, transitory sounds at the same intensity.

Masking: The presence of one sound can mask the perception of another sound. This occurs when two sounds overlap in frequency, so the louder sound dominates what is perceived.

(Source: https://allforturntables.com/2023/09/11/does-more-wattage-mean-louder-2/)

Sound Level Meters

Sound level meters, also known as decibel meters, are devices used to measure the sound pressure level or loudness of sound. They are commonly used in noise pollution studies, environmental assessments, workplace evaluations, and other applications where quantifying sound levels is necessary (Noise & Sound Level Meters).

Sound level meters work by using a microphone to convert sound waves into an electrical signal that can be analyzed to determine the sound pressure level. This signal is then processed through various filters and amplifiers inside the meter to produce a decibel reading on the display (Sound level meter).

There are several types of sound level meters available:

  • Handheld meters – Portable units with built-in microphones used for spot measurements.
  • Integrating meters – Measure average sound levels over a period of time.
  • Logging meters – Record sound measurements continuously over extended periods.
  • Noise dosimeters – Used to measure a person’s noise exposure over time.

Key features of sound level meters include the measurement range in decibels (dB), accuracy, frequency weighting filters, and response time settings. They may also offer data logging, audio recording, and octave or third-octave band frequency analysis (How decibel sound level meters work).

To ensure accuracy, sound level meters must be calibrated periodically using a sound calibrator that generates a known sound pressure level. Proper calibration at regular intervals helps maintain precision between measurements.

Noise Control and Reduction

There are several strategies and techniques available for controlling sound levels and mitigating noise in work environments. According to the Occupational Safety and Health Administration (Occupational Noise Exposure – Exposure & Controls), the most effective method of reducing noise exposure is through engineering controls, which aim to reduce sound levels at the noise source or transmission path. Examples of engineering controls include using vibration dampeners, noise barriers, or acoustic enclosures and soundproofing. Adjusting processes can also reduce noise, such as slowing machine speeds or altering methods and sequences.

Administrative controls can also help decrease noise exposure by limiting workers’ time near loud equipment and organizing schedules to rotate workers through noisy tasks (Occupational Noise Exposure – Overview). Proper maintenance of equipment and facilities is another administrative control. Lastly, providing appropriate hearing protection devices (HPDs) is critical but should not take the place of other controls. Careful selection of HPDs and training workers on proper use helps optimize protection (Three Basic Methods: Workplace Noise Control). Combining engineering, administrative, and personal protective equipment controls allows for an effective noise control program.


In summary, sound pressure level (SPL) is an important metric used to measure noise and its potential impact. The decibel scale allows us to quantify sound intensity and compare different sound sources. While loud noises can sometimes be unavoidable, monitoring and controlling sound levels is critical for hearing conservation and noise reduction.

Understanding safe SPLs and regulations can help us identify risky environments and mitigate harmful noise exposure. Exposure to excessive noise levels can lead to hearing damage over time, so being mindful of sound levels in our everyday environment is important. Techniques like engineering controls, administrative controls, and hearing protection can help reduce dangerous occupational and recreational noise when necessary.

Regular sound level monitoring, noise assessments, and audiometric testing are vital for protecting hearing health. Overall, keeping track of SPLs allows us to minimize noise pollution and its effects as we strive for more comfortable and safe acoustic environments.

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