Measurements · Noise
Sound Pressure Level (SPL)
Also known as decibel level, dB meter, sound level
Sound Pressure Level, the instantaneous weighted level (A/C/Z, fast/slow/impulse).
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What it is
What is sound pressure level (SPL)?
Sound pressure level is the most fundamental acoustic measurement: the sound pressure at the microphone at a given instant, expressed on the decibel scale relative to a reference pressure of 20 micropascals, the quietest sound a healthy young ear can detect. Because the scale is logarithmic, every 10 dB rise represents a tenfold increase in acoustic energy and is heard as roughly a doubling of loudness. SPL is almost always A-weighted (written dB(A)) so that it tracks how the ear responds across frequency. It is reported with a time weighting (Fast, Slow, or Impulse) that sets how quickly the level responds to change. It is the raw quantity from which Leq and every other noise metric are derived.
Because real noise fluctuates constantly, SPL is best read as a live indicator of the moment rather than a summary of exposure.
Band resolution: reported broadband plus 1/1 octave and 1/3 octave. The metric and its frequency band are independent. Check the sound-capable devices below for what each one reports.
Health and operational effects
Loud sound damages hearing, disturbs sleep, raises stress, and masks speech and warning signals, and SPL is the number people watch to see how loud a place is right now. On a worksite or in a venue it gives immediate feedback: it shows when a machine, tool, or crowd pushes levels up so that action can be taken before exposure accumulates. It is ideal for spot checks, for confirming that a control has worked, and for triggering a real-time alarm when a threshold is crossed.
What SPL does not do on its own is quantify a dose, because a single instantaneous level says nothing about how long it lasted. For that reason it is read alongside Leq, the energy-average level, which captures cumulative exposure over a period.
How it is measured
How Sound Pressure Level (SPL) Is Measured
SPL is measured by a microphone and a sound level meter built to the IEC 61672 standard, which defines Class 1 (precision) and Class 2 (general-purpose) instruments. The meter converts the fluctuating pressure into a decibel level, applies the chosen frequency weighting (usually A) and time weighting, and updates the reading many times a second. The Aethair family includes a built-in sound sensor that reports SPL and Leq directly, so continuous ambient noise comes from the same device that measures air quality. Where a precision or standard-compliant survey is required, an external IEC 61672 meter can instead be connected through Thiamis.
Built into Aethair PRO1
Measured by the monitor's own sensors, calibrated before it ships: nothing to add.
An instrument on Thiamis2
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing SPL sensors
For ambient indoor or area monitoring the Aethair's built-in microphone reports the level where the unit is mounted, so it is sited away from air vents, hard reflecting surfaces, and direct machine exhausts that would distort the reading. For an external microphone at a boundary or receptor, standard height and a windshield are essential, since wind across the diaphragm corrupts measurements. As with all noise measurement, the reading depends heavily on distance from the source and on nearby screening, so consistent positioning is what makes results comparable.
Every device and option that measures Sound Pressure Level (SPL) 3
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
Aethair PRO built-in sensors | Built-in sensors | Aethair PRO | Sound Pressure Level (SPL)Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1 |
 Cirrus Research · 151B, 152B, 151A… | Noise Monitors | Thiamis | |
 TSI · SP-SE-1, SP-SE-1-1/1, SP-SE-1-1/3… | Noise Monitors | Thiamis |
Where it is monitored
Solutions That Monitor Sound Pressure Level (SPL)
Each one links to the solution page showing what that industry measures it for.
Noise Monitoring
Core parameterSound pressure level is the fundamental decibel measurement underlying all noise assessment, the instantaneous level from which Leq and the other metrics are derived.
Article Library
Reading on Sound Pressure Level (SPL)
How to Choose an Air Quality Monitor: PRO, IAQ, or Thiamis
Compare Aethair PRO, IAQ, and Thiamis to match the right device to your site, from commercial interiors to industrial and fenceline monitoring.
Related
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Questions
Sound Pressure Level (SPL) FAQ
What is the difference between SPL and Leq?
SPL is the instantaneous sound level at a moment in time, while Leq is the equivalent continuous level averaged over a period. SPL tells you how loud it is right now; Leq tells you the total exposure and is the metric that noise limits are written against. The two are read together: SPL for live feedback, Leq for assessment.
What do Fast, Slow, and Impulse time weightings mean?
They set how quickly the meter responds to changing sound. Fast reacts in a fraction of a second and follows rapid fluctuations, Slow averages over about a second for a steadier reading, and Impulse responds very quickly but decays slowly to catch short bursts. The weighting must be stated because it changes the number.
Why are decibels logarithmic?
Because the range of sound pressures the ear handles is enormous, a logarithmic scale compresses it into manageable numbers. A consequence is that levels do not add arithmetically: two equal sources combine to about 3 dB more, not double, and a 10 dB rise is heard as roughly twice as loud.
How do I monitor sound pressure level?
The Aethair family reports SPL and Leq from its built-in sound sensor for continuous ambient monitoring with alarms. For a precision or standard-compliant survey, pair a Thiamis gateway with an external IEC 61672 sound level meter instead. Use the configurator to combine sound with dust and gases in a full site configuration.
Monitor Sound Pressure Level (SPL) on the Record
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