ISO 80000-8: Quantities and Units of Acoustics
ISO 80000-8 anchors the vocabulary of acoustics so that sound pressure, intensity, power and exposure measurements are comparable across laboratories, product declarations and community noise studies. Use this guide as a ready reference when you prepare compliance reports, validate simulation outputs or integrate data from mixed instrumentation chains.
Before collecting data, revisit the International System of Units overview and the ISO 80000-1 general principles article to confirm symbol conventions and reference values. When acoustic loading interacts with structural design or thermal comfort, pair this chapter with the mechanics guide and the thermodynamics deep dive so multidisciplinary teams keep their terminology aligned.
Many acoustic calculations share logarithmic structures with the ISO 80000-7 light and radiation definitions. Use that comparison to help students, automation scripts or AI assistants understand why decibel scaling appears across different wave phenomena and how to convert between linear and logarithmic expressions without ambiguity.
For a focused treatment of ratio levels, jump to the decibel guide, then review the radian and steradian explainers to align phase, beam coverage, and SPL notation before plotting polar maps or designing beamforming arrays.
When you need detailed walk-throughs of the level quantities defined in this part, consult the sound pressure level, sound power level, and sound intensity level explainers. Each page carries the ISO 80000-8 notation through measurement setups, uncertainty contributors, and application examples you can cite in reports.
What ISO 80000-8 covers
Sound fields
Defines the instantaneous acoustic quantities—pressure, particle velocity and specific acoustic impedance—that characterise how sound waves propagate through fluids and solids.
Level metrics
Standardises logarithmic sound pressure, intensity and power levels referenced to ISO base quantities so decibel statements remain comparable across reports.
Exposure accounting
Introduces sound energy density, sound exposure and sound exposure level to quantify cumulative acoustic dose for hearing conservation and compliance studies.
Application breadth
Supports architectural acoustics, machinery qualification, environmental noise mapping and audio engineering with a shared symbol set and SI-aligned reference values.
Fundamental acoustic field quantities
These instantaneous quantities describe the physical state of the medium as a sound wave propagates. Track them when validating simulations, calibrating impedance tubes or deriving intensity from pressure–velocity measurements.
| Quantity | Symbol | Coherent unit | ISO 80000-8 definition | Practical usage |
|---|---|---|---|---|
| Sound pressure | p | pascal (Pa) | Instantaneous deviation of static pressure caused by a passing sound wave. ISO 80000-8 treats it as a scalar quantity that can be positive or negative around ambient pressure. | Measure with microphones to characterise source strength, feed noise level calculations or convert to decibels relative to 20 µPa for human hearing contexts. |
| Particle velocity | v | metre per second (m/s) | Velocity of the infinitesimal particles of the medium induced by the acoustic wave. Together with sound pressure it describes the sound field at a point. | Use in impedance tube tests, active noise control algorithms or when deriving sound intensity from co-located pressure and velocity probes. |
| Sound intensity | I | watt per square metre (W/m²) | Average rate of acoustic energy flow per unit area in the direction of propagation, equal to the time-averaged product of sound pressure and particle velocity. | Determine the energy radiated by machinery or loudspeakers, inform product labelling and integrate across surfaces to derive sound power. |
| Sound power | P | watt (W) | Total acoustic energy emitted, reflected or transmitted per unit time by a source, independent of measurement distance. | Report source strength for regulatory submissions and compute declared sound power levels used in equipment directives. |
| Specific acoustic impedance | z | pascal second per metre (Pa·s/m) | Complex ratio of sound pressure to particle velocity at a point, characterising how the medium resists acoustic motion. | Match loudspeakers to enclosures, design absorptive materials and interpret reflection coefficients in architectural acoustics. |
| Characteristic acoustic impedance | Z₀ | pascal second per metre (Pa·s/m) | Magnitude of the medium's impedance for plane progressive waves, equal to density times speed of sound in the medium. | Calculate transmission at interfaces between air, water or structural materials and relate to ISO 80000-4 mechanical wave parameters. |
Logarithmic level quantities
ISO 80000-8 expresses many acoustic results as decibel levels so relative comparisons stay manageable over large dynamic ranges. Apply the correct reference values to avoid discrepancies between reports, automation scripts or AI-generated summaries.
| Quantity | Symbol | Level unit | Reference definition | Practical usage |
|---|---|---|---|---|
| Sound pressure level | L_p | decibel (dB) re 20 µPa | Ten times the logarithm to base 10 of the ratio of the mean-square sound pressure to the reference value of 20 µPa squared in air. | Express environmental or occupational noise limits, reference microphone measurements and bridge to A-weighted sound level metres. |
| Sound intensity level | L_I | decibel (dB) re 1 pW/m² | Ten times the logarithm to base 10 of the ratio of sound intensity to the reference intensity of 1 picowatt per square metre. | Compare directional measurements, evaluate near-field contributions and align with ISO sound power determination methods. |
| Sound power level | L_W | decibel (dB) re 1 pW | Ten times the logarithm to base 10 of the ratio of a source's sound power to the reference power of 1 picowatt. | Publish declared sound power levels in machinery datasheets, calculate environmental noise propagation and comply with EU product noise directives. |
| Particle velocity level | L_v | decibel (dB) re 50 nm/s | Twenty times the logarithm to base 10 of the ratio of particle velocity amplitude to the reference of 50 nanometres per second. | Analyse structure-borne sound, vibration control performance and link velocity criteria to ISO 10816 machinery vibration guidelines. |
| Specific acoustic impedance level | L_z | decibel (dB) re 400 Pa·s/m | Twenty times the logarithm to base 10 of the ratio of specific acoustic impedance magnitude to the reference of 400 pascal seconds per metre. | Characterise absorbers, ducts and mufflers when comparing impedance values measured with transfer-function methods. |
Energy and exposure metrics
Beyond instantaneous quantities, ISO 80000-8 establishes how to integrate sound fields over space or time. These metrics underpin environmental impact assessments, workplace hygiene studies and predictive modelling.
| Quantity | Symbol | Coherent unit | ISO 80000-8 definition | Practical usage |
|---|---|---|---|---|
| Sound energy density | w | joule per cubic metre (J/m³) | Instantaneous acoustic energy stored per unit volume, combining kinetic and potential contributions of the medium. | Model reverberant fields, estimate energy balance in enclosures and couple acoustics with ISO 80000-5 thermodynamic analyses. |
| Sound energy flux density | s | joule per square metre (J/m²) | Time integral of sound intensity over a surface, representing total acoustic energy crossing the area. | Evaluate impulse noise events, sonic boom signatures and total energy delivered to barriers or panels. |
| Sound exposure | H | pascal squared second (Pa²·s) | Time integral of mean-square sound pressure over a stated interval, independent of measurement distance. | Compute cumulative dose for hearing conservation, support ISO 1999 noise-induced hearing loss assessments and derive exposure level. |
| Sound exposure level | L_E | decibel (dB) re 400 µPa²·s | Ten times the logarithm to base 10 of the ratio of sound exposure to the reference exposure of 400 micro pascal squared seconds. | Compare intermittent noise events like aircraft flyovers, align with community noise metrics and convert to daily exposure limits. |
| Equivalent continuous sound level | L_{eq,T} | decibel (dB) re 20 µPa | A-weighted (or specified weighting) steady sound level that contains the same sound energy over interval T as the varying sound of interest. | Summarise environmental measurements, calculate day-evening-night levels (L_den) and support occupational compliance logs. |
Working with ISO 80000-8 in practice
Follow this workflow to keep measurements reproducible and traceable when collaborating across teams or using AI-powered analysis.
- 1
Establish the acoustic scenario
Determine whether you are analysing free-field propagation, reverberant rooms or structure-borne sound. ISO 80000-8 definitions ensure you select the right combination of pressure, intensity or impedance quantities before diving into calculations.
- 2
Capture fundamental measurements
Record instantaneous sound pressure, particle velocity or energy averages with calibrated sensors. Revisit the International System of Units overview to confirm microphone sensitivities, transfer functions and traceability.
- 3
Convert to level metrics
Apply ISO logarithmic level definitions to express results in decibels using the correct reference values. Cross-check conversions with calculators such as the decibel to power percentage tool and noise exposure planners.
- 4
Document cumulative exposure
For occupational or environmental studies, integrate mean-square pressure over time to obtain sound exposure and compare with jurisdictional limits using the noise exposure limit calculator.
- 5
Link to adjacent disciplines
When acoustic loads interact with mechanical structures or thermal comfort, consult the ISO 80000-4 mechanics and ISO 80000-5 thermodynamics guides so multidisciplinary teams share consistent terminology.
Acoustic calculators to try
Bridge the definitions in ISO 80000-8 to day-to-day problem solving with these interactive tools from across CalcSimpler.
- Noise exposure limit calculator — Estimate permissible exposure durations from measured sound levels using ISO-consistent decibel arithmetic.
- Decibel to power percentage converter — Translate level differences into linear power ratios when comparing machinery sound power declarations.
- Doppler effect frequency shift — Relate source motion to observed frequency changes while keeping reference to the ISO 80000-3 definition of sound speed.
Further reading inside CalcSimpler
Use these related articles to compare definitions, explore multidisciplinary problems or trace the evolution of key units.
- ISO 80000 overview — See how the acoustics chapter connects with the other 12 parts of the standard for cross-domain projects.
- ISO 80000-4 mechanics guide — Relate acoustic forces and vibrations to mechanical stress, damping and structural responses.
- ISO 80000-5 thermodynamics guide — Connect sound energy balances to thermal comfort, HVAC loads and energy efficiency studies.
- International System of Units spotlight — Refresh SI base units, reference constants and measurement traceability before calibrating acoustic instruments.
- ISO 80000-7 light and radiation guide — Compare how other wave phenomena use analogous level definitions when coordinating multidisciplinary measurement teams.