ISO/TR 25417:2007

Overview

ISO/TR 25417:2007 - Acoustics: Definitions of basic quantities and terms is an ISO Technical Report that harmonizes acoustical terminology, symbols and units used in noise measurement documents prepared by ISO/TC 43 (Acoustics), Subcommittee SC 1 (Noise). It is an informative report (not a normative standard) that lists definitions for basic acoustical quantities used in noise measurement and reporting, with the principal aim of avoiding divergent definitions across ISO documents.

Key points:

• Focuses on terminology harmonization for noise measurement, sound pressure, sound pressure level, sound exposure, peak sound pressure, and related quantities.
• Applies to linear sound in isotropic fluidic media (unbounded liquids and gases without streaming); non-linearity, anisotropy, viscosity and flow effects are outside its primary scope.
• Definitions are essentially consistent with ISO 80000-8 and reference frequency/time weighting conventions in IEC 61672-1.

Key topics and technical content

ISO/TR 25417:2007 provides concise definitions, symbols and units for fundamental acoustical terms:

• Sound pressure (p) - difference between instantaneous total and static pressure; expressed in pascals (Pa).
• Sound pressure level (Lp) - defined in decibels (dB) relative to the reference sound pressure p0 = 20 µPa; includes guidance on indicating frequency and time weightings by subscripts (e.g., LA,F).
• Time‑averaged / equivalent continuous sound pressure level (Leq, Lp,eqT) - time averaging of p^2 over a stated interval T; useful for energy-equivalent noise metrics.
• Peak sound pressure and peak sound pressure level - greatest absolute instantaneous pressure and its level in dB, with notes on frequency-weighted peak measurements (e.g., LC,peak).
• Sound exposure (E) - integral of p^2 over an event or time interval; unit Pa^2·s and used for single-event exposure metrics.

Additional technical guidance:

• Practical measurement limitations mean p^2 is typically interpreted as frequency-weighted and band-limited; appropriate subscripts must be used to clarify weighting and band.
• The report clarifies notation conventions and the meaning of subscripts and time intervals used in noise measurement reporting.

Applications and practical use

ISO/TR 25417:2007 is useful for:

• Standard writers and technical committees developing noise measurement standards or test methods.
• Acoustical engineers, consultants and laboratories preparing measurements, reports or specifications where consistent terminology and symbols are required.
• Manufacturers of sound measurement instruments who document metrics (SPL, Leq, peak levels, exposure).
• Regulators, environmental agencies and researchers who interpret, compare or aggregate noise data from multiple sources.

Using the harmonized definitions improves clarity in reports, legal documents, instrumentation specifications and cross‑standard comparisons.

Related standards

• ISO 80000-8 (quantities and units - acoustics)
• IEC 61672-1 (sound level meters - frequency and time weighting conventions)

Keywords: ISO/TR 25417:2007, acoustics, noise measurement, sound pressure level, sound exposure, peak sound pressure, ISO TC 43, IEC 61672-1, ISO 80000-8.