ISO 24504:2014

Overview

ISO 24504:2014 - Ergonomics / Accessible design provides standardized methods to determine appropriate sound pressure levels for spoken announcements used by products and public address systems. It focuses on audibility in environments where ambient noise (A-weighted) does not exceed 80 dB and explicitly includes consideration of age‑related hearing loss to improve accessibility. The standard applies when a loudspeaker is located a short distance from the user and covers both recorded voice and synthetic speech announcements.

Key topics and technical requirements

• Scope of application: Products and single‑speaker public address systems in indoor and outdoor public spaces (e.g., ticket machines, elevators, stations) where ambient noise ≤ 80 dB(A).
• Not applicable: Headphones/earphones, in‑ear loudspeakers, ATMs/private information devices, systems with automatic level control, emergency alarms, and automobile systems.
• Metrics and concepts:
  • Speech level (A-weighted or octave‑band) and signal‑to‑noise ratio (S/N).
  • Minimum speech level (audibility) and maximum speech level (comfort threshold for listeners).
  • Speech Transmission Index (STI) and simplified STI (octave‑band based; does not account for reverberation).
• Measurement methods: Annex A specifies procedures for measuring spoken announcement SPL and ambient noise (measurement positions, devices, acoustical conditions). Annex D details an STI‑based approach.
• Human factors: Annex B discusses the effect of age-related hearing loss on word recognition and required S/N improvements for older listeners.
• Focus: The standard addresses audibility (being heard) rather than speech understanding or message intelligibility in complex messages.

Practical applications

• Setting design targets for loudspeaker output level in consumer electronics, kiosks, vending machines, elevators and small public‑space PA installations.
• Defining measurement protocols for acoustical engineers and QA teams to verify spoken announcement loudness during product development and field installation.
• Informing accessibility and usability decisions to ensure announcements are audible to older users and the general public in typical ambient noise conditions.

Who should use this standard

• Product designers and manufacturers of consumer/communication devices
• Acoustical and audio engineers specifying or commissioning PA systems
• Accessibility specialists and human factors engineers
• Facilities managers for transport hubs, public buildings, and venues

Related standards

• ISO/IEC Guide 71 (accessible design principles)
• IEC 60268‑16 (STI / speech intelligibility)
• ISO 1996‑1, ISO 8253‑1, ISO 3382‑2 (acoustics measurement references)
• ISO 7240‑16 / ISO 7240‑19 (emergency alarms) and ISO 15006 (automotive announcements) - for applications excluded from ISO 24504

Keywords: ISO 24504:2014, sound pressure levels, spoken announcements, public address systems, ergonomics, accessible design, ambient noise, speech transmission index, A-weighted.