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Mandatory Verification of Audiometric Equipment

A hearing threshold is only meaningful if the audiometer that measured it is telling the truth. Verify the earphones against a reference ear, not just the electronics against a meter.

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Speech Intelligibility (STIPA) Measurement

An announcement that can't be understood isn't an announcement — it's noise. Measure whether the people in a room, a platform, or a stairwell can actually make out what's being said, with a single objective number.

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What Is Speech Intelligibility?

Speech intelligibility is how clearly a spoken message — a station announcement, a fire alarm evacuation instruction, a lecture — can actually be understood by a listener in a given room or sound system, rather than simply how loud it is. A system can be plenty loud and still be unintelligible if the words blur together.

Several factors degrade intelligibility even when overall loudness is adequate: excessive reverberation smears consonants and vowels into each other, background noise masks quieter parts of speech, an uneven frequency response distorts the voice, and a poor signal-to-noise ratio in the sound system itself adds its own degradation on top of the room's acoustics.

Because intelligibility depends on this whole chain — the room, the sound system, and the background noise together — it can't be judged reliably by ear alone, especially for high-stakes systems like a voice evacuation announcement that has to work during an actual emergency.


  • 4 



    Main factors that degrade intelligibility: reverberation, background noise, frequency response, and system signal-to-noise ratio

  • By Ear

    Subjective listening tests are inconsistent between listeners and can't be reliably repeated or compared over time


Objective, Quantitative Evaluation

             
       International Standard

IEC 60268-16:2020 — Sound system equipment – Part 16: Objective rating of speech intelligibility by speech transmission index — defines the test signal, the calculation method, and the measurement procedure that make speech intelligibility a standardized, comparable number rather than an opinion.

         
     STI-Based Automated Analysis

A professional test system sends a standardized test signal through the room or sound system, automatically captures how that signal degrades along the way, and outputs an objective, quantitative Speech Transmission Index (STI) result — no listening panel required.


What Is STI?

                                          Simply put, STI stands for Speech Transmission Index. It has a good consistency with Speech Intelligence and
                                          can reflect and predict actual speech intelligibility well.

  • Languageclarity



    Core Perception ObjectivesDecided to 'not hear clearly'
    1

  • Consonant
    Comprehensibility


    The degree to which consonants are correctly accepted and understood
    2

  • Fidelity of speech modulation envelope & Inquiry


    Voice signal integrityDetermine the recognition of consonants
    3

  • STI (Speech Transmission Index)



    STI = Weighted integral of MTF at key modulation frequencies
    4

  What Is STIPA?

Full STI measurement uses a comprehensive set of modulation frequencies and takes longer to run — appropriate for lab-grade characterization, but slower than most field commissioning work needs. STIPA (Speech Transmission Index for Public Address systems) is a streamlined version of the same underlying method, using a single modulated pink-noise test signal across the octave bands from 125 Hz to 8 kHz to approximate the acoustic character of a human voice.

STIPA trades some of full STI's resolution for speed — a measurement typically takes well under a minute per position — which is what makes it the practical standard for on-site testing of public address and voice evacuation systems, where dozens of measurement points across a facility need to be checked.
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The Role of Speech Intelligibility Measurement

An STI number isn't just a diagnostic curiosity — it drives real decisions across safety, education, communication and experience.
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Ensuring Public Safety
Clear emergency announcements are the lifeline for guiding crowds and avoiding panic in public places such as airports, train stations, and shopping malls.
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Improving the Quality of Education
In the classroom, ensuring that every row of students can clearly hear the teacher's explanation is the foundation for ensuring learning effectiveness and educational equity.
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Improving Communication Efficiency
In conference rooms and lecture halls, clear speech ensures accurate information transmission, reduces misunderstandings, and significantly improves team decision-making efficiency.
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Optimizing User Experience

Good language clarity is an important component of immersive atmosphere and high-quality audio-visual experience in entertainment venues such as cinemas and theaters.

                                                           
                               Typical Application Scenarios

Public Address & Voice Evacuation Systems

Airports, subway stations, stadiums and shopping centers — anywhere an emergency announcement has to be understood by a crowd under stress.

Conference Rooms & Auditoriums

Verifying speakers and remote-conferencing systems deliver clear speech to every seat, not just the front row.

Classrooms & Lecture Halls

Confirming a teacher or lecturer's voice remains intelligible at the back of the room, with or without amplification.

Transportation Hubs

Railway stations and airport terminals with high background noise and long, reverberant concourses that work against clarity.

Large Public Buildings

Shopping centers, arenas and mixed-use commercial buildings where a single sound system has to cover many acoustically different zones.

Emergency Broadcasting Systems

Fire alarm voice evacuation panels and mass notification systems, where regulatory acceptance testing is often mandatory before handover.

                              AWA4959 Speech Intelligibility Measurement
                              System — In Detail

AWA4959 Speech Intelligibility Measurement System

AWA4959 Speech Intelligibility Measurement System 

The AWA4959 is a professional system for objective speech intelligibility evaluation using the Speech Transmission Index (STI) and Speech Transmission Index for Public Address systems (STIPA) methods, complying with IEC 60268-16:2020. It provides accurate measurement of speech transmission performance across sound reinforcement systems, public address systems, conference rooms, auditoriums, transportation facilities and other acoustic environments.

The system integrates an intelligent sound source, a multifunctional sound level meter and an acoustic calibrator into one workflow — from signal generation and field measurement through to STI analysis and evaluation, with results displayed in real time and MTF analysis available across frequency bands to identify exactly what's degrading intelligibility.



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about us
T​​​​hree Decades Building the Reference Standards Themselves
Hangzhou Aihua Instruments has been designing and manufacturing acoustic and vibration measurement instruments since 1992 — including the calibrators recommended on this page. Our sound level meters and calibrators hold National Type Approval Certificates and are CE tested, and Aihua has drafted and co-drafted national standards for sound level meters, giving us a direct hand in the requirements these instruments are built to meet.

That combination — building both the measurement instruments and the calibration references behind them, under one roof — is what lets a sensor manufacturer source a production-line reference standard from the same company whose broader instrument line already meets the standards your customers expect.

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FAQ

  • 1

    What's the difference between STI and STIPA?

    STI is the full, comprehensive measurement method defined in IEC 60268-16. STIPA is a faster, simplified version of the same underlying method, using a single modulated test signal that's quick enough to check dozens of positions across a facility in one session — it's the practical standard for field commissioning of public address and voice evacuation systems.

  • 2

    What counts as a "good" STI score?

    Qualitatively, higher is better on the 0–1 scale, but the specific acceptance threshold that applies to your system is set by the relevant life-safety code, design specification, or client requirement — not by the measurement instrument. Confirm the applicable minimum before comparing a result against it.

  • 3

    How many measurement points does a survey actually need?

    At least one point per roughly 50 m² of listening area, with a minimum of three points for any single space — larger or acoustically varied areas need proportionally more to fairly represent what different listeners actually experience.

  • 4

    Does background noise affect the result?

    Yes — background noise is one of the core factors STI accounts for, which is why the measurement procedure specifies a minimum background signal-to-noise ratio (≥12 dB) for a valid reading. A space that's unusually noisy at the time of test can pull the result down independent of the sound system's own quality.

  • 5

    Can this be used in a room with no installed PA system, like a classroom?

    Yes — in spaces without a sound system, the test signal is reproduced by an appropriate loudspeaker positioned and leveled to represent a typical talker, rather than being injected electronically into a mixing console. The measurement and analysis workflow is otherwise the same.

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