Understanding Voice Intelligibility
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The document discusses new requirements for voice communication systems in buildings according to the 2010 National Building Code of Canada (NBC). It requires a voice communication system be installed in buildings over 1000 occupants that have a 2-stage fire alarm system. The system must use loudspeakers to broadcast prerecorded, synthesized, or live messages with a Common Intelligibility Scale (CIS) of at least 0.70, corresponding to 80% word and 95% sentence intelligibility. Factors like signal-to-noise ratio, distortion, and reverberation can impact intelligibility. Proper speaker layout and coverage is important for design. The document provides an overview of measuring and testing intelligibility.
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Understanding Voice Intelligibility
- 2. • New Code Requirements • What is Intelligibility? • Intelligibility Scale • Measuring Intelligibility • Factors that affect Intelligibility • System Design • Design Challenges • NFPA 72-2010 New Requirements • Summary
- 3. • New NBC Requirements • Voice Communication Design • Understand building and voice system parameters • Speaker layout and design guidelines • What is the cost of voice communication system? • Increase design/construction/testing time • Acoustic engineering • Acoustic modeling software (iTools, BOSE Modeler)
- 4. • Research has shown that: “People are more likely to follow intelligent voice commands rather than act on audible and visual alarm devices.” • Unintelligent voice messages can be ineffective and result in undesired results.
- 5. • 2010 National Building Code of Canada (NBC) includes new requirements relevant to voice communication systems. • These requirements have not yet been adopted by the Ontario Building Code (OBC)
- 6. 2010 NBC 3.2.4.22.Voice Communication Systems (7) Except for Group B, Division 1 and Group F, Division 1 major occupancies, where a fire alarm system is required under Subsection 3.2.4., a voice communication system shall be installed in buildings where a 2-stage fire alarm system is installed and whose occupant load exceeds 1000.
- 7. Buildings impacted by new NBC requirements ARENAS SHOPPING MALLS BANQUET HALLS
- 8. 2010 NBC 3.2.4.22.Voice Communication Systems 1(b) loudspeakers operated from the central alarm and control facility that are designed and located so as to be audible and the messages intelligible in all parts of the building, except that this requirement does not apply to elevator cars. 2) The voice communication system described in Clause (1) (b) shall be capable of broadcasting prerecorded, synthesized, or live messages with voice intelligibility meeting or exceeding the equivalent of a common intelligibility scale of 0.70. (See Appendix A)
- 9. • Definition of Intelligibility • As defined by NBC • “Concept of Intelligibility intended to mean that a person with average hearing and cognitive abilities is able to understand the message that are transmitted into the space occupied by the person.” • Intelligibility as compared to Audibility • Audibility = Loudness (SPL) • Intelligibility = Understanding (CIS)
- 10. • Subjective in Nature • ANSI S3.2, Methods for Measuring the Intelligibility Speech over Communication Systems • Modified Rhyme Test • Phonetically Balanced Word • Alcons (%Alcons) • Objective • IEC 60849, Sound Systems for Emergency Purposes • Articulation Index (AI) • Room Acoustic Speech Transmission Index (RASTI) • Speech Transmission Index (STI) • Common Intelligibility Scale (CIS)
- 11. What does CIS = 0.7 mean? Common Intelligibility Scale of 0.7 corresponds to 80% word intelligibility and 95% sentence intelligibility. STI = 0.5 CIS = 0.7
- 12. • STI-CIS Analyzer • Portable meter to measure intelligibility scale (15s/reading) • Intelligibility measurement in CIS scale • Includes built in sound pressure meter for sound pressure (dBA) readings • Optional RS-232 port for PC download • STI-PA Test Tone • Audio CD recording played on voice system • Exclusive tone recognized by STI-CIS Analyzer only
- 14. Source: Voice Signal Path, Bose Professional Systems
- 15. 1. Signal to Noise Ratio • Audibility • Quantity and Spacing of Speakers 2. Harmonic Distortion • Amplitude distortion • Frequency distortion • Wiring and Power 3. Signal Decay • Reverberation • Echoes
- 16. 1. Building Parameters • Occupancy (airport, auditorium, library) • Background noise (ambient noise) • Volume and shape of room (High ceiling) • Reverberance of room (construction materials, furniture) 2. Voice System Parameters • Signal Generation Equipment (amplifiers) • Speaker frequency range (recomm.150Hz to 11KHz) • Speaker characteristics (coverage angle)
- 17. 3. Speaker Layout • Recommended coverage pattern for speaker intelligibility is edge-to-edge (no overlap) EDGE-to-EDGE S S Speaker S 78 dBA 17.4 ft. Source: Voice Evacuation System Application Guide by System Sensor
- 18. • Large auditoriums, arenas • Transit facilities • Spaces with high ceilings (Atriums) • Spaces with hard surfaces (marble, glass) • High background noise
- 19. • Acoustically Distinguishable Spaces (ADS) • ADS is determined by the system designer during the planning and design phase • ADS Acceptability Criteria: 90% Pass Rate • Minimum of 0.45 STI (0.65 CIS) • Average of 0.50 STI (0.70 CIS) • Main goal of ADS is to avoid over-designing and testing systems to meet intelligibility requirements in challenging areas
- 20. • New Code Requirements • What is Intelligibility? • Intelligibility Scale • Measuring Intelligibility • Factors that affect Intelligibility • System Design • Design Challenges • NFPA 72-2010 New Requirements • Summary
Editor's Notes
- However, voice communication system installations are driven by the Code based on types of buildings (e.g., high-rise) and occupancy classifications (e.g., places of public assembly). The 2010 NBC includes new requirements for voice communication systems (Please note that these have not been adopted by the current 2006 OBC yet):The previous code was not specific as to the voice communication requirements which resulted in some buildings with very poor intelligiility and some with very good. Therefore, there was no consistency.
- The new Code also sets out voice intelligibility criteria to ensure that people can easily understand the message. The Code includes the minimum required CIS which now provides the acceptable the voice intelligibility. Before it was very subjective and hard to determine system intelligibility.
- Definition of intelligibilityAudibility is not the same as intelligibility, audibility means louder than ambient sound level Voice messages can be audible (loud) but not be understood. Therefore, Intelligibility is the ability to understand the voice message
- Voice intelligibility is not a physical measure like feet, volts or decibels. Intelligibility is a benchmark of the degree we understand the voice message. As such, we have two ways to measure intelligibility.1- subjective Phonetically balanced word 256 or 1,000 words to a panel of listenersAlcons –articulation loss of consonants (%)2- quantitative or objective
- It is a weighted average of the response to fluctuating modulation frequencies. The Common Intelligibility Scale (CIS) was created to map all quantitative intelligibility measurement methods to the same scale so that all different results can be compared
- Signal to noise ratioAudibility of the message (how loud) compared to the ambient sound levelQuantity and spacing of speakersHarmonic DistortionAmplitude distortion is due to non-linearity in electronic equipment and amplifiers (transducers)Frequency distortion is due to non-uniform frequency response of transducers and selective absorption of various frequencies in acoustic transmission (therefore quality of the message is important to mitigate distortion)Signal DecayReverberation and echoes are caused by reflections from acoustic environment
- Generation equipment such amplifiers must be consistent of same model/type to ensure uniformity Speaker coverage angle is the angle at which the sound pressure level from a speaker drops to 6dB below its on axis reading.Spkr frequency range is recommended 150Hz to 11KHz which is women and men voice range (human ear is 64Hz to 15KHz)
- 1W spkr produces 81dBA @ 10ftCoverage angle is 120degrees where sound level drops by 6dBA
- ADS: “an emergency communication system notification zone, or subdivision thereof, that might be an enclosed or otherwise physically defined space, or that might be distinguished from other spaces due to acoustical, environmental, or use characteristics, such as reverberation time and ambient sound pressure level”