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Understanding Intelligibility

Tim Kuschel

Acoustic Consultant

GUZ BOX design + audio

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Introduction

“Design + compliance considerations of Sound Systems for Emergency Purposes”

Brief overview of legislationDiscussion on Intelligibility


Introduction : Presenter, Tim Kuschel• Architectural Projects Coordinator

• Acoustic Consultant specialising in architectural + electro-acoustic consulting

• Member, Australian Acoustical Society (AAS)

• Member, Audio Engineering Society (AES)

• Member, Acoustical Society of America (ASA)

• Beta tester for AFMG - EASE software + others


Legislation, Codes + Standards•The National Construction Code (NCC) now incorporates the Building Code of Australia

•This is the main design document for design of new building works•There is no requirement to provide any form of acoustic amenity, within any

classification of building, within the current BCA

Let’s consider a few spaces…


What happens in an emergency?

What is the requirement to provide intelligible speech?

What does the Building Code of Australia require?


BCA 2016: E4.9 Sound systems and intercom systems for emergency purposes

“A sound system and intercom system for emergency purposes complying where applicable with AS 1670.4 must be installed…”Refer BCA for building classifications

AS1670.4-2015: “Fire detection, warning, control and intercom systems—System design, installation and commissioningPart 4: Emergency warning and intercom systems”


Measurement of intelligibility: AS1670.4-2015


Intelligibility value

At all places within the evacuation zone where ambient SPL (noise) is less than 85 dB(A) and RT60 ≤ 1.5 s

CIS ≥ 0.7Or CIS ≥ 0.65 on standby power

Where SNR > 10dB and RT60 < 1.0 s No requirement to measure intelligibility

Where VAD and VWD are used No requirement to measure intelligibility

Where speech intelligibility requirements can’t be met Install VAD or VWD

Where RT60 > 1.5 s ???

Measurement of intelligibility: AS1670.4-2004 (superseded July 2015)


Intelligibility value

At all places within the zone where ambient noise figures are less than 85 dB(A)

STI ≥ 0.5 *Or CIS ≥ 0.65 (0.45 STI) on standby power

In areas having high ambient noise levels Visual + tactile warning devices

* measured in accordance with CIS method – refer AS60849


Source: AS60849-2004 Annex B

Design considerations not adequately covered by current standards:•Large outdoor facilities – Typically low RT60 + with high ambient noise levels

•Duress alarms/Situation awareness•Occupant in-place announcements

•Persons suffering from hard-of-hearing – some inclusions now in AS1670.4:2015•Use of EWS in conjunction with BGM/paging systems – hesitancy to adopt combined

systems, even though professional audio systems may offer significantly improved audio performance and speech clarity


Describing intelligibility

Intelligibility (or speech clarity) is the proportion of a presenters output that a listener can readily understand in their native language

Intelligibility is a measureable valueIntelligibility Scale, PB word scores, CIS, %ALCons, RaSTI, STI, STIPA...


Intelligibility: A brief history1970 - STI/STIPA was developed for testing military communications systems

1985 - It did not see regular use until B+K developed the RaSTI meter1988 - First STI standard for measuring intelligibility in auditoria (268-16)

1989/91 – RaSTI was enshrined in IEC7443, the standard for emergency sound systems and was adopted by other standards

From 1986, TEF and MLSSA systems could measure STI2001 - STIPA was developed to overcome problems with RaSTI (IEC60268-16)

2011 – The standard was further revised (Rev 4) to better define STIPA


STI is now most commonly used for assessment of audio systems – simple testing procedures, quick on site results

Our fellow consultants in EU + UK have moved away from CIS in favour of STI

Several manufacturers now provide measurement tools to directly assess STI


Problems with current methods of certification•Inadequate testing procedures

•Certifiers of new buildings not asking for appropriate test documentation•Lack of correlation between electrical consultants designs, acoustic consultants

requirements/specification + architectural realisations•Installer is required to show compliance with BCA + Standards – not designer

•AS1670.4-2015 provides poor guidance for modern system design + current trends


Risk, Liability + Exposure•Does the installed system provide for safe evacuation of building occupants?

•Is a D&C solution the best outcome for the client/project?•Who is responsible for outcome of installed systems?

•Self certification? •Non compliance?

•Audible compliance...


Intelligibility results may be influenced by many factors. Architecturally, a poor result within room areas may be attributed to:

• Architectural design with little acoustic control – highly reflective surface treatments• Anticipated reverberation times within room areas

• High background (ambient) noise levels when in use•Low ceilings + acoustically reflective floor surfaces

•Long corridors or tunnels


An installed audio system may also present a poor result due to:•Variable ceiling height with sound sources at differing heights – upper floor levels

• The number of installed loudspeakers located in a reverberant environment• Number of loudspeakers generally – additional loudspeakers increase the number of

arrival times at the listener, affecting intelligibility• Distance from loudspeaker/s to listener location

• Directional characteristics of loudspeakers• Overloaded or audible distortion in loudspeakers


•STI results cannot be improved by installing more speakers• STI results cannot be improved by simply turning up the volume. In fact, in some

cases, a louder signal in a reverberant environment can actually reduce intelligibility further!

• STI cannot be improved by changing the ‘tap’ settings


Measuring intelligibility

Older methods still valid: PB word lists, CIS, %ALCons, RaSTI...

Sound level meters with STI/STIPA measurement optionsPass/Fail reports

Certification of installed systems


STI measurements must include:•Several measurement locations within each area of coverage•Several measurements at each location•Average of all measurements within a room•Ambient noise compensation (in the absence of test signal), also at several measurement locations•Measurement for both pre-recorded + live amplified announcements


Measuring intelligibility

Designing for intelligibility


EASE: ‘Enhanced Acoustic Simulator for Engineers’•Detailed room modelling of acoustic spaces•Advanced simulation of audio system performance including SPL, STI and many other values – detailed mapping + presentations•Become aware of obstacles that would remain hidden without simulation.•Analyze and solve acoustical problems before they arise•Ray-Tracing calculations for advanced real-world simulations


More information available from http://ease.afmg.eu/

http://evac.afmg.eu/

Designing for intelligibility


EASE Evac: •Intuitive Room Design allowing for fast layout construction•Precise prediction of SPL + STI•Loudspeaker data for all leading brands•Extensive reports for calculation, presentation and installation


30-day free trial available from http://evac.afmg.eu/

http://evac.afmg.eu/


Image source: www.hln.be

Considerations for revision of future Standards•Duress alarms/Situation awareness•Occupant in-place announcements

•Dual-redundancy for larger installations•‘Designed’ EWS solutions showing compliance prior to construction

•Clearly defined and standardised methods for measurement of intelligibility•Recommended methods of installation/fixing of EWS components



Tim KuschelAcoustic ConsultantGUZ BOX design + audiowww.guzbox.com.au

understanding intelligibility - fpa australia€¦ · understanding intelligibility. understanding...

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