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Eighteen articles on voice alarm systems, all by Nigel Williams, in five topics: a seven-part series on sizing Public Address Voice Alarm (PAVA) standby batteries to BS 5839-8:2023, three pieces on system design, a reference page on intelligibility figures, a series on what a Speech Transmission Index (STI) figure means, the first two of a series on emergency communication in venues, and three guides and a checklist for maintenance. Technical guides, testing advice and honest analysis, written for the people who maintain and manage these systems. No gate, no form, no follow-up call.
Looking for one piece? All papers lists every article, guide and tool on one page, with dates.
Latest
STI measures the channel, not the conversation
What a Speech Transmission Index figure tells a fire alarm technician, and the four things it never hears.
Annual voice alarm service: what you should see done
A read-do checklist for building owners, 21 items over three pause points, from booking the visit to signing for it.
The noise measurement that shrinks a PAVA quotation
One background noise figure sets every tap, the amplifier and the alarm battery load; measure it instead of assuming it.
By question
- Is my voice alarm battery quote too high? Part 2, then part 5, then the battery calculator.
- How do you size standby batteries for a voice alarm? Part 1, part 3 and part 4.
- What should an emergency announcement say? The venue article: five elements, an order, a reading age, a repetition rule and a speech rate.
- Why do PA systems use 100 V line? 100 V line explained, with both worked examples.
- Where are the clause references? In each article's "Where this comes from" table, and under Standards, in our own words.
Standby batteries
Battery series: sizing standby batteries to BS 5839-8:2023
Seven parts, best read in order.
Your next voice alarm battery quote should be smaller than your last
What the 2023 edition changed, and three questions to ask before you sign.
The worked example that doesn't work
The arithmetic error in BS 5839-8:2023 Annex C, traced term by term.
What battery manufacturers should publish, but do not
The 30-minute discharge figure the calculation needs, and who publishes it.
Peukert's law oversizes your voice alarm batteries
The number hidden in the usual equation, and the line at 20 Ah.
A 1200 W voice alarm's battery is sized by its quietest 24 hours
Tripling the amplifier power moved the answer less than doubling the standby current.
Voice alarm panels can cry wolf and still miss real faults
False faults, missed faults, and what to ask whoever maintains your voice alarm.
Still to come: the 1.25 ageing margin, and the data nobody publishes to support it.
System design
What is PAVA?
One sound system doing two jobs: everyday announcements, and emergency voice messages that override everything else.
100 V line explained: why the amplifier's power ends up in the loudspeaker, not the cable
Why 100 V line exists, worked through 20 m of Cat 5e: 40 % of the amplifier's power lost in the cable, or 0.4 % on 100 V line.
Testing and fault-finding
Six assessment points, no misses allowed: the voice alarm intelligibility figures, correctly stated
What BS 5839-8:2023 recommends for speech intelligibility, how it is measured, and when a listening test is enough.
STI series: what a Speech Transmission Index figure means
Three parts, best read in order.
Emergency messaging
Emergency communication in venues
Written for the people responsible for a venue rather than the people who install its systems.
Attention please: the two worst words to start an emergency announcement
The words that open almost every UK emergency announcement came bottom of eight in the study that ranked them.
Fire follows physics. An attacker reads your procedure.
Message libraries are built for fire, which never reads the plan. Why the emergency microphone is a venue's primary control, and who keeps it ready.
Still to come: the certificate measures the half of the chain with no person in it.
Maintenance
Two services and 52 tests: what a year of voice alarm maintenance should contain
What each six-monthly and annual visit should include under BS 5839-8:2023, and who does the weekly test.
Changing voice alarm maintainer? The drawings were never theirs to hand over
What the new firm should check first, and which documents the outgoing firm actually owes you.
Twenty-one loudspeakers or one zone: when voice alarm work stops being a repair
Where BS 5839-8:2023 draws the line between repair and modification, and who signs the certificate.
In preparation
Five pieces, being written or brought up to date from their 2024 masters. Titles only.
- Testing and fault-finding How to test a PAVA loudspeaker circuit: seven checks for fire techs
- Testing and fault-finding Fault-finding loudspeaker circuits with the Zircle impedance meter
- Testing and fault-finding Three voice alarm tests every stadium should run
- System design More loudspeakers won't fix the room
- System design The No B.S. Guide to Speech Transmission Index (STI PA) for Fire Techs: a reference guide to the measurement method, for when a specification asks for it.
Four guides first published in 2024 are among these; until each returns, its old address brings you here. The calculators the articles refer to are under Tools.