All labsAn interactive reference and calculation tool for Public Address and Voice Alarm (PAVA) systems on building services projects, covering fundamentals, architecture, speaker selection, line and amplifier design, standby power, standards, cabling, and commissioning. Companion to the CCTV/Access Control and Fire Alarm training tools.
Public Address (PA) and Voice Alarm (VA) are related but distinct functions that are very commonly delivered together on one piece of infrastructure, referred to as a combined PAVA system. Understanding the difference matters because the life-safety half of the system (VA) is subject to a much stricter design, approval and testing regime than the non-life-safety half (PA).
The general-purpose, non-life-safety function: background music, ambient audio in retail or lobby spaces, and routine paging or announcements (flight calls, staff pages, retail promotions). Loss of PA function is inconvenient but not dangerous.
The life-safety function: clear, intelligible spoken evacuation instructions broadcast automatically on receipt of a fire signal, or manually by trained staff through a dedicated microphone. VA equipment, cabling and power supplies must meet life-safety standards (see Section 7) because occupant safety depends on the message being heard and understood.
One physical system that performs both roles on shared amplifiers and speakers, with the VA/life-safety function always taking priority. On a fire signal, any background music or paging in progress is automatically interrupted and the emergency voice message or live fire officer's announcement takes over the loudspeaker circuits, regardless of what the PA side was doing at the time.
PAVA zones are normally aligned with the fire alarm system's detection zones (see Section 6). When a fire condition is confirmed in a given detection zone, the cause and effect matrix for the building typically drives two different message types:
The head-end of the system: houses the voice alarm control and indicating equipment, message store/digital message generator, tone generators, monitoring electronics and the power amplifiers. Continuously self-monitors for faults (open circuit, short circuit, amplifier failure) and reports status to the fire alarm control panel (FACP) and a local indicator panel.
Route the correct audio source (evacuation message, alert tone, background music, live microphone) to the correct set of speaker zones, based on which detection zone(s) triggered and the programmed cause and effect logic.
Include the dedicated fire officer's microphone (sometimes called an emergency microphone), normally located at the fire command centre / main reception, which can override any zone at any time with a live announcement, taking absolute priority over automatic messages and background music.
Drive the constant-voltage (70V or 100V) speaker lines. Normally configured with standby/redundant amplifiers so that a single amplifier failure does not silence a zone; sized with spare capacity as covered in Section 5.
The wired loudspeaker lines feeding each zone, each supervised for open circuit and short circuit faults (see Section 9), normally fitted with an end-of-line device so the monitoring electronics can distinguish a healthy line from a faulted one.
A dedicated life-safety standby power supply that keeps the VA function operating through a mains power failure, sized to cover a quiescent standby period followed by a full alarm period (see Section 8).
Click any box in the diagram to see its role in the signal path from fire detection through to the speaker in the room.
Click any box in the diagram to see its role, typical connections and key notes.
Recessed or surface-mounted round speaker fitted into a suspended ceiling. The most common type for offices, corridors, hotel rooms and general indoor areas with a regular ceiling grid, giving even downward coverage over a moderate area.
A boxed speaker mounted on a wall or column, used where there is no accessible ceiling void, in spaces with high ceilings, or where a more directional/aesthetic unit is wanted, such as retail units, gyms, or feature areas.
A weatherproof, high-output horn-type unit designed to project sound over long distances or cut through high ambient noise. Used in plant rooms, car parks, loading bays, external areas and other high-noise or outdoor locations where a ceiling speaker could not achieve adequate intelligibility.
| Type | Typical SPL output | Coverage pattern | Typical application area |
|---|---|---|---|
| Ceiling speaker | Low to moderate (representative range approx. 85 to 95 dB at 1W/1m, model dependent) | Wide, even, downward-facing dispersion cone | Offices, corridors, hotel guest rooms, retail ceilings, general indoor areas |
| Wall-mount / cabinet speaker | Moderate (representative range approx. 88 to 98 dB at 1W/1m, model dependent) | Directional, forward-facing dispersion | Areas without ceiling access, high ceilings, retail units, gyms, feature spaces |
| Horn / projector speaker | High (representative range approx. 100 to 115 dB at 1W/1m, model dependent) | Narrow, highly directional, long-throw | Plant rooms, car parks, loading bays, external areas, high-ambient-noise zones |
Constant-voltage distribution (70V or 100V line) lets many speakers, each fitted with a small step-down tap transformer, share one long cable run without a heavy current draw at low impedance. This calculator totals the connected tap wattage against an amplifier zone's rated capacity, then estimates cable voltage drop and power loss over the run.
Amplifiers should never be sized to their exact connected load. A spare capacity margin (commonly around 20%, verify against project specification) covers speaker tap tolerances, cable ageing, future additions and general headroom so the amplifier is not run permanently at its limit.
PAVA speaker zones are normally mapped one-to-one, or several-to-one, against the fire alarm system's detection zones, so that when a specific detection zone goes into fire condition, the control system knows exactly which speaker circuits should receive which message.
Full simultaneous evacuation: every zone in the building receives the evacuate message at once. Simpler to design and commission, but on a tall or high-occupancy building can overload stairwells and exits with everyone leaving at the same time.
Phased / staged evacuation: the fire zone and the zones considered at immediate risk (commonly the floor above and the floor below the fire floor) evacuate first, while the remaining zones receive an alert tone/message and are evacuated in a controlled sequence afterward if required. This is a widely used strategy on taller buildings, but the exact phasing logic is always project and code specific.
This is a simplified, illustrative example of phased evacuation logic (fire floor plus floor above and floor below evacuate, all other floors receive an alert tone). A real cause and effect matrix must be defined and approved for the specific building.
| Floor / Zone | Detection status | PAVA message |
|---|
Voice alarm systems are life-safety equipment and are governed by recognized product and installation standards. The table below lists the key standards commonly referenced on PAVA projects.
| Standard | Scope | Typical region / notes |
|---|---|---|
| EN 54-16 | Voice alarm control and indicating equipment (the VA control panel/amplifier rack itself) | European fire product standard (part of the EN 54 fire detection and fire alarm systems family) |
| EN 54-24 | Components of voice alarm systems, loudspeakers | European fire product standard, complements EN 54-16 |
| NFPA 72 | National Fire Alarm and Signaling Code, includes requirements for emergency voice/alarm communication systems (EVACS) and mass notification systems | United States |
| BS 5839-8 | Code of practice for the design, installation, commissioning and maintenance of voice alarm systems | United Kingdom |
Like other life-safety systems, PAVA standby batteries are commonly sized to sustain a quiescent standby (monitoring) period, followed by a full alarm period with all zones sounding. A commonly cited convention is 24 hours standby followed by 30 minutes of full alarm, but this must always be verified against the current project specification and applicable code edition, since local requirements vary.
Life-safety VA speaker circuits are normally required to be wired in a fire-resistant or fire-survival cable (commonly referred to in the industry by product families such as FP200 or equivalent enhanced fire-performance cable), so the circuit continues to function for a defined period even if it is exposed to fire, rather than failing at the first sign of heat. The specific cable type, fire rating and duration required must be confirmed against the project specification and applicable local code.
Circuit integrity is the broader concept that a life-safety circuit, its cable, containment, fixings and any joints, must keep working for long enough during a fire for its function to be useful (in this case, long enough to complete the evacuation message and process). This depends on more than just the cable itself: fixings, containment and cable routing away from likely fire-affected areas all contribute.
Every speaker circuit is electronically supervised, typically using an end-of-line (EOL) device at the far end of the circuit, so the control equipment can distinguish a healthy loop from an open circuit or short circuit fault. This means a single cable fault is detected and annunciated rather than silently disabling an entire zone without anyone knowing, which is a fundamental life-safety requirement of a voice alarm system.
Fire alarm and voice alarm cabling is normally required to be segregated from general power and data cabling, either by physical separation distance or by using separate, dedicated containment, to reduce the risk of electromagnetic interference and to reduce the chance that a fault or fire event on unrelated cabling also damages the life-safety circuit. Segregation requirements should be confirmed against the applicable wiring regulations and project specification.
Voice alarm messages are only useful if they can be understood, not just heard. The Common Intelligibility Scale (CIS) and Speech Transmission Index (STI) are standard measures of how intelligible a spoken message will be at a given location, accounting for reverberation, background noise and speaker coverage. A typical acceptable STI threshold is often quoted (commonly figures in the region of 0.5 are referenced as an acceptable minimum in general guidance), but the actual acceptance criteria are project and code specific and must be confirmed against the applicable standard and project specification before being used as a pass/fail threshold.
A common rule of thumb is that the voice alarm signal should achieve a sound pressure level a set margin above the ambient background noise at the listening position, often quoted informally as being at least a certain number of dB above ambient (a commonly referenced margin discussed in general guidance is in the region of 6 dB above ambient, or a defined minimum absolute SPL, whichever is greater). This is a rule of thumb only; the actual required SPL margin and any absolute minimum SPL must be verified against the applicable code and project specification for the space in question.
Answer all questions, then press "Check Answers" to see your score. You can reset and retry as many times as you like.
Learn the PAVA full form, system architecture, speaker circuits, amplifier sizing and battery checks through an interactive public address and voice alarm lab.
PAVA means Public Address and Voice Alarm. Twenty speakers tapped at 6 W total 120 W of connected load. Add the required design allowance and check amplifier duty, cable losses and emergency operation.
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