Electroacoustic Calculation for a Voice Evacuation PA System — Online

An electroacoustic calculation shows where — and with how much margin — a voice evacuation and public address (PA) system overcomes background noise and keeps speech intelligible. The VPA online calculator computes point-by-point SPL, STI, and the percentage of the area that meets the code, overlays a heat map on your floor plan, and generates a personalized calculation report for project documentation.

What an electroacoustic calculation is

An electroacoustic calculation verifies that the sound field of a voice evacuation and PA system delivers the required loudness and preserves speech intelligibility throughout the protected zone. The calculation answers four questions:

• what the sound pressure level (SPL) will be at each point;
• by how much it exceeds the ambient noise indoors or outdoors;
• how intelligible the speech is — the STI index per IEC 60268-16;
• what percentage of the area meets the code.

In essence, it is a model: the loudspeaker layout, power, and directivity are mapped onto the geometry of the site, and the output is a map of loudness and intelligibility. A manual calculation based on averages is crude; an accurate picture comes from a point-by-point calculation, which is easiest to run in the VPA online calculator.

Point-by-point SPL and margin above noise

SPL at a given point depends on loudspeaker sensitivity, applied power, distance, and attenuation. The requirement is defined not as an absolute figure but as a margin above noise: the alert signal must clearly overcome the background noise throughout the zone. For indoor spaces, the benchmark is a margin of roughly 15 dB above the design noise level, plus a sensible upper cap so that the sound directly beneath a loudspeaker is not painfully loud.

• adopt or measure the zone's design noise level — an office, a production floor, and a railway platform differ enormously;
• compute SPL on a grid of points, not just at a single central one;
• check uniformity: the spread between "right under the speaker" and "at the zone boundary" must not be excessive.

Choosing the type and number of loudspeakers to match a zone's ceiling height and noise level is covered in the article how to choose loudspeakers.

Speech intelligibility: STI per IEC 60268-16

Speech intelligibility is the whole point of voice announcements: being loud is not enough — the message must be understood. It is rated with the STI (Speech Transmission Index) per IEC 60268-16, on a scale from 0 to 1. Intelligibility depends not only on loudness but also on reverberation, echo, and reflections in the room.

• large reverberant halls "eat up" intelligibility even at high SPL;
• more directional loudspeakers and proper placement help;
• STI is computed at the same points as SPL and checked across the entire zone.

For a deep dive into STI, reverberation, and typical benchmarks, see the article speech intelligibility in voice announcements.

Code compliance: SP 3.13130.2026 and GOST R 42.3.01-2021

The final step is comparing the calculation against the code. For indoor spaces the reference is SP 3.13130.2026 (Russian fire-safety code for voice evacuation systems), for open outdoor areas it is GOST R 42.3.01-2021 (Russian civil alert system standard), while the intelligibility methods rely on IEC 60268-16. The calculation passes when the requirement is met not at a single point but across the required percentage of the zone's area.

• per point — pass/fail on both SPL and STI;
• per zone — the percentage of area meeting the code and a map of "blind" spots;
• evacuation routes and remote corners are checked separately.

The exact thresholds and the list of zones depend on the facility type; the specific requirements are set out in the statement of work — see how to write a statement of work for a PA/alert system.

Why project documentation needs this calculation

The electroacoustic calculation is part of the project documentation: it justifies the number, type, and placement of loudspeakers and the amplifier power, and it makes the design verifiable. Without it, an eyeballed layout easily ends up with zones where the message is inaudible or unintelligible.

Important: VPA supplies the equipment; the design and installation are performed by a licensed contractor. The calculator helps you quickly rough out the configuration and the scope of supply, but the final design, facility classification, and confirmation of code compliance remain with the design organization. The calculation materials are convenient to use as input data and hand over to your designer.

How the VPA calculator performs the full calculation

The VPA online calculator performs the entire calculation automatically, free of charge and with no sign-up:

• computes point-by-point SPL and STI (IEC 60268-16), and checks compliance with SP 3.13130.2026 and GOST R 42.3.01-2021;
• you upload a floor plan — the results are overlaid as a heat map of loudness and intelligibility;
• selects the number and placement of loudspeakers, the amplifier power (25% headroom), the cable cross-section (GOST 31565, Russian fire-safety cable standard), the UPS, and the batteries;
• generates a personalized calculation report with export to Word, Excel, PDF, and DXF (AutoCAD).

If you need a worked example or a sample calculation, don't hunt for a template — run your own calculation in the calculator: it will generate a personalized document for your facility.

Frequently asked questions

Build the electroacoustic calculation for your facility in the VPA online calculator: SPL, STI, code compliance checks, and a heat map on the floor plan — with export to Word, Excel, PDF, and DXF. VPA equipment is certified to EAEU (Eurasian Economic Union) requirements, comes with a 24-month warranty and a service life of 10+ years; we stock a warehouse in Moscow and deliver across all of Russia. Once you have your configuration, click "Request a Quote" and a manager will prepare a proposal for your organization.