Fire Alarm Audibility & Line Loss

Preliminary screening aid only. This tool applies the standard NFPA 72 Chapter 18 audibility targets (public/private/sleeping-area mode) using the inverse-square-law distance attenuation model and a representative wall-loss allowance, plus the standard end-of-line audio circuit voltage-loss method converted to dB. It does not include a manufacturer device database — enter each device's rated dBA at 10 ft from the actual datasheet. Final audibility and line-loss calculations must be documented and submitted per the AHJ's requirements and reviewed by a qualified fire alarm professional, ideally confirmed by field survey/commissioning measurement.

Mode & Ambient SoundTag, notification mode, measured ambient levels

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Space / circuit tag Notification mode Sleeping area (apply 75 dBA at pillow rule)

Average ambient sound (dBA) Maximum ambient sound, ≥60s (dBA)

Device & DistanceRated output, distance and obstructions to the listener

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Device rated output at 10 ft (dBA)

Distance to farthest listener (ft) Walls/partitions crossed

Audio Circuit Line Loss (optional)Constant-voltage speaker circuit (25V/70.7V)

Amplifier line voltage

Total connected speaker taps (W) Wire gauge (AWG, copper)

One-way run length (ft) Target maximum loss (dB)

Result — Audibility Check

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dBA at listener

Required minimum

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Margin

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Distance attenuation

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Wall/partition loss

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Max sound pressure limit

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Governing criterion

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Include Calculation Ledger in report Include OhmZone brand mark in report

Report template (.docx, optional)

Calculation Ledger

clause-by-clause