Speaker Tap & dB Chart

How fire alarm voice-evacuation speaker taps set the sound level, with the two rules that get you from a tap setting to coverage: about 3 dB gained per doubling of tap power, and about 6 dB lost per doubling of distance. The dBA figures are manufacturer-typical for common speakers — design from the actual data sheet.

Speaker taps and output

Manufacturer typical
Typical sound pressure level at 10 ft for each speaker power tap, across common low-profile speakers. Manufacturer-typical — verify against the specific data sheet.
TapdBA at 10 ftStandard tap
1/8 W74–77 dBAOptional
1/4 W77–81 dBAYes
1/2 W80–83 dBAYes
1 W83–86 dBAYes
2 W86–89 dBAYes
Speakers run on constant-voltage lines at 25 V or 70.7 V — the amplifier holds the line voltage and each speaker's tap sets its wattage. 70 V is preferred for long runs and higher total load.

From tap to coverage

Designing a speaker layout is a balance of two levers. The tap sets the level at the source — move up one tap for about 3 dB more output. Distance takes it away — every doubling of the distance from the speaker costs about 6 dB. So you either turn a speaker up or add more speakers closer together to hold the required level across the space. Because voice systems must be understood, not just heard, the goal is even coverage rather than maximum volume; blasting one speaker to cover a large room produces a loud but unintelligible result.

That distinction — audible versus intelligible — is what separates a voice system from a horn. Meeting a decibel level is necessary but not sufficient; the message also has to be understandable, which is the subject of the voice intelligibility reference. The underlying audibility targets are the same relative-to-ambient levels on the audible dBA chart.

Common questions

What are fire alarm speaker tap settings?

Fire alarm and voice-evacuation speakers have a selectable power tap — commonly 1/4, 1/2, 1, and 2 watts — that sets how much power the speaker draws from the amplifier and therefore how loud it is. A higher tap is louder: each doubling of tap power adds about 3 dB. Typical output runs from roughly 77 dBA at the 1/4 W tap to about 89 dBA at 2 W, measured at 10 ft.

How does distance affect speaker volume?

Sound falls off with distance by the inverse-square law: in a free field, the level drops about 6 dB every time the distance from the speaker doubles. So a speaker producing 85 dBA at 10 ft delivers about 79 dBA at 20 ft and 73 dBA at 40 ft. Real rooms with reflective surfaces drop off somewhat less, but the 6 dB rule is the planning starting point.

Are these dB values exact?

No — speaker output is manufacturer-specific and varies by model, so the values here are typical ranges for common low-profile speakers, not code numbers. High-wattage speakers reach 90–96 dBA at 2–8 W. Always design from the specific speaker’s UL 1480 data sheet.

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