Ceiling speaker coverage
r = (H(ceiling) − h(ears)) × tan(θ / 2)
- h(ears) = 1.2 m seated, 1.5 m standing
- θ = the speaker’s dispersion angle
STANDARDS & FORMULAS
PA Auto Speakers
Speakers spread over the rooms by their coverage, and each room’s tap.
Standards and regulations
- BS 5839-8Voice alarm systems - design, installation, commissioning and maintenance
Speaker spacing, A/B circuits and the voice alarm (PAVA) link to the fire alarm.
Formulas
Level from one speaker
L = S + 10 × log10(P) − 20 × log10(d) − off-axis loss
- S = sensitivity (dB, 1 W / 1 m)
- P = tap (W)
- d = distance to the listener (m)
Level from all speakers
L(total) = 10 × log10(Σ 10^(Li / 10))
Target level
L ≥ max(65 dB(A), noise + 10 dB)
Design rules it applies
- Never more than 6 m apart
- Wall speakers in plant rooms, stairs and under ceilings over 6 m
For reference. MO.tool works these out to help your design; the engineer remains responsible for it. Always check the edition of each standard your project uses and the requirements of the local authority (DEWA, ADDC, Civil Defence…).