Audio signals use sound from a horn, drum, whistle or bell to alert people who cannot be seen, and they work at night, in fog and around hills and trees where light fails. Their range falls with distance and is cut sharply by wind and background noise, and every person in earshot hears them, so an audio alarm warns the settlement and also tells outsiders that something has happened.
Part of Signal Systems and Communication
Sound signalling covers the horns, drums, whistles and bells used to send a short alarm or code over distances that voices cannot reach.
Sound Goes Where Light Cannot, And Fades
Sound bends around corners, passes through trees and works at night, which is why audio signals are the usual choice for an alarm that must reach everyone at once. Three limits apply.
- Distance. In open air with no obstacles, a sound falls by 6 dB every time the distance doubles, as Noise Makers derives. Doubling the range of a horn therefore costs a quadrupling of its sound power.
- Wind and ground. Wind bends sound: a signal that carries far downwind may not be heard at half the distance upwind (recalled from acoustics). Hills and dense foliage shade or absorb sound, and a drum carries differently over water, fields and woods.
- Background noise. A signal must stand out against the surroundings. Rain, river noise and machinery shorten the working range.
The Four Instruments
| Instrument | Range in the parent article | What it is for |
|---|---|---|
| Horns and Trumpets | 1 to 3 km | A single carrying note for alerts and assembly |
| Drums | 2 to 5 km in still air | Patterns of beats; low sound that passes obstacles |
| Whistles and Bells | whistle about 500 m | Short-range signals between posts and patrols; bells to assemble the settlement |
These ranges come from the parent article and this corpus has no measured data for them. Test each instrument at the real distances, in the real wind, from the receiver’s end.
The Exposure Cost
The camouflage article gives conversation as audible at 100 to 200 m in still air, wood chopping at 500 m or more and a gunshot at 3 to 5 km (Camouflage and Concealment). A horn that reaches the next settlement reaches the road in between. Sound is for alarms that must be heard, not for routine traffic.
Choosing Between Sound And Light
- By day or night, with line of sight: light is quieter and can be aimed (see Visual Signal Methods).
- Without line of sight: only sound or a runner reaches.
- For an alarm to everyone at once: a horn or bell, sounded from a place everyone can hear.
- For a coded message to one place: light, or a runner (Runner Systems).
Common Mistakes
- Choosing the instrument by its loudest claim. The range is the listener’s range, not the instrument’s.
- Giving each instrument its own code. One code table covers all channels (Simple Code Tables).
- Never testing at night. Night air carries sound farther and background noise is lower, so you learn the true audience only by testing.
Safety
Hearing damage and shared mouthpieces
A horn, whistle or gong sounded near an ear can damage hearing. Practise at a distance from other people, and keep a shared horn’s mouthpiece clean because it can pass infections from one blower to the next.
What’s Next
- Learn next: Horns and Trumpets — the main alarm instrument
- Combine with: Code Systems — turning notes and beats into meanings