• Q1.What are the four most important features of a modern electronic siren?
• Q2.What sound radiation patterns are available?
• Q3.How loud in Watts should the siren be?
• Q4.Which factors most affect the effective range of the siren?
• Q5.How can uniform warning signal coverage be best achieved?
• Q6.Can outdoor warning sirens be effective in alerting people indoors?
• Q7.How effective are voice messages?
• Q8.What is the realistic service life of an electronic siren system?
• Q9.What are the main options for controlling my warning system?
• Q10.Where can I get first-class advice to help me design an effective Emergency Warning System?

Answers

• A1.What are the four most important features of a modern electronic siren?
  • Mechanical strength - resistance to weather and corrosion.
  • Modular electronics in weatherproof or flameproof enclosure.
  • Easy to install - easy to maintain - easy to upgrade.
  • Optimum SPL - Cost performance.

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• A2.What sound radiation patterns are available?
  • Omnidirectional.
  • Directional.
  • Combination, to adapt to specific areas.

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• A3.How loud in Watts should the siren be?

  Sirens are available to handle small 106dB (250W) to powerful 125dB (2250W) outputs.

  Typical effective ranges for omnidirectional radiation are as follows (Example ranges calculated for 70dB at perimeter for attenuation 10dB per distance doubled):

  Siren Size	Effective range
  Small (106dB/250 Watts)	350 -500m
  Medium (115dB/750 Watts)	700 - 1000m
  Large (121dB/1500Watts)	1100 - 1300m
  Very Large (125dB/2250 Watts)	1500 - 1800m

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• A4.Which factors most affect the effective range of the siren?
  • Wind has the greatest effect. SPL reduction up-wind can be as high as 15dB.
  • Temperature gradients in the atmosphere can cause 'shadow' areas.
  • Physical obstructions in the sound path such as buildings, trees and terrain.
  • The noise level in and around the area in which the warning signal must be heard.

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• A5.How can uniform warning signal coverage be best achieved?

  By using more than one siren and locating them to compensate for the effects listed in FAQ 4 above.

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• A6.Can outdoor warning sirens be effective in warning people indoors?
  • This depends on the type of building, the window construction and internal noise levels.
  • For offices, factories, public places, schools, theatres and closed shopping malls, the warning signal should be generated indoors.
  • For industrial applications, visual warning can be used in high noise areas.
  • Outdoor and indoor warning systems can be integrated into a common control system.

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• A7.How effective are voice messages?
  • With careful planning and location of the electronic sirens, intelligible voice messages can be used effectively.
  • The effective range for voice messages is less than for the warning signals.

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• A8.What is the realistic service 'life' of an electronic siren system?
  • A strong loudspeaker constructed of heavy-duty metallic projector horns and a robust galvanized steel-supporting pole should provide a service life of 20 years.
  • The electronics: amplifiers - signal generator - communication interfaces, if protected inside a weatherproof enclosure will provide at least 10 years fault free service.
  • Newer technologies in control and communication may dictate an upgrade in parts of the electronic system at the end of this 10-year period.

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• A9.What are the main options for the warning system control?
  • Two way radio communication using a private network that operates in the VHF/UHF land mobile or scanning telemetry bands. FFSK data for activation and status monitoring and voice.
  • Land line or fibre optic communication with serial data for activation and status monitoring and voice.
  • Integration into an existing Trunked radio system such as TETRA. Activation and status monitoring and voice.
  • Integration into an existing SCADA system. Data activation and status monitoring.

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• A10.Where can I get first-class advice to help me design an effective Emergency Warning System?
  • From a specialised supplier with extensive experience in this field.

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