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Exterior acoustic project - electronic sirens
Exterior acoustic project – public address system
Interior sound distribution project

Acoustic project

The acoustic project defines the arrangement of horns or generally the acoustic elements of warning system (electronic horns, loudspeakers, etc.) in the endangered territory. It is the first step for the design of warning system. In the deployment of horns, following are taken into account particularly:

  • Sufficient acoustic output in the whole endangered territory,
  • Physical options for placement,
  • Availability of electric power,
  • Options of control (radio range, availability of lines, etc.),
  • Availability of prophylactic and servicing activities.

Endangered area

Endangered territory is the area where at the origination of extraordinary event can incur the endangerment of health or life. This area, from the point of the creation of acoustic project, should be covered by a warning signal.

Noisiness of background

There is always some noise in the endangered territory under common conditions. This noise is described as the noisiness of background and is indicated in decibels. It has direct effect on the audibility of horn or acoustic elements of warning system. The noisiness of background can be variable in the course of day. Commonly it is influenced mainly by traffic, industry and various local sources of noise. Its measurement should be made in the most noisy time section of working day, in means for example in the time of peak time in traffic or similar time.

The altitude of built up area

The altitude of built up areas is another significant parameter that influences the acoustic reach of horns. It is almost impossible to determine its exact effect and therefore is regarded based on statistical measurements and empiric experiences. ACUSTICUS Professional enables to determine the ranges of horns based on the adjustment of parameter "The altitude of built up area" on five levels:

  • 0 - 5 m
  • 5 - 10 m
  • 10 – 15 m
  • 15 – 25 m
  • over 25 m

The required level of the acoustic pressure of warning signal

The relation between the required level of the acoustic pressure of warning signal and the noise background can be regulated directly by legislature in case of warning systems in individual countries. Generally is recommended the following relation between noise background and minimum required acoustic pressure of horn´s warning signal:

noisiness of background

minimum acoustic pressure

< 60 dB

55 dB

60 - 75 dB

the same as background

> 75 dB

by 5 dB higher than background

The limit where the acoustic pressure of horn´s warning signal would drop to this level, is considered the limit of horn´s reach. The software is depicting it as the range of horn.

The emission diagram of horn

The horn does not distribute acoustic signal of the same intensity to all directions. The emission diagram illustrates graphically the size of acoustic pressure in individual directions. By different arrangement of baffle boards can be reached various emitting diagrams. The most frequently used ones are as follows:

  • O – almost circular diagram
  • F – diagram with preferred routing (front)
  • 8 – very similar to „O“, slightly prolonged in the shape of numeral 8

By appropriate utilization of the emission diagrams can be optimized the number of used horns in the project.

Routing (azimuth) of horn

Horn can be turned to various directions. In combination with their arrangement, i.e. emission diagram, can be again optimized the layout and the number of horns.

Output of horn

The output of horn is stated as the summary electric output power of all amplifiers in the horns. There are stated various types of powers measured according to various standards for various purposes:

  • Sinusoidal (DIN)
  • Music
  • Peak
  • Nominal
  • P.M.O.O.

These data are rather informative for horns because the substantial parameter of horns is their acoustic pressure.

Acoustic pressure of the warning signal of horn

The output of horn has direct effect on the basic acoustic parameter of horn, i.e. the acoustic pressure of horn´s warning signal. The acoustic pressure of horn´s warning signal expresses the level of sound signal they generate. Besides the output of amplifiers it is influenced also by other parameters, particularly the design of electro-acoustic transducers and of baffle boards. The acoustic pressure depends also on the adaptation of the spectrum of warning signal in acoustic system (electro-acoustic transducer and baffle boards). Most of manufacturers indicate it for signal simulating hooting of typical motor horns at so called fluctuating tone. By means of special modification of this signal the acoustic pressure of electronic horns can be increased artificially. However, this procedure is generally considered unsuitable because it increases the acoustic pressure only for such modified signal and the range for spoken words is significantly lower. The acoustic pressure of effective horns is usually indicated in the distance 30 m from the horn. The acoustic pressure of the equipments with lower output is indicated in the distance 1 m.

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