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Testing of Audible Warning Devices and Vehicle Audible Warning Signals – UN Regulation No. 28

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Testing of Audible Warning Devices and Vehicle Audible Warning Signals – UN Regulation No. 28

The tests are intended to evaluate the acoustic parameters of audible warning devices and the signals emitted by devices installed on vehicles. They make it possible to verify whether the signal is sufficiently audible, clearly recognisable and capable of effectively warning other road users of the vehicle’s presence in a hazardous situation.

The testing scope comprises two levels of assessment:

  • Part I of UN Regulation No. 28 – type-approval testing of audible warning devices, audible warning systems and multiple audible warning systems as separate components;
  • Part II of UN Regulation No. 28 – vehicle type-approval testing with regard to audible warning signals.

Testing of the device makes it possible to determine its sound pressure level, rated frequency and sound spectrum distribution in one-third-octave bands. It enables an assessment of whether the device emits a continuous and uniform sound with the required acoustic characteristics.

For a complete vehicle, the sound pressure level of the signal emitted by the installed device is verified. The test takes into account the influence of the installation location, vehicle structural elements and body components that may attenuate the sound or alter its characteristics.

The measurements may be used:

To verify the conformity of the device parameters with the applicable technical requirements.żu, elementów konstrukcyjnych pojazdu oraz części nadwozia, które mogą tłumić albo zmieniać charakterystykę emitowanego dźwięku.

  • in the type-approval process for an audible warning device;
  • in the vehicle type-approval process with regard to audible warning signals;
  • in the development and validation of audible warning devices and systems;
  • to compare different design variants and device installation locations;
  • to assess the effect of vehicle bodywork on signal audibility;

The measurements may be used:

To verify the conformity of the device parameters with the applicable technical requirements.żu, elementów konstrukcyjnych pojazdu oraz części nadwozia, które mogą tłumić albo zmieniać charakterystykę emitowanego dźwięku.

  • in the type-approval process for an audible warning device;
  • in the vehicle type-approval process with regard to audible warning signals;
  • in the development and validation of audible warning devices and systems;
  • to compare different design variants and device installation locations;
  • to assess the effect of vehicle bodywork on signal audibility;

Scope of measurements

The tests cover:

  • A-weighted sound pressure level;
  • sound spectrum analysis in one-third-octave bands;
  • rated sound frequency.

Measurement ranges covered by the scope of accreditation of the BOSMAL Testing Laboratory, accreditation No. AB 128:

  • sound pressure level: 25–140 dB, direct measurement method;
  • rated sound frequency: 50–5,000 Hz, direct measurement method.

Test objects

The following may be tested:

  • individual audible warning devices;
  • systems comprising several devices operated simultaneously;
  • multiple audible warning systems;
  • motor vehicles equipped with audible warning devices.

BOSMAL also measures the acoustic parameters of devices and systems used in emergency vehicles, in accordance with the scope and requirements agreed with the customer.


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