Technical information -
Audible Signalling Equipment

In industry, international safety standards regulate the appropriate installation of audible signalling equipment. These standards set out the requirements and areas of application of audible signalling equipment.

As a manufacturer of audible signalling equipment for the international market, Auer Signal has many years of experience gained from working on numerous projects in a range of different countries. If you have any questions, please don't hesitate to contact us - we will be happy to help you.

An overview of some key relations

The sound pressure level of an audible signalling device must be at least 15 dB higher than the ambient sound level. The frequency at which the signal is loudest must differ as much as possible from the frequency of the ambient sound. The tone frequency of the audible signalling device must be between 300 and 3000 Hz.

How effective an audible signalling device is will depend on:

  • The sound pressure level in decibels (dB)
  • The tone frequency in hertz (Hz)
  • The distance between the signalling device and the receiver
  • The influence of other sources of interference and ambient noise

The quantifiable factors, such as the sound pressure in decibels (dB) and tone frequency in hertz (Hz), are disclosed for all audible signalling equipment from Auer Signal. The sound pressure level specified for Auer Signal audible devices will have been measured in an anechoic chamber at a distance of 1 m.

1. Volume

The volume of an audible sound or signal is relative. Although an increase in the sound pressure of 3 dB means that the sound energy has doubled, the human ear only senses that the volume has doubled when there has been an increase of 10 dB. Our sense of hearing can therefore be said to work on a logarithmic scale.

As well as the absolute volume of a signal, the perceived volume is also determined by the distance between the sounder and the person. When this distance is doubled, this equates to a 6 dB decrease in the sound pressure. The signal is then perceived to be about 25% quieter. The following range table can be used as a basis for estimating the sound level.

These values only serve as a guideline, however, as environmental factors such as wind speed, wind direction, humidity and weather conditions do also have an effect on audible signals.

When the distance is doubled, the sound pressure drops by 6 dB

Sound pressure level

Audible signalling equipment from Auer Signal is in the range between 60 dB and 127 dB.

Talking: 50 dB
Jet: 120 dB
Pain threshold: 130 dB


2. Tone and frequency

Audible signalling equipment produces different tones at different frequencies.

Electronic sounders and multi-tone alarm sounders

In electronic sounders from Auer Signal, the audible signal is generated electronically by a microprocessor, before being enhanced and then emitted by a loudspeaker. In smaller devices, sound capsules are used as loudspeakers, whilst pressure chamber or traditional loudspeakers are deployed in more powerful devices.

Given that the audible signal is generated electronically, electronic sounders from Auer Signal can produce a wide range of different tones and frequencies. The advantage of this is that there is a huge choice of tones available, meaning that several clearly distinguishable signals can be assigned to different meanings or areas of application. There is also the option of implementing special customer-specific solutions for tones.

As well as the tone, the volume of the electronic
sounders/multi-tone alarm sounders can also be
individually adjusted in the majority of the devices
supplied by Auer Signal.


Electronic multi-tone alarm sounders

Piezo buzzers

Piezoelectric crystals change shape when voltage is applied. Use is made of this property, with piezoelectric crystals being attached to a brass disc and voltage being applied at short intervals. This causes the crystal to vibrate against the disc and generate noise, with frequencies of up to 4000 Hz being reached.

If a special design measure based on the resonance
principle is taken, extremely high sound
pressures can be reached using this method.

Small size, extremely high sound pressure and low energy consumption.

Piezo buzzers afford the advantage that extremely high sound pressure levels can be produced despite a compact design, low energy consumption and relatively cost-effective price.


High-volume panel-mount buzzers for control cabinets, etc. in different sizes

Electromechanical horns and bells

Electromechanical horns and bells are classic forms of audible signalling equipment. As their name suggests, they generate signals mechanically.

Distinctive signal tone and a timeless design.

In the case of the horn, the magnetic force of a coil moves a clapper, which strikes a metallic membrane at a frequency of 100 to 150 Hz, generating the typical low-frequency, easily recognisable horn tone.

In the case of the bell, a clapper strikes a bell dome and creates the typical, distinctive bell tone that cannot be reproduced electronically with the same level of sound quality.


Loud bell with typical bell tone