Alerts that are sure to be heard

Audible signals provide information, a warning or alert, for example in the event of equipment malfunctions or safety issues, or when plants are starting up. To design audible signals that are perfectly suited to the ambient conditions, some terms, i.e. volume, sound pressure and sound pressure level, need to be clarified first.

Humans can hear a sound pressure level from 0.00002 pascals (Pa) to approximately 20 Pa. To make classification easier to understand, this pressure value is converted into a sound pressure level (db), with the above range being equivalent to 0 to 120 dB. This higher value represents the upper limit of hearing, also known as the "pain threshold".

Volume refers to the subjective perception of sound pressure, which cannot be measured objectively. It must be noted that everyone experiences volume differently.

The motto of "the more, the better" does not apply to audible signals. For practical applications, it is firstly important to clarify why audible signals are used. When using local signals to provide notifications and warnings, excessively loud signals should be avoided in areas containing many signalling devices. This is because, on the one hand, they generally increase the noise level (two identical sound pressure levels increase the total sound pressure level by 3 dB) and, on the other hand, they may affect the physical and mental well-being of employees. Too many signals, or disproportionate signals, are overwhelming and harmful to health, lead to sensory overload and result in incorrect responses. This is why hearing protection is recommended at a sound pressure level of 80 dB and above, with this being a mandatory requirement from 85 dB.