PacAtlantic, Inc. - North American distributor of sound and visual signal equipment manufactured by Zöllner GmbH.

Technical Data › Ranges of Audibility

Ranges of Audibility
In dB (A) * in 1 m
SL = Signal Level
A = Distance to sound transmitter in meters (m)
Zet-Horn: 3-phase AC 380-440 Volt; 50-60 Hz; 5,5 kW
Makrofon: Compressed air, CO2, N2/4-10 bar (30 bar)
Uni-Alarm: 230 Volt AC; 24 Volt DC
Example:
Noise level in workshop area: NL = 85 dB (A)
Max. distance person to transmitter: A = 14 m
Necessary transmitter: 1 x Zöllner UA 120 or 3 x Zöllner UA 115
In the example the noise level is 85 dB (A) drawn as a horizontal line. The max. range of audibility shall be 14 m, drawn as a vertical line. Thus a Uni-Alarm Device UA 120 is required.
* The signal level at the receiver has to be at least 10 dB (A) above the ambient noise and should be at least SL = 75 dB (A). DIN 33 404, SOLAS, IMO A.830(19). Distance depending on decrease of signal level; climatic influences and reflection factors excluded. (According to new Europe- Standard EN457/8.1 signal level shall 15 dB (A) or more above noise level.)

Transmitter Determination

According to DIN/ISO/SOLAS a "correct" sound transmitter shall have a signal level (SL) which is 10 to 15 dB above that of the ambient noise level (NL). As the distance between the persons to be warned and the sound transmitters depends on the possibilities for installation, the suitable units are chosen under consideration of their sound pressure level in dB (A) an their range of audibility.

Our "rainbow diagram" (above) gives an outline of the various possibilities available to determine the required number of sound transmitters

The exact calculation of the range of audibility with the sound spreading out freely is based on the following formula:

  • r = 5,6 m
  • L1 = SL signal level of the unit at 1 m; e.g. UA 120 = 20 dB (a)
  • L2 = NL noise level + 10 dB (A) sound pressure level in the ear of the person to be warned according to DIN/ISO
  • NL = noise level, e.g. 85 dB (A)
  • r = range of audibility in meters. Simplified definition: Doubling the distance decreases the sound pressure level by 6 dB at a time.

Zöllner Octave band analysis with realtime analyzer

Calculation of the Number of Required Sound Transmitters

Large rooms require several sound transmitters. In order to avoid shock reactions of persons in such rooms, the sound transmitters shall be installed close to the sources of heaviest noise. Doubling the number of sound transmitters with the same sound level results in an only 3 dB higher sound pressure level:

  • (e.g. 2 x UA 5 with 105 dB (A) result in 105 dB + 105 dB 108 dB(A)).

UA 115 - 500 Hz audible signal level at 8 m.

Zöllner Octave band analysis with portable sound level meter

Main Problem is the Determination of the Existing Noise Level

The existing noise level (NL) can only be determined vaguely without measuring equipment. An exact judgment of the noise level can generally be divided into 2 groups:

  • 3.1 Measurement of the noise level in dB (A); necessary measuring equipment: calibratable sound level meter.
  • 3.2 Analysis of the noise level in one octave band according to DIN/ISO/IMO; necessary measuring equipment: calibratable sound level meter and one octave band filter.

Measurements by a Zöllner Technician

Our technicians have the possibility to carry out noise level measurements at the premises of our clients if requested.

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