Sound Sources

Type 4204 Reference Sound Source

Type 4204 Reference Sound Source

Reference Sound Source is intended for use as a reference source for determination of the sound power output of equipment by the various comparison methods including the method described in ISO 3741, and by the survey methods described in ISO 3747. It is also useful in the field of building acoustics to determine the sound absorption and sound insulation of a room.


  • Comparison method for determination of sound power of noise sources according to ISO 3741
  • Substitution and Juxtaposition methods for determination of sound power of noise sources according to ISO 3747
  • Sound absorption measurements
  • Sound insulation measurements

Reference Sound Source uses a specially designed centrifugal fan driven by a powerful asynchronous motor. The motor is of the external rotor type, and due to the high moment of inertia of the rotor it has a very constant speed of rotation. The motor is mounted on a cast aluminium base, shaped to minimize reflections. The complete assembly of motor and fan is mounted in a cylindrical safety grid fitted with two carrying handles.

Additional features of the compact and rugged product include long-term stability, an individual calibration chart and a safety grid.


  • Fulfills ISO 3741, ISO 3747 and ISO 6926 for calibrated sound power sources
  • Frequency range from 100Hz to 20 kHz
  • Sound power output 91 dB re 1 pW (A-weighted, 50 Hz line frequency) and 95 dB re 1 pW (A- weighted, 60 Hz line frequency)
  • Temperature range –10°C to + 50°C
  • 50 and 60 Hz operation