Reference Sound Source Type 4204 — User Manual2
Type 4204 is also used for measuring environmental correction K
2
when determining sound
power according to ISO 3744. It is also useful in the field of building acoustics to determine the
sound absorption and sound insulation of a room.
The reference sound source consists essentially of a specially designed centrifugal fan driven
by a powerful asynchronous motor. The motor is an external rotor type, and due to its high
moment of inertia, 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
within a cylindrical safety grid fitted with two carrying handles.
The directional characteristic of the reference sound source in the vertical plane varies less than
6 dB for any frequency in the range 100 Hz to 10 kHz (measured in 1/3-octaves) – see
section 3.3. In the horizontal plane, the variation is less than 0.2 dB for frequencies up to
10 kHz (measured in 1/3-octaves). The reference sound source fulfils the requirements for
reference sound sources as stated in ISO 3741, ISO 3747, ISO 6926 and ANSI S12.5. The use
of a reference sound source in noise and sound power measurements on machines is also
described in DIN 45635.
The reference sound source has a frequency range of 100 Hz to 20 kHz. In the range from
100 Hz to 10 kHz, the acoustic power output is greater than 70 dB re 1 pW in any 1/3-octave
frequency band. The A-weighted output is typically 91 dB (50 Hz line frequency) and 95 dB
(60 Hz line frequency). Fig.1.2 shows a typical 1/3-octave frequency response curve of the
Type 4204.
Fig.1.2 Typical sound power spectrum of the Type 4204
901108/1
Sound Power Level of 4204 (dB re 1 pW)
80
100 200 500 1k 2k 5k 10k 20k
75
70
85
Frequency (Hz)
A-weighted level for
60 Hz line freq. and
115 V line volt = 96.0 dBA
A-weighted level for
50 Hz line freq. and
220 V line volt = 91.7 dBA
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