Imposed frequency regulator frequency (Hz)

Speed fan

(RPM)

Pure tone frequency

(Hz)

L (dBZ)

Base noise

Perforated plate^a

30

600

2000

79.8

-

2500

-

64.6

40

800

3150

89.4

69.0

50

1000

4000

93.5

71.3

60

1200

5000

96.7

72.3

70

1400

6300

103.3

72.8