ANSI AMCA-320-2008pdf download Laboratory Methods of Sound Testing of Fans Using Sound Intensity
4.3 Frequency analyzer An octave band or one-third octave band filter set shall meet or exceed the Order 3, Type 1 -D, requirements of ANSI S1.11.
4.4 Reference sound source (RSS) The reference sound source should comply with the requirements of ANSI S12.5.
4.4.1 The RSS shall be a small, modified, direct- driven centrifugal fan having maximum overall dimensions of 610 mm (2 ft) or less.
4.4.2 The RSS shall produce steady, broadband sound over at least the frequency range from 50 Hz to 10,000 Hz. It shall comply in all respects with the performance requirements of ANSI S12.5 except for the spectral characteristics of the 50 Hz and 10,000 Hz one-third octave bands, where the sound power may deviate by up to 6 dB from the sound level of the adjacent one-third octave band. The sound power output shall be high enough so that the sound pressure and sound intensity levels shall be greater than the background noise levels. See Section 7.2.
4.4.3 The RSS shall be equipped with vibration isolators to minimize vibration transmission from the RSS into the structure of the room. The degree of isolation should be 20 dB or more. If metal springs are used as vibration isolators, rubber pads shall be used between the isolator and the structure of the room.
4.4.4 To ensure compliance with the stability requirements of ANSI S12.5, all operating parts of the RSS shall be rigidly and permanently attached. No rubbing or wearing parts shall be permitted (except lubricated bearings) and protection shall be provided against corrosion.
4.4.5 The RSS calibration shall consist of a determination of the sound power level radiated by the source when it is in operation on a reflecting plane with radiation into a free field above that plane. The calibration shall be in accordance with the requirements of ANSI S12.5, or as provided in Annex F. The maximum time interval since calibration shall not exceed that specified by the manufacturer, or three years, whichever is shorter. Note: The RSS is used to qualify the performance of the sound intensity measurement system and