NF EN 25136 : 1994

Cooperating organizations
National foreword
Foreword
Method
1. Scope
2. Normative references
3. Definitions and symbols
4. Test facilities and instrumentation
5. Test arrangements
6. Test procedure
7. Calculations
8. Information to be recorded
9. Information to be reported
Annexes
A. (normative) Computational procedures for calculating
     A-weighted sound power level from octave or one-third
     octave band power levels
B. (normative) Determination of the signal-to-noise
     ratio of sound to turbulence noise in the test duct
C. (informative) Guidelines for the design and
     construction of an anechoic termination
D. (informative) Evaluation of performance of anechoic
     terminations
E. (informative) Example of a sampling tube
F. (informative) Measurement of the swirl component
G. (informative) Bibliography
Tables
1. Precision of the method of measurement
2. Cross-sectional areas of ducts
3. Maximum pressure reflection coefficients
4. Limiting values of the directivity constant K
5. Flow velocity correction, C3, in decibels, for the
     frequency response of the sampling tube
6. Modal correction, C4, for the frequency response of
     the sampling tube
7. Radial positions of the sampling tube
A.1 Values of Cj
B.1 Maximum allowable difference between the sound
     pressure level readings of a microphone fitted with
     a nose cone, LPNC, and of a microphone fitted with
     a sampling tube, LPST, as a function of the
     turbulence noise suppression delta Lt, of the
     sampling tube, for a minimum signal-to-noise ratio
     of sound to turbulence noise of 6 dB
E.1 Turbulence noise suppression, delta Lt, of the
     typical sampling tube shown in figure E.1 as
     compared with a 13 mm nose cone
Figures
1. Test arrangement and limiting dimensions of test
     ducts, intermediate ducts and transitions
2. Limiting curves for the directivity of the sampling
     tube (broad-band noise of one-third octave bandwidth)
3. Radial position of the sampling tube
C.1 Examples of anechoic terminations
C.2 Example of one-sided anechoic terminations
C.3 Example of anechoic termination
C.4 Example of two-sided anechoic termination
C.5 Examples of throttling sections
E.1 Schematic drawing of a typical sampling tube
E.2 Typical mountings of microphone and sampling tube
National annexes
NA (informative) Committees responsible
NB (informative) Cross-reference

Specifies a method for testing ducted fans to determine the sound power radiated into an anechoically terminated duct on the inlet and/or outlet side of the equipment. Applies to fans that emit steady, broad band, narrow band and discrete frequency sound. Coverage includes: definitions and symbols; test facilities and instrumentation; information to be recorded; information to be reported. Also give detailed tables and annexes.