Description of BS ISO 9611:1996 1996

1.1 General

This International Standard specifies an approximate method of characterizing sources of structure-borne sound by the measurement of one-third-octave-band free velocity level spectra (or, if appropriate, octave-band velocity level spectra) on the supports or other connection points of machines mounted on resilient isolators. This structure-borne sound emission is considered with respect to the airborne or liquid-borne sound radiation of structures connected to the source under test. The results are only valid for applications in which the machine is mounted on sufficiently soft isolators on a sufficiently stiff and heavy foundation.

NOTE 1 More conditions are given in annex H. A survey of the theoretical background is given in annex E.

It is possible to satisfy the requirements for the test arrangement in almost any surroundings.

Velocities measured at defined contact points give no complete description of structure-borne sound emission of the machinery. But, under specific conditions as described in this International Standard for resiliently mounted machinery, they give a subset of the source data required for a characterization.

The results can be used

1. to obtain data for technical specifications;

2. for comparison with machines of similar type and size; and

3. to obtain input data for computations on the transfer of structure-borne sound.

1.2 Frequency range

The frequency range for which the method is applicable is limited by a low frequency f₁ and an upper frequency f₂.

The low frequency limit f₁ is set by the requirement that the supports vibrate freely; i.e. they are not affected by the isolators and the foundation structure on which the isolators are mounted. Annex A gives instructions on how to determine f₁.

The upper frequency limit f₂ is determined by assuming that the supports behave as point sources of structure-borne sound. Annex B gives guidelines for the determination of f₂.

NOTES

1. For many machines, isolators can be selected which provide a frequency f₁ between 20 Hz and 40 Hz.

2. Many machines have such a structure that f₂ has a value between 1 kHz and 4 kHz.

1.3 Type of noise

This International Standard applies to steady noise.

1.4 Degrees of freedom

The procedures are described for all six components of the velocity: three orthogonal translational velocities and three orthogonal angular velocities.

If it can be shown that, for a specific machine and a specific application, fewer components are sufficient to characterize the source, then it is permissible to reduce the number of measured components (see annex F).

1.5 Types of connection point

The procedures in this International Standard are described for the main supports of a machine. The method is, however, applicable to other mounting faces at resilient elements such as the flange for a flexible coupling in the shaft of a diesel engine or the connection with pipes. In such cases, the methods for the determination of f₁ and f₂ (see annexes A and B) can be adapted to the unique conditions that apply.

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