Acoustic Intensity Data and Analysis

Sound intensity is one of the most effective tecniques to determine sound power level and to perform a mapping of the major sources laying inside a measurement surface. The international standard ISO 9614-1 provides practical guidelines to achieve this aim and requires the calculation of different indicators giving information about the quality of the determination and hence the grade of accuracy. If one of the field indicators does not meet the requirements, the test procedure should be modified. Moreover the Standard suggests also to check two criteria.

All the tests must be performed for each set of measurements on each measurement surface used. Finally a table and a flowchart specify the actions to undertake if the chosen measurement surface is not in accordance with the standard requirements. The data to be collected are the pressure and sound intensity levels in octave or 1/3 octave bands

This computer code has been developed with the two-fold objective to calculate the sound power of a source from intensity measurements and to allow a 3D representation of both the source outer surface and the map of interpolated results on the measuring grid.

The code complies with the prescriptions of ISO 9614 and is particularly helpful when one of the field indicators specified in the standard does not satisfy the necessary requirements so that measurements must be repeated by successive refinements of the measurement grid and, therefore, the computation may be rather time consuming.

A table gives a comprehensive insight of the field indicators computed for each one of the surfaces included in the computations.

The acquisition and calculation procedure includes the treatment of one-octave and one-third-octave band data.

It also performs a three dimensional visualisation of pressure and intensity fields on the measurement surface by colour contour plots. The possibility of drawing three dimensional objects inside the measurement surface and the linking with a FFT analyser makes the program suited also for research and development purposes.

It is always possible to set up the acquisition procedure (measurement sequence or random access to the data structure) to decide how to fill up or to complete the segments.

Another important feature of the program is the visualization of more than one 3D surfaces in the same time. All that enables the user to check the source behaviour of several frequencies at the same time.

3D EDITING AND REPRESENTATION

Starting a new project, the first step to be taken is to define the geometry of the measurement surface and the structures contained inside and outside it.

The editing of the geometry is already implemented in AIDA. The program can represent two different kinds of objects: frames and measurement surfaces. Frames are the rectangular elements used to represent the source and the environment around it: bench, floor, walls, etc. Measurement surfaces are the rectangular elements used to represent the set of segments enveloping the sound source.

Each segment defines a measurement position. The user can draw several surfaces and put them together to build a more complex one. The program will provide a 3D graphical and numerical output for each surface, giving also a ranking of the sound power levels coming from each one of them. The user can represent pressure and sound intensity fields in three dimensions.

All that enables the user to check the source behaviour on several frequencies at the same time. Different "easy to customise" colour scales are available.

SOUND POWER DETERMINATION

If the two criteria and the flowchart given by the International Standard are fullfilled then the user will have achieved the final result within the selected grade of accuracy.

The Sound Power levels are calculated for each surface and can be displayed also for the overall measurement surface with or without "A" weighting. It is also possible to exclude some frequencies from the calculation procedure selecting them directly from a list.

Main features

· Sound power determination in accordance with ISO 9614 International Standard
· Direct editing of the geometry for the measurement surface
· Transducer database
· Octave – 1/3 octave visualization of pressure and intensity levels for each segment
· 3D representation of pressure and sound intensity
· 3D representation of the main frequencies of interest (Multi frequency view)
· Different “easy to customise” colour scales available
· Automatic report generation