Standards Development

Scope

The main field of application of the calculation method roughly outlined in the following (stochastic energy-based ray tracing, also in combination with deterministic strategies) is the prediction of sound pressure levels, energy related impulse responses and derived quantities like reverberation times and speech transmission indices for given pairs of source and receiver inside completely or partially closed rooms. Calculations are based on octave-frequency bands 125 Hz – 8 000 Hz1) with the assumption of incoherent contribution of partial sounds. Interference effects in narrow frequency bands with only one or few sources are outside the scope.

The method is specific to support the design of working areas from small workshops up to large production halls where noise levels are typically high and shall be considered in all planning phases. It is also applicable to determine the disturbance by speech, to evaluate the intelligibility of spoken information in presence of background noise and to support the realization of the best possible acoustic environment in the planning phase of open plan offices, restaurants and other rooms where technical or communication noise is an issue or where intelligibility is important. Sources are machinery and other technical equipment, loudspeakers emitting warning signals or spoken information or – in communication areas like eating rooms or service halls – speaking persons.

This Standard is not a complete and unambiguous description step by step – it describes some of the applicable principles and is an attempt to reach a common view for the different activities necessary to support planners in the design phase of such working areas. But nonetheless minimum requirements are formulated and presented in form of test cases with results serving as reference. These results have been obtained applying proven theory and are validated in laboratory or in field tests.

Not the detailed algorithms are standardized therefore, but the grade of agreement with given reference results for a sample of test cases. Software-tools applying methods that are in accordance with the so defined requirements can be qualified as “Quality assured according to ISO 11690-3”.

The calculation methods in accordance with the frame and the requirements formulated in this Standard can be used to link the emission of machinery, technical equipment, human sources like speaking people, geometrical and acoustical properties of the room with all fittings and equipment to the resulting sound impact, reverberation time and speech intelligibility. They can be used for noise prediction purposes in the frame of the hazard analysis in the planning phase of workrooms.

1) Footnote: For the calculation of sound exposure at workplaces it is generally sufficient to use the frequency bands from 125 Hz up to 4000 Hz. The frequency band 8000 Hz is necessary if the speech transmission STI index according to IEC 60268-16:2011 shall be included in an evaluation.

Purpose

The calculation of sound propagation indoors is widely applied in national and international context. Different methods are applied. Due to differences in used quantities, parameters and different methods for calculation and determining the uncertainty, the comparability of the results is only possible to a limited extent. Stakeholders have indicated on several platforms that a common basis for dealing with that matter is needed and would be beneficial for them in order to improve established procedures. Stakeholders underline that worldwide market relevance is given.

The proposed revision of ISO/TR 11690-3 is the first step of the project “Revision of the series ISO 11690”.

The existing series refers to the state of the art in calculation about 25 years ago. In the mean-time software tools have been developed and are available that allow a detailed modeling of even complex shaped rooms with machinery and/or with acoustically optimized furniture in extended office areas.

The core of the intended revision is the description of minimum requirements for a calculation method that shall be applied with quality assured tools to predict sound pressure levels, energy- based impulse-responses and other target parameters derived from these like spatial sound decay curves, reverberation times and speech transmission indices STI. Taking into account the fact that different mathematical strategies are possible to perform such calculations and to fulfil these requirements it is not planned to “standardize” the detailed procedures or even the algorithms, but to offer test-cases with reference solutions and maximal acceptable deviations. These test-cases are restricted to scenarios where the correct solution is known from theory and has been validated experimentally with acceptable confidence. Software-tools applying methods that are in accordance with the so defined requirements can be qualified as “Quality assured according to ISO 11690-3”.

The description of spatial sound decay curves in rooms as shown with figures 1 and 2 in ISO/TR 11690-3:1997 and many other remarks and explanations about the dependency of sound propagation in rooms from their acoustic properties shall be removed from this part 3 and integrated in a revised ISO 11690-2. Applying a quality assured calculation method with reference to ISO 11690-3 some typical examples of acoustic room treatments and layouts of workplaces should be presented with this part 2.

The new part 3 opens also the possibility to make part 1 more concrete. The revised part 1 shall clearly distinct the noise prediction and acoustic optimization for planned workrooms where decisions are based on calculations and for existing workrooms where a mix of measurements and calculations should be applied. Emission values declared by the manufacturers shall be included in the framework of input data and this shall be supported by default values for spectra and directivities.

Summing up the new structure shall include more variability to apply existing knowledge about emission values, apply the state of art to calculate sound propagation and allow the prediction of sound with all types of rooms and interior fittings. It shall also create a better link between declared and guaranteed emission values of machines and technical equipment with the prediction of noise at workplaces in the frame of the analysis of possible hazards.