Overview
ISO 21955:2021 - Acoustics specifies an experimental method to transpose dynamic forces generated by an active component measured on a test bench to the forces that will act on a final receiving structure. The standard guides how to characterise an active source intrinsically (blocked forces and static behaviour such as impedance/mobility), set up test-bench measurements, and predict transmitted forces to evaluate structure-borne noise and vibration. It is intended for use with systems mounted to buildings (compressors, generators) or vehicle bodies (engine powertrains, electrical actuators).
Key topics and technical requirements
- Characterisation of the active component: measure blocked forces and static properties (impedance/mobility) as frequency-dependent quantities intrinsic to the component.
- Test-bench and setup requirements: defines requirements for test benches and measurement conditions, including a validity criterion for transfer function (FRF) measurements.
- Transfer matrices and modelling: determination of transfer matrices for the test bench (TB), final receiving structure (RS), connecting device (spring-like matrix S), and active component (AC) to enable force transposition.
- Dynamic force measurement methods: guidance on both direct and indirect measurement approaches; Annexes provide practical methods (FRF measurement in Annex B, dynamic forces in Annex C).
- Data processing and reporting: instructions for data handling, processing and the minimum data required in test reports (see Clause 6 and Annex D).
- Special cases & simplifications: procedures for strong decoupling, very similar bench/receiving structures, rigid vs non-rigid receiving structures (see Clause 5.6).
- Informative annexes: theoretical development (Annex A), measurement procedures, a worked example (Annex E), and block-sensor method (Annex F).
Practical applications and users
Who benefits:
- NVH engineers and acousticians predicting vibration and radiated sound from components.
- Component suppliers and integrators exchanging intrinsic component data to avoid full prototypes.
- Test laboratories establishing validated test-bench procedures for dynamic-force characterisation.
- Simulation engineers using measured blocked forces and transfer data as input to vibroacoustic models.
- Design teams optimizing vibration isolators, mounting interfaces, or structure modifications.
Practical uses:
- Predicting transmitted forces and structure-borne noise before integration.
- Specifying component acceptance criteria between supplier and integrator.
- Guiding isolation and mounting design to reduce vibration transferred to a building or vehicle.
Related standards
- ISO 20270 is complementary - it addresses in-situ measurement of blocked forces. ISO 21955 provides an intrinsic, bench-based characterization useful as input to simulation and integration specifications.
Keywords: ISO 21955:2021, acoustics, dynamic forces, test bench, receiving structure, blocked force, frequency response function, FRF, structure-borne noise, vibration isolators, vibroacoustic.