Structure-borne sources

A machine fixed to a building radiates sound twice: directly from its own vibrating surface, and indirectly by injecting structure-borne power into the structure, which carries it away and re-radiates it in distant rooms. The five pages of this section cover both paths: one estimates the direct radiation from the surface vibration itself, and the other four characterise the second, sneakier structure-borne path end to end, from describing the vibration and characterising the isolators to quantifying the power and predicting the level a listener finally hears.

The language comes first. Mechanical mobility and the FRF family (ISO 7626-1) defines the motion-per-force frequency-response functions (receptance, mobility, accelerance and their reciprocals) that every later standard speaks, with the closed-form SDOF resonator as the reference and the ISO 7626-2 measurement acceptance criteria. Source and receiver mobilities are what decide how much power actually couples across an interface, which is why this vocabulary matters.

Two pages then characterise the path elements. Transfer stiffness of resilient elements (ISO 10846) measures the dynamic transfer stiffness of the isolators, mounts and hoses inserted precisely to break the transmission path, by the direct and indirect (transmissibility) methods. Sound power from surface vibration (ISO/TS 7849) handles the direct radiation: the airborne power estimated from surface velocity and a radiation factor, without any acoustic measurement.

The last two pages close the chain on the source and the receiver. Structure-borne sound power of equipment (EN 15657) measures what a machine injects, via the reception-plate method, and derives the plate-independent source quantities (blocked force, characteristic power level, free velocity). Installed structure-borne sound (EN 12354-5) consumes exactly those quantities, couples them through source and receiver mobilities, and predicts the sound pressure level in the receiving room, which is where this section meets the sound insulation models.

Pages in this section

• Mechanical mobility and the FRF family (ISO 7626-1): the FRF family, conversions and the SDOF reference resonator.
• Bending-wave transmission at plate junctions (Cremer/Craik/Hopkins): the wave-approach transmission coefficients for rigid X, T, L and in-line junctions, their angular average and the derived coupling loss factor and Kij.
• Transfer stiffness of resilient elements (ISO 10846): dynamic transfer stiffness of isolators by the direct and indirect methods.
• Sound power from surface vibration (ISO/TS 7849): radiated airborne power from surface velocity and a radiation factor.
• Structure-borne sound power of equipment (EN 15657): the reception-plate method and plate-independent source quantities.
• Installed structure-borne sound (EN 12354-5): the predicted receiving-room level from installed equipment.