Source: https://jmrplens.github.io/phonometry/vibration/structural/ # 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. Six pages cover both paths, three of them here and three elsewhere on the site: one estimates the direct radiation from the surface vibration itself, and the other five 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)](https://jmrplens.github.io/phonometry/vibration/mechanical-mobility/) 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. Three pages then characterise the path elements. [Bending-wave transmission at plate junctions (Cremer/Craik/Hopkins)](https://jmrplens.github.io/phonometry/vibration/junction-transmission/) follows the power across the structure itself, with the wave-approach transmission coefficients for rigid X, T, L and in-line junctions, their diffuse-field angular average, and the coupling loss factor and vibration reduction index Kij they yield — and, for joints no wave model describes, the experimental route that inverts the same coupling loss factors from measured subsystem energies. [Transfer stiffness of resilient elements (ISO 10846)](https://jmrplens.github.io/phonometry/vibration/transfer-stiffness/) 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)](https://jmrplens.github.io/phonometry/devices/emission/vibration-sound-power/) 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)](https://jmrplens.github.io/phonometry/buildings/design/structure-borne-power/) 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)](https://jmrplens.github.io/phonometry/buildings/design/installed-structure-borne/) 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](https://jmrplens.github.io/phonometry/buildings/insulation/) models. ## Pages in this section - [Mechanical mobility and the FRF family (ISO 7626-1)](https://jmrplens.github.io/phonometry/vibration/mechanical-mobility/): the FRF family, conversions and the SDOF reference resonator. - [Bending-wave transmission at plate junctions (Cremer/Craik/Hopkins)](https://jmrplens.github.io/phonometry/vibration/junction-transmission/): 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, plus experimental SEA: coupling loss factors inverted from measured energies by power injection, with the modal densities they need. - [Transfer stiffness of resilient elements (ISO 10846)](https://jmrplens.github.io/phonometry/vibration/transfer-stiffness/): dynamic transfer stiffness of isolators by the direct and indirect methods. ## See also Pages elsewhere on the site that this section leans on: - [Sound power from surface vibration (ISO/TS 7849)](https://jmrplens.github.io/phonometry/devices/emission/vibration-sound-power/): radiated airborne power from surface velocity and a radiation factor. - [Structure-borne sound power of equipment (EN 15657)](https://jmrplens.github.io/phonometry/buildings/design/structure-borne-power/): the reception-plate method and plate-independent source quantities. - [Installed structure-borne sound (EN 12354-5)](https://jmrplens.github.io/phonometry/buildings/design/installed-structure-borne/): the predicted receiving-room level from installed equipment. ## What this section does not cover The junction coefficients are a **closed-form idealisation** for a rigid, simply supported junction between homogeneous plates, not a measurement: the empirical vibration reduction index obtained from a direction-averaged velocity level difference is ISO 10848, in [Laboratory flanking transmission](https://jmrplens.github.io/phonometry/buildings/insulation/flanking-lab/). The straight-section coefficient is undefined for the T and L geometries, which have no collinear third plate, so only the corner path applies there. The FRF page implements ISO 7626-1 and the ISO 7626-2 acceptance criteria for an attached exciter; **impact-hammer excitation (ISO 7626-5) is named for context only**, with nothing that synthesises or processes an impact spectrum, and the conversions return element-wise *free* reciprocals — correct for a driving-point or single-path use, not for a full FRF matrix, whose blocked matrix quantities are not built. On the isolator page, parts 4 and 5 of ISO 10846 are not implemented, and two of the standard's own validity checks are described rather than computed: the rigid blocking-mass inequality, and the clause 7.6 linearity criterion (two input spectra 10 dB apart agreeing within 1.5 dB). Finally, nothing here designs an isolator or a floating base: the pages characterise elements and predict transmission, and the sizing decision stays yours.