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. Seven pages cover both paths and the question that is not about sound at all, four of them here and three elsewhere on the site: one estimates the direct radiation from the surface vibration itself, 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, and the seventh asks instead whether the shaking damages the building.

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.

Three pages then characterise the path elements. Bending-wave transmission at plate junctions (Cremer/Craik/Hopkins) 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) 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, and their low-frequency stiffness by the driving-point method, one value per one-third-octave band. 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.

One page here asks a different question of the same shaking. Vibration damage to structures (DIN 4150-3) is not about what a building radiates but about whether it cracks, and it answers with a screening comparison rather than a verdict: the guideline values for the peak particle velocity, chosen by building class and by how often the vibration occurs at a foundation and in the topmost floor plane, and by pipe material on a buried pipeline. Keeping under one is where experience says the question stops; exceeding one sends the reader to the stress calculation, not to a finding of damage. Predicting a building’s own frequency (ISO 4866) is what those guideline values are read at when nobody could measure it: the empirical predictors of Annex D, the error each one admits, and the damping range the annex reports without offering a way to predict it.

• 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, 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): dynamic transfer stiffness of isolators by the direct, indirect and driving-point methods, in one-third-octave bands, with the checks of the rig.
• Vibration damage to structures (DIN 4150-3): the guideline peak velocities of Tables 1, 2 and 3, the reading of Bild 1 between them, and the bending stress a measured velocity implies.
• Predicting a building’s own frequency (ISO 4866): the four empirical predictors of Annex D, the ± 50 % they admit, and the measured damping range.

• 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. 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, one of the standard’s own validity checks is described rather than computed: the linearity test (two input spectra 10 dB apart must give transfer-stiffness levels within 1.5 dB, clause 7.7 of ISO 10846-2, -4 and -5 and clause 7.6 of ISO 10846-3). Finally, nothing here designs an isolator or a floating base: the pages characterise elements and predict transmission, and the sizing decision stays yours.