---
title: "Structure-borne sources"
description: "The chain from a vibrating machine to the noise heard rooms away: the ISO 7626 FRF family, ISO 10846 isolator transfer stiffness, ISO/TS 7849 radiated power from surface vibration, the EN 15657 reception plate and the EN 12354-5 installed prediction."
---

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)](/phonometry/guides/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.

Two pages then characterise the path elements.
[Transfer stiffness of resilient elements (ISO 10846)](/phonometry/guides/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)](/phonometry/guides/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)](/phonometry/guides/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)](/phonometry/guides/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](/phonometry/guides/sections/sound-insulation/) models.

## Pages in this section

- [Mechanical mobility and the FRF family (ISO 7626-1)](/phonometry/guides/mechanical-mobility/):
  the FRF family, conversions and the SDOF reference resonator.
- [Bending-wave transmission at plate junctions (Cremer/Craik/Hopkins)](/phonometry/guides/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.
- [Transfer stiffness of resilient elements (ISO 10846)](/phonometry/guides/transfer-stiffness/):
  dynamic transfer stiffness of isolators by the direct and indirect methods.
- [Sound power from surface vibration (ISO/TS 7849)](/phonometry/guides/vibration-sound-power/):
  radiated airborne power from surface velocity and a radiation factor.
- [Structure-borne sound power of equipment (EN 15657)](/phonometry/guides/structure-borne-power/):
  the reception-plate method and plate-independent source quantities.
- [Installed structure-borne sound (EN 12354-5)](/phonometry/guides/installed-structure-borne/):
  the predicted receiving-room level from installed equipment.
