ISO 16940:2008

Overview

ISO 16940:2008 - Glass in building - Glazing and airborne sound insulation - Measurement of the mechanical impedance of laminated glass specifies a laboratory method to measure the loss factor and the equivalent bending rigidity modulus of laminated glass test pieces. The standard is intended to compare the mechanical (damping and stiffness) properties of different interlayers and to relate these parameters - together with density and glass thickness - to the sound transmission loss (STL) of glazing.

Key topics and technical requirements

• Measurement principle: input mechanical impedance (transfer function between injected force and velocity) is measured on a beam sample to identify resonance frequencies and modal bandwidths.
• Loss factor calculation: η = Δf / fres,i where Δf is the resonance bandwidth and fres,i is the ith resonance frequency. If –3 dB points are not available, a –2 dB correction using a factor (1.31) is permitted.
• Sample and fixation: beam samples (narrow strips) are used to reduce modal density; nominal glass pane thickness for comparison is 4 mm. Samples are glued to a 15 mm impact button and measured at mid-span.
• Instrumentation: environmental chamber (or conditioned room), white-noise generator (0–5 000 Hz), shaker, power amplifier, impedance head (force transducer + accelerometer), measuring amplifiers and FFT dual-channel analyser or equivalent software.
• Test conditions: measurements at (20 ± 1) °C with at least 1 hour thermal conditioning of samples.
• Modal data and derived parameters: resonance frequencies and loss factors for the first three modes are recorded; Annex B describes computation of equivalent bending rigidity from modal data; Annex C (Cremer equation) shows how to calculate STL and one-third-octave band results. The weighted sound reduction index Rw (ISO 717-1) should be reported.

Applications and who uses it

• Glass manufacturers and R&D teams - evaluate and compare damping properties of different interlayers for laminated glass.
• Acoustic consultants and façade engineers - predict glazing airborne sound insulation performance (STL) from material measurements rather than full-size acoustic tests.
• Test laboratories and quality control - routine measurement to verify product consistency and to support acoustic declarations.
• Product developers - optimize laminate constructions (interlayer type/thickness) to improve sound insulation in buildings, vehicles or partitions.

Related standards

• ISO 12543-1 (laminated glass definitions)
• ISO 140-1 and ISO 140-3 (laboratory sound insulation measurement requirements)
• ISO 717-1 (rating of airborne sound insulation)
  (Annex C of ISO 16940 references the Cremer approach for STL calculation.)

Keywords: ISO 16940:2008, laminated glass, mechanical impedance measurement, loss factor, bending rigidity, sound transmission loss, glazing acoustics, interlayer properties, STL, Rw.