Airborne Sound Insulation in Buildings By Tong Yeung Wilson Acoustics Limited www.wal.hk

Content Sound Insulation Rating Sound insulation Wall Door Window Floor Wilson Acoustics Limited www.wal.hk

Sound Insulation Rating Sound Transmission Class (STC) Noise Isolation Class Impact Insulation Class Normalized Sound Pressure Level Difference Weighted Sound Reduction Index Weighted Normalized Impact Sound Pressure Level Wilson Acoustics Limited www.wal.hk

Sound Transmission Class Sound transmission losses in 16 1/3 octave bands from 125 to 4000Hz Values are compared with a reference contour such that no individual transmission loss may lie more than 8dB below the contour Sum of negative discrepancies may not exceed 32 Wilson Acoustics Limited www.wal.hk

Sound Transmission Class Wilson Acoustics Limited www.wal.hk

Sound Transmission Class Usually designed with higher STC, e.g. 5dB Construction often perform less well in building than in lab Higher STC, less chance of complain but not necessarily increase the costs Limitation at low frequency below 125Hz Wilson Acoustics Limited www.wal.hk

Poor transmission loss at low frequencies limits overall STC improvement suggested by better performance at higher frequencies Wilson Acoustics Limited www.wal.hk

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STC Examples Wilson Acoustics Limited www.wal.hk

Weighted Sound Reduction Index Similar to Sound Transmission Class, but follow ISO 717 standard Frequency range: 100-3150Hz Wilson Acoustics Limited www.wal.hk

Noise Isolation Class Sound Isolation between 2 enclosed spaces that are acoustically connected Normalized Noise Isolation Class Adjusted space to furnished rooms such that RT60=0.5s Adjustment factor = 10log(T1/T0) Wilson Acoustics Limited www.wal.hk

Impact Insulation Class By a standardized tapping Machine with 5 brass hammers at 10Hz Measure in the room below the floor 1/3 octave band from 100 to 3150Hz Compare value with reference contour similar to STC calculation method Wilson Acoustics Limited www.wal.hk

Floor Tapping Machine Wilson Acoustics Limited www.wal.hk

Wall Single-Leaf Partition Performance Mainly depends on: All kinds of solid homogenous panels Drywall Plywood Glass Solid concrete Concrete block Performance Mainly depends on: Mass Stiffness Wilson Acoustics Limited www.wal.hk

Wall insulation performance Mass Transmission loss increases with mass Heavier the panel, less it vibrates Apply to thin panel at frequencies below coincidence frequency Wilson Acoustics Limited www.wal.hk

100mm concrete, 16mm plywood, 13mm gypsum board Wilson Acoustics Limited www.wal.hk

Wall insulation performance - Coincidence dip Stiffness and the Coincidence dip At a critical frequency, wavelength of free bending waves in panel coincides with wavelength of sound in air. Coincidence dip: below the critical frequency to an octave or more Stiffer and thicker, lower the frequency Less effect with higher damping Wilson Acoustics Limited www.wal.hk

Coincidence effect Wilson Acoustics Limited www.wal.hk

Critical frequency calculation E.g. Concrete of 100mm: A = 18700 Coincidence frequency =18700/100 =187Hz Wilson Acoustics Limited www.wal.hk

Wall insulation performance Avoid the effect of coincidence dip Use different thickness so that critical frequency does not fall in the range of important for building acoustics (80-4000Hz) Increase damping: separate 1 thick wall into 2 thinner walls, loosely glued together to allow sliding friction in between and increase transmission loss Wilson Acoustics Limited www.wal.hk

Gypsum board glued together (STC 31) Gypsum board screwed together (STC 31) Single layer (STC 28) Wilson Acoustics Limited www.wal.hk

Wall insulation performance - Corrugating panels Adding ribs, joists, studs increases stiffness in one direction Also introduces additional coincidence dip Wilson Acoustics Limited www.wal.hk

Two-leaf Partition Weight of the layers Depth of air space Sound absorbing material in layers Any connection between the layers Wilson Acoustics Limited www.wal.hk

Two-leaf Partition – Cavity Depth Larger the space, higher the transmission loss Mass-air-mass resonance occur reducing Trapped air acts as spring Larger the air space or heavier the material, lower the resonance frequency Wilson Acoustics Limited www.wal.hk

Two-leaf Partition – Cavity Depth Solid curve: double 3mm glass with airspace of 6mm (STC 28) Dotted curve: double 3mm glass with airspace of 19mm (STC 32) Dash curve: single layer of 3mm glass (STC 29) Wilson Acoustics Limited www.wal.hk

Two-leaf Partition – Cavity Depth fmam=K[(m1+m2)/dm1m2]0.5 where fmam = mass-air-mass resonance frequency, Hz m1 = surface mass of the first layer, kg/m2 m2 = surface mass of the second layer, kg/m2 d = their separation, mm K = 60 for an empty cavity, 43 for a cavity filled with sound- absorptive material Density of sound-absorptive material is not very important to transmission loss - increase transmission loss above resonance frequency - limit negative effect from cracks or leaks at the partitions. Wilson Acoustics Limited www.wal.hk

Two-leaf Partition – Mechanical Coupling Mechanical connection transfers vibrations and is more effective to transfer sound than in air Use resilient connection if mechanical connection cannot be avoided Sound absorptive material becomes useless with mechanical connections Wilson Acoustics Limited www.wal.hk

Two-leaf Partition – Design of Mechanical Coupling Lightweight steel studs Wood studs with resilient metal channels on one side and both side Staggered wood stud Steel studs with resilient metal channels Double wood studs Wilson Acoustics Limited www.wal.hk

Different wall material Concrete-block wall porous and cannot give STC as great as the mass law Can be improved with suitable sealing such as a layer of drywall, plaster Masonry Wall Very high sound insulation in principle Two blocks are not solidly connected Mount with drywall surfaces Wilson Acoustics Limited www.wal.hk

Insulation of Door Similar principle as insulation of walls Leakage of sound through the edge is important Rubber or neoprene gaskets are effective sealing material Wilson Acoustics Limited www.wal.hk

Insulation of Door – Double door Less expensive but more effective way to improve STC Commonly used as communication room in hotel Can be used with sound absorption material between doors (can provide STC of 45 or higher) Wilson Acoustics Limited www.wal.hk

Insulation of Door – Automatic door bottom Control leakage under door Wilson Acoustics Limited www.wal.hk

Insulation of windows Follow mass law Have coincidence dip Laminated glass provide greater transmission loss at frequency near coincidence dip 4mm glass (STC 28), 12mm glass (STC 36), laminated 12mm glass (STC 38) Wilson Acoustics Limited www.wal.hk

Insulation of windows – Double glazing Not necessarily better performance than single glazing due to coincidence dip Improve by increasing mass and separating distance Double 3mm glazing with 6mm airspace: STC 31, no air space: STC 34, air space of 100mm: STC 42 Wilson Acoustics Limited www.wal.hk

Insulation of windows – Other methods Slanted glazing Avoid multiple optical reflections No enhancement of sound insulation than parallel glazing Triple glazing Nearly the same performance as double glazing Higher transmission loss below mass-air-mass resonance Heavy gas filling STC rating is usually small Significant improvement at mid-range frequency Use with combination of thermal insulation Wilson Acoustics Limited www.wal.hk

Insulation of floor Airbone sound insulation Impact sound insulation Heavy enough to provide good airborne sound insulation Impact sound insulation Controlled by resilience of the floor surface layers Soft resilient layer. E.g. carpet increases IIC from 40 to 65 or more Carpet increases IIC from 43 to 73 Wilson Acoustics Limited www.wal.hk

Insulation of floor – floating floor Floating floor: when hard floor surface cannot be avoided Wilson Acoustics Limited www.wal.hk

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