Abstract:

Objective: The airborne sound insulation performance of timber structure walls is investigated across a full frequency range. It aims to identify the bottlenecks limiting the sound insulation of conventional light wood frame walls, explore the effect of installing sound insulation layers, altering frame type, and setting up windows on wall sound insulation performance, and propose a high airborne sound insulation grade timber wall system. This research provides technical support for the efficient application of timber structure walls in prefabricated buildings. Method: Using the impedance tube method, small-scale material layer experiments were conducted to compare the sound insulation performance of industrial-grade elastic rubber sheets (rubber sheets), polyurethane rubber soundproofing and shock-absorbing sheets (polyurethane sheets), and polystyrene extruded sheets (XPS sheets) within the 60-6 300 Hz frequency range. Full-scale walls sound insulation tests were performed using in the 100-5 000 Hz frequencies range using the laboratory method. We obtained single-value sound insulation levels for 18 central frequencies in 1/3 octave bands, determining the wall’s weighted sound insulation index (R_w), spectrum adaptation terms, and sound insulation grades. These were compared with autoclaved lightweight concrete (ALC) walls and cross-laminated timber (CLT) walls widely used in prefabricated buildings. Result: The rubber sheet showed higher sound insulation across the full frequency range compared to the same thickness polyurethane and XPS sheets, with sound insulation performance improving with increased sheet thickness. A 10 mm thick rubber sheet exhibited the highest sound insulation efficiency within the test range. The sound insulation of conventional light wood frame walls increased with sound wave frequency but exhibited significant resonant sound insulation dips at 125 Hz and coincident dips at 3 150 Hz, with an R_w of 43 dB. When used as partitions or enclosures, the airborne sound insulation grades were 4 and 3, respectively. Adding a 10 mm thick rubber sheet between the wall frame and oriented strand board (OSB) slightly improved the sound insulation (R_w increased to 45 dB), but the grade remained unchanged. Conventional light wood frame walls with and without rubber sheets did not meet current national standards for sound insulation in ordinary residential walls. When using a light steel frame with double gypsum board (GB) on both sides, the R_w increased to 50 dB, raising the airborne sound insulation grades to 6 and 5 for partitions and enclosures, respectively. Adding 10 mm compressed glass wool strips between the GB and light steel frame further increased R_w to 51 dB, meeting national standards for residential wall sound insulation. Composite to 200 mm thick single-layer and composite ALC walls, the thickness and surface density of light steel frame walls decreased by 35% and 70%, respectively, while achieving higher sound insulation. In the 160-630 Hz frequency range corresponding to noise from road traffic, industrial operations, and daily life, the light steel frame walls system showed significantly improved sound insulation. Installing a window with an R_w of 33 dB in a conventional light wood frame wall did not significantly change the full-frequency sound insulation curve, with an R_w of 44 dB, raising the sound insulation grades to 5 and 4 for partitions or enclosures, respectively. Converting the GB on one side of the conventional light wood frame wall to double-layered, adding a 10 mm thick rubber sheet between the wood frame and OSB, and setting up a metal damping keel between the wood frame and GB created a composite wall with a window. This wall achieved an R_w of 48 dB, eliminating or significantly reducing the low-frequency resonance dips and high-frequency coincidence dips, raising the sound insulation grades to 6 and 5, respectively, meeting national standards for residential walls. Conclusion: Compared to light wood frame walls, CLT walls exhibit lower airborne sound insulation performance. Resonance dips, coincidence dips, and sound bridging effects are the key factors limiting the sound insulation performance of conventional light wood frame walls, preventing them from meeting national standards for residential walls. Replacing wood frames with light steel frames, installing sound insulation layers, and increasing the number of wall panels effectively improve wall airborne sound insulation performance.

Key words: timber structure walls, airborne sound insulation performance, sound insulation layers, light steel frame, weighted sound insulation index