The acoustic benefits of timber

Nelson Airport 2

In this subject overview

This is a high-level introduction to the unique makeup of timber and its acoustic benefits.

Be sure to review the NZ Wood Guide for more detailed and in-depth guidance.

Why timber

Timber’s sound performance makes it music to the ears

The first three words that come to mind when defining the acoustics of timber materials are resonant, stiff, and lightweight. This makes timber an ideal material for musical instruments and vibrant spaces such as concert halls and cultural spaces such as wharenui and fale. The visual and aural experience provided by timber adds a sense of comfort and warmth that isn’t imparted by other materials. 

Timber is a versatile and easy-to-work-with product that can be designed to be a sound reflector, absorber, or diffuser. This, combined with its pleasing aesthetic, makes it a commonly used surface treatment that can achieve various acoustic outcomes.

The stiff and lightweight nature of timber, unfortunately, makes it a poor sound insulator. However, this can be overcome with a range of strategies, such as structural isolation and using reconstituted wood products with more mass and damping.

The unique makeup of timber means that it can enhance the sounds you want and dampen the sounds you don’t. 
It does this in three different ways: reflection, absorption and diffusion.
Making sounds clearer for listeners

Timber, in its natural state, is a good reflector of sound. For example, a pine board reflects approximately 90% of the sound that hits it (NRC 0.1). This can be improved to 95% or greater by using products like plywood or painting the surface. 

Sound reflectors are often needed in concert halls, churches and other music performance spaces, where early and lateral reflections assist with clarity and enveloping the listener within the performance. They are also used in lecture theatres and large meeting rooms where strong early reflections assist with enhancing speech clarity.

Image: Christchurch Town Hall

St Hildas Anglican Chruch

Nick Officer, First Light Studio. p. David Hensel

St Hildas Anglican Church Island Bay inside

Well-designed wood can excel at insulating sound


Mass and sound insulation go hand in hand. In fact, one of the first things a young acoustic consultant learns about is mass law, which states that a doubling of mass provides a 6 dB improvement in sound insulation.

This means that timber is often seen as inferior to heavier products, such as concrete, with respect to sound insulation. For example, a 150mm thick cross-laminated timber panel has a sound insulation performance of STC 36 compared to STC 55 for 150mm of concrete thickness. 

However, with smart design strategies and attention to design and construction detail, this doesn’t have to be the case.

Air is key to good timber soundproofing

The most effective strategies for improving the sound insulation performance are using air cavities and structural disconnections. A classic example of this is the double stud wall construction or acoustic floating floor (see Figure 13 – NZ Wood Guide, Chapter 13.5).

Source: "Figure 13. Double stud timber frame wall" of NZ Wood Design Guides, Chapter 13.5: Acoustics, May 2020

Reconstituted wood products such as Triboard™ and Strandboard® improve the acoustics of natural timber products by increasing the mass and damping. These are often utilised in wall and floor systems, enabling high levels of sound insulation to be achieved with timber.

Meeting and exceeding noise control targets with timber

For apartment design, the code minimum performance is STC 55, however, higher-quality developments often target ratings of up to STC 65+. 

Light timber frame construction is a common and well-known construction technique in New Zealand. The acoustic design of light timber frame buildings has progressed significantly in the past 10 years. It is now common to see systems and projects achieving performances of up to STC 65.

Source: “Figure 18. A generic lightweight floating floor system” of NZ Wood Design Guides, Chapter 13.5: Acoustics, May 2020

Mass timber is starting to make significant inroads into the market. Like light timber frame, it is common to see systems and projects achieving performances of up to STC 65. Mass timber can achieve even higher performances due to its increased weight (see Figure 42 – NZ Wood Guide, Chapter 13.5).

Source: Figure 42. A generic lightweight floating floor system on CLT” of NZ Wood Design Guides, Chapter 13.5: Acoustics, May 2020

Turning timber’s trash into treasure

Uses of timber waste products such as sawdust have been shown to have a use in improving sound insulation performance. Research undertaken by the University of Auckland and Scion (Chung, H., Emms, G., & Fox, C. (2014). Vibration reduction in lightweight floor/ceiling systems with a sand-sawdust damping layer. Acta Acustica United with Acustica100(4). has shown that a floor system with the upper cavity filled with a 60/40 sand/sawdust mix can achieve STC 65+ (see Figure 20 - NZ Wood Guide, Chapter 13.5).

Source: “Figure 20. Vibration damping floor topping using sand and sawdust in a cavity” of NZ Wood Design Guides, Chapter 13.5: Acoustics, May 2020

Flattening flanking sound

A key consideration for timber buildings is the control of flanking sound. This is critical in apartments and other buildings with high sound insulation performance requirements. Flanking sound travels around the wall or floor by some other path, which can significantly degrade the onsite performance (see Figure 6 - NZ Wood Guide, Chapter 13.5). For the example in Figure 6, the wall may be rated STC 65, but the floor flanking path would reduce the onsite performance to approximately STC 45. 

Designers should keep the following in mind to minimise flanking sound:

  • Wall and floor linings shouldn’t be continuous between acoustically separate spaces.
  • Minimise the use of timber blocking.
  • Avoid connecting double stud walls together.
  • Small air cavities (<45mm) should be avoided.
Source: “Figure 6. Horizon flanking paths for airborne sound in double stud walls via continuous floor diaphragms” of NZ Wood Design Guides, Chapter 13.5: Acoustics, May 2020