Acoustic Window Designs

Modern institutions and industries require acoustic control that most buildings were never designed to provide. Multi-use buildings, lightweight materials and the vogue for large areas of glass present a challenge. Almost all challenges can be overcome but two key points of sensitivity are the windows and doors.  Doors being the most critical access and touch point, while windows being the visual stimulus between spaces and activities that the eye is drawn to.

Blocking sound while admitting light and providing access are difficult objectives to achieve. Modern buildings depend on natural light to minimise power consumption and carbon footprint, while good observation provision is vital in most music and media applications – such as live control rooms, music and theatrical rehearsals, live performances and for mixing, mastering and broadcasting.

Audio and media spaces are often deliberately located away from a building’s most active outer areas and therefore external natural light may already be in limited supply. Acoustic windows provide architects and interior designers with huge opportunities to open up claustrophobic niches and bring a real sense of space and natural light back into working environments.  When combined with strong aesthetics and function these complement and add to internal build design.

IAC Acoustics’ range of windows are laboratory certified to achieve Rw47-68dB performance, which is sufficient for almost all professional applications, but we have also developed solutions which can push the acoustic performance up to around Rw80dB. The main performance limiting factor is usually the host walls into which the windows are to be fitted, or when there are essential flanking paths around adjacent space.

Principal Design Features

Acoustic performance isn’t the only consideration for the designer. In the case of theatres and concert halls, an impressive aesthetic is essential but almost every space in which human beings live and work can benefit from inspired design. Acoustic windows are not incompatible with a designer’s quest for an attractive design and actually can provide architects with extended opportunities to achieve cool creative and visually stunning spaces. For example, many acoustic windows have angled panes that serve the practical purpose of preventing direct sound reflections but they can also be incorporated as a design statement, especially when paired with matching acoustic doors and other features. The principle of angled planes can be extended to other features of the acoustically isolated space or the building in general. Acoustic control and building aesthetics are therefore a two-way street and each will often inform the other.

Sound insulation between rooms and spaces is always limited by the weakest element – which is usually the construction of the partition walls separating them. Unless your application justifies a comprehensive rebuild, this limit will therefore usually be a constraining factor on the acoustic performance of the window. Acoustically the main design variables are the thickness of the glass and the air gap between the panes.

Logically, the thicker the glass, the greater the sound insulation, but there are diminishing returns after about 60dB especially for mid to high frequencies. Typically the variable thickness of the glass is beneficial in absorbing varied frequency profiles. In some cases, there are other reasons affecting the choice of thickness too – such as operator safety in engine test facilities or on firing ranges. Bullet-proof glass can be incorporated into an acoustic window and still provide an excellent acoustic outcome.

The air gap between panes is a vital element of acoustic performance. Firstly, because sound-waves need space in which to decay, and secondly to prevent a standing wave developing between the panes. Each of these factors interacts with the other, which is why the design of acoustic windows is typically customised to suit specific project requirements and conditions.

Size and Geometry

Another benefit of angled panes is that they avert problems with visual reflections (mirroring or the inception effect) which can impact on room users. This is especially true of internal windows and if the window uses three or four panes of glass they can potentially produce multiple staggered reflections.

The primary motive, however, is acoustic. In particular, angled windows help destroy standing waves between parallel room walls. Angles are typically upward or downward to suit the room conditions – reflected waves can be sent toward absorbent surfaces such as carpets, acoustic wall panels or ceiling tiles. This technique is particularly valuable in areas used for mixing and recording. Recording engineers need to know they are hearing ‘pure’ sound uncoloured by room interference.

In confined environments like voice over booths, a microphone is often close to the window into the control room. In this close proximity the microphone collects reflections and the outcome is often a cluttered vocal sound that is difficult to mix. An angled acoustic window here would be an ideal solution but the space is necessarily limited. At least 5 degrees of slope are needed to gain a worthwhile benefit. In tricky scenarios like this, IAC Acoustics provide a bespoke service and custom design a window based on an outboard of the partition, so that the solution is matched perfectly in aesthetics and acoustics with the particular site.

Acoustic windows also vary greatly in size. Viewing windows are often as large as three metres in width, or there may be multiple windows separated by mullions for larger glazed installations. We provide acoustic solutions for all these scenarios.

Summary

Whether you work in the arts, media and music industries or just need a quieter office space or space  division, acoustically designed windows are a necessity in the modern world, but their additional architectural benefits should never be overlooked. At IAC Acoustics, our engineers enjoy working with acoustic windows precisely because of the challenges and creative opportunities they often provide. Custom designed acoustic windows should be seen as an opportunity to provide your facilities with individuality and style as well as industry-leading acoustic quality.

Guy Pulley
+61 (0) 2 8781 0430
guy.pulley@iac-australia.com.au