Acoustic Window Design
Typical Applications
Acoustic Windows have a very broad spectrum of applications. Internal acoustic windows are typically present alongside acoustic doors in multi-room configurations to provide noise reduction and isolation between activities and spaces. IAC Acoustics’ window systems have been installed in a huge amount of commercial and industrial enterprises including education, engine test facilities, theatres, courts, audiology and observational research. The most significant area of application however is for music and media – whether that’s live to control room, music practice, voice over, mixing and mastering, broadcast or any other application in that discipline, where visibility is required in a multi-room configuration.
These audio and media applications are invariably in heavily treated acoustic room environments, perhaps isolated from the main active areas of buildings and usually away from external windows and natural light. Acoustic windows therefore provide the opportunity for architects to open up the design space, bring light into the working environment, while critically maintaining the acoustic specification required. This is of course in addition to the core specification need for working visibility between two spaces.
IAC Acoustics’ range of acoustic windows or vision panels offer laboratory certified performance of Rw47-68dB, typically enough for most professional applications. We have developed customised project solutions which push performance up towards Rw80dB, typically the limiting factor is the host partition construction and flanking paths in and around the space.
General Design Features
The other benefit to architects in the development of the spaces design, is that acoustic windows look cool! When done right, they bring a quality aesthetic finish to a space, especially when they are engineered with angled panes and matched with acoustic doors. Clients and architects are often interested in the options for angled panes, to understand why they are needed, and how they affect the performance of the acoustic window. There are a number of factories to consider in acoustic window design, generally either acoustic or relating to practical application and in-field use.
The acoustic performance of a window is ultimately determined by the host partition – the window could be of higher design specification, but ultimately the sound transmission between rooms would be limited by the weakest element. Beyond this window performance is determined by the thickness of the glass and the air gap between panes – the variable combination between the two offer a very broad spectrum of performance and design options. Logic applies – the thicker the glass then the better the performance. Up to a point, where diminishing returns occur with incremental thickness once you reach higher performance levels, approximately over 60dB. However, the frequency spectrum will continue to be affected by changes in glass thickness, so for applications which would have a significant amount of low frequency noise this could be beneficial.
This variable glass thickness determines coincidence dip – sound waves and frequencies absorbed by say 12.8mm laminated glass would be different to that of 16.8mm laminated glass. By combining the two variable thicknesses in an acoustic window application noise reduction performance is enhanced across a broader frequency range. Air gap and absorption between glass panes is vital to window performance. Sound waves need space to decay, and on impact with the second pane, absorption is needed within the acoustic window to reduce standing waves in the cavity between panes. It’s the inter relationship between air gap and glass thickness which requires the acoustic engineering, testing and project experience to deliver a high performance acoustic solution to specification.
Angled Panes and Customised Designs
Typically angled panes are used for two reasons. To reduce visible reflections in the acoustic windows, i.e. the mirror or ‘inception’ effect. This reflection effect is compounded in application if the window utilises a 3 or even 4 pane design, so is a legitimate practical consideration for the room users. The other design consideration is for acoustics – to reduce the build-up of standing waves in the room space. By angling panes, up or down, sound waves can be deflected back to areas of absorption, i.e. ceiling absorbers or carpets. This is particularly relevant to mixing desks and playback where speakers may be directed towards an acoustic window. Engineers need to hear pure uncoloured sound ideally without any sonic interference from the room environment.
In close working environments, such as voice over booths, where the user and microphone may be in close proximity to the acoustic window through to the control room, angled panes again reduce standing waves. This affects microphone pick-up, cluttering the vocal and making it hard for the producer to get the audio mix to the correct levels of speech intelligibility.
If installing an acoustic window to a space with an existing partition, there may not be enough room to fit in the angle pane requirement, typically 5 degrees slope, which offers the best compromise between acoustic needs of maintaining the air gap and managing standing waves, balanced with aesthetics and reflection management. In these applications IAC Acoustics has a customised window design service which provides a structure outboard of the partition, acoustically and aesthetically matched to contain the window. This gives the space needed to accommodate the angle while maintaining the specified air gap.
Acoustic window sizes are also hugely variable. Overall square metrage is the determining factor for practical pane size, but viewing windows can go upto 3 meters wide, and beyond with multiple adjacent installations or mullioned configurations. Systems can also be fire rated offering significant high performance integrity and insulation protection up to 120 minutes. For applications requiring greater levels of physical safety, bullet proof glass can be used in engine test facilities or firing ranges.
Summary
High performance acoustic windows are a necessity in numerous applications in the arts, media and music industries. They add significant benefit to architectural design and aesthetic, while helping support the enhancement of room acoustics. Take a look at the recent installation of matching acoustic doors and windows at the doctor mix studio, where you can see the design, build and installation of the acoustic window system.
Acoustic windows are one of the most exciting products to work with for both architects and IAC Acoustics – they offer a huge scope of design and customisation, enabling a space to add a stylish feature and individuality with practical purpose. I look forward to helping you with any new design specifications for your next project!
Paul Gilbert
Sales Manager – Architectural Products
+44 (0) 1962 873144