CASE STUDIES
Acoustic Glazing

Introduction 

The purpose of this Acoustic Glazing White Paper is to provide an introductory definition of acoustic glazing, methods of measuring transmission loss and to provide general recommended roles and responsibilities for acoustic glazing selection on projects. The paper can be used as an introduction to acoustic glazing and as a general procedural guideline but each project is unique and should be specific to your own project for a successful acoustic glazing selection process.

The acoustic glazing selection can be a complicated and laborious process if the owner is targeting high acoustic performance or is unsure of what their targeted performance should be. However, by educating ourselves about acoustic glazing systems and understanding the capabilities of a system, we can mitigate potential risks and exposures that acoustic glazing can create. Ultimately, if the owner knows the sound loss they intend to achieve, the architect designs accordingly and the builder is educated about these systems, we can manage owner expectations and deliver an end product that achieves the owner’s targeted performance.

Defining Acoustic Glazing

Acoustic glass is constructed from combinations of various glass types along with acoustical window frames that assist in reducing sound transmission (transmission loss) from unwanted noises (1).

It is important to note that in discussions regarding acoustic glazing, there is the composition of the acoustic glass itself and there is the complete acoustic glazing assembly. The acoustic glass (Fig. 1) would consist of glass lite(s), laminate and potentially air space between the lites. The complete acoustic glazing assembly (Fig. 2) consists of the acoustic glass and the frame.

The purpose of acoustic glazing is to create a Sound Transmission Loss (STL or TL), which is the reduction of energy as it is transferred through a barrier (interior partition, exterior wall, etc.). The TL is measured by the resulting change in decibels, as measured across a range of frequencies, between the source of the sound and the opposite side of the sound barrier (partition) and is given as a singular number noted as STC and/or OITC.

STC (Sound Transmission Class) – a single-number rating denoting the sound isolating properties of a building partition over the sound frequency range 125Hz to 4000Hz. This value is used most often for interior partitions. (3)

STC is used most often for interior partitions. It is also used in qualifying exterior wall acoustic performance. Although Viracon does not recommend using STC for exterior wall glass selection (1), do not assume STC performance is not applicable when evaluating exterior glazing performance.

OITC (Outdoor-Indoor Transmission Class) – a single-number rating denoting the sound isolation properties of a building façade element over the sound frequency range of 80Hz to 4000 Hz to account for lower frequency transportation noise. (3)

It should be noted that although STC & OITC are the most commonly used method of measurement, the TL at each frequency should also be carefully observed. It is possible to meet the targeted STC & OITC but to be underachieving on specific frequencies at the same time. Specifically, lower frequencies (bass) are more noticeable to the human ear. For example, if the project is in close proximity to loud music, it is irrelevant if you meet or exceed the STC and OITC ratings, but underachieve on low frequency TL, because it will be the low frequencies that are most noticeable.

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