One of the primary concerns when specifying a demountable wall system is acoustics. This aspect of a product can be more difficult to evaluate than it sounds. Not only are there many factors that can affect the acoustics of a system, there is also a lot of misunderstanding and misinformation that accompany them. Below are some facts and tips that can assist in accurately and effectively figuring out what will best work for a given project.
The Issue with STC
One of the most common ways of measuring and comparing acoustic properties is an STC, or sound transmission class, rating. While it can be a useful tool to evaluate differences in performance among systems, it is important to also be aware of some of the flaws that accompany this rating number. One of the most common issues is determining what was actually tested to achieve the listed rating. Many of the STC ratings touted by companies do not reflect how the system will perform in the field, because they were obtained by testing only a certain component of the wall or evaluating it in unrealistic or unusual conditions. For instance, a rating may have been achieved by testing a sidelite wall only; while this can provide an idea of function, it does not account for sound leakage at doors, which is a major factor in acoustic performance [we touch on this idea more below]. Companies also often test after implementing measures that wouldn't be standard to their field installation, such as stuffing the framing with insulation for better performance.
Glass Wall Acoustics
While there are certainly steps that can be taken to improve acoustic performance, and while some wall systems clearly function better than others when it comes to sound leakage, there are certain factors that are true across essentially all products. The first is the STC of glass itself. For standard 1/2" glass, the generally accepted STC rating is 36 [for 3/8" glass this drops to 34 STC, and for 1/2" laminated it jumps to 38 STC]. This means that while a framing system can certainly perform worse depending on its makeup and installation, you cannot really achieve any better than these listed STCs for glass walls. Another aspect to consider is the field conditions that will vary from project to project. While no company is going to do their official STC testing on a wall with an uneven floor or ceiling, this is often the reality in the field and should be considered when evaluating systems. One way to do this is to look for a system that can be installed tight to an opening and for which glass is field measured in pieces, which can help to ensure that there aren't excessive gaps or shimming in the field when conditions are less than ideal.
Door and Hardware Considerations
Doors can be a very tricky aspect of acoustic performance. When chosen correctly, doors and door hardware can contribute greatly to improving acoustic performance. The corollary to this, of course, is that the wrong door choices can undo all of the effort that went into picking a well-performing system. On top of the floor conditions that were referenced earlier, uneven floors can also lead to large undercuts on doors, which will of course lead to acoustic leakage. Using a system that provides gasketing on the three sides of a door frame, along with an acoustic drop seal to combat the undercut, can assist with acoustically sealing a door. Doors conditions are also one of the main reasons that completely frameless glass systems do not perform well acoustically: because there is no door frame, there are necessarily gaps between the door and sidelite glass, as well as an undercut on the door.
Still have questions regarding acoustic performance of glass wall systems and how to choose what's right for your project? Reach out and let us know! With systems that can reach up to a 49 STC, we're happy to assist with options and find the best solution for your needs.