by David Ingersoll
Design/construction teams are constantly balancing the desire for a high-quality look and feel with adherence to acoustical requirements and project budgets. This is especially true when it comes to wall and ceiling choices. Whether selecting from basic wall and ceiling panels or custom woodwork, noise is a primary consideration—no matter how it looks, it has to perform.
As with any construction project, it is most cost-effective to create an acoustically correct wall and ceiling system during the planning stage, rather than address the problem later. By being more informed upfront, construction teams and specifiers can eliminate guesswork and choose a solution that performs properly by delivering acoustically correct wall and ceiling panels in any environment.
Understanding NRC and STC
Many project teams neglect critical ratings that denote noise control performance. The noise reduction coefficient (NRC) and sound transmission class (STC) play important roles in guiding how well a new space will perform, acoustically speaking.
While NRC and STC are often lumped together in a generic category of noise reduction, these ratings serve dramatically different purposes. NRC boils down to the amount of energy absorbed when a sound wave comes into contact with a surface—in this instance, a wall or ceiling finish. By giving early thought to the room’s finishes and surfaces, the acoustical engineers can ‘tune’ the room for optimal performance based on the end user’s needs.
When an acoustical engineer evaluates NRC, he or she is looking at the reverberation time or the RT60 of the space. Reverberation time represents how long a sound lasts within a given space before it dissipates, or specifically how long it takes a signal or a sound to drop 60dB. A decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity, often power or intensity. When measuring reverberations, the standardized testing method relies on a 60db range for the purpose of achieving a baseline. Construction teams should determine the appropriate reverberation time for each room or section of a building. For example, a hotel lobby with a broad open area might be admissible to a higher reverberation, whereas a library demands a lower reverberation level.
Throughout typical construction projects, there are spaces fitting each category of NRC tolerances. For example, homes, libraries, and corporate offices have lower limits, while lobbies, auditoriums and theaters have higher ones. The bottom line is, the room needs to perform well and to achieve this state, the acoustics must be ‘tuned.’ If a conversation cannot be held, or if announcements over a public address system sound muddled, the space in question has a reverberation problem. When you can hear too much—like the confidential conversation happening in the next room—there is a problem with STC.
STC is a measuring stick for how much sound is blocked out of a space. Project teams may choose noise-blocking materials for apartment or office settings, where it is essential to control noise from room to room.
Planning for performance and style
Of course, as much as noise control is important, most building owners and facility teams are under equal pressure to make the space look good. While the aesthetics can drive the price tag higher, advanced planning can enable acoustical teams to achieve a pleasing space both visually and auditorily.
Major headaches can be avoided when construction teams work in tandem with acoustical engineers from the beginning of the planning process. Early involvement can also reduce labor rates by allowing general contractors to layer in acoustical solutions during the initial wall and ceiling installation, rather than hiring costly specialty contractors to install acoustical solutions after the fact.
If beauty is important, project teams can build in architectural treatments around sound control elements in the design phase, rather than ending up with generic, rectangular tiles that simply control noise without a custom look. Understanding each component of wall and ceiling specifications, and its role in solving acoustical challenges, can help construction and design teams specify customized finishes for a better price with lower labor costs.