When conference rooms, boardrooms, AV centers, or hotel ballrooms “leak noise” from one partitioned space into another, there is often a really simple reason: The operable wall system may not actually be designed to “keep the peace.”
In designing and specifying operable walls for spaces like these, often overlooked is the distinction between operable walls designed primarily for “space management” and those designed for “sound control.” But there is a very real distinction, made clear in the Construction Specifications Institute’s (CSI’s) Master Format, the specifier's bible. Operable walls meeting the specifications of Division Section 10 22 23 are defined as “operable partitions/portable panels”; those meeting the specifications of Division Section 13 48 00 have to do with “sound control.”
While almost all of the operable walls manufactured today have some sound-controlling properties, few can provide the sound-control properties of a wall designed to do just that - an important consideration when the goal is measurable “true” sound isolation.
Demystifying the Specification
The sound properties of all movable walls are often identified by a single-number rating: Sound Transmission Class (STC), which represents the performance of the system in a laboratory from 125 Hz to 4K Hz. However, a better indication of the sound-controlling property of a wall is Noise Isolation Class (NIC), which represents the performance of the system once it has been installed. And, this is an important distinction.
Very often, walls are sold with very high STC ratings. In the field, however, the NIC rating may be as much as 10 points lower. While 10 points may not sound like a big difference, it actually means that the uncontrolled noise will be twice as loud as it tested in the laboratory. A leading industry expert recently wrote that, to be a successful installation, the difference between STC and NIC should not exceed 12 points. In this case, less is more: The smaller the differential between STC and NIC, the better the in-field noise-reduction performance.
The important questions guiding the specification are:
- How will the divided spaces be used? Are low-frequency noises (such as thumping music) a factor?
- What level of privacy (noise control) is needed in the divided spaces?
- What is the NIC rating and is it within 5 points of the STC?
- Will the wall still pass in-field testing if pass-through doors are required?
In many applications, sound control is a combination of art and science, and the science is a bit more complicated today. Controlling low-frequency noise is one very common example since it actually falls out of the NIC or STC curve, and success or failure of such a project may depend on controlling transmission loss at much lower frequencies. In these cases, acoustical consultants are best-equipped to interpret the science and guarantee success.
Sound-control operable walls will cost more than operable partitions designed for “space management.” And, that’s an investment decision that has to be made in the early stages of the project-planning process. While sound-control operable walls can help manage space, operable partitions will not necessarily allow you to control sound.
Ken DeLasho (firstname.lastname@example.org) is president of the sales division at IAC America, Bronx, NY.