Unveiling Acoustic Door Ratings: Demystifying STC and Enhancing SCIF Room Design
Acoustic testing allows specialized door manufacturers to give their acoustic doors a performance rating, designated as the sound transmission class (STC) rating. Recently, AMBICO set out to design an STC 55 rated Steel door and frame assemblies. Aided by independent testing, we were challenged to refine our Sensitive Compartmented Information Facility compliant door and frame assemblies to meet the high standards set out in ICD/ICS 705 for SCIF rooms. We also completed a similar design for wood door and steel frame acoustic applications.
Understanding Sound Transmission Class (STC) ratings
The purpose of an acoustic door and frame assembly is to limit the amount of sound transmission from one side of the assembly to the other. Working in unison, the frame, door, seals, and threshold are all integral parts that work together to achieve an STC rating, which is a rating that is tuned to the frequencies that the human ear can hear in a laboratory test. During laboratory testing, noise is generated on one side of the door and frame assembly and is measured on the other. The difference in readings is called the transmission loss and is calculated following the ASTM E-90 standard. In accordance with ASTM E-413, the transmission loss at 16 frequencies is compared to the standard STC curve to determine the STC rating.
What is a SCIF room?
A SCIF room, which is used by the United States Department of Defense and the United States Department of State, is a secure room used by elected officials and national security personnel to conduct classified information and be set up permanently or temporarily. As a result, SCIF rooms often have acoustic security requirements including denying aural access to classified information. While lower-rating STC 25-50 is available and recommended for less sensitive locations such as schools, boardrooms, or performing arts centres, a SCIF compliant door must meet the ICD/ICS 705 standard determined by the Department of Defense in the United States and is typically STC rated 50 or 55.
How acoustic testing allowed us to improve our STC Rated doors
For the higher-rated STC 55 opening, our design team was determined to design a clean and functional door that consisted of a single panel without built-in reveals that limited the thickness to 2-3/4” where standard builders hardware could be utilized alongside cam lift hinges. They focused on using a low-profile perimeter seal system that works well with mortise or surface latching hardware using standard industry backsets. This assembly can be readily configured to accept high security and access control hardware used on SCIF doors in accordance with ICD/ICS 705. As a result of continuous testing and refinement, our team was able to successfully design an STC 55 door that complied with ICD/ICS 705 standards and a fire rating of up to three hours.
We are proud of the many enhancements that went into this multi-stage testing program and the valuable attributes that this new product offers. AMBICO continues to develop our acoustic door and frame assembly product line with an attention to detail that benefits our customers and end-users.