07 Jan 2013

Listen Up – How Sound Transmission Class Ratings Relates to SCIF Security

0 Comment

When it comes to breaching a facility’s audio security, sometimes it doesn’t take high tech electronics. All it takes is the lowest tech of all: ears. That’s right. All the high tech security in the world does not help if a classified conversation can be heard by a covert operative standing nearby. This is why the DOD created a series of sound transmission class ratings to standardize the science of audio security.

What Do STC Ratings Cover?

The established Office of the Director of National Intelligence (DNI) guidelines are designed to protect classified conversations from being inadvertently overheard outside a SCIF. This is not intended to protect deliberate technical interception of audio communications.

The ability of a SCIF structure to retain sound within the perimeter is rated using a descriptive value, the Sound Transmission Class (STC). To satisfy the normal security standards of SCIFs, the following transmission attenuation groups have been established:

  • Sound Group 3 – STC 45 or better. Loud speech from within the SCIF can be faintly heard but not understood outside the SCIF. Normal speech is unintelligible with the unaided human ear.
  • Sound Group 4 – STC 50 or better. Very loud sounds within the SCIF, such as loud singing, brass music, or a radio at full volume are audible by the human ear faintly or not at all ouside of the SCIF.

How Is Audio Security Compliance Assured?

First, it is vital that you conduct audio tests to verify that security standards are met. Tests may be instrumented or non-instrumented as approved by the AO. Use the test methods that are detailed in the CSP. Other requirements are as follows:

  • If you are performing instrumented acoustic tests, it is vital that those who conduct the tests are trained on audio testing techniques.
  • With all SCIF doors closed, test all perimeter walls and openings (e.g., air returns, doors, windows, etc.) at multiple points to ensure that either Sound Group 3 or 4 is met.
  • Other testing requirements indicate that audio test sources must have a variable sound level output.
  • The output frequency range must include normal speech.
  • Place test speakers six feet from the test wall and four feet off the floor.

Audio gain of the test source will produce “loud or very loud speech” as defined by Sound Group 3 or 4 levels respectively.

  • As an alternative, instrumented testing should be performed to Noise Isolation Class (NIC) standards. Results must comply with NIC 40 for Sound Group 3 and NIC 45 for Sound Group 4.
  • All non-instrumented tests must be approved by the AO.

Audio integrity of a SCIF is paramount to its ability to keep conversations from being overheard. When it comes to securing a SCIF, no detail is too inconsequential to consider. The nation’s security could depend on it.


When it comes to securing the nation’s secrets, Jaye Andone is an expert. Her company, SCIF Global Technologies, is in the business of designing, manufacturing, and transporting Sensitive Compartmented Information Facilities worldwide.

[top]
About the Author


Jaye Andone is president and CEO of SCIF Global Technologies. Jaye will most likely be your first point of contact to lead you through the process from concept to procurement of your facility. Request a Quote or give her a call: 904-524-0911

Leave a Reply

Your email address will not be published. Required fields are marked *