The acoustic protection guidelines listed below are designed to protect classified conversations from being overheard outside a SCIF and not intended to protect against purposeful technical interception of audio communications. A SCIF structure and its ability to retain sound within the perimeter is rated using the Sound Transmission Class (STC).
Sound group ratings are divided into two groups: Sound Group 3 and Sound Group 4. All SCIF perimeters are designed and constructed with meeting the standards of Sound Group 3 or better in mind. Acoustic protection and perimeter construction specifications for Wall A, B, and C can be found in previous articles.
Sound Group 3 has a STC 45 or better. In this sound group, loud speech from within the SCIF can be faintly heard but not understood outside the SCIF. To the unaided ear, normal speech is unintelligible. Sound Group 4 has a STC 50 or better. In this group, loud sounds within the SCIF can be heard with the human ear faintly or not at all outside the SCIF.
Acoustic Testing
Audio tests must be conducted to verify all acoustic protection standards are met. With approval by the AO, these tests may be instrumental or non-instrumental and the test method used must be noted in detail in the CSP. All non-instrumental tests must be approved by the AO. Only qualified personnel with training on audio testing techniques will be allowed to conduct instrumental acoustic tests.
With all doors closed, all SCIF perimeter walls and openings (air returns, doors, windows, etc.) must be tested along several points to ensure that either Sound Group 3 or 4 is met. All audio test sources must have a variable sound level output with the output frequency range including normal speech. Test speakers must be placed six feet from the test wall and four feet off the floor. As noted by Sound Group 3 and 4 respectively, audio gain of the test source must produce “loud or very loud speech”.
Instrumental testing can be performed to Noise Isolation Class (NIC) standards. These results must comply with NIC 40 for Sound Group 3 and NIC 45 for Sound Group 4.
Sound Transmission Mitigations
In most cases, SCIF perimeter construction and acoustic protection should provide the necessary protection for Sound Group 3. However, when Sound Group 3 or 4 can’t be met within the normal SCIF construction standards, there are supplemental mitigations used to protect classified discussions from being overheard.
These mitigations can include (but aren’t limited to):
- Structure enhancements can be used to increase the resistance of the perimeter to vibration at audio frequencies.
- SCIF design can include a perimeter location or stand-off distance. This prevents non-SCI-indoctrinated person(s) from traversing beyond the point where SCI discussions can be intercepted.
- In conjunction with an amplifier and speakers or transducers, sound masking devices can be used to generate and distribute vibrations/noise.
- Speakers and transducers must produce sound at a higher level than the voice conversations within the SCIF.
- Speakers and transducers must be placed close to or mounted on any paths that allow audio to leave the area including doors, windows, walls, vents, etc.
- Wires and transducers must be, to the greatest extent possible, located within the perimeter of the SCIF.
- During TSCM evaluations, the sound masking system will be subject to inspection.
- A speaker may be installed outside the SCIF if the AO determines the risk to be low and meets the following conditions:
- Cable exiting the SCIF must be encased within rigid conduit.
- Sound masking system must be subject to review during TSCM evaluations.
- For common walls, speakers/transducers must be placed in a location so the sound optimizes the acoustical protection.
- For all doors and windows, speakers/transducers must be placed close to the aperture of the window/door. The sound must be projected in a direction facing away from conversations.
- Once the speakers/transducers are in an optimal location, the system volume must be set and fixed. Volume level is determined and adjusted by listening to conversations outside the area to be protected. The speaker volume will then be adjusted until conversations are unintelligible from outside the SCIF.
- Sound-source generators must be located within the SCIF.
- AM/FM receiver cannot be present on sound-source generators.
- If the sound-source generator has the capability to record sound, that function must be disabled.
- The following are examples of government-owned/sponsored sound-source generators:
- Audio amplifier w/ standalone computer (no network connection)
- Audio amplifier w/ a cassette tape player, CD player, or digital audio player, or w/ digital audio tape (DAT) playback unit
- Integrated amplifier and playback unit incorporating any of the above music sources
- A noise generator or shift noise source generator using either white or pink noise
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Technical Specifications for Construction and Management of Sensitive Compartmented Information Facilities
SCIF Container Series | Part 1: Site Evaluation
SCIF Container Series | Part 2: Design Planning Checklist
SCIF Container Series | Part 3: Perimeter Wall Construction – Wall A
SCIF Container Series | Part 4: Perimeter Wall Specifications – Wall B
SCIF Container Series | Part 5: Perimeter Wall Specifications – Wall C
SCIF Container Series | Part 6: Vents and Ducts
SCIF Container Series | Part 7: Modular SCIFs
SCIF Container Series | Part 8.1: Intrusion Detection Systems
SCIF Container Series | Part 8.2: Intrusion Detection Systems
Information has been gathered from sources deemed reliable but not guaranteed and is subject to change without notice. The information contained in this site is provided for informational purposes only.