What Is Acoustic Testing and How It Works

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What Is Acoustic Testing and How It Works

When discussions involving classified information must take place within a SCIF, your program typically falls under a Type II or Type III Compartmented Area (CA). One of the additional requirements outlined in the IC Tech Spec for Type II and III CAs is maintaining a Sound Transmission Class (STC) or Noise Isolation Class (NIC) rating. These values fall under one of two categories, depending on the SCIF requirements. Your Accreditation Official will inform you which STC value your facility must meet.

• Sound Group 3 – STC 45 or better: Loud speech from within the SCIF may be faintly heard but not understood outside the SCIF. Normal speech is unintelligible to the unaided human ear.

• Sound Group 4 – STC 50 or better: Very loud sounds inside the SCIF—such as loud singing, brass instruments, or a radio at full volume—may be heard faintly or not at all outside the SCIF.

• NIC Ratings: NIC 40 is required for Sound Group 3, and NIC 45 is required for Sound Group 4.

Once your SCIF space is fully fabricated and ready for acoustic testing, several specialized pieces of equipment are required. These include a 12-sided speaker, an audio and acoustic analyzer, and an audio generator. With this equipment, trained audio technicians begin testing with all SCIF doors closed. White noise is played through the speaker, positioned six feet from the test wall and four feet from the floor, covering all required testing frequencies simultaneously.

The technician begins by measuring reverberation time. This involves recording a benchmark level, then turning on the speaker and timing how long it takes for the sound to decay back to the benchmark level after the speaker is paused. This process is repeated three times, and the times are averaged.

The second part of the test involves measuring sound transmission. With the speaker active inside the SCIF, the technician records sound levels from outside the test wall using the acoustic analyzer at specified distances, in thirty-second intervals. This shows how much sound escapes the source room.

Next, a benchmark measurement of ambient noise is taken from outside the testing wall with the speaker turned off. The speaker is then turned back on, and the technician walks along the exterior wall or partition, recording the sound level at specific frequencies. The process is then repeated with the speaker placed outside the SCIF to measure how sound penetrates the space from the exterior.

This testing process can take anywhere from a few hours to several days, depending on the size of the secure area and the amount of ambient noise. Ensuring that the Acoustic Testing Technician’s workspace remains uninterrupted is essential, as unexpected sounds can influence test results.

Once all data is collected, the Acoustic Testing Technician will calculate the STC or NIC rating for your secure facility.

If your existing SCIF requires acoustic testing or retrofitting to meet required STC values, contact us at Faraday Defense to ensure full compliance.