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STC: Deciphering ICD 705 Acoustic Requirements and when “testing” is required (Part II)

ICD 705 further provides for three separate means of testing for acoustic integrity.  The primary means as already noted is elevated sound that can be heard but should not be intelligible. The second form of preferred testing is listed as follows:

C. Acoustic Testing

1. Audio tests shall be conducted to verify standards are met. Tests may be instrumental or non-instrumental as approved by the AO. Test method used shall be detailed in the CSP.

2. Instrumental Acoustic Tests

a) Only those with training on audio testing techniques shall conduct instrumental acoustic tests

b) With all SCIF doors closed, all perimeter walls and openings (e.g., air returns, doors, windows, etc.) shall be tested along multiple points to ensure that either Sound Group 3 or 4 is met.

c) Audio test sources shall have a variable sound level output.

d) The output frequency range shall include normal speech.

e) Test speakers shall be placed six feet from the test wall and 4 feet off the floor.

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

This test consists of amplified sound that is verified by a “sound professional” where sound is created at an amplified level (loud or very loud speech) and no intelligible words of information should be discernible outside of the secure space.  Again, per 705 policy, sound can be heard, but it should not be intelligible.

The last “alternative” test listed (and therefore the least preferential), is an ASTM standard “NIC 45” test which is believed to be an equivalency to STC 50.  While it comes close, this test has become recognized within the Intelligence Community as a “policy glitch” that needs to be amended, as most will fail this type of testing.  The reason for the failure is that the ASTM standard requires specific ranges be tested for a NIC 45 test that range far beyond the “human vocals” range of 300Hz-3kHz.  While those frequencies are included in the NIC, there are also frequencies below and above 300-3KHz in the NIC calculation.  No account can be given for those additional frequencies, which can dilute the final “pass/fail” test result by several points…The problem that exists is the knee jerk reaction that occurs when an acoustical fail is suspected.  The first thought is to seek out a commercial sound testing firm and have them perform a sound test of the perimeter wall systems.  It is very important therefore, that the second test as outlined above be conducted, NOT the NIC 45 test, which typically shows a failure every time.

Finally, yet another impediment to the NIC 45 testing…All sound masking devices must be turned off in order to conduct an instrumented test that qualifies under the ASTM standard.  So, the very countermeasures that may be put into place to ensure the acoustic integrity of the space,  in fact are not allowed to be operational during testing and the equivalency of those sound masking countermeasures couldn’t even be considered.  ICD 705 clearly accepts sound masking as an effective countermeasure tool when it makes sense to use them, as the policy indicates here:

c) Sound masking devices, in conjunction with an amplifier and speakers or transducers, can be used to generate and distribute vibrations or noise; noise sources may be noise generators, tapes, discs, or digital audio players.

In addition, it shouldn’t be left out how 705 defines the value of closed off perimeters and stand-off space as a countermeasure as well, which goes hand in hand with the SID for your space:

b) Facility design can include a perimeter location or stand-off distance which prevents non-SCI-indoctrinated person(s) traversing beyond the point where SCI discussions become susceptible to interception. For example, use of a perimeter fence or protective zone between the SCIF perimeter walls and the closest "listening place" is permitted as an alternative to other sound protection measures.

SPG’s experts understand the criticality of fundamental details, such as how your wall systems are put together to get a successful acoustic test result for Accreditation.  Whether it be instrumented testing for Acoustics, TEMPEST Emanations, or critical isolation of spaces of any kind, the cost of including SPG on your project can literally be “pennies on the dollar” in ensuring your facility is constructed the right way, the first time.  Click on the “Contact Us” button and one of our experts will be happy to start getting your project on the right track!


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