Acoustical Leakage

It’s the oldest form of eavesdropping. Defined as: “a back-formation from eavesdropper, one who eavesdrops, from Middle English evesdropper, from evesdrop, place where water falls from the eaves, from Old English yfes drype.” 
(The American Heritage® Dictionary)

Acoustical leakage, or sound migration, is what allows the eavesdropper to eavesdrop. Sometimes the acoustical leakage is free and clear; an open discussion in a public area, like a restaurant or train. This happened recently to a financial dealmaker. He blew a $15 billion takeover by discussing it in a train. He didn’t know a rival was sitting within earshot. Disasters like this happen quite often. All I can advise is be more circumspect with your confidential conversations.

Acoustical leakage often occurs even when specific steps are taken to keep conversations private, like closing an office or conference room door. But, as sure as sound wants to migrate, outsiders want to hear. Who or what is to blame when this inside information gets out?

Inadequate Anti Acoustical Leakage Construction

Aside from structural requirements, walls are built to provide privacy, primarily visual privacy. Little thought is given to privacy from acoustical leakage. Thin walls and loose fitting doors are the biggest leakers, with open air plenum ceilings and duct work doing their share of leaking as well.

Ideally, acoustical leakage mitigation should be addressed by the architect and installed during the initial construction phase of the building project. Since this is rarely done, you have likely come to this page seeking recommendations for a solution to your acoustical leakage problem.

Acoustical Leakage Solutions

Acoustical leakage can be mitigated two ways: making the audio leakage unintelligible, and/or soundproofing the area where confidential conversations take place, e.g. offices, board and conference rooms.

The Unintelligible Solution

The economical solution to unwanted sound migration is, elevate the ambient sound. Be sure to do this in the areaes where eavesdroppers do their listening, not within the room the conversations take place. This is usually accomplished by placing loudspeakers in the ceiling playing white or pink noise.

In cases where ceiling speakers are too expensive, or not appropriate, free-standing sound generators can be used. Many companies already do this in their open office areas to add privacy for their people working in cubicles.

The white/pink noise sounds like radio static, but more pleasing to the ear. You can listen to what it sounds like here: white / pink

This background sound becomes unnoticeable after a few minutes, and migrating speech from private areas becomes unintelligible. This is the least expensive and easiest to employ option for deterring eavesdropping.

The Construction Solution

Soundproofing is easy to install during the construction of a building, and it can still be added as an afterthought. Construction methods vary but the goal remains the same—absorb the sound before it reaches the other area.

A common misconception among contractors is that soundproofing means throwing up another layer of drywall. Wrongo.

Soundproofing Tricks

• Add different sound absorbing material to walls in layers. This forces the sound to go through materials of different densities – thus absorbing the sound’s energy more quickly. Sandwiched layers of special rubberized sheeting, and cloth coverings between layers of drywall accomplish this.
• Create dual walls with air spaces between walls. No common studs, and use sound reducing glue instead of nails.
• Attaching noise generators to common wall surfaces and cavities.
• Special sound panels, baffles and other isolation technologies are also available.
• FutureWatch: Metamaterial.

Product manufacturers can help you determine the best application for your situation.

Acoustical Leakage Mitigation Tutorials

• The ABCs of Soundmasking
• Noise Masking Primer
• Protecting the Confidentiality of Sensitive Conversations through Soundmasking
  
• Prediction of Speech Transmission Index in Open-Plan Offices
  

Acoustical Leakage Mitigation Resources

• Information Security Incorporated 301-565-8168 Government-level sound masking. Noisebath® and Eavestopper®.
• Free-standing white noise generators.
• Research Electronics, Inc. 615-528-5756 White noise generator – ANG-2200®
• Eckel Noise Control Technologies 617-491-3221 Tiles, sheeting, baffles, etc. – SuperSoft®
• Atlas Sound 800-876-7337 Sound masking loudspeakers and systems

Acoustical Leakage Solved – Now What?

It’s time to consider your other eavesdropping vulnerabilities, visual and electronic surveillance. Contact us. We can help you solve these and other information security concerns. We provide free advice, and free no-obligation quotes for services.

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Kevin D. Murray CPP, CISM, CFE is an information security consultant and Technical Surveillance Countermeasures (TSCM) specialist with over four decades of experience.

Murray Associates is an independent security consulting firm, providing eavesdropping detection and counterespionage services to business, government and at-risk individuals.

Headquartered in the New York metropolitan area, a Murray Associates team can assist you quickly, anywhere in the United States, and internationally.