Essentials of Effective Speech Privacy:Consistent Sound If you are considering using a sound masking system to improve speech privacy in your facility, your objective is most likely to either to protect confidential conversations or to reduce conversational distractions between workspaces. In either case, your goal is to reduce speech intelligibility while maintaining a comfortable work environment.
Increasing privacy while maintaining employee comfort is a common concern. Many studies have been conducted on this subject, with one of the more recent and in-depth coming from the National Research Council of Canada.
Their research revealed that office workers in typical open office environments were only comfortable if the ambient background sound was in the very narrow range of 45 dB - 48 dB. At levels below this range, intruding speech became sufficiently distracting, affecting worker concentration. If levels exceeded 48 dB, the ambient sound itself was considered to be annoying or unpleasant to many of the workers. Achieving privacy and comfort simultaneously depends on a masking system's ability to deliver consistent “sound uniformity” within these narrow tolerances.
Within this topic of “sound uniformity,” there are two aspects that should be evaluated: “spatial uniformity” and “spectral uniformity.” The extent to which each of these is met determines the privacy performance of any sound masking system.
Consistent Volume“Spatial uniformity” refers to the evenness of sound delivery (volume) throughout treated areas and directly impacts user comfort and speech intelligibility. However, achieving adequate spatial uniformity of ambient sound has always been a serious challenge for indirect field masking systems. Their above-ceiling placement causes problems because of the sound absorbing and blocking characteristics of typical ceiling and plenum materials, plus the numerous irregular openings that cause widely-varying sound levels from point to point. Even a 3 dB variation from one workspace to another has a dramatic effect on speech intelligibility, yet it isn’t uncommon to find indirect field systems with volume fluctuations of 4 to 5 dB. Consistent Frequency Balance “Spectral uniformity” refers to the evenness with which the proper balance of frequencies is maintained from one point to another within the treated area. Reliable speech privacy requires that the balance of frequencies be precisely tuned and exhibit little variation across the treated areas.
It is possible for indirect field systems to exhibit fairly good “spatial uniformity” (volume balance) - when considered on an average basis - while its “spectral uniformity” (frequency balance) fluctuates significantly. Although some spectral imbalances can be corrected though expert tuning, others are unavoidable due to distortions caused by the ceiling assembly and obstructions along with variances in the plenum space above (see: effects of speaker placement). Compensating for resulting losses in privacy can require up to 3 dB increases in volume - negatively affecting the comfort of your workers.
(The section on Tuning discusses spatial & spectral uniformity solutions for indirect field systems, but because of their added expense, they are rarely used. Most indirect field providers will say that a wider variation in masking sound level is acceptable, if the issue is addressed at all.) Privacy vs. ComfortConsidering that 45 dB is needed to achieve a minimum level of speech privacy in open office setting, and that settings above 48 dB are considered to be annoying or unpleasant to many workers, you’re faced with choosing between employee comfort and adequate privacy.
For example, if you installed an indirect field system and needed more than just minimum privacy, you could have the system calibrated to a minimum volume of 47 dB at any point in the room. However, given the known limitations of indirect field systems in achieving spatial and spectral uniformity, this has some rather significant effects on worker comfort.
From a spatial uniformity standpoint, if your system exhibits a typical 3 - 4 dB volume variance, some of your employees would be hearing to 50 - 51 dB, which could clearly offer superior speech privacy, even if they are annoyed by the excessive noise.
From a spectral uniformity standpoint, areas in which the frequency balances were distorted could be exposed to 50 dB of sound and have less speech privacy than someone only hearing 47 dB. Or worse yet, areas with 47 db could be receiving the equivalent privacy of less than the necessary 45 dB.
You are left facing two choices: either leave the system adjusted to the higher average volume, annoying a significant percentage of users, or lower the average volume, compromising speech privacy for a substantial percentage of the users. These limitations have unfortunately contributed to the opinion among some users that background sound systems are either too loud or are not very effective. Privacy with ComfortThe VoiceArrest™ Speech Privacy System uses Direct Field Technology to radiate sound directly into treated areas without any interference to alter or distort the frequency balances. This allows the VoiceArrest™ system to be pre-tuned with the ideal sound spectrum for masking speech intelligibility. Also, the VoiceArrest™ System’s spectral uniformity isn’t dependent on variable outside influences such as the knowledge and expertise of installers, the quality or accuracy of their instrumentation or their skill in tuning a system. Pre-tuning ensures that your installation will meet the highest, most consistent privacy performance standards available.
Between its Direct Field Technology, pre-tuned spectrums and specially designed Ultra-Wide Dispersion emitters, the VoiceArrest™ System consistently delivers virtually perfect spatial & spectral uniformity.
You don’t have to make a choice between privacy and comfort. The VoiceArrest™ System with Direct Field Technology allows you to set the volume to 48 dB for maximum speech privacy knowing that the precise uniformity will offer your employees’ a comfortable working environment with far fewer distractions.
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| Figure 1 above illustrates the difficulty in achieving good uniformity with an older-style above-ceiling system. The assumption is that the ceiling will "spread out" the sound in the plenum, improving the uniformity. What actually happens is that the plenum typically causes a lack of uniformity. Plenums hide large structural elements, such as HVAC ductwork or structural beams, which effectively compartmentalize the sound. Even if the plenum is atypical and contains no large elements, openings in the ceiling for air returns and lighting fixtures permit proportionately more sound to be emitted below them. | | By contrast with an above-ceiling system, the uniform gray in Figure 2 illustrates the good uniformity possible with an in-ceiling background sound system. By properly choosing emitters or speakers with ultra-wide dispersion, the background sound exhibits greater uniformity at the listener's ear elevation (variability of less than 1 dB). |
Continue on to Essential #2: Tuned Sound >
Ready to find out how the VoiceArrest™ Speech Privacy System can raise the privacy levels of your workplace? Contact one of our acoustic consultants today!
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