Essentials of Effective Speech Privacy: Properly Tuned Sound Masking
Since you are in essence shopping for privacy, the clear question to ask is: Which system offers the highest, most consistent privacy throughout entire treated areas?
The essential ingredient to the effectiveness (privacy per decibel delivered) of any white noise/sound masking installation is its ability to provide precise sound uniformity across treated areas. Similar to having a grand piano tuned so that the sound it produces matches a precisely-defined sound spectrum, tuning a sound masking system refers to the process of adjusting specific speakers to compensate for spatial and spectral inconsistencies in order to achieve the highest possible privacy levels throughout treated areas.
As a result of their speaker placement, indirect field or plenum-based systems require precise tuning after installation to compensate for distortions to the spectrum from the ceiling assembly and/or obstructions and variances in the plenum space above. Large structural elements, such as HVAC ductwork or structural beams effectively compartmentalize the sound, while openings in the ceiling for air returns and around lighting fixtures permit proportionately more sound to be emitted below them.
At first glance, indirect field systems look like they can be adjusted to provide correct frequency distribution and operating level of ambient sound. However, this is only true if considered on an average basis. A closer examination of the treated area shows that even a highly-tuned plenum-based system will still vary considerably in the all-important frequencies related to speech intelligibility, as well as in volume levels when you compare one workstation to the next. Achieving adequate spatial & spectral uniformity of ambient sound is a serious challenge for systems placed in the plenum. Even a 3 dB variation from one workspace to another can have a dramatic effect on speech privacy, yet the performance of most above-ceiling systems varies by more than that.
Theoretically there are some measures that can be taken to mitigate these problems, such as providing each loudspeaker with volume and frequency control, using many more loud-speakers (spaced 10’ rather than 15’ apart), and providing sound-attenuating “boots” at each opening in the ceiling. Realistically, these measures are rarely employed because of the resulting costs to the project. Some indirect field providers claim they can provide strict uniformity without these corrective measures, but most will simply say that a wider variation in masking sound level is acceptable, if the issue is addressed at all.
Reduced Volume with Increased Privacy
The exceptional spatial and spectral uniformity that the VoiceArrest™ Speech Privacy System delivers allows it to operate at substantially lower sound levels than other systems while still providing equivalent or better privacy. Most sound masking systems must be operated at 48-51 dB in a well-designed open plan office in order to provide adequate privacy conditions for most occupants. The VoiceArrest™ Sound Masking System, in contrast, can deliver more effective sound masking at a noticeably lower volume (45dB). In the graph to your left, you’ll notice the Direct Field Difference. Where older, above-ceiling systems produce significant amounts of volume in the less important, lower octaves (125Hz, 250Hz, and 500Hz), the VoiceArrest™ System delivers more energy in the critical higher octave bands that contribute the most to speech privacy (1000Hz, 2000Hz and 4000Hz). The result is that above ceiling systems produce a significant amount of unnecessary noise, while the VoiceArrest System’s more targeted sound results in more effective, more comfortable privacy.
> For more detail on how why their design means older style systems can’t eliminate this wasted noise, read the Quieter Sound section!
The VoiceArrest™ Sound Masking System delivers this targeted sound spectrum uniformly throughout the coverage area. Direct Field Technology means the spectrum is not distorted by the ceiling assembly or obstructions and variances in the plenum space above. This allows the VoiceArrest™ System to be pre-tuned with the ideal sound spectrum for masking speech intelligibility.
Amazingly, the variation in the spectral balance at any office or cubicle is typically within 1 decibel of optimum at any octave band over the entire critical voice frequency range of 250 Hz to 4,000 Hz.
Although typical indirect field systems may appear to exhibit fair uniformity as measured by an A-Weighted Sound Pressure Level Meter (measures average volume levels), their variation within the critical speech bands far exceeds that routinely provided by the VoiceArrest™ System.
No Re-Tuning Required
Depending on the age of the technology of an indirect field system, it may require re-tuning on annual basis to correct for frequency drift; they all should be re-tuned after major furniture reconfigurations. This entails hiring a trained technician to bring out equipment to check and adjust each of the speakers. This ongoing need for re-tuning the system – and the associated cost – is seldom brought up, and few systems are maintained well enough to prevent additional privacy loss.
With the VoiceArrest™ System, there are no ongoing maintenance costs to budget for. You receive the same high standards of privacy year in and year out. The frequency balance is stable, and you can reconfigure the furniture as often as needed; it won’t affect the quality of privacy you receive.
Continue on to Essential #4: Quieter 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!
