Setting the Stage for Speech Privacy

It pays to keep a common sense approach to office acoustics. There are numerous practical and economical ways to cut down on unwanted noise transmission that are not only highly effective, but necessary first steps towards building a desirable acoustic environment. Remediation strategies such as electronic sound masking can only be effective if the underlying structural environment is relatively sound.

As acoustical consultants, CCR ASSOCIATES is frequently called in to assess ongoing acoustical problems in currently occupied office space. Once on site, it often becomes apparent that many acoustical problems are due to structural/design problems in the office, and that these design problems must be resolved before one can accurately assess the potential effectiveness of sound masking. Wall and ceiling voids, open air grills, low/no cubicle walls, poorly sealing doors and windows, poorly designed workstations, etc. are all very common. Common sense dictates that sound will transmit through openings, and that these openings should be sealed, if possible.


The chart above demonstrates how important it is to fix any underlying structural acoustical problems before attempting further remediation. Until an office reaches a Privacy Index of 60 or above, little acoustical benefit can be gained from sound masking or other electronic acoustical remediation. Above 60, increases in PI through sound masking or other means are considerably more effective.

Measuring Speech Privacy - Guidelines for Success

Though it may seem subjective, speech privacy can be measured, and the overall acoustical effectiveness of an environment can be objectively calculated. Our main tools of measurement are the Articulation Index (AI) and the Privacy Index (PI).

Articulation Index is a measurement of speech intelligibility, taking into account the following factors:

• The spectrum of normal human speech
  
• The sound attenuation (loss in intensity due to sound absorption and dispersal) between talker and listener
  
• The spectrum of background noise at the point of the listener.
  

The range of AI is between 0 and 1, where 0 indicates complete lack of intelligibility, and 1 indicates complete intelligibility.

Privacy Index is a measurement of speech privacy. PI can be derived from the AI measurement using the following formula:

PI = 100(1-AI)

The relationship between PI and AI is inverse (as the AI increases, the PI decreases) and nonlinear. The range of PI is between 0 and 100, where 0 indicates complete lack of privacy, and 100 indicates complete privacy.