Achieving Speech Privacy in Acoustically-Challenging Environments

Is your office space an acoustic nightmare?

basketballWhat defines an “acoustic nightmare”? A high school gymnasium is a good example of one. You remember how loud those could get: how sound tended to bounce around and echo, and how conversations whispered in one corner could seemingly be heard everywhere else in the building!

Though most offices aren’t built in gymnasiums, they’re often built in similar acoustic environments. The aesthetic value of a converted warehouse, for example, with its exposed brick walls and open ceiling attracts many businesses. Others have hardwood floors or tile, which also look very nice. ABCUnfortunately, there’s an acoustic trade-off for such aesthetics. The reason such decorative touches make speech privacy such a challenge are fairly straightforward: hard surfaces reflect sound, and whether you’re in a gymnasium or a converted warehouse, there’s little to absorb sound waves.

Absorb, Block, and Cover – “The ABC’s” – represent the three ways you can improve your acoustic environment and achieve necessary privacy levels.

Absorption of sound waves by using a high-NRC-rated ceiling tile or acoustic wall panels,
Blocking by using high-STC-rated panels, partitions, walls, windows, etc.
Covering by adding a source of unstructured [i.e., not music, which is information and therefore distracting], low-level background sound, known as sound masking or white noise

chart_smAll office environments will require some combination of these three tools to provide an acoustically pleasing atmosphere. In most cases, no one tool by itself will solve your privacy needs. While Covering provides the greatest increase in privacy per dollar invested, it must be used in conjunction with the proper mixture of Absorption and Blocking components in order to achieve specific speech privacy levels.

What if it doesn’t work?

A common question asked when considering covering- sound masking- to achieve desired privacy is this: “What if it doesn’t work? What if it doesn’t provide the speech privacy we need?” To answer that question, let’s go back to the gymnasium example.

Imagine moving your open office personnel into the gymnasium with 60” systems furniture panels – which would truly represent an acoustic nightmare! If we then installed a sound masking system but made no other changes, you likely wouldn’t notice any significant improvement. Why?

Let’s look at how the Privacy Index works.

The Privacy Index (PI) is a measure for rating the speech privacy performance of an architectural space (in other words, the lack of speech intelligibility) where the PI is calculated from the Articulation Index (AI) according to the following: PI = (1 – AI) * 100%. The levels run as shown on the graph below:

The Privacy Index

The Privacy Index

Returning to the example, if the PI in the gymnasium you moved your office into was originally 30% with just the 60” systems furniture panels, and a sound masking system raised the PI to 62%, even though you received a 32% increase, you still effectively have little to no speech privacy. The common assumption at that point is that the sound masking system is ineffective, that “it didn’t work.” This reflects a relatively common misunderstanding of the ABC’s. It is not really a question of whether the sound masking system works, because it did successfully significantly raise the PI – by 32%! Neither of the other two acoustic tools (by themselves, or in combination) could have provided this same increase in privacy for anywhere near the same investment. The real question is whether adding the sound masking system – alone – will get you above the critical 80% threshold and into the Normal Privacy category. In most cases, the answer is yes. However, acoustically-challenging environments such as a converted warehouse, will likely require some mix of the other tools in order to reach a Privacy Index of greater than 80%. For example, sound masking may get you 70% of the way, and adding acoustic ceiling tiles or wall panels may then put you over the top and get you to 85%.

In an ideal world where cost was not a factor, everyone would employ all three and crank their Privacy Index up somewhere near 100%. However, cost does matter, so the trick is to maximize the Privacy Index score while minimizing the cost. In a case where a customer is looking for a single tool that will offer the “most bang for the buck,” that tool would be the VoiceArrest Sound Masking System. If it doesn’t get you all the way to your privacy goal, the benefit per dollar spent makes it the best place to start. Then, if additional privacy is needed, one of the other more costly options can be employed.