I just returned from a conference in Europe where I was asked a question that comes up from time to time. So, today’s post addresses that question, plus a similar misunderstanding about how sound masking works.
After some discussion about the types of noises that our sound masking system could help address, a client asked where it should be installed. She assumed that the loudspeakers would need to be located between the noise source and the listener. For example, noises from outside the building would require the loudspeakers to be near the window, while noises from a corridor would require the loudspeakers to be near the doorway.
This assumption is based on the idea that sound masking somehow blocks or reduces noise transmission. Since traditional acoustical control methods such as physical barriers and absorption work this way, some assume masking does too. But masking doesn’t disrupt sound transmission. Rather, it interferes with a listener’s ability to hear the noises that arrive at their ear. So, masking has to be implemented such that the masking sound is delivered in the area where the listener will be. In other words, it’s the location of the listener that matters, not where the noise comes from.
There’s another misconception about how sound masking works. When clients are trying to address facilities with higher levels of noise (or a need for greater speech privacy levels), they sometimes ask what impact these needs will have on the number of loudspeakers used in the masking system. They assume that a higher density of loudspeakers will provide a greater amount of masking. But the masking system’s effectiveness isn’t increased in this way. Rather, the degree of masking is most closely related to the overall masking volume.
Of course, the loudspeakers must be installed in such a way as to provide uniform delivery of the masking sound throughout the space, as well as the correct spectrum; however, once those two requirements are met, the need for greater masking levels is met by increasing the system’s volume (which can be done up to the limit for comfort). You can also tweak the level of various frequencies, but you run the risk of reducing comfort if the results greatly vary from the generally accepted masking spectrum.
Again, the misperception about loudspeaker density is understandable, given that increasing the blocking and absorption of noise typically requires the addition of more material (beyond the differences in performance of various materials, of course).
Sound masking is a truly unique method of providing acoustic control. It’s part of what makes this business so fascinating!