Sound masking is a sound that makes speech unintelligible, and a quiet space more comfortable. It is the complex sound that must have broadband; meaning, a) a sound that covers an extensive band on the frequencies that we can hear, and b) it must be a sound that is non-intrusive and non-fatiguing. Some people may mistake sound masking as either white or pink noise. It is neither. Sound masking has its own acoustical signature and properties.
White vs. Pink Noise
White noise is a sound that has equal power at all the frequencies, and when listened to, sounds much like pure static on the radio. Pink noise has equal power at all of the octaves and therefore sounds much smoother and more pleasant. Pink noise is a closer approximation of what a proper sound masking system should sound like. In the technical sense, sound masking is a broadband sound from roughly 65 hertz, your bass, to 13 kilohertz, or your treble. That is also non-repetitive and has an approximate three to five-decibel roll off per octave into the higher frequencies.
How Does Sound Masking Work?
Sound masking works by gently raising the ambient background sound uniformly in an environment with a clean, consistently random broadband, non-intrusive sound. In environments where there is too little broadband ambient background, noise and speech can be easily heard. Imagine sitting in a quiet library. Now imagine someone talking or tapping a pen. Think how intrusive even the loud whispering or the tapping of the pen is. Both sounds are quite intrusive and will break your concentration.
Now imagine sitting on a beach. A beach is a restful place. A place where it’s easy to collect your thoughts. The beach, however, compared to the library, is a place with lots of sound, pleasant sounds, broadband sounds; sounds that are similar to pink noise and sound masking. The ocean waves are a beautiful background sound that creates an environment that is not only comfortable but a place where sounds around you appear to disappear. The ocean has natural sound masking, with waves generally louder than the other incoming noises around. It masks the sounds around you as you sit on the beach.
Therefore, sound masking works like a signal to noise ratio, or put another way for the designed workplace: a speech to ambient background sound ratio. Ambient background sound is essentially any sound that is not in the foreground, such as direct speech. Ambient sound merely is background noise. An example of ambient background sound to speech is a crowded coffee shop. People are talking all around you, which is background noise. However, it is an environment where you are still able to do independent work, as well as have a conversation with someone. When ambient background sound is low, you can hear speech, but when ambient background sound is raised, it is difficult to hear the same dialogue. That is how sound masking works.
How Do We Evaluate Sound Masking Quality?
In today’s workplace, office design is creating more open, collaborative environments, and reducing the number of closed office environments. The fad is towards more energy efficient and sustainable materials, such as reclaimed metals, woods, and glass – but these are all hard surfaces, which reflect sound. Sound absorption materials like partitions and acoustical ceiling tile are used less and less in today’s workplace design. Sound masking is an excellent choice for handling sound and facilitating a much more comfortable work environment. How do we evaluate sound masking and know when it is of high quality?
Let us turn now to the two critical criteria for any sound masking system. The two criteria are privacy and comfort. Remember, the only consumable for sound masking is the sound. The industry maintains a standard for speech privacy, known as ASTM E-1130. The standard says that if you have an Articulation Index, or AI, of .2 or less, you achieve standard speech privacy. If you have an AI of .05 or less, you achieve confidential speech privacy. The Articulation Index, in essence, is a measurement of the percentage of a sentence that can be understood.
Clinical researchers have determined that if an individual can hear more than 20% of what is being spoken, then they can understand the conversation. If you hear less than 20%, a person is not able to discern the content of the conversation, and therefore, you have speech privacy. Most manufacturers of sound masking equipment can achieve speech privacy. Again, with a loud enough sound or noise, you can mask speech. In the quest for masking speech, the more important criteria is obtaining comfort while maintaining speech privacy. So let’s turn and look at comfort.
To help us understand sound, let us look at an example that many can easily relate to. Let’s look at the lighting industry. Imagine yourself in an office environment that uses fluorescent lights. Imagine the lights from those fluorescent has a very narrow color tone. For instance, the light has a red color and a blue color. Now imagine the light is also flickering. Imagine that you walk away from the flickering fluorescent light into the sunlight. Instantly, you feel relief as you walk into a uniform, full broadband of light frequencies. All the colors are now natural, easy on your eyes and relaxing.
The flickering fluorescent light fatigues us because it forces our minds to gather the information of a repeat and process the lack of color. We strain to filter this information so that we can think about what we are seeing and doing. When you walk out of the office into the sunlight, you are relieved because you are now receiving the full broadband spectrum. You are instantly relaxed because your mind is no longer processing specific data.
What Are the Principals of Rich Sound Masking?
Sounds and sound masking work in a very similar fashion. Five principles formulate rich sound for sound masking. Starting with the consumable itself, the sound; you need a broadband sound with an environment to make it comfortable. Like the lighting example, the origin of the sound needs to cover the full spectrum. Sound masking systems that only deliver a portion of that spectrum, like lousy fluorescence, will cause fatigue and discomfort. Comfort quality comes from a full broadband spectrum. Second, is a sound with a proper wrap around. If something has a pattern or a repeat, like a flickering light, and we can detect it, then it has an inadequate and improper wrap around. This is also called “cycling,” and our brains pick that up as information; which in turn, fatigues us because we try to push out that information.
Nothing in nature actually cycles, which is one of the things that makes nature so relaxing. Number three on the list is multiple noise sources. Again, there’s a natural phenomenon within a random environment, which creates comfort. Babbling brooks, oceans, winds across plains of wheat. All of these random sounds create comfort, and our body relaxes to it. It is not information overload. Uniformity of sound is our fourth critical criteria. A sound masking system must have no more than a tolerance of plus or minus one decibel, or dB.
The industry standard has been, and many systems allow a tuning differential of plus or minus three dB. This is a tremendous amount of noise difference and creates a condition of a potential six-decibel swing. Therefore, imagine that you are targeting 47 dB for your sound masking system. This is a smart volume level for most sound masking systems to create comfort and privacy. One area is tuned at 44 decibels, and the next area is tuned at 50 dB. That’s a six-decibel swing. Both areas are now problems. The area at 44 dB may be comfortable, but there is no privacy. At 50 decibels, you certainly may obtain speech privacy, but it will not be a comfortable environment. Never underestimate the importance of a uniform sound. A system must be consistent and non-disruptive throughout the space. Last, tuning flexibility.
A sound masking system should allow you to adjust it to mute the criteria of privacy and comfort. All performance specifications must lead us to speech privacy and a comfortable sound. Now, why do people put sound masking in a space? People are an organization’s greatest asset. It is the intellectual capital, hard work, effort, energy, and time that an individual invests that makes any organization successful. The individual, however, is also the most expensive asset of an organization. Therefore, giving the individual the ability to think and do their work is paramount to everything else. That is why we should provide them with quality light, heat, air conditioning, shelter, and a work environment that enables for concentration.
The Bottom Line of Sound Masking
Employees will only produce their best work in a non-stressful, comfortable work environment. Without proper acoustics, that work environment is unobtainable. Here’s a bonus area for you, the one question that most ask regarding sound masking is: What is the difference between white noise and pink noise? Again, white noise and pink noise are not sound masking. However, white noise charts like white light. It has all the same power or energy across all frequencies. Pink noise charts like pink light, and has equal energy per octave. An octave is an interval between one pitch and another with half or double its frequency. In low frequencies, you have a narrow column. For example, between the octave 63 and 125. In higher frequencies, a wider column between octaves. 2,000 and 4,000.
Think of energy as a marble. If you took ten marbles and put them into a narrow column, it would rise higher than if you took ten marbles and put them in the broader column where it would flatten out. Pink noise energy is reduced in the higher frequencies. Interestingly, because of the way our ears listen and wait for frequencies for sound pressure level, white noise sounds hissy. With many high frequencies, pink noise is flatter and more comfortable.