Sound masking systems have been used to improve speech privacy and control noise for decades, but many people are still unfamiliar with this technology. Below are some of the most commonly asked question about sound masking.
1. How can you cover noise with sound?
Adding sound in order to control noise seems contradictory. But the problem with many offices is that they’re actually too quiet. They just don’t have an effective ambient level. And in this ‘pin drop’ environment, even the smallest noises disrupt a person’s train of thought. It’s also really easy to hear other people’s conversations, whether desired or not. That’s why people describe these spaces as noisy.
Sound masking solves this problem by distributing a comfortable background sound throughout the space. This new baseline level – typically around 40 to 48 dBA (A-weighted decibels) in commercial interiors – covers up any noises that are lower in volume than itself and reduces the disruptive impact of those that are higher by minimising the amount of volume change that occurs.
When introducing a masking sound to a workplace, there shouldn’t be a hum or a whoosh or a buzz. If the system is properly designed, installed and tuned, people usually compare the sound to softly blowing air. It’s subtle, but very effective.
2. Can I use my airflow system to provide masking?
Airflow systems turn on and off throughout the day in order to regulate a building’s temperature. It can’t be relied on to provide constant coverage. And, when it’s on, the sound it produces isn’t at an appropriate volume or in the correct frequency spectrum to mask speech.
3. Is sound masking the same as white noise?
‘White noise’ is a specific type of sound that was used in early sound masking systems back in the 1970s. Those systems were really inflexible and people often shut them off because of the hissing quality of their sound. But the term ‘white noise’ was widely adopted and today it’s often used interchangeably – though incorrectly – with ‘sound masking’.
4. Is sound masking the same as noise cancellation?
‘Noise cancellation’ is another well-known term, thanks to the popularity of headphones offering this feature. In more traditional applications, this technology uses microphones to detect a noise, which signals a device connected to a loudspeaker to produce an equal and opposite sound wave. This wave is projected in the same direction as the noise, largely eliminating it. It’s most effective for continuous, low-frequency sounds such as engines and traffic. But its applications are limited because the noise source and the listener have to remain in the same position to experience the effect. Cancellation doesn’t work in an office because it can’t address the variable and high-frequency nature of speech or moving employees.
5. Will I hear the sound?
Sound masking needs to be heard if it’s going to work, but it’s designed to be as unnoticeable as possible. The sound doesn’t contain distracting patterns and it’s tuned so volume changes aren’t heard as occupants move through a facility. Occupants come to consider it a natural part of their environment in a short period of time.
That said, in order to allow integrators to properly tune the masking sound for a space, the system must offer small adjustment zones (one to three loudspeakers) with very fine volume and frequency control in each one.
6. Will the sound masking automatically adjust to noise levels?
When first introduced to sound masking, many people ask whether it will raise or lower in volume according to what’s happening in the space. Masking is a continuous signal. When changes are made to it, the risk is that people will notice. If they do, it will become one of the noise distractions, rather than the solution to them, especially if it’s done too fast or too often, or the changes are too dramatic, or applied to the wrong area.
Auto-sensing sound masking systems can make volume changes of as much as seven dBA in as little as 15 to 20 minutes, which is too fast. And, of course, if the changes aren’t made quickly enough, the masking volume is out of sync with the current noise level. For example, a co-worker begins a brief, but loud, conversation. The system reacts to this change and begins gradually raising the masking level in an area. The masking goes unnoticed as it rises, but the conversation can be heard until it reaches the required level. But your co-worker has finished speaking. Now, the masking starts slowly ramping down in volume.
It’s important to remember that this feature isn’t predictive. It’s simply reactive, adjusting the volume based on noises that were created in the past. It’s too low when it’s needed and too high when it isn’t. It doesn’t ensure that the proper masking volume is achieved at the right moment.
A consistent masking sound reliably covers up many of the conversations and variable noises in a facility, thereby reducing disruptions to occupants. Consistency also makes the masking ‘disappear’ from occupants’ consciousness.
7. Will I be able to hear my closest neighbour?
As noise travels, its volume decreases to a level that’s covered up by the masking sound, so it follows that this technology requires some distance to work.
The typical background sound level in most offices is so low that voices carry over a distance of nine to 15 metres (30 to 50 feet) or more. Sound masking dramatically reduces that distance. The exact amount is affected by office layout and any other acoustic treatments, but 4.5 to six metres (15 to 20 feet), or approximately two workstations, is a good expectation. It can be less.
Over shorter distances, sound masking may not prevent a person’s voice from being heard, but it will prevent nearby occupants from understanding what’s being said. This is a key benefit, because understandable speech is the least private and causes the most distraction. A distinct impact will be noticeable from private office to private office.
8. Can I just treat the noisy areas of my workplace?
Treating particular areas isn’t recommended because if the masking sound is present in one area and not in another, it will draw attention to itself as occupants move around. Also, sound masking works at the ear of the listener. It’s impossible to treat individual private offices or selected areas in an open plan space, or just suspend a loudspeaker over the one person with a particularly loud voice. Uniform coverage is needed to ensure comfort and effectiveness.
9. Can I use sound masking if I’ve already moved into my facility?
Yes, sound masking can be retrofitted. In fact, at that point, it may be the only realistic way of addressing noise or speech privacy complaints. Budget pricing is low relative to retrofitting other acoustic treatments and installation can be handled with only minor disruption. And it can be applied to both open plans and closed rooms.
10. Can I use a desktop device or an app?
Desktop devices and apps simply aren’t commercial grade solutions. Because installation is limited to areas with desktops or workstations, these devices leave the rest of the facility without masking coverage. Their sole purpose would be to allow the user to increase their personal level of noise control.
If used on its own, this type of device only offers the illusion of speech privacy. In other words, because the user can’t easily hear others around them, they believe those people can’t hear them either. However, if the listener isn’t using such a device or doesn’t have it set to an appropriate level, the listener will be able to clearly understand the conversation.
And the quality of the sound these devices produce is, at least to some degree, connected to the quality of loudspeaker driver they use. No matter what mobile is used, it’s not going to be able to generate the frequency spectrum required to produce a truly comfortable and effective masking sound. A masking system’s loudspeaker driver must be 100 to 200 millimetres (four to eight inches) in diameter and rated from 10 to 25 watts to produce the full sound masking spectrum, which is typically specified from 100 to 5000 hertz (Hz).
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The author, Niklas Moeller, is vice-president of K R Moeller Associates Ltd, manufacturer of the LogiSon Acoustic Network sound masking system (logison.com.au). He also writes an acoustics blog at soundmaskingblog.com.
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