Sound Masking Explained: Enhancing Privacy and Reducing Distractions
In modern office environments and other shared spaces, managing noise levels can be challenging. Sound masking is a powerful tool for creating comfortable and productive environments by reducing noise distractions and enhancing speech privacy. By reducing noise distractions and enhancing speech privacy, sound masking technology creates a more consistent and comfortable acoustic environment.
What is Sound Masking?
Sound masking is the inclusion of generated sound (commonly, though inaccurately, referred to as "white noise" or "pink noise") into an environment to mask unwanted sound. It relies on auditory masking. Sound masking is not a form of active noise control (noise cancellation technique); however, it can reduce or eliminate the perception of sound. Sound masking is applied to an entire area to improve acoustical satisfaction, thus improving the acoustical privacy of the space.
Auditory Masking Explained
Picture this if you will: you’re working on a mix, and you realize two instruments are clashing, covering each other up, and competing for the same sonic space. This is a telltale sign of auditory masking-also known as frequency masking.
Frequency Masking
Frequency masking is an auditory phenomenon that occurs when two similar sounds play at the same time, or in the same general location. One masks the other, confusing your perception of either sound. One could imagine frequency masking being quite useful to prehistoric humans: simply wait for the rain to fall and your prey won’t hear your footsteps in the forest.
In mixing music, frequency masking can be either encouraged or problematic (but not bad) depending on its context:
- Encouraged masking: when two sources blend, there is likely some overlap in a frequency range, and therefore some amount of masking happens. This is similar to the use of distortion in mixing.
- Problematic masking: when two sources blend, but their frequencies tend to obscure rather than compliment each other. This can be frustrating because it is difficult to listen, analyze, and understand where tracks compete across an entire mix.
When masking is problematic, it can lead to an unprofessional sound. Luckily the condition is treatable!
How Sound Masking Works
Sound masking involves adding a background sound, often referred to as pink noise, to an environment to cover up unwanted noises. By introducing a consistent background sound, sound masking raises the ambient noise level in an environment, making speech noise less intelligible and therefore less distracting. Sound masking specifically blends into the background and is less noticeable, unlike white noise, which includes all frequencies at equal intensity.
Sound masking systems use speakers (emitters) to distribute a carefully engineered sound throughout a space. Sound masking seeks to reduce the intelligibility of sound from a source by reducing the signal-to-noise ratio.
Sound masking is significant and prioritizes modifying the background sound (in contrast to background noise); however, there is substantial evidence produced and published by Banneker (BBN) and Kavanaugh indicating that acoustical satisfaction within a space cannot be guaranteed without consideration of the three principal parameters of architectural acoustical design, formalized and established in the early 1900s by Sabine.
A sound masking system can be used to reduce the impression of intruding sound (reducing annoyance, distraction) and improve acoustic privacy (including speech privacy). Sound masking systems are often relied upon as a basis of design with Sound Transmission Class (STC, as supported by ASTM E336) or Noise Isolation Class (NIC, as supported by ASTM E336) to ensure an appropriate level of privacy between contiguous rooms.
Various organizations (ASTM, ASA/ANSI, GBI, LEED, ASHRAE, WELL, etc.) define unique categories for labeling acoustical zones with purpose and/or function.
Sound masking is an effective solution in masking intruding noise. Several cases exist where sound masking has been successfully installed for exterior applications, the most common target of concern being roadway noise. In one example application, a large artificial waterfall was constructed as part of the garden exterior of an urban hotel in Santa Rosa, California.
Types of Sound Masking Systems
There are two primary types of sound masking systems:
- Plenum Sound Masking Systems
- Direct Field Sound Masking Systems
Plenum Sound Masking Systems
The plenum is the space between a "dropped" ceiling and the upper deck to the floor. In plenum sound masking systems, which employ a network of loudspeakers located completely within the plenum, were the first such systems developed and have been in use since the 1960s.
Plenum-based speakers typically range 4-10 inches (10-25 cm) in diameter and generally face upwards, towards the upper deck. This is done to reflect sound from the speakers to broaden, as much as possible, the footprint from the speaker in the work area. As with any commercial-grade sound masking system, an in-plenum sound masking system requires proper layout design, commissioning, and verification of the performance. Disregarding the importance of any of these stages in implementation will result in a sound masking system that does not perform according to the specifications of an acoustician.
Only the most sophisticated sound masking systems can control the background sound level and spectra of masking sound accurately and precisely throughout a space, made possible only with the smallest zones (spatial limits around a speaker) and sophisticated electronics and software. Uniformity can be achieved by adjusting the acoustic output of individual or a small groups of speakers. Adjustments routinely include changes in the output volume and output spectra of individual speakers.
Direct Field Sound Masking Systems
Direct field sound masking systems have been in use since the late 1990s. The name takes after the mechanics of sound transmission which considers the "direct sound path" from the loudspeaker emitted towards the recipients (listeners) underneath. Initially used as an accessory for open office cubicles, direct field systems have been fully integrated into at least one open office furniture system and have been designed to be installed both in dropped ceilings and in offices without any absorptive ceiling systems.
When installed in dropped ceilings, direct field systems use speakers that are mounted facing down. When a ceiling tile is not available, they are mounted facing down on any available structure, sending the masking noise directly into the intended space. Theoretically, a direct field system would benefit from speakers that are omnidirectional, meaning that they transmit energy equally in essentially all directions. However, direct field systems require tighter arrays of loudspeakers given the polarity of the emission of sound.
Common instruments that encounter masking
You’re likely to run into issues with kick and bass masking each other a fair amount, as they both compete for the low end of the mix.
How to unmask your mix
There are a few techniques that can be used to unmask your mix.
Sidechain compression Another way to unmask instruments is with sidechain compression, which means in simplest terms, we can duck one instrument’s volume when the other plays. Let’s take our kick and bass again. Bass parts are often sustained, whereas each kick drum impact is going to be quick and percussive. Because the bass is constant, our ear may naturally gravitate towards that, masking the kick drum in return.
Dynamic EQ or multiband compression Dynamic EQ or multiband compression apply the same concepts as above, but we’re only ducking the masked frequency when the kick hits.
Use panning to your advantage The kick and the bass generally play up the middle, but not every instrument does. Take a high-hat pattern and an acoustic guitar. They’re presented on their own, but they will clash in the mix.
Applications of Sound Masking
Sound masking is provided in the area where conversations should not be heard - not necessarily in the area where the conversation is taking place. For instance, a psychiatrist would not want those in the waiting room to overhear a private conversation with a patient, so sound masking is provided in the waiting area, but not in the psychiatrist's office.
Here are some common applications of sound masking:
- Open office plans: Open offices can be either too quiet (where someone dropping a pen in the next cubicle is distracting) - or too noisy (where the conversations of others in the office make it impossible to concentrate).
- Private offices: Private offices and other enclosed spaces often appear to provide privacy but do not. Many times, walls are lightweight and do not extend to the ceiling deck, but only to the ceiling tile. In these cases, sound can easily travel through partitions or over the walls.
- Public spaces: Sound masking is useful for reception areas, pharmacies, waiting rooms, and financial institutions.
- Healthcare: In healthcare, it plays a vital role in meeting speech privacy codes.
Benefits of Sound Masking
Speech privacy and increased productivity by not be impacted by wandering sound as you perform your duties are two key benefits.
Sound masking enhances speech privacy, minimizes distractions, and creates more functional interior environments. By making conversations less intelligible, the system improves speech privacy and reduces the cognitive load caused by overheard speech.
Sound masking excels in large or open-plan environments where traditional soundproofing methods aren’t practical. In offices, it allows teams to collaborate without disturbing nearby coworkers.
DIY vs. Professional Sound Masking
Avoid placing too many emitters in one area, as this can lead to an overly dampened sound environment. Failing to identify and cover key reflection points can result in suboptimal sound quality.
Sound Masking vs. White Noise
White noise contains all frequencies at equal intensity, making it more noticeable and potentially irritating. White noise plays all frequencies at once, often resulting in a harsh or fatiguing sound. Sound masking, on the other hand, is engineered to match speech frequencies and delivered at just the right level to enhance privacy without becoming noticeable.
The table below highlights the key differences between white noise and sound masking:
| Feature | White Noise | Sound Masking |
|---|---|---|
| Frequency | All frequencies at equal intensity | Engineered to match speech frequencies |
| Sound Quality | Harsh and potentially irritating | Blends into the background, less noticeable |
| Purpose | Masks all sounds | Enhances speech privacy and reduces distractions |
Acoustic Considerations
Acoustic masking is just one tool in the acoustic consultant’s toolkit. While it enhances speech privacy, it doesn’t block sound or reduce echo in the way other treatments do. This table reinforces the role of sound masking within a larger acoustic design strategy.
