Sound Masking Technology Explained
Sound masking is the inclusion of generated sound into an environment to mask unwanted sound. It is a proven acoustic strategy used to enhance speech privacy, reduce distractions, and improve comfort in shared environments. Sound masking means controlling background sounds in a developed environment.
It sounds counter-intuitive, but adding sound to a space actually makes the space seem quieter. This is because the added sound reduces the intelligibility of human speech. Sound masking is an ambient sound, similar to the sound of airflow, that’s specifically engineered to the frequency of human speech. You can target conversational distractions and make them less distracting.
How Sound Masking Works
Sound masking seeks to reduce the intelligibility of sound from a source by reducing the signal-to-noise ratio. It relies on auditory masking. By making conversations less intelligible, the system improves speech privacy and reduces the cognitive load caused by overheard speech.
In order for Sound Masking to work, it must reduce the difference between the steady background level and the transient levels associated with both speech and other sounds. The system capabilities must also be determined based on the amount of people in the office.
The technology used in a Sound Masking system usually consists of a dedicated Sound Masking Generator which is a device that you install in the area you want to mask. The main element which you have to consider is the size and placing of the speakers which will create the white/pink noise, as well as the Sound Masking Generator.
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.
Sound Masking vs. White Noise
Unlike white noise, sound masking is specifically engineered to match the frequencies of human speech and to sound comfortable, even pleasant, to the human ear. White noise and sound masking are not the same. 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.
Adding noise to unwanted noise may seem counter-intuitive, but white noise provides a non-repetitious broad band sound.
Types of Sound Masking Systems
There are two main types of sound masking systems: plenum-based and direct field.
Plenum Sound Masking Systems
In plenum sound masking systems, a network of loudspeakers is located completely within the plenum. The plenum is the space between a "dropped" ceiling and the upper deck to the floor. Plenum sound masking systems 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.
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.
Applications of Sound Masking
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. 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.
Here are some specific applications:
- 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. 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.
Various organizations (ASTM, ASA/ANSI, GBI, LEED, ASHRAE, WELL, etc.) define unique categories for labeling acoustical zones with purpose and/or function.
Benefits of Sound Masking
A sound masking system can be used to reduce the impression of intruding sound (reducing annoyance, distraction) and improve acoustic privacy (including speech privacy). Speech privacy and increased productivity by not be impacted by wandering sound as you perform your duties are two key benefits.
In recent years a number of psychological studies have been undertaken in office environments to gauge the need and effect of Sound Masking. In one study it was found that there is a modest stress increase and diminished motivation caused by typical office noises, including speech.
Typically an office without Sound Masking will have an ambient sound level of under 40 decibels. An Ambient level is defined by the noise which occurs when nobody is present in the room. Conversational speech levels tend to be near 65 decibels causing conversations to be understood, and distracting to others, from up to 15 metres away.
The Smart Sound Masking System
The good news is that privacy and comfort are not mutually exclusive. A low-level background sound is produced by speakers placed in the plenum and an adaptive sensor placed in the sector with the speakers that is both adaptive and adjustable. You’ve heard of a smart phone? Well, this is the smart sound masking system in that it anticipates what changes need to be made and adjusts automatically. This system represents sound masking at its best in that it is highly effective all day. *The background noise emitted by the speakers will adapt based on the needs of the workplace, fluctuating higher and lower as is necessary.
Sound Masking as Part of an Acoustic Design Strategy
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.
| Acoustic Problem | Sound Masking Solution | Other Acoustic Solutions |
|---|---|---|
| Lack of speech privacy | Reduces intelligibility of speech | Sound barriers, sound absorption |
| Distracting noises | Masks distracting sounds | Noise cancellation, soundproofing |
| Poor acoustic comfort | Creates a more comfortable sound environment | Acoustic panels, sound diffusers |