FACILITIES MANAGEMENT WHITE PAPERS

Electronic Sound Masking

Understanding sound masking technology and key selection criteria

Niklas Moeller
LogiSon Acoustic Network

More than 40 million North Americans work in open plan offices featuring partial height panels. Granted, cubicles make better use of space and improve communication flow, but they are an acoustic challenge.

Traditional walls have given way to modular furniture systems, more employees use the same space, and everyone is seated closer together. At the same time, new construction methods, absorptive treatments and quieter equipment have lowered the background sound level.

That may sound good – and to some degree, it is – but without adequate background sound, it is easier to hear the distracting activities happening around you.

Are closed offices the solution? You expect acoustic privacy, but in fact, sound often leaks from one office to the next through the ceiling or air transfer components. Then a closed door means nothing.

If you work in a modern facility, you can likely relate. Usually you are spending time on work that requires concentration. Disruptive conversations and noises make it harder for you to complete tasks. Errors happen more often, adding to stress. It takes more effort to focus, which tires you out, affecting your mood and, ultimately, your productivity.

This is where sound masking comes in.

What is sound masking?

A sound masking system consists of a series of speakers, typically installed above the suspended ceiling, which distribute an engineered background sound throughout a facility. This sound is most often compared to that of softly blowing air.

The primary benefits of this technology include increased speech privacy, reduced distractions due to noise, and a generally more comfortable working environment. It is easily installed in new or existing facilities of any size, providing an effective way of addressing acoustic problems at nominal cost and without remodeling.

How does it work?

If you have ever run water at your kitchen sink while trying to talk to someone in the next room, you will understand how masking works. You can tell your conversational partner is speaking, but it is difficult to comprehend what they are saying because the running water has raised the noise floor in your area.

The noise floor is the level of constant sound present in a space. If it is too high, you will find it irritating. Too low, and you can easily overhear conversations and noises.

Masking creates a noise floor that is high enough to cover up noises and low enough for comfort, which, for most facilities, is in the range of 42 to 48 dBA.

You must be able to hear the masking sound for it to be effective, but it is designed to be as unnoticeable as possible. It does not contain distracting patterns, and it is tuned so you do not hear volume changes as you move through your facility. Employees come to consider it a natural part of their environment within a short period of time.

For more information about how sound masking works, see my other white paper on FMLink: Achieving Effective Office Acoustics.

System types

There are a variety of sound masking systems available today. Their design and performance vary dramatically:

Centralized system

The earliest systems were centralized. They consist of centrally-located electronic components, which are used for sound generation, amplification and equalization, and also provide volume control. Groups of speakers are connected to the output of these components. All of the speakers broadcast the same sound and any adjustments are applied to the entire group or zone. Limited volume adjustment is also possible at each speaker. Zones are hardwired and, depending on the system’s design, can be up to hundreds of speakers in size.

Diagram 1: Centralized system

Decentralized system

The next development was the decentralized system, which is also referred to as distributed or self-contained. They consist of master and satellite units. The masters house the electronics for sound generation, amplification and output control. Up to two satellites are connected to each one and reproduce its sound. Local volume and frequency adjustments are made by entering the ceiling and accessing the master’s control, typically with a screwdriver. Global volume changes and timer functions are centrally controlled. Paging and timer zones are hardwired. This type of system offers much smaller masking zones of one to three speakers.

Diagram 2: Decentralized system

Networked system

The most recent development is the networked system. It consists of distributed components that are digitally and remotely controlled using a centrally-located panel or computer software. A single line of cable carries all power, control and audio signals to the components. All types of zones are digitally assigned and can be changed without re-cabling. Fine volume and frequency adjustments can either be made globally and/or down to zones as small as one to three speakers (225 to 675 ft²; 21 to 63 m²).

Diagram 3: Networked system

Desktop device

Desktop products are also available. These are standalone devices, not a facility-wide solution. They consist of electronics and speakers that are mounted within a workstation or sit on a desk. Because each user controls the volume, these products may reduce noise disruptions, but cannot be relied upon to increase speech privacy or provide consistent masking levels.

Diagram 4: Desktop device

Selection criteria

Carefully selecting a masking system based on its performance capabilities will help ensure that your needs are met both now and in the future.

For most facilities, a high level of flexibility is the key to achieving effective masking and maximizing occupant comfort. That is because it is not enough to just introduce any sound into your space. It has to be the right sound, in the right place, at the right time.

The system’s masking performance is largely determined by the following factors:

Masking generation

The number of masking generators the system includes determines the number of independently adjustable zones it offers and whether it will be affected by phasing (i.e. uncontrollable variations in the masking volume caused by the canceling and reinforcement of identical sound waves as they meet between speakers).

Determine how many masking generators the system provides and whether these are centrally located or distributed. If they are centrally located, ensure that the system is designed with at least two sound generators per zone and that the speakers are wired in an interlaced manner such that adjacent speakers emit different masking signals.

Zone considerations

Zone size affects the ability to adjust the masking to meet local needs and acoustic conditions. The smaller the zone, the more flexible the system will be because settings can be customized to each small area. Ask what size of zone the system offers and whether these are the same for both volume and frequency adjustment.

Most systems are also able to zone for paging, timer functions, keypads and other accessories. Ask how many zones the system offers for each of these functions and whether they are independent of one another. If the system only provides one zone, it may be necessary to install several such systems in order to provide adequate control of these features within your facility.

Also ask whether zones are hardwired or digitally assigned. Hardwired zones require additional cabling and a contractor to make changes. Digitally-assigned zones are changed from a control panel or computer.

Adjustment capabilities

The adjustment capabilities the system offers within each zone also affect the ability to adjust the masking sound to meet local requirements. Ask what kind of frequency (none, whole contour, 1 octave, or 1/3 octave control) and volume (large or fine increments) adjustment the system offers and over what zone size. The finer these adjustments, the greater control you have over the system’s output.

Masking works best when it is inconspicuous. Total variations of more than 1 to 2 dBA (variations of +/- 0.5-1.0 dBA) can call attention to the sound and may reveal its source. Inquire as to the range of variation the system specifications permit across the space.

The system should be professionally tuned.

Speaker type

The uniformity of the sound is also affected by speaker orientation, location and spacing.

Most manufacturers offer a variety of speaker models, but the most common and best-performing is still the in-ceiling, upward-facing speaker. Wall-mounted, downward-facing, under-floor and desktop models can be useful in situations where you cannot access the ceiling or suspend anything in it, such as atriums, spaces with hard ceilings and historical properties. However, downward-facing speakers are prone to volume variations due to a ‘spotlight’ affect.

Where the speakers are installed also affects the system’s ability to provide consistent coverage throughout your facility. For example, speakers installed within workstations are limited to areas with workstations. A versatile system can be installed in areas with suspended ceilings, in areas with hard surface ceilings, in areas with no ceilings, and in both open and closed plan spaces.

If you have an open ceiling, consider a system with attractive speakers and tidy cabling, so that they will not detract from the design.

Control options

The method of control affects the ease, cost and amount of disruption associated with making changes. It also impacts the likelihood that the masking and other functions will be modified if you move furniture or personnel in the future. Ask how many features can be modified and from what type of access points.

Timer functions

A timer allows the masking volume to vary in accordance with activity levels during the workday. Some systems also offer an acclimatization or ramp-up feature, which can be used to gradually introduce the masking sound in retrofit installations. Ask whether the system offers these functions and, if so, the configuration parameters it permits.

Other important items to consider when selecting a system include:

Scalability

Scalability affects the system’s ability to be installed in facilities of various sizes. Consider how much space the associated equipment will consume. Systems with centralized components may not be cost-effective for small installations and may take too much space in large ones. Systems with distributed components that require physical adjustment at the speaker may not be practical for large installations. Systems that offer central control of distributed components are suitable for installations of any size.

Paging & music

Most masking systems provide simultaneous paging and music distribution through the same set of speakers. However, depending on the type of system, they require different third-party equipment to be added. Ask what types of equipment you will need. If you select a system that cannot provide paging, it cannot be easily added later should your needs change.

Certifications

Ask the vendor to provide documentation of the system’s certifications. All components must be safety tested (UL or equivalent) and some also need to be tested for electromagnetic interference (FCC). In the United States, all masking systems installed in, or extending into, the plenum must be UL 2043 tested for flame and smoke resistance. Low-voltage systems must use Class 2 rated power supplies.

Service

Because success depends on more than just the right product, it is also important to select a system that is supported by professionals who can properly implement it and provide you with ongoing support. Determine what services are offered in conjunction with the system you are considering.

Final thoughts

Sound masking is part of a proactive approach that provides employees with the type of workplace they need to excel. It is also likely to be one of the smallest investments you make in your facility.

Early consideration of a sound masking system in your construction plans can reduce project costs and help maintain the flexibility of your space for future renovations. It is also very effective when used in combination with floor-to-ceiling wall systems and is comparable to increasing their Sound Transmission Class (STC).

Masking can also reduce, but not necessarily eliminate, the requirements for other acoustic treatments. Adding sufficient physical barriers and absorptive materials to the design can further minimize the distance over which noises are heard and the system’s volume can be decreased without affecting its performance level.

For answers to frequently asked questions about sound masking, visit the FAQs section of our website.

Niklas Moeller is Vice President of LogiSon Acoustic Network. He is involved in every aspect of the sound masking industry – from R&D to international market development – and frequently presents on the subject of workplace acoustics.