Your questions answered: How to design for office sound masking

Sound masking has never been more important in the office. 

In this Nov. 10, 2021, “How to design for office sound masking” webcast, the challenges and solutions of architectural acoustics were discussed, along with information on how to identify how these acoustic principals affect speech privacy, noise distractions and workplace comfort.  

Some questions that were left unanswered during the broadcast are answered here.  

The expert presenters were Nathan Van Ness and Jeremy Krug from Biamp Systems. 

What is the average cost per square feet in additional cost that should be considered? 

While equipment costs have been predictable in the past, it’s wise to expect they may increase in the future like so many other products. However, the biggest factor in masking cost is labor. In the past we would say that between $2 to $2.50/square foot would be average, but that maybe closer to $2.50 to $3/square foot in the future. And labor rates in a major city like New York City or Chicago will be higher than Denver or Nashville. So, expect major markets or union buildings to reach about $4/square foot. 

What about large free open area return grilles in the ceiling with a return air plenum? 

Historically, the most difficult problem for an indirect (in-plenum) solution has been the inconsistency of the ceiling. Plenum returns are just holes in the ceiling that let sound through louder than the sound that passes through the grid tiles. At a minimum, we have sound deflectors for return vents and the best solution is either an addressable, network-based masking control system or a direct (down-firing) masking system. 

We just installed baffles on 2-foot spaces across an open office. Is this blocking and absorption? 

If the baffles are soft, then they are absorbers. (f they are hard wood or metal panels then they are diffusors. Some sound energy that reaches them will be absorbed, which will reduce the overall noise level in the space. But baffles don’t attract sound, so sound that doesn’t reach them will travel as normal. 

Are your systems able to automatically compensate for HVAC systems ramping up and down? 

The masking industry has investigated this in the past and the consensus among acousticians is not to try to chase the HVAC noise. The amount of energy added by masking is so low by comparison that even if masking is set at the optimal level w/out HVAC and then HVAC switches, the overall level difference will not be significant and may not change at all in areas where the HVAC is quieter. 

How do aerodynamics affect sound levels in offices, such as surrounding airflow? 

If you mean air moving outside of the building as in a windy city or high floor, the biggest factor will the quality of window materials and installation. High-quality windows will hold back more sound and keep the office quieter inside. If you mean airflow sounds inside the building, then please look at some of the questions and responses about HVAC systems. 

Are there health issues caused by the sound masking systems? 

To our knowledge, no sound masking-related health issues have been documented. And there’s no reason to believe that the background sound produced by Biamp’s sound masking solutions would ever cause adverse physical reactions. There is research and a lot of user experience to show that low levels of consistent background noise are calming to people (and many animals) and reduce stress hormone levels like cortisol. This is why sound masking is used in nurseries to help babies sleep, in spas, health care facilities and why we go to the ocean to relax. 

Can you take credit for mechanical noise when designing sound masking? 

Most mechanical noise that is not HVAC related in a building is “transient,” meaning it appears and disappears. Things like elevators, toilets, doors or other building systems switching on and off are transient mechanical sounds. These don’t help a masking system, but a masking system can help make these less noticeable to the occupants because the louder consistent background noise will reduce the difference between the quiet environment and the louder transient sound. 

Is each emitter individually adjustable? Some occupants may be particularly sensitive to the noise and would like the volume reduced in their areas. 

Our network-based indirect sound masking system has the advantage of individual loudspeaker adjustment, whereas our direct solution allows adjustments per zone, not per emitter. While adjustment is possible, we really do not recommend trying to cater to individuals any more than you might try to adjust the temperature for every individual. Reducing masking above one person creates an eavesdropping zone where that person can now hear other people talking while others cannot hear them. 

Can you demonstrate the sound masking noise with a sample online? 

Because we don’t know if a listener will listen on headphones, laptop speakers, a cellphone, etc. sound masking needs to be heard in person, not over an internet connection. 

What is considered best type of soundproofing and layout for trying to control outdoor noise such as refrigeration compressors? Try to absorb and also deflect sound upward and away from personnel? 

Sound travels through hard materials, so decouple the equipment from the ground and especially from rooftops using springs, rubber bushings or similar materials. Create a secondary structure around as many sides of the equipment as possible, including below devices on rooftops, to try to hold sound within the space. Directing sound upward as you describe can work for low-rise buildings, but can backfire with multifloor buildings because it acts like a megaphone on the ground aiming that energy at upper floors. 

Why would you ever use indirect sound masking? 

We use it when ceilings are very consistent, like older-style spaces with consistent grid tile throughout the space or open-to-structure spaces with high deck heights of 14 to 20 feet. We also use it when architects or designers insist on “not seeing” the speakers for aesthetic reasons (and this could include using underfloor systems). And for particularly large projects that need a cost-effective solution, indirect masking for 100,000-square-foot buildings and larger can sometimes be a lower cost. 

The owner complained that boat tour ticket takers at a window facing outdoors at a corner of the room can’t hear the customers outside place an order. My first attempt is covering a large portion of the ceiling with convoluted commercial acoustical foam. I’ve also placed near field sound absorbing panels on each side of the ticket takers. There is a nonfunctional plexiglass cove barrier behind the ticket takers that the owner doesn’t want to change to a proper acoustical barrier. 

Ask the architect to volunteer as a ticket seller for a few days. We all love beautiful looking spaces and sometimes have to figure out ways to make them sound good too. I don’t imagine that sound masking would help in this case because the customer and ticket seller are likely as close as possible, but still separated by a window. So, the most likely solution would be preventing as much sound as possible from getting into the ticket taker space (probably more blocking around that space and absorbers inside the booth) and probably adding a window intercom system, which we do not make, but are widely available. 

This system used to be Cambridge Sound, right? 

Yes, Cambridge Sound Management was acquired by Biamp Systems in late 2018. 

Is there a product that is furniture-like, upward-emitting and moveable by the occupant? Picture a nicely finished pedestal with the emitter at its top surface. This may be used in an open office environment. 

None that we’re aware of and, if there is such a product, it wouldn’t provide the full benefits of a properly installed sound masking system. In particular, masking needs to go “where the ears are that shouldn’t hear.” Many people would tend to place a masking device close to themselves and think they are getting privacy. Really the masking needs to go by all the other listeners and, if it can be moved, then someone who wants to eavesdrop could simply move that device. 

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