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Podcast w/ Bennett Liles: Acoustics and Sound Masking From Cambridge Sound Management

From Sound & Video Contractor Magazine, this is the SVC Podcast with David Sholkovitz. Show notes for the podcast are available on the web site of Sound & Video Contractor Magazine at

Today’s office environment has changed. The concept of private offices and even cubicles is giving way to open rooms, open ceilings and a shared space that has privacy at a premium. David Sholkovitz of Cambridge Sound Management is going to give us the details on the science and mechanics of sound masking. That’s coming up next on the SVC Podcast.

David, thanks so much for being with us on the SVC Podcast from Cambridge Sound Management and we’re going to be talking about acoustics and sound masking. That’s something we haven’t done many of these podcasts on so that’s going to be a real treat. First, tell us about Cambridge Sound Management. How long has that company been around?

All right. Thanks, Bennett. I appreciate you having me here. I look forward to teaching a little bit about sound masking. So in regards to Cambridge Sound Management, we were actually founded in 1999 in Cambridge Massachusetts. Our founder is an MIT Ph.D. with a pretty deep heritage in acoustics and audio engineering. He actually worked at a pretty highly-regarded acoustical consulting company in the Boston area called BB&N. They did a lot of R&D and research in acoustics and actually are accredited with essentially inventing electronic sound masking many years ago. So kind of that heritage in acoustics coming from our founder and then over the last couple of years – 10 years or so – we’ve really worked a lot on our product development and engineering initiatives to bring to market products that are easy to install in modern facilities. And I think in about 2003 we had our first commercialized sound masking product, so it’s been over 10 years now, really, in the market. [Timestamp: 2:06]

Yeah, and your outfit got in on the ground floor of this technology. I’m not sure that ten years ago anybody would even have known what that was or had ever heard of it. So why is that so important now? What has changed in today’s office environment that has caused sound masking to become such a big topic now? 

In the past 10 years the workplace has really changed drastically. There’s about 75 million Americans who identify themselves as office-based knowledge workers who are working in an office or corporate environment. It’s been a big impact on them. From a physical perspective, there’s many changes to the office environment coming along with the open floor plan. Obviously the elimination of the private offices and lowering of cubicles and developing open floor plan spaces that help drive collaboration in communication, that’s been a major trend. Also with furniture and more natural light and use of architectural products like glass and steel for a modern look and feel and also to help with letting more daylight in to help with LEED certification has been a big thing. I mean I think generally the shift into the open office has been great. It’s been good for us and it’s been good for many other office building products that are in the modern office. For employees there’s been some downsides of that, of course, because of course some of their privacy has gone away. So a lot of the sound issues have been created because of the elimination of sound absorption material. So no carpet, there’s less partitions. There’s many open ceilings so the ACT’s – acoustical ceiling tiles – that have played a big role in acoustics by absorbing sound in the office, those are gone in a lot of open ceiling designs, so you’ve got exposed ceilings. You’ve got a lot of sound basically floating around there, so we’ve seen a big uptick in sound masking because of these different trends. It’s pretty affordable technology to go and retrofit into a space instead of having to rebuild it to improve acoustics, which can be very costly. [Timestamp: 4:09]

Yeah, collaboration is a great thing but when you’re trying to concentrate on something I guess it’s good to be able to sort of turn it off and quit collaborating for a few minutes.

Yeah, it’s definitely a balance, I think, of being able to communicate; obviously work with others, right, but also have your focus time or your “me” time to be able to concentrate. I think facility managers in H.R. and management teams try to always find that balance with a comfortable office, but then one that they can create some level of privacy, especially depending on the line of work where some people may need to focus, like a software engineer or R&D developer. [Timestamp: 4:45]

So you’ve got active systems now instead of just passive sound-absorbent materials like tiles and carpet so how does all that work? How does the science of sound masking work, the basics of it? 

Yeah, so sound masking is the process of adding to an environment a low-level, unobtrusive sound, and the sound has been engineered at the same level as of human speech frequencies to help protect confidentiality of conversations and to reduce distractions. So we’re basically adding sound to make it feel quieter, so it’s a little bit reversed in how it sounds. We’re actually making it a little louder to make it feel quieter. The key to all of this is reducing the intelligibility of speech, so making it harder to understand what people are saying, that helps make it actually make it a more comfortable environment. So sound masking, it’s not cancelling speech. I think it’s good to make that statement. It’s also not absorbing speech. It’s not blocking sound, but it’s making it harder to hear people at a distance which makes it less distracting. So most office environments with some masking on, a worker would likely hear every word of another employee 40 feet away without a phone. But without sound masking in an office you can hear that person from quite a distance talking. Then once you add the sound masking there you’re introducing some sound into the background. It makes the conversations less intelligible and then therefore less distracting to people. There’s lots of different analogies, but it’s almost like just creating a comfort level by giving a little bit of background sound. It’s like when you’re in Starbucks or the coffee shop. There’s actually a lot of people who like working there because there’s this comfort level with kind of the ambient sound in the background. And similar to an office, some of our clients have offices that are not necessarily always too loud, but also too quiet. Those are some of the worst culprits when it comes to an office because when an office is very, very quiet you can hear everything around you and that’s annoying. [Timestamp: 6:34]

Yeah, nobody wants to talk.

Yeah, so it’s like – and it’s also, then, when it’s an office where a lot of people are talking, that can be distracting. So sound masking helps in both of those situations.

Yes, sort of covering a distracting sound with non-distracting sound.

Yeah, yeah.

And Cambridge has the QtPro system. You have several different models. What are the components of one of these sound masking systems? It’s active so it would have to be composed of several different parts and pieces that have to be centrally controlled.

There are three main components. So while there’s a lot of technology going on, if you break it down into these three components it’s actually a relatively simple system and this kind of simplicity is part of our value proposition for installers. The three main components, you’ve got a control module and also an amplifier. We’ve got different versions, but the control module is the brains of the system. It’s creating the sound- masking sound and it’s got the circuit board and the microprocessor and all the hardware – most of the hardware components. And then you’ve got cables, which is basic CAT-5 cables, which connect the control module to emitters. And then you’ve got emitters. So control module, cables and emitters are the three primary components. We only have one type of emitter, which makes it very easy so there’s one type of emitter for any sort of installation. And then we’ve got different control modules depending on the needs of the customers. And the cables daisy chain the emitters together, so basically it’s a daisy chain system of emitters which are very small – 3-inch emitters. I think we’ve got inch-and-a-half drivers inside of them so they’re very small speakers, essentially, that are spread out in a grid format. So if you look at those three, those are the three main components of a system, so it’s a relatively kind of a simple complex. There’s more complexity of course in the software and how it all works, but as far as installing, those are kind of the three areas. [Timestamp: 8:22]

Now, when you’re going to install one of these you don’t just go in and start hooking things up. You have to sort of analyze the environment. Are there specific measurements that you have to make to determine the settings on the system?

It depends on the complexity of the client site that you’re in. It’s a pretty much plug-and-play system so there’s no commissioning or tuning that needs to be done. As far as measurements, yes there are measurements out there. There’s the privacy index, there’s the SPP, which is speech privacy potential. That’s how you measure speech safety in an enclosed office, like a conference room. So there’s generally that you want to look at those things when you’re in a space. Generally you want to just understand the speech intelligibility, so how does the environment react to noise and to sound? You can get pretty technical if you want to do a deep dive into a space, but a lot of it is just understanding, once the system is deployed, getting the right dB level; making sure the zones are set up correctly in the environment. So yeah, there’s different things that you can do. There’s a lot of standard kind of acoustical measurements out there that are pretty well-known and agreed to by the community. [Timestamp: 9:31]

And of course these are active systems and we were talking earlier about how a lot of the absorbent materials have been phased out of modern offices. What are those typically? Carpets, drapes, acoustic tiles and things like that with just sound-absorbent material?

Yeah, that’s correct. Yeah, acoustical ceiling tiles are the big one because the square footage that you’ve got coverage of that, the ceiling is everywhere. So those are the big one to absorb sound, so as soon as you blow those out and you’ve got an exposed ceiling, you’ve lost a lot of sound absorption space, or coverage I guess. Carpet, as you mentioned, is definitely a big one. Again, that’s everywhere and if it’s a fully-carpeted building that used to absorb a lot of sound. Now you’re seeing offices that have either hardwood floor or they’re doing concrete floors completely or tiles or whatever, or selective carpet usage. Cubicles, the fabric on cubicles is designed for sound absorption. And then you have companies that have gotten pretty creative with drapes and panels and even plants that were designed to absorb sound, you know, artificial plants and some other cool things. There’s some pretty funny products out there that absorb sound, that are also pretty quirky. [Timestamp: 10:42]

And with all of the experience that your outfit has had in acoustics and sound masking what would you say is the most difficult or challenging part of installing a good sound-masking system?

You need to make sure that you’ve set up the zones correctly in an environment, so proper zoning, I think, would probably be the most challenging thing. Some masking systems must be flexible enough to accommodate complex architectural spaces, using a ceiling-height furnishing type would come into play. You’d probably want different zones to get a consistent sound field created. So there’s some tweaking you need to do in the zones. By dividing a system into zones, though, it does make it easy because you can kind of break it into smaller pieces. So if you’ve going into an office that’s got a lobby with 20-foot ceilings, you can do a zone there that just covers the lobby area, do another zone that maybe comes through the hallway, and then another zone in an open office and another zone for private offices. So by zoning, breaking a space into its different variables, for an average office size – I don’t know, if you’re doing 5,000-8,000 square feet or something like that – you just want to make sure you get the zoning right. I would probably say that’s the most challenging. We do designs. We have a design team that can help do that here for you, we just need the acoustical ceiling plan layout so we can make a design, put emitters in the right place. I think once the ideal sound-masking kind of frequency level is established, the other thing is just amplifying it to the right level, and that’s just a sound level check. It takes a little bit of engagement to get that right, but zoning, I would say, is probably the trickiest part. [Timestamp: 12:16]

I guess that could be complicated as far as the zones if you’ve got some sound leakage between the rooms.

You know you always want to have the sound-masking system laid out where the unintentional listener is, right? And when it comes to between rooms, if you’re doing a full deployment we’re going to have an emitter about once every 100 square feet, including that both in rooms and in open office areas so we cover the whole space. By covering the whole space you ensure that you’re helping to mask sound in all the right areas. You may have the zone level a little bit lower in a private office because you don’t need it as loud because you’ve got some natural sound blocking going on with the glass and the walls, so you have a little lower level in there. But it definitely helps cover the leakage. [Timestamp: 12:57]

Well, I know there are all kinds of tricks to the trade and there’s no substitute for experience in doing this and it’s been great to get the quick two-dollar tour on the science of sound masking. In Part 2 we’ll get into the privacy index, direct field systems and thing like that. David Sholkovitz from Cambridge Sound Management, thanks for being here with us David.

Thanks, Bennett. I appreciate it.

From Sound & Video Contractor Magazine, this is the SVC Podcast with David Sholkovitz. Show notes for the podcast are available on the web site of Sound & Video Contractor Magazine at

Despite all the exact science behind acoustics and sound masking, it comes down to experience when installing a system to limit noise AND increase privacy. David Sholkovitz of Cambridge Sound Management is back to wrap up his talk about the science and mechanics of sound masking. That’s coming up right now on the SVC Podcast.

David, thanks for being back with us for Part 2 on the SVC Podcast from Cambridge Sound Management, sound masking system experts. We talked last time about the basic science of it and science sets the stage but then actual field experience comes into play. Tell us about some of your more challenging projects with the QtPro sound masking system. That’s the one you handle.

Yeah, that’s correct. Yeah, you always have some challenges when you work in all sorts of vertical markets. We will jump from doing a hospital to a university to corporate offices, call centers, things in the U.S. and in 30 different countries. So you run into all sorts of architectural designs that make sound masking deployments challenging. I think one that jumps up to me is actually in Stanford University. They’ve got – well, there’s two different things. One is there’s a very complicated library that we did there and then there’s another situation, and I believe it’s at Stanford, which is a classroom environment. So the university wanted to have the ability for a teacher to give a lecture in a big classroom size, kind of stadium seating like normal – but they also used that classroom to do breakout sessions so the students would then take a task and work together in teams. And they didn’t want the students to have to get up and leave the room to go have privacy in their different breakout sessions, they wanted to do it in the room. So the installation company and the AV company and I think some of their in-house engineers used our products in a real cool way, which was basically when the teacher is talking there’s no sound masking on because you want to hear the teacher speak, right, very clearly. And then the teacher would have the students break out into their breakout sessions in the room and they would slowly ramp on the sound masking actually in the classroom and that would allow the teams to break out in their sessions, so their business plans or whatever they were working on together with sound masking on to protect them from hearing each other and to reduce distractions. And then when the professor was ready to speak again, he or she will turn the sound masking – ramp that down and then comes back to the non-sound masking environment where you can hear everything. They thought it was kind of a cool way of deploying it into their control systems. We have an API, so I think they’re using an AMX or Crestron system. It can all be controlled through the system. But that’s kind of cool how they’re turning it on and off. That’s very unusual. Usually sound masking is something that’s on all the time in an office. But in this situation it was kind of cool how they use it to cover up speech when the students were in breakout sessions and then turn it off when the professor had to speak and address the class. [Timestamp: 3:19]

You know, that’s something I didn’t consider before but turning it on and off could create a whole different environment especially if you do it in a subtle way. And if it works right, the people there just hear what they need to hear but they probably don’t give it a second thought. 

That’s an unusual circumstance. Like you said, usually you don’t want people to know it’s there so it’s always on in the background in an open office or a call center or wherever you have it. In this case it was kind of interesting because it does come on and off with the control system depending on what the teacher is doing. And most of our more challenging ones are just doing drop ceilings, or sorry, open ceilings where we’re, you know, a lot of renovated lofts and locations that are kind of half glass/half brick, doing a lot if refurb buildings where we’ve just got to do a lot of mounting. We’ll have rods that actually bring the emitters down. Our product’s really easy, or it’s good for open ceilings because it’s coming straight down into the space; it’s not a plenum solution so it’s easy to mount the emitters. We have black ones so a lot of – we do a lot of black ceilings, which is kind of a trend of having an open ceiling that’s painted black. But yeah, there’s always a lot of challenges out there. [Timestamp: 4:28]

Yeah, you can be very subtle with one of these systems. So give me the basics on what this does. I think on your site there’s the ABCs of sound management. Absorb, block and cover.

Yeah. These are really the fundamentals of not necessarily sound masking, but the fundamentals of architectural acoustics and things to consider in an acoustical way about building a space. So we have A, B and C – absorb, block and cover. Absorb is the principal of adding sound absorption material into a space to absorb sound. So this is adding carpet, ceiling tiles, drapes, furniture, cubicles; those artificial materials that are set up to absorb the sound in an area. And then of course you’ve got block, the B, which is building walls, building up cubes, building private offices. You’re literally blocking sound. You’re putting something up there that’s supposed to block it and be more permanent. And then there’s C, which is cover, which is where sound masking comes into play. That’s about creating an ambient background sound to help cover up sound. So together the ABCs of acoustics help form kind of a fundamental baseline for how an architect or an AV consultant or audio consultant can go into a space and think about the different things to tackle to make a comfortable acoustical environment. And it’s important not just to focus on one or the other. I mean we often tell customers that it’s not just sound masking. If your space is having other issues you may want to consider adding in some sound absorption material as well along with some sound masking from the cover side to make sure that they’re fully addressing the acoustical challenges of a space. And this applies both for private offices, enclosed areas, and open offices as well. [Timestamp: 6:12]

And one of the things that you mentioned before, I think it was in Part 1, is the Privacy Index. What exactly is the Privacy Index?

Measuring the speech privacy is very essential for organizations to try to achieve a level of confidentiality and privacy in their offices. The Privacy Index is an industry-wide term of measurement that’s used by acoustical technicians across the country. It’s been widely supported by different associations and groups. I guess generally when we have the system – so say we install a sound masking system, we generally want to achieve a normal speech privacy index of 80 or greater. So it’s from zero – I think it’s 0 to 100. It’s not on an even curve. So 0 is absolutely no privacy, 50 is still pretty much absolutely no privacy, and then starting at 60 and above is where you start to see measurements that would actually create some privacy for people in the space. So I guess with sound masking we’re trying to shoot for a privacy index of 80 percent or greater, which is an open plan area. At 80 percent you’re starting to have some – you’re starting to have speech be unintelligible; 85 is a really good goal to have in an open office space. And then if you’re going into a closed office, a private office, you want to hit the 90-95 percent on the privacy index level to have full, very confidential privacy in an office. So to sum it up it’s a scale of privacy for individuals that’s used by designers and acoustical consultants to measure the comfort level and the privacy level in the space. To boost sound masking you want to get in the 80-85 area for an open office space to make it comfortable, but you’re not hearing people’s conversations at a certain distance away from you. [Timestamp: 7:59]

Okay. And I know that can be critical in establishing the right environment in a conference room or in a busy office with a lot going on all the time. I’ve also heard of the direct-field system versus the in-plenum type.

Those are essentially the two types of sound masking systems that are on the market. So our products are direct-field and direct-field means that the sound masking speaker is facing down into the office environment so the only thing between the speaker and people in the environment is air itself. And in-plenum speakers tend to be a little bit wider, a little bit bigger, and they are facing up and then they fire the sound up and then it reverberates off the ceiling and then bounces back down through the ceiling into the space below it. Most of the traditional systems are all in-plenum, so there’s speakers that get hung on wire from the ceiling and fire the sound up and then bounce that down. And those were used for many years. We actually patented and developed direct-field sound masking so we have smaller speakers. There’s more of them in and environment because they’re smaller, but they go into the ceiling facing down or mounted in an open ceiling and then they send the sound masking directly down into the space. Those are kind of the two different systems that are out there and you really – I would just urge installers and also end users to think about what works best for them in their environment. The direct-field system we feel strongly it’s very effective in being able to eliminate hot and cold spots and make it easier to install because it’s just a tiny speaker that can be mounted anywhere or put into a ceiling tile and doesn’t need to be mounted in the plenum, but generally we feel like it’s got a higher quality level when you’re introducing that sound right into the space. It’s just more effective. So those are kind of the two different systems that can be used. [Timestamp: 9:48]

So when people come to you and they’re interested in a sound masking system, I guess they’ve usually done a little bit of research. So what types of places can benefit the most from a good sound masking system? We mentioned classrooms and boardrooms.

Classrooms, boardrooms. The most common application are open floor plan offices. We have a lot of people in one space and generally offices that have no background sound or they’re very quiet are good candidates for that. And then also those offices that are – where you have like a sales center, if you have a call center where there’s a lot of people chatting and talking and it’s a whole lot of human speech going on, sound masking also can help in that environment and reduce distractions. But yeah, private offices, call centers, engineering labs are big. From a vertical market we do a lot in healthcare, hallways, nursing centers, waiting rooms, patient rooms, doctors’ offices. Those types of areas are good because you need to protect conversations between doctors and patients and patients and staff and there’s HIPAA regulations and other things that help regulate healthcare facilities to make sure those conversations stay private, so healthcare is big. Hospitality, we’re doing hotels here and there and then we have the tech sector in general is big. These companies are moving towards office spaces and they’ve got a lot of engineering and R&D centers where we cover it up. And then government is a big vertical for us as well. So the applications of office/conference room/private room – every vertical market has those spaces so there tends to be   very wide variety of uses of sound masking throughout – in almost every industry, so that’s great. [Timestamp: 11:23]

Why do you use a multi-channel sound masking system? Is that so that you can create different zones?

It’s not for different zones. Our systems are set up so we can have up to six zones on one amplifier. That’s separate from multi-channel. So why do we use multi-channel? Well, when identical signals reproduce through two loudspeakers placed a distance apart, comb filtering affect is basically heard by the listener as they move through a space. So if you didn’t have a multi-channel distribution you could actually hear the difference in sound between speakers. Absolutely not what we want to do. So this audible difference, if you had two speakers using the same channel you could localize it and you could tell where the speakers are in the ceiling, but more importantly you would notice it more. The comb filtering is technically due to the fact that as some frequency is emitted the audio signals are basically summing each other and at other frequencies the audio signals between the two sound sources are cancelling, which would reduce it. So by using four non-coherent noise sources or channels, we’re able to lay out the masking system to minimize the effects of comb filtering by basically ensuring that no two like noise sources are playing through adjacent emitters. So you know you’re never going to hit two of the same noise sources in the same area close to each other, which at the end of the day makes it much more comfortable and a much more effective sound masking system because you can’t localize it and you can’t hear the difference between the speakers so it gives it a very even distribution. [Timestamp: 12:54]

Okay. And on power consideration, I guess these things don’t use a whole lot of power any more than a home stereo system would or anything, but how quick are they to come back up if, say, you have a power outage?

Yeah, so our typical control module will take about 20 seconds to reboot after a power outage for our Qt100, 300 and 600. It’s about 20 seconds, so it’s not long – not a long reboot period. And then on the power, you’re correct. They draw very little power. Our Qt100 devices powers only seven watts – draws at seven watts. Our biggest control module only draws 27 watts of power and that’s to cover 72,000 square feet on 27 watts. So it’s like an exit sign as far as the amount of power that’s actually drawing off the system. [Timestamp: 13:43]

Yeah, looks like a real bargain in terms of the effect versus the power that it uses. So what’s happening at Cambridge Sound Management? Have you got any interesting projects in the works coming along?

We just launched a project at Infocomm for conference rooms, so the Qt Conference Room Addition. This is our first product that was built for targeted sound masking. The control module and the signs go in a conference room which will alert the participants that their meeting is being protected and then the speakers actually go outside of the conference room, outside of the glass walls or other walls if it’s drywall or whatever. So this is our first targeted application for conference room AV and we hope the AV installers who are doing a lot of conference rooms can help create awareness with end users that there is a privacy issue and that there’s a technical solution to solve that. We call this the privacy solution for conference rooms. So this has been a big focus for us in the second quarter and third quarter. We do a lot of retrofits and there have been lots of new construction projects. When it comes to new design those projects typically take a little bit longer and we’ve worked with various architects on those. I can think of a lot of pretty interesting companies that I probably shouldn’t name, but different tech companies and financial services companies doing some pretty big installs. I think it’s good to see the market rebound a little bit, especially in commercial real estate and commercial development. We’re seeing a rebound of the economy and things are getting better so people are investing in their offices as well. And then yeah, I guess we’re seeing more integration with control systems of sound masking so it’s kind of being a more common staple within especially conference rooms and high-end conference rooms that sound masking is kind of a core component of the AV buildout. So there’s always interesting things coming on so it’s fun because we do a lot of the designs for our installation partners so we see a lot of designs and help lay it all out. And then of course go there and commission, if necessary, with our partners to make sure everything is done according to plan. So it’s always busy. [Timestamp: 15:43]

Yeah, it sounds like it. It’s an incredibly interesting line of work and the science behind it is complex and just amazing. The systems can create a real effect and a whole new ambient environment. Thanks very much for taking us through this and kind of getting us up to speed in sound masking technology. It’s David Sholkovitz from Cambridge Sound Management. Come see us again sometime.

All right. Thanks a lot, Bennett. I appreciate the time today.

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