A Beautiful Combination

Absorption, Blocking and CoverLast week, I talked about what’s involved in ridding your space of as many preventable noises as possible. This week, I’ll describe how to deal with the remaining – totally unavoidable – noises made by people simply ‘being’ and doing their jobs.

These noises have to be controlled through design. After all, we want to create environments that are comfortable for people to work in and support what they’re doing. Most still spend at least 60 to 70 percent of their time on individual work that requires concentration, and a further 20 percent on the telephone or in conversation within their workspace. They should be able to focus on these tasks and talk without feeling like they are disrupting or being overheard by everyone else.

So, we finally arrive at the ABCs...

A is for Absorption. Absorptive materials reduce the volume of sounds that bounce off them. By using these materials on ceilings, walls and workstations, you reduce the overall volume and echoing that makes spaces uncomfortable (think of a gymnasium). Because absorption only works on noises that reflect off a surface, it typically has greater influence on sounds that are created farther away from you. Absorptive flooring, on the other hand, prevents noise from being created in the first place by preventing or reducing the sound of footsteps.

B is for Blocking, which is achieved by using physical barriers. Barriers won’t completely stop noise transferring from one side to the other, but they’ll lower the volume of sounds as they pass through them. There’s no doubt that blocking can reduce flexibility, but it’s an essential strategy, especially in areas where people are working in close proximity to each other (last week’s point about density). None of the other acoustic treatments have any effect over very short distances. But barriers do. In other words, if you dispense with them, you’ll reduce the acoustic performance of the space in a way that can’t be offset by other design decisions. Given that noise is such a common complaint and that people costs far outweigh facilities in the long term, in my opinion eliminating barriers can’t be rationalized by the typical cost or aesthetic grounds.

C is for Cover, which refers to the use of sound masking. Historically, this technology is the least known and understood noise control method. That’s one reason why I find it such a fascinating field to work in! Sound masking uses a system of loudspeakers to distribute a comfortable and unobtrusive background sound that interferes with your ability to hear conversations and noise. It’s the only acoustical technology that can actively control the background sound (adjust both the volume and frequency) in your space. When properly implemented, it’s highly effective at covering human speech and the noises not addressed by the other methods (or, in the case of loud noises, diminishing their impact on occupants by reducing the amount of change between baseline and peak volumes).

The key message to take away from this post is that you need to use a balanced combination of all of the methods of noise control in order to succeed acoustically, because each one makes a unique contribution to the overall result. I believe the best analogy is the three-legged stool. If one of the legs falls off, so do you. I regularly run across projects where the client initially believed they could eliminate one aspect of the acoustical plan and simply compensate with another. It never works.

We’re regularly called in to provide an after-the-fact solution for a space that has next to no absorption and is wide open. Sound masking is very effective, but it shouldn’t be seen as a silver bullet. While it will undoubtedly do its job and provide great benefit to these spaces, the truth is that the final result won’t be as good as it could have been.

I’m not sure what the origin of this problem is. Consider a balanced diet, for example. You wouldn’t say, “I’m not keen on vegetables, so I’ll make up for it by eating more pasta.” In extremely cold weather, you don’t think to yourself, “If I just put on these gloves, I won’t need a hat or jacket.” In these situations, everyone appreciates the role each item plays in the solution, but that’s not often the case in acoustical design.

Hopefully this post highlights the role each noise control method plays in the final result. A, B, C, D, E and R – what a beautiful combination!

If you’d like to read more about this subject, see Design Tips on www.logison.com.



Next week: The myth of ‘meeting’ ASTM standards for sound masking.

Content coming soon.

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