USSI | An Acoustical and Industrial Building Podcast

When comparing decibel values, that best way to think about it is to consider how decibel values combine. For example, the combination of a sound having a level of 50 dB, and a second sound having an equal sound level of 50 dB is 53 dB. In shorthand (but not arithmetically correct) 50 dB, quote-unquote, plus 50 dB is 53 dB. This gives us a good rule of thumb to live by:

Two equal sound levels combine to be 3 decibels greater than the individual. 65 dB "+" 65 dB = 68 dB

When two sound levels differ by 10 decibels or more, when combined, the lesser level can be ignored. 65 dB + 75 dB = 75 dB

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Decibel boundaries. Zero decibels is the threshold of human hearing; that is, 0 dB is the minimum sound level an average listener can hear when no other sound is present. At 120 to 140 decibels, sound pressure is great enough to cause our ears to begin to hurt. So nearly all sounds we typically encounter fall between 0 and 120 decibels. We can even narrow that range down a bit.

For everyday purposes, a bedroom will typically be in the 35-45 decibel range and a typical office environment will be around 45 to 55 decibels. When we speak to each other from arms' length away, we hear about 60 decibels. When we shout at each other from arms length away, the level jumps up to 80 or 90 decibels.

In terms of "how loud," sound levels at or greater than about 85 decibels, such as a lawnmower when mowing, are considered loud. Sound levels of 100 decibels or more are very loud, can feel unpleasant, and can cause hearing damage in less than 1 hour of exposure. Typical amplified music concerts are typically over 100 decibels and can reach 120 decibels or more.

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First of all, the term "frequencies," is a short-hand way of talking about the frequency content of the noise control problem at hand. It is a critically important consideration, because noise control treatments are generally most effective at a particular frequency, or range of frequencies. Some noise regulations even specify sound level limits on a per-frequency basis. 

You can think of sound frequencies like musical pitch. Low frequencies would be the low notes, and high frequencies would be the high notes. If a chorus, band, or orchestra all played random notes simultaneously, it would probably sound more like noise than music.

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The number one thing you need to do is to make sure that you are controlling the loudest noise source and making it quieter. If you don't do that, you risk doing nothing at all in the way of noise control. If one noise source is very loud, then a relatively quieter noise source can seem as if it isn't even there at all. Industrial noise control must recognize this dynamic, which leads me to the fundamental tenet of noise control design: "Treat the loudest source (or source group) first." Noise control is very much a top-down process.

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Yes! Every single project should consider noise control. It could simply start with asking the question, "do we think noise might be an issue here?" and go from there. If the answer is a confident "no," then you're done and you move on. If the answer is "yes," or "I'm not sure," then more work is needed.

Tim has three arguments for considering noise control on every project.

1. Noise Control costs much less in the design stage than during post-construction mitigation.
2. Noise should be a facility design consideration because noise controls can affect other operational parameters.
3. If you don't consider noise in the planning and design stages, you have already taken some good options off the table. I have a good story for this, but we're short on time. I'll just say that cost-effective noise control options could include choosing a different site (with fewer or farther away neighbors), buying more land, or orienting the facility a different way. Of course once you buy and build, you're pretty much stuck with what you have.

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The term "noise control" is fairly self-explanatory, it simply means reducing or mitigating unwanted sound. "Unwanted sound" is the definition of noise.

If you want to control, or mitigate, noise you need to look at one or more of three things: #1) the source of noise, that is, the machine or process causing the noise, #2) the receiver or receiver location of noise, that is, where the noise is a problem or potential problem, which could be a neighboring homeowner, or a property line location, etc. The third thing you want to consider is the path between the source and the receiver. So for noise control, think source-path-receiver, source-path-receiver, in that order.

It's always best to control the noise at the source if you can, because the less noise that's generated in the first place, the less you have to control. 

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Welcome to the United Steel Structures Incorporated Sound Science Podcast! Noise control should be considered early in the design process of an industrial building to avoid costly solutions in the future if noise proves to be a problem after installation and start-up. Every month, Director of Industrial Acoustics Dr. Tim Simmons and Estimator Zachary Jones will share why noise control is important, describe regulations that drive noise goals, explain acoustical terminology, and much more. If you have projects that require noise control or want to learn more about the technical side of Sound Science, then this podcast is for you. USSI has over 40 years of experience and has completed over 4,000 projects while working with major clients throughout the oil and gas industry, including Williams, XTO Energy, MarkWest, and many more.

Learn more about our company at www.ussi.com. We want to hear from you so please send us your questions at [email protected].