United Steel Structures - Podcasts

# Part 2 Acoustical Rules of thumb and Demystifying the Decibel

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

We want to hear from you so please send us your questions at podcast@ussi.com

# Part 1 Acoustical Rules of Thumb and Demystifying the Decibel

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.

We want to hear from you so please send us your questions at podcast@ussi.com

# What are "sound frequencies" anyway?

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.

We want to hear from you so please send us your questions at podcast@ussi.com

# The Fundamental Tenet of Noise Control - and Why It is Important to Understand It

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.

We want to hear from you so please send us your questions at podcast@ussi.com

# Should I consider noise control on every project?

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.

We want to hear from you so please send us your questions at podcast@ussi.com

# What is noise control?

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.

We want to hear from you so please send us your questions at podcast@ussi.com