Sound and Its Control

 How do they do it?  Your teenager is busily doing his homework, the sound on their stereo speakers cranked up way past the point of your comfort.  As the heavy bass beats against your eardrums, their sound waves continue to travel throughout the house, crashing into walls and uprooting small objects from their positions on shelves.  Thankfully, controlling this uncomfortable sound level is relatively easy, as you scream out, “Turn that music down!”

     Many dangerously loud sounds are not so easily controlled, as when they take place in industrial settings.  Here, when complex machinery and manufacturing processes are at full tilt, one can’t just turn a single knob or pull a plug to gain relief.  Controlling sound levels in factories, power plants, and construction sites is often a complex task, relegated to engineers with state of the art equipment meant to measure and assess sound exposures in order to devise a strategy to control them.  Let’s take a look at a few of these control methods.

     For our example, we’ll consider the challenge faced by a fictitious company, Widget USA.  Business has picked up, and they need to install an additional manufacturing line in their factory.   Now widget manufacturing machinery is notoriously noisy, and management is thinking ahead about protecting widget line workers from potentially dangerous sound levels.  Their manufacturing engineers dutifully keep this in mind while devising their requirements specification, a list of “must haves” routinely included in quotation requests to potential manufacturers bidding on the job.  Of utmost concern is to limit the number of decibels (dB) that the new widget machine can produce.  If a  manufacturer under consideration is unable to meet these requirements, Widget USA will take their business elsewhere.  This methodology essentially nips the excessive noise problem in the bud, eliminating the noise source before it is introduced into the factory, and this is by far the best way of dealing with our scenario.

     Well suppose things aren’t as neat for Widget USA.  Their factory contains many existing manufacturing lines with old, noisy machines.  Sure, they’d like to replace them with newer, quieter ones, but there’s a problem, and it’s one all-too familiar to most companies:  the expense involved.  How can they most effectively deal with this situation? 

     Perhaps Widget USA can modify their existing machinery, or perhaps their overall noise reduction objectives can be achieved by simply replacing worn parts that have a tendency to vibrate.  If this measure isn’t sufficient, perhaps sound barriers can be introduced.  Whether these are installed around entire machines or parts thereof, they are often effective at absorbing excessive noise.  Barriers such as these are made of materials like plastic foam and mass loaded vinyl (MLV) which serve to muffle sound waves.

     Yet another approach to noise containment is to provide workers in the vicinity of the machinery with sound-absorbing personal safety equipment, ear plugs and the like.  If the noise present is loud enough, perhaps a wall, reminiscent of the type often built along stretches of populated highway can be erected.

     Yet another way to deal with undesirable sound levels is to divert the noise to a location not normally occupied by humans.  This is the tact often taken with industrial boilers.  Their highly pressurized steam expands so rapidly it can create a deafening roar, and engineers often design piping systems which stem from the safety valve on the boilers themselves up to the roof of the building housing them.  In this way the steam and its accompanying noise is safely redirected outside, where only the birds passing overhead will be bothered by it.

     This wraps up our discussion on sound, its measurement and containment.  Perhaps you’ve learned a trick or two to help alleviated unwanted sounds in your environment, whether it’s produced by your teen or your neighbor’s leaf blower.