A long time ago, in this galaxy right here, a movie called “Star Wars” was released. It was 1977, and, as a 10-year-old boy, the previews (that’s what we called “trailers” back then) grabbed my complete attention. I was fascinated by sound effects like the evil roar of the Empire’s TIE fighters, the sleek whistling hum of the Rebel’s X Wings, the terrifying explosion of Alderaan, and the victorious one of the Death Star. Imagine my surprise when, later that year, in 6th grade science class, we learned that SOUND DOESN’T TRAVEL IN A VACUUM!
Turns out, though, that sound DOES travel quite well through air. You’re almost certainly experiencing some right now – it’s actually quite difficult to eliminate ALL the sounds from any given area. Like anything that travels, it’s got a start and an end point, and we can measure parameters at both to quantify levels of sound power (at the starting point) and sound pressure (at the end point.)
Power is defined as the amount of energy transferred or converted per unit time, and applies to any form of energy…sound included. Philosopher types can debate the question “If a tree falls in the forest and nobody’s there to hear it, does it make a sound?” all day long, but engineers know the answer is “Of course it does!” Whether the sound comes from a hammer hitting a nail, a stereo’s speakers, a tree falling in a deserted forest or whatever, we can quantify the power generated in watts, just like any other generation of power.
Pressure is defined as the amount of force applied to a specified area. When we hear a sound, it’s because a sound wave created by the energy transfer at the source – perhaps by a tree hitting the ground in a forest – causes changes in the relatively low pressure being applied to our eardrums by the low power of the sound being generated in the quiet forest. This is measured in pascals – the SI unit of measure for pressure.
These units of sound power & sound pressure are used all the time by professionals who are calculating acoustic levels. For example, they’ll be used to determine how powerful a PA system has to be in a room of a certain size to hear a lecturer, or a singer, or a symphony. Each of those setups will need different sound power generation values for listeners to get the desired effect of what they’re hearing.
For those of us who are keen on preventing hearing loss, we’re going to concern ourselves with the sound pressure level. This is a logarithmic measure of the ratio of the sound pressure being applied to a reference, or base level, sound pressure. Most of the time, that reference level is the hearing threshold of a typical person without any hearing impairments, and it’s measured in decibels…a unit that most of us are at least somewhat familiar with. There are two ways to determine the sound pressure level: you can do the math, or you can use a measurement device, like EXAIR’s Model 9104 Digital Sound Level Meter.
Compressed air use is LOUD. EXAIR has solutions for that, though. If you’d like to find out more, give me a call.
Russ Bowman, CCASS
Application Engineer
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