It’s the energy that we measure with our sound level meters. And it changes with location and the acoustical environment. That’s where sound pressure level comes in. That’s because sound is affected by physical objects and distance. But the sound power level doesn’t tell us how loud the diesel is in the real world. Whether that diesel is running next to you or across the field, its sound power level is the same. It’s the sound energy being emitted by the source. Sound power level is a fixed theoretical value. When it comes to magnitude, we can understand it two ways: sound power level ( Lw) and sound pressure level ( Lp). Sound Power Level and Sound Pressure Level Our ears are most sensitive to mid-frequency sounds (500 to 4,000 Hz), so we use frequency-weighted metrics to account for this. High-frequency sounds (1,000 to 20,000 Hz) whistle or hiss. Low-frequency sounds (20 to 500 Hz) rumble (like that diesel). From far away, the rumble of a large diesel engine is quieter than it would be if you were standing next to it. A sound’s magnitude decreases with distance. We generally describe sound in frequency and magnitude, which is analogous to pitch and loudness. Sound travels through the air or through objects and, when it reaches our ears, we hear it. For an acoustician, sound is fluctuations in pressure, particle displacement, or particle velocity propagated in any medium, or the auditory sensation that may be produced by it.įor everyone else, sound is something we hear. Let’s start by understanding what sound is.
![dba decibel scale dba decibel scale](http://image.slideserve.com/165122/decibel-scale-l.jpg)
This post outlines a few acoustical concepts that might help clarify some of the technical language we use in our field. Most folks know that a decibel is a measure of sound, but there’s much more to it than that. And yes, as friendly as your acoustical consultant may be, some of the language we use is anything but. Under “decibel” you might see something like this: “10 times the common logarithm of a ratio of two quantities linearly related to power.”įor many laypeople, definitions like the one above can muddy key takeaways in a report prepared by their friendly acoustical consultant. Open an acoustical engineering report and flip to the glossary.