(We will soon see why!) Sound pressure level is therefore defined as You can try this out yourself: Sound pressureĭue to the way our hearing works, it makes sense to use a logarithmic unit to describe loudness. In other words, if we increase the sound by some factor (for example 2, as in this example where we double the sound pressure), most people will perceive the increase as roughly equally strong, no matter how strong the sound was originally! If we compare these three sounds, we hear that we perceive increase from double to quadruple sound pressure as roughly as strong as the increase from the original to the double sound pressure. Instead, let’s say that we take the doubled sound pressure and double it again, so that we get the quadruple sound pressure of the original. This is despite the fact that the increase, as measured in Pascals, is the same in both cases! If we listen to these three sounds in order, most people will perceive the increase from double to triple sound pressure as weaker than the increase from original to double sound pressure. Then we take the original sound and triple its sound pressure. We perceive this as a noticeable increase in loudness. Let’s say that we take a sound and double its sound pressure. But the manner in which we perceive it is not quite obvious. (As sound pressure is thus also a kind of pressure, we measure it in the pressure unit, Pascal.) As sound waves become stronger, that is, as the pressure difference between wave peak (denser air, positive sound pressure) and wave trough (thinner air, negative sound pressure) becomes larger, we do of course also perceive that the sound becomes louder. How do we perceive loudness?īasically, we measure sound pressure as the deviation from the approximately constant atmospheric pressure, as you can see in the figure above. Atmospheric pressure (around 100,000 Pascals). This is a fundamental quantity used everywhere where sound is described quantitatively. In this first part, we begin by discussing what decibels are. In this article series, we will therefore go through the most important acoustic quantities. airports, roads, and concerts are allowed to make. These quantities affect us all, not least because noise regulations use them to describe how much sound e.g. We use these to make sound into something that we can discuss in a more concrete and objective manner. To make sound into something that we can measure, describe, compare, and handle, many different acoustic quantities have been introduced. For example, would you and I agree that this sound is stronger than that sound? And if so, how much stronger is it? Still, it is difficult to describe, compare, and process these subjective experiences. When these sound waves hit our ears, our auditory system translates them into something that we can perceive consciously - and thus, we hear that the sound is there. At the sound wave’s peak, the air is at its densest, while at the wave’s trough, the air is at its thinnest. These fluctuations start at sound sources, for example loudspeakers, and spread out like waves. Sound is, simply put, weak but rapid fluctuations in air pressure: The air becomes a tiny bit denser, a tiny bit thinner, denser, thinner, and so forth.
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