The distance between one wave and the next gives the wavelength. Pitch relates to the frequency, or how many times a second the particles vibrate. (To convert from a decibel reading in air to a decibel reading in water, you should add 61.5dB.) This means that you cannot directly convert decibel levels from air to water. Water is much more dense than air, so the standard pressure is different. They relate the intensity of a pressure wave to a normal or standard pressure.įor the human ear in air, the quietest noises we hear are around 10dB whereas sounds of 130dB are considered painful. This is actually a measure of intensity, which relates to how much energy the pressure wave has. Loudness of sound is measured in decibels (dB). When you show sound waves on a graph, the amplitude is the height of the waves from their middle position and reflects how loud the waves are.

This is also related to the maximum distance particles are moved from their normal position as they vibrate, much like how tall the ripples are in the pool mentioned before. Volume (also called loudness) relates to the maximum pressure produced as particles are squeezed together as they are made to vibrate. We describe the sounds that we hear using several different terms and measure them in different ways. It is these changes in pressure that can be detected by organs such as the human ear and are sensed as sound. Pressure increases when particles are squeezed together and reduces when they move apart. These changes in particle spacing are also changes in pressure. Similar to water ripples, pressure waves move outwards from the sound source. The effect is very much like dropping a stone into a pool of water and causing a ripple pattern (sound waves) extending outwards from the original source (your clapping hands). The particles close to your hands are pushed outwards and bump into neighboring particles, and these then move and bump into more particles. This effect ripples out and away from your hands as a small group of sound waves. When you clap your hands, you force air particles together and then apart. The particles vibrate back and forth in the direction that the wave travels but do not get carried along with the wave. Sound is a pressure wave caused when something vibrates, making particles bump into each other and then apart. Logarithms are used to compute sound intensity and decibel level When data provided in terms of exposure are presented in decibels, we can select materials with various sound absorbing qualities and arrange them in deflective geometries to mitigate unhealthful noise.The Decibel Scale and Using Logarithms to measure Sound Intensity The so-called, “3db rule” addresses the human perception and impact of sound (or noise, which is any unwanted sound) on the ear’s “structure.”Īrchitectural design presumes, typically, to provide a healthful environment. Therefore a small increase in decibels represents a large increase in intensity.

Like earthquake measures on a Richter scale describe potential impacts to buildings, decibels measure impacts to our ears on a standard scale.Īn increase of 3dB doubles the sound intensity but a 10dB increase is required before a sound is perceived to be twice as loud. So, these are used to quantify the range of sounds that impact human hearing. Why are these waves measured logarithmically rather than linearly? Is frequency and intensity of occurrence important for designing structures in high seismic zones?Ī decibel is literally 1/10th of a bel, which is a relative unit used to express the ratio of one value of a power or root-power quantity to another, on a logarithmic scale.

As a wave metaphor, consider seismic wave measurements that are logarithmic rather than linear, like the Richter scale. Something increasingly louder over a period of time may require a little while for you to notice that your ear has been exposed to louder and louder noise, but depending on how much louder will require a logarithmic scale than a linear scale to be useful. Something abruptly louder for a short amount of time allows you time to recover to the norm. Consider your ears’ sensitivity to sound in the short term and long term.

Sound intensity formula