![diffraction aperiodic sound diffraction aperiodic sound](https://image3.slideserve.com/6554601/examples-of-diffraction-l.jpg)
The forces arising from the new inhomogeneity accelerate the particles toward lower pressure. When we excite the medium by creating a disturbance in its structure, coupling between adjacent particles makes the disturbance try to even out, globally. In practice, neither of these can be controlled independently of the other. This is simply one point in which we explicitly control the sound pressure or the velocity vector of the field. To get a hold of the process of sound propagation, we first look at a simple example: a point source. Often we make the further assumption that at each point, the velocity vector equals the gradient of the pressure field, though this way we lose part of the generality of the model. From Newton’s laws we then get a relatively simple partial differential equation which tells that pressure gradients cause acceleration of particles and that the velocity at some point causes the pressures to change around it. These mean properties are used as a stepping stone to the analytic model of a sound field, which simply forgets that the molecule level ever existed, assigns a real velocity vector and a real pressure measure to each point in space and lets these vary over time. Only after we upset the balance do the mean properties ripple. Similarly the expected velocity (with direction) of particles over an arbitrary volume will be zero-at large scales the gas will tend to stay put even if the molecules themselves move quite a bit. In a closed system of moving particles the sum kinetic energy will stay constant and statistical physics predicts that the mean distance between the equally repellant particles will try to even out. In the case of sound, the density is just the usual weight per unit of volume of gas and the stiffness is borne of a balance of repulsive forces between molecules and their mean kinetic energy (temperature). In the latter case we talk about anisotropy, which fortunately does not occur in gases. In addition to this, the binding forces can be different depending on direction. Note that both density and the stiffness can vary within the substance: the medium can be inhomogeneous. The other important intrinsic property of the medium is its density-together density and the strength of the binding forces determine the speed of wave motion in the medium. It also determines the kinds of vibration which can propagate in the medium: unlike solids, gases and liquids lack transverse binding forces and so only longitudinal energy transfer is possible. This is what makes wave propagation, a form of energy transfer, possible.
![diffraction aperiodic sound diffraction aperiodic sound](https://cdn.britannica.com/s:800x450,c:crop/69/151069-138-C551DC5C/Explanation-diffraction.jpg)
Additionally there must be a kind of stiffness which holds the adjacent parts of the medium together. Obviously the medium needs to be elastic in order to generate any waves at all. To create waves we need a medium in which to put them. That’s what we will try to construct, next. But usually no time is left for a nice intuitive picture of the thing to build up. That is something we’re all told on high school physics courses. This is a field rich in applications and interesting discovery, not all of which seems intuitive at first sight.Īs one application perceptual sound codecs could be mentioned-how can an MP3 codec throw 90% of an audio signal away and still reproduce a perceptually near perfect replica of the original?
![diffraction aperiodic sound diffraction aperiodic sound](http://lh3.ggpht.com/_wUDOCViv9D0/SiCzz_u3kII/AAAAAAAAAf4/rFLBL6eRVAE/s800/imaging2.jpg)
Taking into account the peculiarities of the human sensory organ and the psychology of perception in general, one is taken into the field of psychoacoustics-the study of human auditory perception and its underlying mechanisms. The relevant topics include the wave characteristics of sound: diffraction, reflection, interference and so on. When taking a closer look at sound as a physical phenomenon, many interesting characteristics of sound come to proper focus. It is not entirely clear how sound is actually generated in physical objects, why different objects do not all sound alike or how all this relates to our sensory apparatus.
![diffraction aperiodic sound diffraction aperiodic sound](https://4.bp.blogspot.com/-jl8Ou2HDB_E/UHP-DgqSHWI/AAAAAAAACE8/rEm66GBsaeQ/s1600/aperiodic.png)
These are the basic questions of the nature of sound, the reasons for our hearing anything at all and the mechanics underlying the sensation. But although we hear sounds every single day of our life, there are many aspects to experience that one usually doesn’t pay attention to. Sound is something most of us know and love.