The Science of Soundwaves and Their Applications

wave created by superposition and is less than the amplitude of either component wave. Superposition is a concept that describes the way in which sound waves, and waves more generally, interact. In essence, two waves passing through the same point in space at the same time combine in a linear fashion to create a single new wave. If the displacement from equilibrium caused by the first wave equals "a" and the displacement from equilibrium caused by the second wave equals "b", the resulting displacement from equilibrium for the combined wave will be "a + b". This is an algebraic addition. Since "a" and "b" can be positive, negative, or equal to zero, the resulting sum can also be positive, negative, or equal to zero. The period is the time required for a single wavelength to pass a fixed point of reference. The period of a sound wave is the inverse of its frequency. The phase of a wave is an expression of how far through its cycle of oscillation it has progressed. Because the mathematical description of wave motion is similar to the mathematical description of motion in a circle, wave phase is expressed in degrees or radians. A wave completes its cycle in 360°, just as a circle is completed in 360°. Half a cycle is 180°, and a quarter cycle is 90°. The relative phase of two similar waves is a measure of how synchronized they are. The speed of a wave is the ratio of distance travelled to time required, for example, the distance travelled in one second. The speed of sound is no different than the speed of an object. Usually the speed of sound is thought of in terms of one cycle of a wave. In one cycle, sound travels a distance of one wavelength. The time required for one cycle is the period, so the speed is the ratio of the wavelength to the period. Dividing by the period is the same as multiplying by the frequency, so the speed of a wave is often expressed as the product of wavelength and frequency. The wavelength is the distance between one peak or crest of a sound wave and the next corresponding peak or crest. The product of the wavelength and the frequency of a sound wave yields the velocity of that wave. The waveform is the detailed way in which a parameter changes during the oscillation of a wave. For sound, that parameter will usually be pressure. In practice, this is the shape of a wave on a graph. Waveform is perceived as timbre. The muffler of the car is part of the exhaust system, which carries out several functions. They are getting hot, noxious exhaust gasses from the engine to a place away from the engine compartment, significantly muting the noise output from the engine, and in the case of modern cars, reduce exhaust emissions. The exhaust system includes many parts for doing the functions listed above. Included in the picture below the exhaust manifold, “y” pipe, catalytic converter, resonator, exhaust pipe, muffler, and tail pipe. The muffler’s job is to muting sound output and is preformed in many ways. The three ways that it accomplishes this task is absorption, restriction, and reflection. They can use all three methods or just one, they all work. I am going to elaborate on the reflection method because it mutes sound the best. A reflection muffler is the type of muffler that I will be elaborating on. It is the most sophisticated type of muffler. They often utilize absorption principles in conjunction with reflection to make the ultimate high-performance silencer. The sound wave is used against itself in the reflective muffler. When two like waves collide, they “cancel” each other and leave no energy except a spot of low-grade heat. Conventional reflection mufflers use U bends within the muffler to reflect the flow and sound back and forth in a S curve through the body of the muffler. This type of muffler provides the most sound volume reduction. Chambered mufflers have angled walls within the muffler body to reflect the sound and flow from side to side. If you ever decide to open up one of these mufflers it is easy to see the restrictions within. There will be areas of heat discoloration on the side of the muffler anywhere there is a restriction in flow. This is usually at the first V wall separating flow and the first reflection back toward the middle of the muffler. There are numerous ways and engineering tricks to make a reflective muffler, too. Hedman Hedders made a muffler that looks a lot like a glass pack with a catch. The outer casing is sized so that high-pitched engine sound is reflected back into the core of the muffler. Where those high-pitched waves meet their death is where they slam right into a torrent of more sound waves of like wavelength coming straight from the engine. This is a 2000 Eclipse GT Stock Muffler. In this muffler, all the sound must pass through the small-perforated holes in the short pipe in the first chamber. The second larger chamber is more of an echo or resonance chamber for sound reflection. The exhaust then flows out the pipe to the tip with its own little muffler built into it. In these designs one can see that the science of the sound wave is applied in muffler design. In reducing the loudness of the sound wave the used interference by a reflection chamber where these sound waves are used in superposition to destroy each other by colliding into one another, cancelling out. Another unusual application of sound wave science is in the design of office equipment. People like their equipment to be very quiet. In the case of building computers, when they are complete with all of their components running, they have to pass a certain decibel level. The dB level is the intensity or amplitude of the product. In one case, a product was made and passed the dB test and was put out on the market. Then there were many complaints because the machine claimed to be really loud. The engineers felt the same way too and ran the dB tests on it again and again and every time it passed the dB specifications. Finally, they came to the conclusion that it was the fan that was making the sound and it wasn’t the dB rate that was high, it was the frequency of the sound. To pass high frequencies sound the intensity doesn’t have to be that high. So that is why the fan passed the test but still had a pitch, which was noticeable and irritating to the human ear (Desai N.Pag.). In conclusion, the science of sound can be used in everyday applications. The mechanics of a muffler and the dB’s of a fan are just a few examples. The physics of sound will continue to evolve as human being continues to advance in technology.