Design Limitations for Speakers

Design Limitations for Speakers Introduction There are many factors which determine the characteristics of a loudspeaker; to produce a successful design a careful balance of many factors must be achieved. Most of the challenges and considerations of loudspeaker design stem from the inherent limitations of the drivers themselves. Desirable Characteristics Real-Word Implementation For a coherent approach to loudspeaker design to be established, one may elucidate the problem by considering two main sets of criteria; the desired characteristics of the finished system and the limitations which impinge on the achievement of these desired characteristics. The key desirable characteristics for the finished system are listed below. Reproduction of all frequencies across input range Flat frequency response across input range Adequate Damping Good Efficiency Adequate SPL or perceived loudness Minimal distortion Minimal noise Many of the above considerations are quite obvious. In terms of frequency response it is desired that the response of the system as a whole should be as flat as possible, since to truthfully reproduce a signal all frequencies across the input range should be represented equally. Weems (2000, p.14) notes that â€Å"smoothness of response is more important than range†. Naturally noise and distortion are undesirable for accurate signal reproduction. Damping is an important concern; when a signal is no longer applied to a loudspeaker there will be a natural tendency for the cone to continue to move under its own inertia. Thus damping must be employed in order to ensure that the SPL generated by such movement is sufficiently low and relatively inaudible. Rossing (1990, p.31) refers to damping as â€Å"loss of energy of a vibrator, usually through friction†. This is a simplification, however, the back EMF generated by the driver and the varying impedance seen by the amplifier of the crossover/driver network play an important role. As Weems (2000, p.17) rightly says â€Å"there are two types of damping, mechanical and electrical†. Another quite obvious consideration is that the loudspeaker must indeed be loud enough. This is related to the issue of efficiency, since the more inefficient the speaker, the more power will be needed to drive it. The choice of enclosure design plays quite a significant role here, as will be seen shortly. In terms of limitations, there are several immediate problems posed by the nature of the drivers themselves that must be addressed. Firstly, the sound from the back of the speaker cone is 180 degrees out of phase with the sound from the front. This phase separation means the sounds will cancel each other at lower frequencies, or interfere with each other in a more complex manner at high frequencies; clearly neither is desirable. In some senses it would be ideal to mount the drivers in a wall with a large room behind, the so-called â€Å"infinite baffle†, having the sound from the rear of the cone dissipate in a large separate space, being thus unable to interfere with the sound produced by the front. In reality this is impractical; however some provision must be made to isolate sound from the rear of the cone. To this end, some sort of enclosure must be made for the drivers, yet this presents a new set of considerations. Without an enclosure, a loudspeaker is very inefficient when the sound wavelengths to be produced are longer than the speaker diameter. This results in an inadequate bass response; for an 8 inch speaker this equates to anything below around 1700Hz[1]. So the infinite baffle is terribly inefficient in terms of the SPL produced at lower frequencies. Furthermore, the free cone resonance of the speaker works against the flat frequency response that is desired; input frequencies close to the resonant frequency will be represented too forcefully. Another real-world complication is the fact that for high-fidelity applications, no one loudspeaker will be able to handle the entire range of input frequencies; â€Å"the requirements for low frequency sound are the opposite to those for high frequencies† (Weems, 2000, p.13). Higher frequencies require less power to be reproduced, but the driver must respond more quickly, whereas low frequencies require a larger driver and hence greater power to be effectively realised. In view of the above, multiple drivers must be used, with each producing a certain frequency range of the input signal; at the very least a woofer and tweeter are required. In order to deliver only the appropriate frequencies to each driver, a device known as a crossover must be implemented. This can take the form of passive filter circuits within the speaker itself, or active circuitry that filters the signal prior to amplification. In the latter case, multiple amplifiers are needed, making this a more costly approach. The fundamentals of crossover design will be dealt with in a separate document and are hence not dealt with in detail here. Enclosure Design Faced with the reality that an enclosure is in almost all cases a practical necessity, perhaps the most important aspect of speaker design in the design of the enclosure itself. The first step in producing a successful design is to decide upon the drivers to be used and use this as a basis for choosing a cabinet design, or to decide upon the desired cabinet type first and allow this to inform the choice of driver. In general, most of the design work with regard to the cabinet is focused firmly toward the woofer, since the enclosure design is most critical with regard to midrange/bass performance. In typical 2-way designs, the tweeter is mounted in the same box as the woofer, but it is the latter which largely defines the cabinet dimensions. In the past the design of enclosures was often something of a hit-or-miss affair, however the research of Thiele (1971) and Small (1973) has led to a much more organised design process. Most transducers today are accompanied by a comprehensive datasheet of Thiele-Small parameters, which allow most of the guess work to be taken out of enclosure design. Ignoring more exotic enclosure designs, the first question is whether the enclosure should be ported or sealed (it should be noted that in reality even â€Å"sealed† enclosures are very slightly open or â€Å"leaky† in order to allow the internal pressure to equalise with the surroundings). If a driver has already been chosen, this can be determined from the Efficiency Bandwidth Product, which is defined as: EBP = Fs / Qes(1) Where Fs is the free air resonance of the driver and Qes the electrical Q or damping. In general, an EBP of 50 or less indicates a sealed box, whilst an EBP above 90 suggests a ported enclosure (Dickason, 2000). In between, the choice of enclosure lies more or less with the designer and a driver that falls in the middle should perform acceptably in either closed or ported situations. So, what are the advantages and disadvantages of sealed vs ported enclosures? A sealed enclosure is very simple to build, whilst a ported enclosure requires some degree of tuning to ensure the port is matched correctly to the driver – in the ported or â€Å"bass reflex† design a tube extends into the cabinet allowing some air to escape from inside; if correctly tuned the air that leaves the port is delayed in phase by 180 degrees, hence reinforcing the sound from the front of the cone. With a sealed enclosure the air inside acts as an approximately linear spring for the transducer cone and assuming the driver has a low Fs, a healthy bass extension with a gentle roll-off of -12dB per octave can be expected. The disadvantages are several; the enclosure may need to be quite large to achieve an acceptable Qtc (the damping value for a sealed system) and efficiency is poor. Further, with a sealed enclosure the driver reaches maximum excursion at resonance, which translates to greater distortion. Therefore a driver for use in a sealed enclosure requires quite a large linear throw to perform well. By contrast, in correctly tuned ported enclosures the driver is maximally damped at resonance, so a large linear throw is not critical and distortion is lower as a result. The basic methods of sealed and ported cabinet design shall now be explained. Sealed Enclosure Design To design a sealed enclosure the basic methodology is quite straightforward; the essential challenge is simply to find the optimum volume for the cabinet for the chosen driver. First one must decide on the value of the damping constant Qtc; the optimum value is 0.707 since it gives the lowest -3db break frequency and hence the best potential for bass extension, as well as good transient response. If the enclosure size is too large at this optimum value then Qtc may be increased, resulting in a trade-off between bass performance, transient response and enclosure volume. However, the more Qtc is increased, the more boomy and muddy the sound will become. Depending on the application, the enclosure size may not be important; in this case an optimum Qtc is encouraged. Once Qtc is known, the constant ÃŽ ± may be calculated using the below formula, where Qts is the total Q factor of the driver at resonance (this may be obtained from the manufacture’s data sheet). ÃŽ ± = [Qtc/Qts]2 – 1(2) Having calculated ÃŽ ±, the correct enclosure volume Vb is trivial to determine using the relationship below. Note that Vas is the equivalent volume of air that has the same acoustic compliance as the driver; again this may be obtained from the datasheet or experimentally. Note from equation (1) that a lower Qts will result in a higher ÃŽ ±, and hence a smaller enclosure. Thus for two transducers with equivalent acoustic compliance, a lower Qts will result in a smaller enclosure. Vb = Vas/ÃŽ ±(3) Assuming the required box volume is acceptable, one may then also calculate the resonant frequency of the system (fs is the free-air resonant frequency of the driver): (4) Once fc is known the -3db break frequency may also be found: (5) Recall that below this frequency the roll-off is -12dB per octave and one can gain a fairly good impression of the bass performance to be expected. Naturally it is desirable for f3 to be low for maximum extension into the bass area, hence a low fs is a characteristic one should look for when choosing a driver for sealed enclosure use. If it is felt that the break frequency is too high, then a different driver must be selected for the sealed implementation. Ported Enclosure Design For ported cabinet design, the equations are more complex and it is generally not practical to attempt to design such an enclosure by hand. Instead there are a number of free and commercial software calculators available that simplify the process. One good freeware calculator is AJ Vented Designer[2]. Using such a program enables the designer to quickly ascertain what size enclosure and port is required for a given driver and whether this is feasible – for certain combinations the port may not physically fit within the enclosure for example. In addition, the program also plots the theoretical frequency response of the design, which simplifies matters greatly. Acoustic Damping and Avoiding Resonance In addition to the type of enclosure and the calculation of the required volume, diameter and size of ports (if ported), there are several other design considerations. Firstly, standing waves within the enclosure must be minimised. Thus enclosures are often stuffed with fibreglass, long-fibre wool or polyurethane foam. In addition to standing waves and the resonance of the enclosure, one must also bear in mind the possibility of dimensional resonances with sealed designs. To avoid this it is prudent to ensure that length, width and height of the enclosure are all different and to not centrally mount the drivers. The choice of cabinet material and thickness are also factors that require careful consideration; in general wood is the most appropriate material and a thicker structure is likely to be more rugged and be less susceptible to undesirable vibration. The structure should also be isolated from the floor since vibrations passed to a floor (especially a wooden floor) can cause the floor to vibrate which will muddy or colour the sound. Spikes or stands are commonly used to achieve this. Conclusion There are many factors that affect speaker design but perhaps the most important is that of the enclosure itself. More exotic enclosures such as band-pass and transmission line configurations are beyond the scope of this document, however it should be noted that there are many different approaches beyond the common sealed or ported methodologies. As with any engineering problem, successful speaker design requires a careful balance of many often opposing factors to be reached. Sources Borwick, John. (2001). Loudspeaker and Headphone Handbook, Focal Press. Dickason, V. (1995). The Loudspeaker Design Cookbook, Audio Amateur Publications. Rosenthal, M. (1979). How to select and use loudspeakers and enclosures, SAMS. Rossing, T. (1990). The Science of Sound, Addison-Wesley. Weems, D. (2000). Great sound stereo speaker manual, McGraw-Hill. 1 [1] Nave R, Coupling Loudspeaker to Air. http://hyperphysics.phy-astr.gsu.edu/Hbase/hframe.html [2] http://www.ajdesigner.com/speaker/index.php

Anne Robert Jaques Turgot and His Relevance to the French Revolution :: essays research papers fc

Introduction Anne Robert Jaques Turgot, baron l' Aulne, was born in Paris on May 10, 1727 to a noble French family of Normandy. Following in the footsteps of his ancestors, who had furnished the state with numerous public officials, Turgot would achieve public renown as Intendent of Limoges and later as Controller General of all France. Although Turgot ended his public career in unfortunate circumstances, being dismissed by Louis XVI for ineffectiveness, his political theories became a major influence in the remaining years of the Old Regime. The depth of Turgot’s economic thought was not recognized at the time because it largely went against what the ruling aristocracy wanted to hear. His clairvoyance is much more fully noted in light of the last two centuries. Furthermore, Turgot was one of the King’s last controller-generals before the French Revolution ended the monarchy. When his political and economic ideals are considered against this backdrop their importance as well as thei r contradictory nature become apparent. Turgot's main contribution to economic theory is his Reflections on the Formation and Distribution of Riches. Apart from this short but highly systematic account of the nature of economic development, Turgot's other relevant writings are sparse and far from cohesive. Since this paper will consider his economics with regard to his political thought, only Turgot’s theories on the nature of government influence, free trade, and taxes will be examined. Furthermore, an explanation of Turgot’s theory on administration will be provided. In gaining an understanding of Turgot’s political and economic thought a powerful example of the problems that manifested themselves in the revolution is provided. Turgot was the model of an enlightened, reform-minded administrator and this may be glimpsed in the liberality of his economic ideas. However, while he certainly advised reforms in administration, they were simply intended so that the King could more effectively centralize pol itical power. Laissez-Faire and Free Trade: As a young man Turgot was very close to Claude Marie Vincent, the Marquis de Gournay. Vincent was not only a friend but also Turgot's mentor in economics and administration. It is in tribute to Vincent that after his death Turgot developed his ideas on laissez-faire government in a paper called, the "Elegy to Gournay" (1759). Within this paper Turgot condemns the foolishness of mercantilist regulation of industry while expounding the benefits of free domestic and foreign trade following from the presence of free exchange. In a detailed analysis of the market process, Turgot writes that self-interest is the prime mover in the market process and that in a free market the individual interest must always coincide with the general interest.

Sop for Informationsecurity

STATEMENT OF PURPOSE Name: Degree sought: Information Security and Computer Forensics (ISCF) My decision to pursue Post Graduate study in the United Kingdom is underscored by my desire to be a part of the post graduate program at your institution. This university offers the flexibility needed for such a vast rapidly changing field. The facilities and the faculty at the university are par excellent. Information Technology is an industry that has changed our lives. In a very short period it has changed the way we have looked at the things since centuries. It is one industry that is going to shape our future for centuries to come. So doing a masters degree in Information Security and Computer Forensics (ISCF) is next logical step in my career. My interest in Information Security blossomed during my Graduation where Computer Science was my major subject. Right since the beginning of my undergraduate study Information Systems and Security is a subject that has fascinated me a lot. The subjects I have studied at my graduation level include Computer Science, Statistics and Mathematics. This laid strong foundation for my course in Computer Science. My undergraduate studies already focus on the Information processing and security and also statistical analysis of data which are extensively used in Information processing. After this I have joined level 1 course of M. I. T (Master of Information Technology) which was a joint program organized by B. M. Birla Science Centre (India) and University of Udine (Italy). During Level 1 of Masters degree, my interest for Information Security got even more boost with subjects like Advanced Computer Networks, Computer Security and Management Information Systems and I was awestruck by the vastness of Information Security and how far we can use this features to secure our data and also safeguarding our networks. All this gave me a strong desire to do a full fledge masters degree in Information Security and Computer Networks and the course offered by your university in Information Security and Computer Forensics (ISCF) will be an ideal course for me to become master in the area which I have been fascinated since long years. For the past months I have done a certification in Computer Networks from Zoom Technologies. This short sting has given me invaluable practical experience in various Computer Networks. During this time I have come across several professionals. Most of them working in different areas of communications and information technology. Interactions with them have made me realize how rewardful it will be doing a masters and later PhD in this area. My discussion with them convinced me that specializing in Information Systems and Security will suit me very well. It has given me the confidence to pursue a Masters degree and also kindled a desire to do research in this area. After proper examining contents of the course in Information Security and Computer Forensics (ISCF) provided by the University I am very much convinced that this course would give me a cutting edge in the area of Information Security and Computer Forensics and a lifetime opportunity of doing a research. It is strong belief in my family that the UK education system has the best to offer in the whole world. If I can get an opportunity to be a part of that intellectual stimulating environment, I am sure my talents will be put to optimal use. With all the educational background and qualifications I have, I hope University will consider me for pursuing Masters Degree. Yours sincerely,

Motivation Motivation And Job Satisfaction, Individual...

Motivation Varying employee needs lead to different kinds of motivation. Different kinds of motivation influence employees’ job satisfaction. Employees’ motivation will be affected by factors such as occupation, gender, social culture and organisational structure. This study will attempt to explore the differences in motivation between core-workers and periphery workers, and whether these differences in motivators are distinctive. Previous researchers have directed most of their attention towards the questions like, why people behave as they do on the job and what can be done to influence employees’ work motivation? Several theories of work motivation have been formulated to identify factors that influence work behaviours and factors that contribute to the maintenance and termination of these behaviours (Maslow, 1954; Herzberg, 1966). Although motivation as a concept represents a highly complex phenomenon that affects, and is affected by a multitude of factors in the organi sation (Kanungo, l994), it is accepted by most scholars and practitioners that thereisa positive relationship between motivation and job satisfaction, individual performance, and physical and mental health. They believe that behavioural influences, such as job satisfaction, have a very important impact on quality of service, organisational commitment and total organisational effectiveness (MacRobert, et al. 1993; Beall 1994; Joseph and Deshpande 1997; cited: Lewis et al.2001; Morgan et al. 1995). Based onShow MoreRelatedJob Satisfaction Is Extremely Vital To Any Organization1435 Words   |  6 Pages Job satisfaction is extremely vital to any organization that without it there can be a decrease in employee commitment. Lack of such an important variable can lead to employees quitting their jobs (Alexander, Litchtenstein and Hellmann,1997). 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