The Visitation of the Gods Assignment Example | Topics and Well Written Essays - 500 words

The Visitation of the Gods - Assignment Example The writer does succeed in creating a sense of apathy by exploiting expected events. The plot is unconventional and the events effortlessly flow into each other to give way to a sense of unity.  Miss Noel, a young and idealistic teacher is the main protagonist, which acts as a suitable foil to the somewhat less upright and opportunistic Principal and the supervisors. The characters in the story are somewhat flat, especially the visiting officials. The writer on purpose has kept the antagonists flat to enhance the sense of apathy and hopelessness permeating the story. This provides a suitable and grave background against which is depicted the internal conflict in the protagonists’ consciousness that is Miss Noel. The grossness of the characters indicated by the expressions like â€Å"the supervisors, with murmured apologies, belched approvingly† do contributes to the filthy ethical environment in the play. In the story ‘The Visitation of the Gods’, Gilda C ordero-Fernando intricately uses the setting as a background against which unfolds the contrived yet disgusting drama of school inspection. At the very start of the story, the austere setting of the school is elaborately highlighted to depict the ordinariness and unquestioning helplessness of the school staff. However, as the drama of visitation starts unfolding itself, the setting starts altering with the improvised stuff like bougainvillea pots, mattresses , nd cushions, china, crockery, napkins, etc to highlight the conceitedness of the visiting officials. The hastily improvised stuff creates the sense of a satin patch on the otherwise drab and ordinary life of the school teachers. The writer aptly elaborates on the settings accompanying every event in the story to build on the readers’ sense of waste and apathy. In the story, Gilda uses the third person omniscient point of view.

Civil Disobedience - Gandhi Essay Example | Topics and Well Written Essays - 750 words

Civil Disobedience - Gandhi - Essay Example e to easily suppress the incidences of violent uprising, but the civil disobedience movement was launched on a widespread scale and proved to be a tactic that the British were simply unable to defeat through military means. Gandhi has played an unforgettable role in the history of India and is referred to as Bapu, or the Father of the nation, due to his valuable contribution in bringing about a retreat of British forces from India. Gandhi first commenced the civil disobedience in South Africa, when he was practicing as a lawyer. Angered by the discrimination that was heaped upon black South African majority and his Indian brothers by the white minority, Gandhi encouraged these people to refuse to cooperate with practices they were expected to follow that only denigrated them more. He gave up his lucrative legal practice in order to become the leader of the Indian community that was comprised of despised traders and laborers. (www.india-today.com) and devised his policy of civil disobedience or a quiet non violent refusal to comply with unjust practices that were an attack on human dignity. Gandhi later utilized the civil disobedience movement very successfully in his home country of India, in resisting British rule and demanding that they leave India. He initiated the Non cooperation movement in 1921-22. Indians boycotted British goods and chose to use only Indian products. The crowd and masses quite simply refused to obey orders and the British found themselves helpless in dealing with people who openly disobeyed rules but did not resist arrest and did not retort with violence to any draconian British measures to maintain law and order. There was however, a constant demand from the asses for the British to quit India. Two decades after the movement was first commenced, Gandhi was successful in achieving the goal of Swaraj, or complete independence.(www.india-today.com). Falk (2003) has argued that the potential of the civil disobedience movement in bringing

Descartes Essay Example | Topics and Well Written Essays - 1750 words

Descartes - Essay Example There must be a proper procedure of metaphysical verification through which the mind can get certain of what it thinks and there must be strong emphasizing proofs for his. But later on refuting has own arguments to some extent, Rene argues that since he is certain about the fact that he is thinking about something, so he can conclude on this tautology that man is something which has the ability to think. Existence of God is one of the most important and centric circle of attention for the mediator. He builds the proofs for the existence of God by building an argument based in the human mind processes. He says that the human mind of packed with the idea of existence of God and if by any means this idea is created then it must be created by God himself. Humans are weak and don’t have powers to illusion the minds so impeccably so this lead to the fact that this idea of God’s existence is injected in the human minds by the God himself which depicts the existence of God. ... He argues to get rid of all the dogmas and really believe. In this paper, one out of six meditations will be summarized and discussed. Explanation In the sixth meditation, concerning the Existence of material things, and the real Distinction between Mind and Body, Rene tries to explore the hidden phenomena in the clear distinction of one’s self with external events and object along with the strong emphasis to prove that things outside self and God exists. While discussing the credibility of mind-body dualism, meditator argues that the human behind always feel the internal needs for something that are triggered by the external factor but this cannot be felt outside the body for example he says that he can feel heat, pressure, tickling and hunger within his body but he cannot feel these physical characteristics and happening outside his body. He asks a series of question and says why is human body self centric and why we cannot feel the physical variants of other people (Descart es and Stanley, 193). The main argument which is built by the meditator is that human body and body yare not interdependent and they can exists without each other for example he says that human body has a certain characteristic of extension which is inherent in it. The human body gets extended with the passage of time but the human mind is not extendable and remains of the same size this means that this basic characteristic of extension does not co-exist in the human mind and body so human mind and exist without body and work on its own. The meditator then argues that the human mind and body are dependent upon the physical objects and substances which do not only cause the triggering of internal demands of the human mind and body, they also play a colossal role to satisfy

Management strategic-------Carry out a strategic analysis of the UK Assignment

Management strategic-------Carry out a strategic analysis of the UK grocery market using appropriate strategic management models - Assignment Example All these analyses have been carried out from the point of view of Tesco. However, references to UK general grocery market have been made times and again when required. The report concludes with the key takeaways from this detailed strategic analysis. 2. Overview of UK Grocery Market Retailing is one of the main contributors to UK economy with over 12% share. This sector acts as a bridge between production and consumption and is also a great generator of employment. In addition to the organized sector, there are a large number of unorganized players who are self-employed. UK grocery market has witnessed changes across both horizontal and vertical dimensions in the past few years. Horizontally, food retailers have ventured into other retail segments such as consumer goods, clothes, services and so on. Vertically, there has been a shift of power in the supply chain from the manufacturers to large organized retailers. This had a huge impact on the dynamics of the industry (Institute of Retail Studies 2003). 3. Internal Analysis of Tesco Tesco is primarily a food retailer with more than 2500 stores across the globe, a majority of which are in UK. The company has lately ventured into other business segments such as financial services, insurance, electrical appliances, telecommunications and insurance (Data Monitor 2004). SWOT analysis can be effectively used to carry out an internal assessment of Tesco. 3.1. Strengths One of Tesco’s biggest strengths is its continuously increasing market share. As of July, 2011, its market share is above 30% (Institute of Grocery Distribution). Tesco has almost doubled its market share in the past 7-8 years speaking high volumes of its growth. This growth has been enabled because of the continuous geographical expansion and opening of new stores. In addition, Tesco has strategically focused on non-food segment of the business and now it contributes very significantly to its revenues. Tesco has realized the importance of web i n its marketing. It has one of the biggest online supermarkets in the world. Tesco has a great brand image among its customers. It is known for high quality goods, innovative measures and efficient processes. Tesco’s lead over other players in UK market is huge. This has been made possible due to economies of scale it has gained over the years. 3.2. Weaknesses Tesco’s success story has largely been possible due to the UK market. However, it is susceptible to risk in case of change in government regulations. Tesco has a largely untapped market in emerging economies such as China and India. In addition, Tesco has been very aggressive in its expansion strategy and acquisitions. This has meant taking a large amount of debt affecting its balance sheets. Such a capital structure would work till the going gets good but may backfire in tough times. 3.3. Opportunities Tesco has opportunities from two perspectives. One is the geographical expansion in emerging markets as discuss ed above. The second opportunity is to make efficient use of its scale and venture into new business segments. The margins in the food industry are declining and it is profitable to consider new avenues. Tesco has already started working on the same with new segments such as skincare (Data Monitor 2004). In this way, it would also be able to realize economies of scope. 3.4. Threats UK grocery market has witnessed a lot of price wars. This has especially occurred due to entry of

The United States Annexation of Hawaii Essay Example for Free

The United States Annexation of Hawaii Essay The United States annexes Hawaii in 1900 is Imperialism.Because it had to do with hawaii and their economical power.It also had to do with them other countries fighting over them.It also had to do with Hawaii being scared of countries and their territory nations. The Untied States wanted Hawaii to become a state .In 1959 the Untied states government annexed Hawaii and was later declared a state. The reason why is because British and French governments negotiation on Hawaii for economic privileges. So Hawaii was fearful that it would become one of the territory nation . So the United States signed a treat with them. Which they decalred a friendly relationship. The United States attempts to mediate in the Venezuela -Great Britain dispute in 1895 is Intervention.Because it had ivolvement with foreign power in affairs for another nation.It achieve the stronger powers. There was a dispute between Venezuela and Great Britian. That even Cleaveland invoked the Monroe Doctrine. The United States secretary toke interpretation on the Monroe Doctrine when the dispute occurred between British Guiana and Venezuela.Monroe Doctrine gave United States the authority to mediate the border dispute on the Western Hemisphere.The reason why this was happening because Venezuela and Great Britian disputed over the boundaries deprarting the Venezuela and British Guiana.The bountries claimed gold was in their territory.So thats when United Stated sent a message to the world that they would enforce the monroe Doctrine.They made it clear to them that it was going to be enforced. The United States declines to give aid to Hungarian patriots in 1849 is Isolation.Because it was remaining apart from other nations affairs. Hungary was basically classfied as a national independent country. Note:There is like nothing on Hungarian and why the United Stated declines them Ive looked everywhere I asked my mom if you have any info I will be gladly to refix this one and resubmit it.

Factors Can Affect Validity Reliability Of Systematic Review Nursing Essay

Factors Can Affect Validity Reliability Of Systematic Review Nursing Essay Systematic review with meta-analysis are considered more objective than other types of reviews such as traditional reviews because it involve the application of scientific strategies in ways that limit the bias but the interpretation of the systematic process like any other type of research is subject to bias and this articles will illustrate the sources of bias in every step of conducting a systematic review and what is its types and ways. Keywords: Systematic review, Bias, Meta-analysis Introduction A systematic review is an overview of many studies that used clear and reproducible methods while a meta-analysis is a mathematical synthesis of the results of two or more primary studies that address the same hypothesis in the same way. Systematic reviews are very popular so about 2500 new English language systematic reviews are indexed in Medline annually (Mother D, Tetzlaff J, Tricco a, et al). While the number is impressive ,the quality of their reporting is not always ideal which lead to some kind of biased results and thus shrink their usefulness. Although meta-analysis can increase the precision of a result, it is important to ensure that the methods used for the review were valid and reliable. (Greenhangh. 1997) Speaking generally,there are two sources -at least- can generate bias in systematic reviews: the risk of bias in the included studies which it can exaggerate the results of a treatments effectiveness by 18% (Pidal J, Hrobjartsson A, Jorgensen KJ, et al) and the review itself as it has a little control over the reporting of RTCs but it can apply considrable control over conducting and reporting the review, thereby minimizing the bias of review itself. In this article we will try to spot the sources of bias in every step of conducting a systematic review and what is its types and ways and after that we will talk in details about each factor might cause a bias including publication bias, time lag bias, citation bias, the influence of external funding on the validity of systematic review and outcome reporting bias. Assessing the Quality of a Systematic Review General Tips (step-by-step) Fundamentally, the quality of a systematic review and the reliability of its result are contingent on both the quality of the included studies and the quality of the methodology used to produce the systematic review. The first most important step in conducting systematic review is proposing a clear, specific,focused and concise question which will guide the review process after. Searching for articles to be included can be retrieved by electronic databases, searching by hands through appropriate journals and by contacting researchers in the area of interest. To avoid the bias in the retrieval of articles the search strategy specified in the protocol must include as much details as possible. In most cases this amounts of to a list of keywords and how they will be combined for use in electronic search engines. Some knowledge of the capability of each subject specific database is important at this point, as some databases operate a thesaurus search system and others operate on the basis of keywords only. Next step, selective inclusion studies may bias the results of systematic reviews if selected based on report characteristics which called Biased inclusion criteria and low methodological quality of studies included in a systematic review is another important source of bias (Strerne JAC, Egger M, Smith GD 2001) and inclusion of data from sources other than randomized trials reduces the reliability of the conclusions of a systematic review on issues of prevention and treatment, so they should be thoroughly considered and properly defined to avoid ambiguity and to inform the validity of the review. As protocol availability may decrease the biased post-hoc changes to methods and selective outcome reporting, this information should be included in the review protocol to minimize this bias. Even if the study has high internal validity, it may not to be generalizable(high external validity). There is often a trad-off between internal and external validity. To decide about the generalizability of the study is to explore whether the study population appears to be representative of the population to which you wish to apply the results and even in similar populations, differences in the settings and in culture or other contextual factors, should also be considered.(Petticrew M, Robert, H 2008) Reviewing the results of a number of studies of course itself provides a est of generalizability, if the results have been replicated in several settings with different population, then this gives an indication of whether the results are transferable. If the number of studies is large enough, it can suggest the range of effect sizes to be expected in different settings. Generalizability is not often assessed separately in systematic reviews, though consideration of the issue is included in some critical appraisal checklists. (Deeks J, Dinnes J, DAmico R, Sowden A, Sakarovitch C. 2003) The risk of bias of a particular study is a key component in the assessment of studies that affect the validity of the results of a systematic review. Therefore, reducing the risk of bias assessment can be completed by using scales, checklists and every individual component should be reported for each study.(Sandrson S, Tatt ID, Higgins JP 2007). As the protocol developing, all the outcomes derived from the included studies should be considered and the outcome of primary importance should be differentiated from the secondary outcomes as recent surveys have showed that the outcomes selectively reported in final reports were significantly more likely to be statistically significant than those omitted (Chan AW, Hrobjartsson A, Haahr MT, et al 2004). Therefore, if a review does not identify important variables clearly, the review risks being subject to bias. So, the reviewer might select statistically significant variables and ignore the ones were initially important by the reviewer. When it comes to analysing data, the analysing method is determined by the review question and the type of data collected and it should include a narrative synthesis for describing the results and risk of bias. The next step is usually determining if statistical synthesis is appropriate to apply or not. Indeed, such forced analysis might in the axiom garbage in garbage out, providing useless results which it will discussed Later. When the results of the analysis are ready, there are many different way to represent them but sufficient details should be presented to dtermine the potential threats to validity. As conclusion in the review, the reviewer should discuss the risk of bias, strength, limitation, weakness and applicability of the evidence for each main outcome to ensure that clinicians have all the information to interpret the results. A table outlining the users guides to the Medical Literature highlight critical appraisal questions for systematic reviews and meta-analyses may help to reduce the bias in every step when conducting a systematic review.(Table 1) Table 1. Questions should be considered in determining if the results of systematic review are valid. ( adapted from Crowther, MA. Cook, DJ 2007) Did the overview address a focused clinical question? Were the criteria used to select articles for inclusion both defined and appropriate? What is the likelihood that relevant studies were missed? Was the validity of the included studies assessed? Were the assessment reproducible? How precise were the results of the overview? In assessing the value the review, it is important to consider the following question: Can the results be applied to my patients, and will the results help me care for my patients? Are the benefits worth the harms and costs? Garbage in garbage out? The quality of component trails is important as an example if the raw material is not that quality, then the findings of reviews may also be the same. So what we put in exactly what we get out. Clearly, the studies included in systematic reviews should ideally be of high methodological quality and free of bias as possible. The biases that threaten the validity of clinical trials are relate to systematic differences in the patients characteristics at baseline (selection bias), unequal provision of care apart from the treatment under evaluation (performance bias), biased assessment of outcomes (detection bias) , and bias due to exclusion of patients after they have been allocated to treatment groups (attrition bias).(Altman 1991) Some reviews produced discordant results precisely because the authors chose to ignore the quality of component trails. The same reviewers were considerably more thorough in their attempt to identify all-relevant trails,Independent of publication statue or language of publication. Although the quality of component trails happened to be more important in this particular situation, the dissemination of findings from clinical trials is known to be biased, and a comprehensive literature search is an essential intergradient of high-quality reviews. (Eddger,M. Dickersin, K. Smith,G, S 2001) Putting the light on dissemination of research findings, Scherer et al. showed that only about half of abstracts presented at conferences are later published in full. The fact that sustainable proportion of studies remains unpublished after the study had been completed must be a concern as a large information remains hidden from reviewers. Making things worse, the dissemination of research findings is not a random process, rather it is strongly influenced by the nature and direction of results. (Eddger,M. Dickersin, K. Smith,G, S 2001) Type of reporting bias Definition Publication bias The publication or non-puplication of research findings, depending on the nature and direction of results Time lag bias The rapid or delayed publication of research findings, depending on the nature and direction of results Duplicate publication bias The multiple or singular publication of research findings, depending on the nature and direction of results Citation bias The citation or non-citation of research findings, depending on the nature and direction of results Language bias The publication of research findings in particular language, depending on the nature and direction of results Outcome reporting bias The selecting reporting of some outcomes but not others, depending on the nature and direction of results Figure 1.2 (Adapted from Eddger,M. Dickersin, K. Smith,G, S 2001) Publication Bias In a 1979 article on the file drawer problem and tolerance for null results Rosenthal said, where the journals are filled with the 5 per cent of the studies that show type I errors, while the file drawers back at the lab are filled with the 95 per cent of the studies that show non significant results. (Rosenthal R. 1979). The file drawer problem has long been recognized in the social sciences: as a review of psychology journals found that of 294 studies published in 1970s, 97% rejected the null hypothesis at the 5% level.(Sterling TD.1980) It is thus possible that studies which suggest a beneficial treatment effect are published, while an equal mass of data pointing the other way remains unpublished. In this situation, a systematic review of the published trails could identify a spurious beneficial treatment effect, or miss an important adverse effect of a treatment. In the field of cancer chemotherapy such publication has been demonstrated by comparing the result from studies identified in a literature search with those contained in an international trials registry (see figure 1.2). (Simes RJ. 1986) Time lag bias Published studies continued to appear many years after approval by the ethic committee. Among proposals submitted to the Royal Prince Alfred Hospital Ethics Committee in Sydney, 85% of studies with significant results as compared to 65% of studies with null results had been published after 10 years (Stern JM, Simes RJ. 1997). The average time to publication was 4.8 years for studies with significant results comparing to 8.0 years for studies with null results. In fact, the time lag was attributable to differences in the time from completion to publication.(Eddger,M. Dickersin, K. Smith,G, S 2001) 0.7 1.0 1.3 Published 16 (1908) Registered 13 (2491) Survival ratio (95% confidence interval) Figure 1.2 (adapted from Simes) These findings indicate that time lag bias may be introduced in systematic reviews even when most or all trails will eventually be published. Trails with positive results will dominate the literature and introduce bias for several years until the negative results finally appear. The influence of external funding and commercial interests Many systematic reviews are funded by organizations such as pharmaceutical companies. As in the design of randomized trials, the design of systematic reviews can be influenced (particularly through manipulation of inclusion and exclusion criteria) to select a particular set of studies. As a result, such systematic reviews may present a biased viewpoint. Careful assessment of the quality of the systematic review should reveal the flaws in their design. Another way in which bias can be introduced is through biased interpretation of the results of a systematic review funded by industry or authored by investigators who are influenced by industry.(Crowther, MA. Cook, DJ 2007) External funding was associated with publication independently of the statistical significance of the results. Funding by government agencies was significantly associated with publication in three cohorts of proposals submitted to ethics committees whereas pharmaceutical industry sponsored studies were less likely to be published in two studies. Indeed, the pharmaceutical industry tends to discourage the publication of negative studies which it has funded. (Eddger,M. Dickersin, K. Smith,G, S 2001). Duplicate publication bias Once a list of articles is obtained, they should be reviewed by two or more individuals and compared with a list of pre-developed inclusion and exclusion criteria The production of multiple publications from single studies can lead to bias in a number of ways. Two or more systematic reviews on the same topic may arrive at different conclusion, which raise concern about validity. Studies with significant results are more likely to lead to multiple publications, which makes it more likely that they will be located and included in a meta-analysis. Moher and Johansen and Gotzsche described the difficulties caused by redundancy and the disaggregation of medical research when results from multicentre trail are presented in several publications. It may be impossible for reviewers to determine whether two papers represent duplicate publications of one trail or two separate trails, since example exist where two articals reporting the same trail do not share a single common author. (Eddger,M. Dickersin, K. Smith,G, S 2001). Citation bias The perusal of the reference lists of articles is used to identify additional articles that may be relevant. The problem with this approach is that the act of citing previous work is far from objective and retrieving literature by scanning references lists for many possible motivations such as decoration and showing up-to-dateness and knowledge may thus produce a biased sample of studies. (Eddger,M. Dickersin, K. Smith,G, S 2001) Language bias Language bias still evident in many reviews (Hearther, 2009). Reviewers are often exclusively based on trails published in English. For example, among 36 meta-analyses reported in leading English-language general medicine journals from 1991 to 1993, 26 had restricted their search to studies in English language. Reviewers in other countries will published their work in local journals as well as English language journal if their results are positive while negative results will just be published in local journals. This is demonstrated for the German language literature when comparing articles published by the same author, 63% of trails published in English had produced significant results as compared to 35% of trails published in German. Thus bias could be introduced in meta-analyses exclusively based on English-language reports.(Figure 1.3) (Eddger,M. Dickersin, K. Smith,G, S 2001) Figure 1.3 (adapted from Egger et al.) Outcome reporting bias Reporting the outcome can be influenced by the results: the outcome with the most favorable findings will generally be reported. (Eddger,M. Dickersin, K. Smith,G, S 2001). The future of unbiased, systematic reviewing Reporting biases is potentially serious problem for systematic review. While the Cochrane Collaboration has a simple aim -help people to make well informed dicisions about healthcare-, there are many challenges that must be met to achieve this aim. Ethical and social challenges include finding ways to continue to build on enthusiasm while avoiding duplication and minimizing bias, to ensure sustainability and to accommodate diversity. Logistical challenges include finding ways to identify efficiently trails and manage criticisms and updates of reviews. Methodological challenges include developing sound guidelines for deciding what types of studies to include in reviews, effective ways of communicating the results of reviews and summarizing the strength of evidence for specific effects. (Eddger,M. Dickersin, K. Smith,G, S 2001). Conclusion and Summary points In summary, There are numerous ways in which bias can be introduced in reviews and meta-analysis of controlled clinical trials. All these biases are more likely to affect small studies therefore, their results need large treatment effect to be significant. On the other side, the large studies invest more money and time that means they are more likely to be high methodological quality and published even if their results are negative. Bias in a systematic review may become evident through an association between the size of the treatment effect and study size. Reliability and validity often not established within quality assessment instrument (Heather, 2009).If the methodological quality of trials is inadequate the findings of reviews of this materials may also be compromised. Publication bias can distort findings because trials with statically significant results are more likely to be published, and without delay, than trials without significant results. Among published trails, those w ith significant results are more likely to get published in English, more likely to be cited, and more likely to be published more than once which means that they will also be more likely to identified and included in reviews. The choice of the outcome that is reported can be influenced by the results. The outcome with the most favorable findings will generally be reported, which may introduced bias. Criteria for inclusion of studies into a review may be influenced by knowledge of the results of the set of potential studies. The definition of eligibility criteria for trails to be included, a comprehensive search for such tails, and an assessment of their methodological quality are central to systematic reviews. Systematic reviews are thus more likely to avoid bias than traditional, narrative reviews.(Eddger,M. Dickersin, K. Smith,G, S 2001) Nevertheless, the systematic review is a powerful research methodology which answers question on the the basis of good evidence and provides researchers with a valuable, impartial, comprehensive and up-to-date summary of the work conducted in a specific area.

Crossover Design for Speakers

Crossover Design for Speakers Crossover Design In terms of crossover design, there are two distinct options; passive or active crossovers. Passive crossovers are the most common implementation, since only one amplifier is required. In this case, filters comprising passive components (inductors, capacitors and resistors) are used to ensure that the correct frequency range is supplied to each driver. Low-pass, high-pass and band-pass filters are commonly used and need to be matched to ensure that the frequency roll-offs compliment each other, such that in the crossover zone(s) the combined acoustic output of the drivers maintains a flat frequency response. In terms of these passive filters, it is the order of the filters used that is the primary consideration. A first order filter has a roll-off of -6dB per Octave and a Butterworth characteristic. First order filters are undesirable for two reasons; a +3dB peak is introduced at the centre of the crossover band and the crossover bandwidth is large due to the gentle roll-off, which means the drivers need to be capable of handling a greater frequency range. However, first order filters require the least components, incur less power loss as a result and do not introduce a phase change in the output. Second order filters are the most commonly used type in passive crossovers, since they are relatively simple but solve the problems associated with first order filters. The roll-off is -12dB per octave and the filters may be designed with a Linkwitz-Riley characteristic which maintains a flat frequency response across the crossover band, unlike the combination of Butterworth filters. Third order filters offer a roll-off of -18dB per octave, however there is a problem of phase separation; in a two-way configuration there is a phase shift of 270 degrees which â€Å"can result in lobing and tilting of the coverage pattern† (DellaSala, G. 2004). Some designs such as the D’Appolito configuration[1], which uses three drivers, actually make use of this phase separation in order to minimise lobing, however the D’Appolito configuration is notoriously complex and difficult to implement well without precise driver measurements. If a high-order crossover is desired, fourth order filters are perhaps the best choice. Although they are more complex in terms of design and require more components, the advantages are a small crossover bandwidth (roll-off is -24dB per octave) and a 360 degree phase shift; hence no phase correction is required. Passive crossovers beyond fourth order are generally not considered. Borwick (2001, p.267) notes these â€Å"are seldom used in passive crossover designs because of their complexity, cost and insertion losses†. The other approach to crossover design is the active crossover. In this case active filters (normally based around op-amps) are used to divide the input signal into the required frequency bands prior to amplification; the crossover has multiple outputs and a separate power amplifier is needed for each frequency band. Some audiophiles complain that active crossovers (which normally employ high-order active filters) are not a good choice, due to the poor transient response of high order filters. However as Elliot (2004) notes, â€Å"the additional control that the amp has over the drivers behaviour improves the transient performance, and especially so at (or near) the crossover frequency the most critical frequency point(s) in the design of any loudspeaker†. Apart from the increased complexity and multiple power amplifier requirement, active crossovers are far superior to their passive counterparts in almost every way, although some purists may disagree. Good quality op-amps are cheap, as are the required resistors and capacitors (since these do not need to handle much power). The active solution means frequency response is no longer defined by the quite complicated combined resistive, capacitive and inductive load of the passive crossover and drivers. Thus the frequency response of the crossover is independent of dynamic changes in the load. Furthermore, the active crossover makes it easy to tune the crossover dynamically; with most commercially available active crossovers one can simply dial in the required frequency bands. Efficiency is improved with active crossovers, since no power is lost by the amplifier in driving passive inductors or resistors. The amplifier also has the best possible control over transient response, since there is nothing between it and the driver other than cable. Thus the amplifier can respond directly and â€Å"presents the maximum damping factor at all times, regardless of frequency† (Elliot R. 2004). In view of the above one may then wonder why passive crossovers continue to remain so popular, since it seems far more logical to implement frequency division before amplifying the signal. Ease of installation is perhaps the main factor. Almost all commonly available hi-fi systems use speakers with passive crossovers. For the consumer this makes things easy; the speakers are simply connected to the amplifier and installation is complete. In contrast, turnkey active solutions for the average consumer are not forthcoming, although rack-mounted â€Å"professional† active crossovers can be obtained for quite reasonable prices (around  £150 for a 4th order 2 way Linkwitz-Riley design)[2]. However, these require a fair amount of audio engineering expertise to set up correctly and the typical home listener simply does not possess this knowledge. For the high-budget client seeking the best audio reproduction, active crossovers are certainly the best option; the technical advantages have been seen to be numerous. This is offset by the fact that the system will be far more complicated to correctly install, but it is assumed in this case that complexity of installation is of little concern to the high-budget client who is unlikely to handle the installation themselves in any case. For the low-budget client, the best solution is the passive crossover. It is a simple option, only requires one amplifier and yet produces acceptable sound quality. It is far from the best solution, but adequate if a competitive price point is desired. In conclusion, all but a few dyed-in-the-wool purists will agree that the active crossover is a superior solution in terms of quality and control. What it lacks in simplicity is outweighed by a far superior level of control over frequency response and the drivers themselves. However, due to issues of complexity one can expect that the traditional passive crossover shall continue to lead a healthy existence in the majority of loudspeaker designs. Sources Borwick, John. (2001). Loudspeaker and Headphone Handbook, Focal Press. DellaSala, G. (2004). Filter Crossover Types for Loudspeakers, Audioholics Magazine. Dickason, V. (1995). The Loudspeaker Design Cookbook, Audio Amateur Publications. Elliot R. (2004). Active vs Passive Crossovers, Elliot Sound Products. Rossing, T. (1990). The Science of Sound, Addison-Wesley. 1 [1] D’Appolito’s full 1983 paper may be obtained here: http://www.aes.org/e-lib/browse.cfm?elib=11762 [2] For example the Samson S-2: http://www.inta-audio.com/products.asp?partno=sto-oth-sam2w