Misplaced Pages

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96-546: Rather than purchase off-the-shelf components, loudspeaker design engineers often define desired performance and work backwards to a set of parameters and manufacture a driver with said characteristics or order it from a driver manufacturer. This process of generating parameters from a target response is known as synthesis. Thiele/Small parameters are named after A. Neville Thiele of the Australian Broadcasting Commission , and Richard H. Small of

192-496: A dynamic loudspeaker 's driver is its electrical impedance as a function of frequency . It can be visualized by plotting it as a graph , called the impedance curve. The most common driver type is an electro-mechanical transducer using a voice coil rigidly connected to a diaphragm (generally a cone ). Other types have similar connections, though differing in detail, between their acoustical environment and their electrical properties. The voice coil in moving coil drivers

288-615: A 5 V input. A driver with a measured V a s {\displaystyle V_{\rm {as}}} of 7 L at 0.5 V, may show a V a s {\displaystyle V_{\rm {as}}} increase to 13 L when tested at 4 V. Q m s {\displaystyle Q_{\rm {ms}}} is typically stable within a few percent, regardless of drive level. Q e s {\displaystyle Q_{\rm {es}}} and Q t s {\displaystyle Q_{\rm {ts}}} decrease <13% as

384-509: A cut in funding of $ 43 million over three years when accounting for inflation. In the 2019–20 federal budget funding was around $ 3.2 billion over three years ($ 1.06 billion per year) for the ABC. The Enhanced Newsgathering Fund , a specialised fund for regional and outer-suburban news gathering set up in 2013 by the Gillard government , was $ 44 million over three years as of

480-461: A cut of $ 254 million (4.6% ) to funding over the following five years together with the additional unfunded cost of the news channel meant that the ABC would have to shed about 10% of its staff, around 400 people. There were several programming changes, with regional and local programming losing out to national programs, and the Adelaide TV production studio had to close. In November 2016

576-414: A dB) in frequency response. If the performance of speaker system is critical, as with high order (complex) or heavily equalized systems, it is sensible to measure T/S parameters after a period of run-in (some hours, typically, using program material), and to model the effects of normal parameter changes on driver performance. There are numerous methods to measure Thiele-Small parameters, but the simplest use

672-429: A few hundred hertz). In addition, distorted or non–sine wave signals can cause measurement inaccuracies. Inexpensive voltmeters are also not very accurate or precise at measuring current and can introduce appreciable series resistance, which causes measurement errors. A third method is a response to the deficiencies of the first two methods. It uses a smaller (e.g., 10 ohm) series resistor and measurements are made of

768-428: A high Z m a x {\displaystyle Z_{\rm {max}}} – the measured value of Z m a x {\displaystyle Z_{\rm {max}}} will always be somewhat low. This measurement can be corrected by measuring the total voltage across the calibration resistor and the driver (call this V {\displaystyle V} ) at resonance and calculating

864-526: A large number of ABC Local Radio stations, several digital stations, and the international service Radio Australia . ABC Television operates five free-to-air channels, as well as the ABC iview streaming service and the ABC Australia satellite channel. News and current affairs content across all platforms is produced by the news division. The postal address of the ABC in every Australian capital city

960-444: A new logotype and brand positioning under its tagline, Yours . The 2002 silver logo is no longer in use by the corporation. The operations of the ABC are governed by a board of directors, consisting of a managing director, five to seven directors, and until 2006, a staff-elected director. The managing director is appointed by the board for a period of up to five years, but is eligible for renewal. The authority and guidelines for

1056-612: A new system, similar to that of the BBC, for appointing members to the board. Under the new system, candidates for the ABC Board would be considered by an independent panel established "at arm's length" from the Communications Minister. If the minister chose someone not on the panel's shortlist, they would be required to justify this to parliament. The ABC chairman would be nominated by the prime minister and endorsed by

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1152-630: A publication in an Australian journal. This paper remained relatively unknown outside Australia until it was re-published in the Journal of the Audio Engineering Society in 1971. It is important to note that Thiele's work neglected enclosure losses and, although the application of filter theory is still important, his alignment tables now have little real-world utility due to neglecting enclosure losses. Many others continued to develop various aspects of loudspeaker enclosure design in

1248-405: A quiet acoustic environment. The most common ( DIY -friendly) method before the advent of computer-controlled measurement techniques is the classic free air constant current method, described by Thiele in 1961. This method uses a large resistance (e.g., R t e s t {\displaystyle R_{\rm {test}}} = 500 to 1000  ohms ) in series with the driver and

1344-458: A reduced amount". In all, over a five-year period, there were 737 redundancies, a further 866 resignations, and 203 retirements; but the total number of staff only fell by 313 due to the ABC hiring 650 staff over that period. In June 2021 the ABC announced its plan to move around 300 staff to offices in Parramatta , in a plan which would see 75% of journalists and producers moving out of

1440-596: A result of commercial agreements with digital platforms flowing from the Morrison government 's News Media Bargaining Code . In May 2024 the ABC started moving from its Ultimo office to a new Parramatta office. The first program to be broadcast from the new studio in Parramatta was ABC Radio Sydney Mornings . The ABC logo is one of the most recognisable logos in Australia. In the early years of television,

1536-416: A signal generator is used to vary the excitation frequency. The voltage across the loudspeaker terminals is measured and considered proportional to the impedance. It is assumed that variations in loudspeaker impedance will have little effect on the current through the loudspeaker. This is an approximation, and the method results in Q {\displaystyle Q} measurement errors for drivers with

1632-486: A strong, generally reversible effect; typical suspension materials become stiffer at lower temperatures. The suspension experiences fatigue , and also undergoes changes from chemical and environmental effects associated with aging such as exposure to ultraviolet light, and oxidation which affect foam and natural rubber components badly, though butyl, nitrile, SBR rubber, and rubber-plastic alloys (such as Santoprene ) are more stable. The polyester type of polyurethane foam

1728-483: A vented box) which was evidence of the interest in many types of enclosure design at the time. Progress on loudspeaker enclosure design and analysis using acoustic analogous circuits by academic acousticians like Harry F. Olson continued until 1954 when Leo L. Beranek of the Massachusetts Institute of Technology published Acoustics , a book summarizing and extending the electroacoustics of

1824-522: Is PO Box 9994, as a tribute to the record-breaking Test batting average of Australian cricketer Sir Donald Bradman . After public radio stations were established independently in the state capitals from 1924, a licensing scheme administered by the Postmaster-General's Department was established, allowing certain stations (with "Class A" licences") government funding, albeit with restrictions placed on their advertising content. In 1928,

1920-571: Is highly prone to disintegration after 10 to 15 years. The changes in behavior from aging may often be positive, though since the environment that they are used in is a major factor the effects are not easily predicted. Gilbert Briggs, founder of Wharfedale Loudspeakers in the UK, undertook several studies of aging effects in speaker drivers in the 1950s and 1960s, publishing some of the data in his books, notably Loudspeakers: The Why and How of Good Reproduction . There are also mechanical changes which occur in

2016-467: Is itself one of the Thiele/Small parameters. The variation in loudspeaker impedance is a consideration in audio amplifier design. Among other things, amplifiers designed to cope with such variations are more reliable. There are two main factors to consider when matching a speaker to an amplifier. This is the minimum value in the impedance vs. frequency relationship, which is always higher than

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2112-445: Is moving in a magnetic field. When the loudspeaker coil moves in response to a signal from the amplifier, the coil generates a back EMF that resists the amplifier signal and acts as a "brake" to stop the coil movement. The braking effect is critical to speaker design, in that designers leverage it to ensure the speaker stops making sound quickly and that the coil is in position to reproduce the next sound. The electrical signal generated by

2208-715: Is politically independent and accountable such as through its production of annual reports and is bound by provisions contained within the Public Interest Disclosure Act 2013 and the Public Governance, Performance and Accountability Act 2013, with its charter enshrined in legislation, the Australian Broadcasting Corporation Act 1983 . ABC Commercial , a profit-making division of the corporation, also helps to generate funding for content provision. The ABC

2304-426: Is required when using and interpreting T/S parameters. Individual units may not match manufacturer specifications. Parameters values are almost never individually taken, but are at best averages across a production run, due to inevitable manufacturing variations. Driver characteristics will generally lie within a (sometimes specified) tolerance range. C m s {\displaystyle C_{\rm {ms}}}

2400-399: Is suspended in a magnetic field provided by the loudspeaker magnet structure. As electric current flows through the voice coil (from an electronic amplifier ), the magnetic field created by the coil reacts against the magnet's fixed field and moves the voice coil (and so the cone). Alternating current will move the cone back and forth. The moving system of the loudspeaker—consisting of

2496-469: Is that their ratios are more important than their actual value, removing the effect of poor meter frequency response. Australian Broadcasting Corporation The Australian Broadcasting Corporation ( ABC ) is the national broadcaster of Australia . It is principally funded by the Australian taxpayer and is administered by a government-appointed board . The ABC is a publicly owned body that

2592-500: Is the constant voltage measurement, where the driver is excited by a constant voltage, and the current passing through the coil is measured. The excitation voltage divided by the measured current equals the impedance. A common source of error using these first two methods is the use of inexpensive AC voltage meters. Most inexpensive meters are designed to measure residential power frequencies (50–60 Hz) and are increasingly inaccurate at other frequencies (e.g., below 40 Hz or above

2688-474: Is the least controllable parameter, but typical variations in C m s {\displaystyle C_{\rm {ms}}} do not have large effects on the final response. It is also important to understand that most T/S parameters are linearized small signal values. An analysis based on them is an idealized view of driver behavior, since the actual values of these parameters vary in all drivers according to drive level, voice coil temperature, over

2784-417: Is the ratio of the nominal load impedance (driver voice coil) to amplifier output impedance, is adequate in either case for well-designed solid state amplifiers. Tube amplifiers have sufficiently higher output impedances that they normally included multi-tap output transformers to better match to the driver impedance. Sixteen ohm drivers (or loudspeakers systems) would be connected to the 16-ohm tap, 8 ohm to

2880-418: Is vibrating in the speaker's magnetic field with maximum peak-to-peak amplitude and velocity . The back EMF generated by this movement is also at its maximum. The electrical impedance of the speaker varies with the back EMF and thus with the applied frequency. The impedance is at its maximum at F s , shown as Z max in the graph. For frequencies just below resonance, the impedance rises rapidly as

2976-559: The Australian Broadcasting Act that meant the ABC would receive its funding directly from the federal government. Licence fees remained until 1973, when they were abolished by the Whitlam Labor government , on the basis that the near-universality of television and radio services meant that public funding was a fairer method of providing revenue for government-owned radio and television broadcasters. In 2014

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3072-600: The Australian Labor Party at the 1972 election), as well as Sir Henry Bland, David Hill was close to Neville Wran , while Donald McDonald was considered to be a close friend of John Howard . From 2003 the Howard government made several controversial appointments to the ABC Board, including prominent ABC critic Janet Albrechtsen , Ron Brunton , and Keith Windschuttle . During their 2007 federal election campaign Labor announced plans to introduce

3168-638: The Chifley government decided that the ABC would be directly funded by the taxpayer, with licence fees subsumed into general revenue. Later funding was supplemented with commercial activities related to its core broadcasting mission. The Australian Broadcasting Commission became the Australian Broadcasting Corporation in 1983. The ABC provides radio, television, online, and mobile services throughout metropolitan and regional Australia. ABC Radio operates four national networks,

3264-446: The FM band, broadcasting from Adelaide . It was initially known as ABC-FM (later ABC Classic FM) – referring both to its "fine music programming and radio frequency". ABC budget cuts began in 1976 and continued until 1998, the largest cuts (calculated by the ABC as 25% in real terms) coming between 1985 and 1996. The Australian Broadcasting Corporation Act 1983 changed the name of

3360-470: The Journal of the Audio Engineering Society , restating and extending Thiele's work. These articles were also originally published in Australia, where he had attended graduate school, and where his thesis supervisor was J. E. Benson. The work of Benson and Small overlapped considerably, but differed in that Benson performed his work using computer programs and Small used analog simulators . Small also analyzed

3456-753: The University of Sydney , who pioneered this line of analysis for loudspeakers. A common use of Thiele/Small parameters is in designing PA system and hi-fi speaker enclosures ; the TSP calculations indicate to the speaker design professionals how large a speaker cabinet will need to be and how large and long the bass reflex port (if it is used) should be. The 1925 paper of Chester W. Rice and Edward W. Kellogg , fueled by advances in radio and electronics, increased interest in direct radiator loudspeakers. In 1930, A. J. Thuras of Bell Labs patented (US Patent No. 1869178) his "Sound Translating Device" (essentially

3552-441: The Z min point the impedance is again largely inductive and continues to rise gradually with frequency. The frequency F s and the frequencies above and below it where the impedance is ⁠ 1 / √ 2 ⁠ Z max are important in determining the loudspeaker's T/S parameters . These can be used, for example, to design a suitable enclosure for the driver, especially for low frequency drivers. In fact F s

3648-492: The leader of the opposition . A new merit-based appointment system was announced on 16 October 2008, in advance of the new triennial funding period starting in 2009. In 2013 the Coalition government introduced a merit-based system for appointing the board based on the recommendations of a nominations panel. However, the panel was ultimately only advisory, with almost all of the board members in 2018 directly appointed by

3744-553: The 1960s and early 1970s. From 1968 to 1972, J. E. Benson published three articles in an Australian journal that thoroughly analyzed sealed , vented and passive radiator designs, all using the same basic model, which included the effects of enclosure, leakage and port losses. Beginning in June 1972, Richard H. Small published a series of very influential articles on direct radiator loudspeaker system analysis, including closed-box, vented-box, and passive-radiator loudspeaker systems, in

3840-489: The 2019–20 budget, a reduction of $ 28 million per year since the 2016 Australian federal election . This came after speculation that the fund would be removed, to which Acting managing director David Anderson wrote to Communications Minister Mitch Fifield expressing concerns. Despite the cuts made by Prime Minister Tony Abbott and Communications Minister Malcolm Turnbull and the freeze introduced by Prime Minister Malcolm Turnbull and Communications Minister Mitch Fifield,

3936-411: The 8 ohm tap, etc. This is significant since the ratio between the loudspeaker impedance and the amplifier's impedance at a particular frequency provides damping (i.e., energy absorption) for the back EMF generated by a driver. In practice, this is important to prevent ringing or overhang which is, essentially, a free vibration of the moving structures in a driver when it is excited (i.e., driven with

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4032-449: The ABC absorbed $ 254 million in federal budget deficits. In the 2018–19 budget handed down by then-Treasurer Scott Morrison , the ABC was subject to a pause of indexation of operation funding, saving the federal government a total of $ 83.7 million over 3 years. In fiscal year 2016–17, the ABC received $ 861 million in federal funding, which increased to $ 865 million per year from 2017 to 2018 to 2018–19, representing

4128-476: The ABC announced that ABC News 24, ABC NewsRadio , as well as its online and digital news brands, would be rebranded under a unified ABC News brand, which was launched on 10 April 2017. Michelle Guthrie took over from managing director Mark Scott , whose second five-year contract finished in April 2016. Between July 2017 and June 2018, the whole of the ABC underwent an organisational restructure, after which

4224-447: The ABC had been using Lissajous curves as fillers between programmes. In July 1963, the ABC conducted a staff competition to create a new logo for use on television, stationery, publications, microphone badges and ABC vehicles. In 1965, ABC graphics designer Bill Kennard submitted a design representing a Lissajous display, as generated when a sine wave signal is applied to the "X" input of an oscilloscope and another at three times

4320-402: The ABC itself has published financial data that shows an increase in the taxpayer appropriation to the ABC of 10% in real terms (i.e. above inflation) between 1998 and 2021. In 2023, fulfilling one of Labor's election pledges, the ABC moved into a five instead of three-year funding term. Electrical characteristics of a dynamic loudspeaker The chief electrical characteristic of

4416-605: The ABC music label. In 1991 the corporation's Sydney radio and orchestral operations moved to a new building, the ABC Ultimo Centre, in the inner-city suburb of Ultimo . In Melbourne, the ABC Southbank Centre was completed in 1994. In 1992 Australian children's television series Bananas in Pyjamas first aired. International television service ABC Australia was established in 1993, while at

4512-511: The British Broadcasting Corporation ( BBC ), which is funded by a television licence , the ABC was originally financed by licence fees on households with a broadcast receiver. However, the licence fees soon proved to be insufficient due to Australia's small population and the vast area to be serviced. In 1947 a proposal to increase the fee for a broadcast listeners' licence from £1 to £1/5/ was scotched, and in 1949

4608-577: The Communications minister, despite some being rejected by the panel or not being considered at all. As of March 2024 board members include: The ABC is primarily funded by the Australian government , in addition to some revenue received from commercial offerings and its retail outlets . The ABC's funding system is set and reviewed every three years. Until 1948 the ABC was funded directly by radio licence fees; amendments were also made to

4704-467: The DC resistance of the voice coil, i.e., as measured by an ohmmeter . Minimum impedance is significant because the lower the impedance, the higher the current must be at the same drive voltage. The output devices of an amplifier are rated for a certain maximum current level, and when this is exceeded the device(s) sometimes, more or less promptly, fail. Due to the reactive nature of a speaker's impedance over

4800-476: The Radio and Television Divisions were no longer separate entities each under a director, instead being split across several functional divisions, with different teams producing different genres of content for television, radio and digital platforms. The Entertainment & Specialist (E&S) team focussed on comedy, kids' programs, drama, Indigenous-related programs, music, other entertainment and factual content;

4896-472: The Ultimo building by 2025 to reduce costs. Rental from some of the vacant space in the city centre would earn additional income to offset the ongoing effects of the significant funding cuts since 2014 and the recent indexation freeze. In December 2021 the ABC announced that, in addition to the 83 additional positions already established, it was to create an additional "50-plus" new jobs in regional Australia as

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4992-594: The actual test current I = V / ( R t e s t + Z m a x ) {\displaystyle I=V/(R_{\rm {test}}+Z_{\rm {max}})} . You may then obtain a corrected Z m a x {\displaystyle Z_{\rm {max}}} = Z m a x ( u n c o r r e c t e d ) × R t e s t / I {\displaystyle Z_{\rm {max(uncorrected)}}\times R_{\rm {test}}/I} . A second method

5088-399: The amplifier output stage which manifests as heating in the output devices. The phase angle varies most near resonance in moving coil loudspeakers. If this point is not taken into consideration during the amplifier design, the amplifier may overheat causing it to shut down, or cause failure of the output devices. See Power factor for more detail. A loudspeaker acts as a generator when a coil

5184-565: The appointment of directors is provided for in the Australian Broadcasting Corporation Act 1983 . Appointments to the ABC Board made by successive governments have often resulted in criticism of the appointees' political affiliation, background, and relative merit. Past appointments have associated directly with political parties – five of fourteen appointed chairmen have been accused of political affiliation or friendship, include Richard Downing and Ken Myer (both of whom publicly endorsed

5280-442: The attendant rise in resistance that is the cause of the power compression. Elegant magnet and coil designs have been used to linearize B l {\displaystyle Bl} and reduce the value and modulation of L e {\displaystyle L_{\rm {e}}} . Large, linear spiders can increase the linear range of C m s {\displaystyle C_{\rm {ms}}} , but

5376-473: The audible effects of such changes in published speaker reviews, the relationship of such early changes to subjective sound quality reports is not completely clear. Some changes early in driver life are complementary (such as a reduction in f s {\displaystyle f_{\rm {s}}} accompanied by a rise in V a s {\displaystyle V_{\rm {as}}} ) and result in minimal net changes (small fractions of

5472-417: The audio band frequencies, giving a speaker a single value for 'impedance' rating is in principle impossible, as one may surmise from the impedance vs. frequency curve above. The nominal impedance of a loudspeaker is a convenient, single number reference that loosely describes the impedance value of the loudspeaker over a majority of the audio band. A speaker's nominal impedance is defined as: The graph shows

5568-553: The calculated sensitivity value ( η 0 {\displaystyle \eta _{0}} ) can appear to drop by >30% as the level changes from 0.5 V to 4 V. Of course, the driver's actual sensitivity has not changed at all, but the calculated sensitivity is correct only under some specific conditions. From this example, it is seen that the measurements to be preferred while designing an enclosure or system are those likely to represent typical operating conditions. Unfortunately, this level must be arbitrary, since

5664-550: The case. In June 2020 the ABC announced it needed to cut 229 jobs, a number of programs, and reduce its travel and production budgets after the Turnbull government 's announcement of a freeze to indexation of its budget in 2018 this was estimated at the time to cost the ABC A$ 84 million over three years, however the actual appropriation did not decrease and the ABC chair was quoted as saying it would actually increase "but by

5760-727: The coil heats and the value will typically double by 270 °C (exactly 266 °C for Cu and 254 °C for Al), at which point many voice coils are approaching (or have already reached) thermal failure. As an example, f s {\displaystyle f_{\rm {s}}} and V a s {\displaystyle V_{\rm {as}}} may vary considerably with input level, due to nonlinear changes in C m s {\displaystyle C_{\rm {ms}}} . A typical 110-mm diameter full-range driver with an f s {\displaystyle f_{\rm {s}}} of 95 Hz at 0.5 V signal level, might drop to 64 Hz when fed

5856-494: The coil travels back along the speaker cable to the amplifier. Well-designed amplifiers have low output impedance so that this generated signal has minimal effect on the amplifier. Characteristically, solid state amplifiers have had much lower output impedances than tube amplifiers. So much so, that differences in practice between a 16-ohm nominal impedance driver and a 4-ohm nominal impedance driver have not been important enough to adjust for. The amplifier damping factor , which

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5952-405: The cone, cone suspension, spider, and voice coil—can be modeled as an effective mass (spring–mass system) , a mass suspended by a spring. This system has a characteristic mass and stiffness , and a resonant frequency at which the system will vibrate freely. This frequency is known as the "free-space resonance" of the loudspeaker and is designated by F s . At this frequency, the voice coil

6048-449: The drive level rises from 0.5 V to 4 V, due to the changes in B l {\displaystyle Bl} . Because V a s {\displaystyle V_{\rm {as}}} can rise significantly and f s {\displaystyle f_{\rm {s}}} can drop considerably, with a trivial change in measured M m s {\displaystyle M_{\rm {ms}}} ,

6144-411: The equivalent electrical circuit models. Some of these values are neither easy nor convenient to measure in a finished loudspeaker driver, so when designing speakers using existing drive units (which is almost always the case), the more easily measured parameters listed under Small Signal Parameters are more practical: These values can be determined by measuring the input impedance of the driver, near

6240-535: The era. J. F. Novak used novel simplifying assumptions in an analysis in a 1959 paper which led to a practical solution for the response of a given loudspeaker in sealed and vented boxes, and also established their applicability by empirical measurement. In 1961, leaning heavily on Novak's work, A. N. Thiele described a series of sealed and vented box "alignments" (i.e., enclosure designs based on electrical filter theory with well-characterized behavior, including frequency response, power handling, cone excursion, etc.) in

6336-700: The examination of over 9,200 documents, including internal emails. In February 2020 the case was dismissed by the federal court . In June 2020, the AFP sent a brief of evidence to the Commonwealth Director of Public Prosecutions (CDPP), the federal public prosecutor, recommending charges be laid against journalist Dan Oakes for breaking the Afghan Files story, but in October 2020, the CDPP dropped

6432-404: The firm GR Research has publicly reported several such investigations of several manufacturers' drivers. Other studies suggest little change, or reversible changes after only the first few minutes. This variability is largely related to the particular characteristics of specific materials, and reputable manufacturers attempt to take them into account. While there are a great many anecdotal reports of

6528-470: The frequency at the "Y" input. The letters "ABC" were added to the design and it was adopted as the ABC's official logo. Kennard was presented with £ 25 (about AU $ 850 in 2024) for his design. On 19 October 1974 the Lissajous curve design experienced its first facelift with the line thickened to allow for colour to be used. It would also be treated to the 'over and under' effect, showing the crossover of

6624-459: The frequency increases towards F s and is inductive in nature. At resonance, the impedance is purely resistive . As the frequency increases above F s , the impedance drops—it behaves capacitively . The impedance reaches a minimum value, Z min , at some frequency where the behaviour is fairly resistive over some range. A speaker's rated or nominal impedance ( Z nom ) is derived from this Z min value, explained ahead. Beyond

6720-847: The government established the Australian Broadcasting Commission (ABC) on 1 July 1932, under the Australian Broadcasting Commission Act 1932 . to take over the Australian Broadcasting Company and run the National Broadcasting Service. The ABC became informally referred to as "Aunty", originally in imitation of the British Broadcasting Corporation's nickname . The structure and programming

6816-557: The government established the National Broadcasting Service to take over the 12 A-Class licences as they came up for renewal, and contracted the Australian Broadcasting Company , a private company established in 1924, to supply programs to the new national broadcaster. After it became politically unpopular to continue to allow the Postmaster-General to run the National Broadcasting Service,

6912-414: The impedance curve of a single loudspeaker driver in free-air (unmounted in any type of enclosure). A home hi-fi loudspeaker system typically consists of two or more drivers, an electrical crossover network to divide the signal by frequency band and route them appropriately to the drivers, and an enclosure that all these components are mounted in. The impedance curve of such a system can be very complex, and

7008-447: The input impedance of the driver, measured near resonance. The impedance may be measured in free air (with the driver unhoused and either clamped to a fixture or hanging from a wire, or sometimes resting on the magnet on a surface) and/or in test baffles, sealed or vented boxes or with varying amounts of mass added to the diaphragm. Noise in the measurement environment can have an effect on the measurement, so one should measure parameters in

7104-615: The large signal values of B l {\displaystyle Bl} and C m s {\displaystyle C_{\rm {ms}}} must be balanced to avoid dynamic offset. The mechanical components in typical speaker drivers may change over time. Paper, a popular material in cone fabrication, absorbs moisture easily and unless treated may lose some structural rigidity over time. This may be reduced by coating with water-impregnable material such as various plastic resins. Cracks compromise structural rigidity and if large enough are generally non-repairable. Temperature has

7200-449: The life of the driver, etc. C m s {\displaystyle C_{\rm {ms}}} decreases the farther the coil moves from rest. B l {\displaystyle Bl} is generally maximum at rest, and drops as the voice coil approaches X m a x {\displaystyle X_{\rm {max}}} . R e {\displaystyle R_{\rm {e}}} increases as

7296-496: The line in the design. To celebrate its 70th anniversary on 1 July 2002, the ABC adopted a new logo, which was created by (Annette) Harcus Design in 2001. This logo used a silver 3D texture but the crossover design was left intact and was then used across the ABC's media outlets. After the on-air revival of the 1974 logo since 2014, the ABC gradually reinstated the classic symbol. The most recent change happened in February 2018, with

7392-453: The load current is minimum (and the voltage is minimum across the load) and vice versa, and as a result the power dissipation in those devices is least. But due to the complex and variable nature of the driver/crossover load and its effect on the phase relationship between the voltage and current, the current will not necessarily be at its minimum when the voltage across the output devices is maximum - this results in increased power dissipation in

7488-509: The moving components during use. In this case, however, most of the changes seem to occur early in the life of the driver, and are almost certainly due to relaxation in flexing mechanical parts of the driver (e.g., surround, spider, etc.). Several studies have been published documenting substantial changes in the T/S parameters over the first few hours of use, some parameters changing by as much as 15% or more over these initial periods. The proprietor of

7584-564: The new ABC Specialist team created content across the arts, science, religion & ethics, education and society & culture; while the Regional & Local team focussed on regional and local content. Around 23 September 2018 Guthrie was fired. A leadership crisis ensued after allegations arose that Chair, Justin Milne , had, according to the MEAA , engaged in "overt political interference in

7680-604: The operating conditions are continually changing when reproducing music. Level-dependent nonlinearities typically cause lower than predicted output, or small variations in frequency response. Level shifts caused by resistive heating of the voice coil are termed power compression . Design techniques which reduce nonlinearities may also reduce power compression, and possibly distortions not caused by power compression. There have been several commercial designs that have included cooling arrangements for driver magnetic structures, which are intended to mitigate voice coil temperature rise, and

7776-428: The organisation to the Australian Broadcasting Corporation, effective 1 July 1983. Although funded and owned by the government, the ABC remains editorially independent as ensured by the 1983 Act. At the same time, the newly formed corporation underwent significant restructuring, including a split into separate television and radio divisions, and ABC Radio was restructured significantly again in 1985. Geoffrey Whitehead

7872-706: The resonance frequency, at small input levels for which the mechanical behavior of the driver is effectively linear (i.e., proportional to its input). These values are more easily measured than the fundamental ones above. The small signal parameters are: These parameters are useful for predicting the approximate output of a driver at high input levels, though they are harder, sometimes extremely hard or impossible, to accurately measure. In addition, power compression , thermal, and mechanical effects due to high signal levels (e.g., high electric current and voltage, extended mechanical motion, and so on) all change driver behavior, often increasing distortion of several kinds: Some caution

7968-452: The running of the ABC that is in clear breach of the ABC charter and the role of the chairperson" by interfering in editorial and staffing matters. After pressure for an independent inquiry or statement from Milne, or his resignation, following meetings by ABC staff in various locations, on 27 September Milne resigned. In February 2019, after the roles of ABC chair and managing director had been vacant for more than four months, Ita Buttrose

8064-639: The same time Radio Australia increased its international reach. Reduced funding in 1997 for Radio Australia resulted in staff and programming cuts. The ABC Multimedia Unit was established in July 1995 to manage the new ABC website, which was launched in August. The ABC was registered on the Australian Business Register as a Commonwealth Government Entity on 1 November 1999. In 2001 digital television commenced (see Online, below ). At

8160-528: The same time the ABC's multimedia division was renamed "ABC New Media", becoming an output division of the ABC alongside television and radio. In 2002 the ABC launched ABC Asia Pacific , the replacement for the defunct Australia Television International operated previously by the Seven Network . A digital radio service, ABC DiG , was also launched in November that year. On 8 February 2008 ABC TV

8256-400: The simple formula above does not as easily apply. The nominal impedance rating of consumer loudspeakers systems can aid in choosing the correct loudspeaker for a given amplifier (or vice versa). If a home hi-fi amplifier specifies 8 ohm or greater loads , care should be taken that loudspeakers with a lower impedance are not used, lest the amplifier be required to produce more current than it

8352-416: The systems including enclosure losses. Richard H. Small and Garry Margolis, the latter of JBL , published an article in the Journal of the Audio Engineering Society (June 1981), which recast much of the work that had been published up till then into forms suited to the programmable calculators of the time. These are the physical parameters of a loudspeaker driver, as measured at small signal levels, used in

8448-418: The voltage across the driver, the signal generator, and/or series resistor for frequencies around resonance. Although tedious, and not often used in manual measurements, simple calculations exist which allow the true impedance magnitude and phase to be determined. This is the method used by many computer loudspeaker measurement systems. When this method is used manually, the result of taking the three measurements

8544-623: Was broadly modelled on the British Broadcasting Corporation, and programs not created in Australia were mostly bought in from the BBC . In 1940 one of the ABC Board 's most prominent members, Dick Boyer , was appointed to the ABC, becoming chairman on 1 April 1945. Today known for the continuing series of Boyer Lectures initiated by him in 1959, he had a good but not too close working relationship with Sir Charles Moses (general manager 1935–1965 ), and remained chair until his retirement in 1961. He

8640-407: Was designed to handle. Using a 4 ohm loudspeaker system on an amplifier specifying 8 ohms or greater could lead to amplifier failure. Impedance variations of the load with frequency translate into variation in the phase relationship between the amplifier's voltage and current outputs. For a resistive load, usually (but not always) the voltage across the amplifier's output devices is maximum when

8736-592: Was determined to maintain the autonomy of the ABC. The ABC commenced television broadcasting in 1956. ABN-2 in Sydney was inaugurated by prime minister Robert Menzies on 5 November 1956, with the first broadcast presented by Michael Charlton , and James Dibble reading the first television news bulletin. Television relay facilities were not in place until the early 1960s, so news bulletins had to be sent to each capital city by teleprinter , to be prepared and presented separately in each city. In 1975, colour television

8832-400: Was established as the Australian Broadcasting Commission on 1 July 1932 by an Act of federal parliament. It effectively replaced the Australian Broadcasting Company , a private company established in 1924 to provide programming for A-class radio stations. The ABC was given statutory powers that reinforced its independence from the government and enhanced its news-gathering role. Modelled after

8928-522: Was managing director of the ABC at this time. Following his resignation in 1986, David Hill (at the time chair of the ABC Board) took over his position and local production trebled from 1986 to 1991. Live television broadcasts of selected parliamentary sessions started in 1990, and by the early 1990s, all major ABC broadcasting outlets moved to 24-hour-a-day operation. In 1991 the ABC helped launch Australian children's music band The Wiggles , under

9024-571: Was named chair. Buttrose named David Anderson as managing director in May 2019. On 5 June 2019 Australian Federal Police (AFP) raided the headquarters of the ABC looking for articles written in 2017 about alleged misconduct by Australian special forces in Afghanistan, later dubbed the Afghan Files . The raid was countered by lawyers for the ABC in litigation against the AFP, challenging

9120-415: Was permanently introduced into Australia, and within a decade, the ABC had moved into satellite broadcasting , greatly enhancing its ability to distribute content nationally. Also, in 1975 the ABC introduced a 24-hour-a-day AM rock station in Sydney, 2JJ ( Double Jay ), which was eventually expanded into the national Triple J FM network. A year later, a national classical music network was established on

9216-449: Was rebranded as ABC1 , and a new channel for children, ABC3 , was funded and announced by the Rudd government in June. A new online video-on-demand service launched in July of the same year, titled ABC iview . ABC News 24 , now known as ABC News, a channel dedicated to news, launched on 22 July 2010. On 20 July 2014, ABC1 reverted to its original name of ABC TV. In November 2014

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