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Mine "Nye" IMF Electronics høyttalere

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Made4u

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Som mange av dere alt vet så kjøpte jeg et par "nye" IMF Electronics høyttalere i fjor, modellen jeg har leitet etter i alt for mange år. Endelig kom et par for salg her til lands, jeg hadde nesten gitt opp håpet om at det noen gang skulle skje, så hadde innfunnet meg med at jeg en eller annen gang måtte reise utenlands for å importere et brukt par hit. Nå slapp jeg det og jeg fikk dem også for en lavere pris enn hva jeg regnet med å måtte betale.

Akkurat den versjonen/modellen jeg har er også sjelden å se for salg på verdensbasis, årsaken er jo den at det ikke ble produsert så mange par av den, foruten mitt par så vet jeg bare om ett annet par i Norge (og kanskje finner man bare de to parene her til lands?, det er derimot enklere å finne andre modeller eller andre versjoner av mine, selv om også de er veldig sjeldne).

For dem av dere som husker hvor store mine gamle IMF'er var, disse er godt større enn alle de andre parene, litt for store og dominerende til å fremstå som noen design-perler. Men det kompromisset det er å skulle ha disse i stuen, det kompromisset har jo vært sterkt ønskelig fra min side så jeg er strålende fornøyd nå. En drøm har gått i oppfyllelse, endelig!!

Forrige eier har malt dem sorte, akkurat det er noe jeg ikke er begeistret for. Planen min er derfor å en gang forsøke å endre dem tilbake til den opprinnelige finish'en, men akkurat det kommer til å bli et prosjekt uten like, som derimot krever at jeg får råd/hjelp av noen som kan mer om slik enn hva jeg selv kan. Dem skal også få nye kondensatorer i delefilteret, altså skal det på sikt oppgraderes, men det skal jeg få hjelp av en kamerat som er service-tekniker til å gjøre, han har både utdanning og jobberfaring innen elektro som er noe jeg ikke har. Kit til delefilteret skal handles hos Falcon.Acoustics som har spesialisert seg på restaurering av IMF-høyttalere og som selger komponentene til disse. Vil ta noe tid før høyttalerne er ferdig restaurert og oppgradert med nye komponenter, enn så lenge spiller de fortreffelig slik de står i dag.

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IMF Electronics var en Britisk høyttalerprodusent kjent for sine transmissionline-høyttalere, et kompleks konstruksjons-prinsipp hvor høyttalerne innvendig er utstyrt med en lang labyrintformet gang som leder fra baksidet av basselementet og til to åpne porter i kabinettet, en kostbar men også vanskelig måte å bygge høyttalere på og som dessuten medfører at høyttalerne nødvendigvis må bli store av fysisk størrelse. Derfor er det produsert få transmissionline høyttalere, det er ikke så lønnsomt for produsentene og markedet ønsker også mindre høyttalere. IMF høyttalerne ble konstruert av en legendarisk høyttalerkonstruktør med navn John Wright, dessverre døde han av kreft så alt for tidlig, det ville vært spennende om han levde lenger og kunne utviklet flere transmissionline-høyttalere enn hva han fikk gjort.

Transmissionline høyttalere er nok mest beryktet for sin bass-gjengivelse, det er også derfor prinsippet er tatt i bruk. Bassen alle IMF-modeller produserer er til å få hakeslepp av, jeg har i alle fall aldri hørt noe som i gang er i nærheten, tross jeg har hørt mye som også er alvorlig kostbart. For min del er det derimot høyttalernes musikalitet som er årsaken til at jeg har valgt ut mine, de evner å spille som en drøm rett og slett. Det forutsetter derimot at kildemateriellet er av god kvalitet, dersom ikke så er høyttalerne brutalt ærlige, altså låter det absolutt ikke godt dersom lyd teknikerne som har produsert et album har gjort en dårlig jobb - og det forekommer i aller høyeste grad og er et kompromiss alle med kostbare stereoanlegg må leve med. Dårlig kildekvalitet blir avslørt så til de grader, dessverre er ikke alle album produsert for å skulle gjengis på gode full-range stereoanlegg, de er mastret for å låte ok på radio og på anlegg som ikke spiller på fult register, det er litt sørgelig egentlig. Men dersom man spiller et album hvor lyd-teknikerne har gjort en god jobb, da låter det rett og slett himmelsk med riktig elektronikk for å gi høyttalerne signal. Akkurat det er en problemstilling alle med kostbare stereoanlegg må leve med, dessverre og kanskje skal jeg også si heldigvis, er mine høyttalere mye mer avslørende enn det meste annet.

Her følger informasjon om mine høyttalere, både bildene og teksten er hentet fra informasjons-brosjyrer fra IMF Electronics, først i senere blogg-oppdateringer vil jeg poste bilder av mine høyttalere og å skrive mer om dem samt mine erfaringer med dem.

 

 IMF Electronics - Reference Standard Professional Monitor Mk.IV (Improved)

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Full transmission line loading is retained, the rear of the bass driver being exhausted into a tapered and filtered passageway. The result is an extension of performance, below audibility down to frequencies where bass is felt rather than heard. Colouration is minimised by progressive damping whilst dynamic range is increased. Only transmission line loading can provide the true impact experienced in the concert hall. The individual bowing of the celli to the slap of a bass drum is reproduced within the listening room rather than in a box.

The IMF Reference Standard Professional Monitor Mk. IV loudspeakers are supplied in matched 1 mirror-image' pairs. The drive units are clustered inwards to avoid reflections from wall boundaries and to maintain phase symmetry on the listening axes. To ensure that they are correctly orientated, the facia panels are also mirrorimage and each loudspeaker should be positioned with the 'IMF' logo inwards.

The loudspeakers must be supported on the stands supplied. The speakers are designed for optimum results when supported off the floor so as to provide air space under the enclosures. (Such an arrangement also inhibits structural acoustic feedback.) The overall height of the loudspeakers when on the stands is arranged so that the drive units are at the correct level when the listener is seated. The stands also tilt the speakers back; an integral part of the overall design concept to maintain optimum phase at high frequencies with evenness of response both axially and hemispherically.

Positioning of the loudspeakers in the room is less critical for transmission line loading than other systems, but it is still advisable to arrange the room for best siting where possible. Small loudspeakers give increased bass output, at the expense of colouration, by the additional room gain of a wall or corner position. The IMF Monitors are little affected by this and do not rely on a corner to maintain bass response. Therefore moving the speaker forward, away from a corner, even by a small distance can provide a marked reduction in room colouration components.

Spacing of the speakers should subtend an angle from the listening position of between 60 ° and 90° The distance of the listener from the speakers should ideally be not less than the distance that the speakers are spaced apart. Whether to angle the speakers inward will be dependant upon this spacing to listener ratio. However, by virtue of the skewed polar distribution of these Monitors, very little angular rotation should be necessary, and probably no more than 15° even when the listening position is close relative to their distance apart.

The loudspeakers should be connected to the amplifier, in phase with each other, using highcurrent carrying wire of at least 5 amp rating. The longer the connecting cable, the heavier should be the gauge, to avoid loss of power and amplifier, damping. The use of screened wire is neither necessary nor recommended.

A fuse can be fitted in series with the positive of each lead to provide a degree of protection against accidental sustained overload, particularly applicable where very high power amplifiers are employed. A fuse value of 3 amp (fast blow) is suggested. Unfortunately this provides no guarantee that the loudspeakers may not be damaged by transient overload before the f use blows. Experience shows that under normal conditions of use for speech and music (not discotheque or public address), damage is usually caused by intermittent fault conditions developing in the amplifier, rather than normal overload.

The basic crossover configuration is shown in Figure One, although more actual components are employed. Three controls are incorporated i n the circuit: a low frequency 'FlLTER', and a frequency response 'TILT' control with 'SLOPE' adjustment. These are accessible, after removing the facia plate, retained by four finger nuts, situated at the bottom of the loudspeaker grill. Beneath this is the control panel illustrated i n Figure Two. The threeposition pre-sets may be adjusted using a wide blade screwdriver.

The 'TILT' and 'SLOPE' controls act in conjunction with each other to determine the energy response between 300 Hz and 15 kHz. The Tilt control in the 'RISE' position causes a lift across these frequencies of about 1 dB whilst the'FALL'setting results in the opposite. (See Figure Three.) The Slope control affects the response above 2 kHz approximately + 1 dB by use of the'AD D'and 'CUT'settings. (See Figure Four.) The Slope control functions at all settings of the Tilt control and therefore a wide range of combinations are available. (See Figure Five). By operating the switches on low level random noise (from an off-station tuner), these functions can be quickly assessed. Each control setting is deliberately made fine and no configuration will impair the inherent smoothness and phase coherence of the loudspeakers.

The speakers are supplied with these controls in their 'FLAT' settings which nominally provides the mostuniform response under anechoic test conditions. This may not be optimum where room characteristics, positioning, the response of ancilliary equipment and even personal preference dictate different settings. For example, speakers situated near reflective surfaces may benefit from lowering the Slope control 'CUT', whilst for dry listening acoustics the preferred setting may be 'ADD'. Use of the loudspeakers under conditions of high ambient noise, or in a bass heavy environment, may benefitfrom lifting the Tilt control 'RISE', then making final adjustments with the Slope control. Possible settings for quiet conditions would be to turn the Tilt control to 'FALL' and perhaps restore the treble energy by switching the Slope control 'ADD'. Such combinations would produce a marginally receded midrange- a loudness contourthat may be preferable at relatively lower listening levels.

There is no basic reason whythe response of one speaker may not be adjusted differently from that of the other, to compensate for their different locations in the room. However this may not always be a totally satisfactory subterfuge since it impairs matching between the loudspeakers.

The low 'FILTER' controls energy at the bass, near and below sub-sonic frequencies. (See Figure Six.) Switched to 'IN' it provides some protection from DC pulses, such as rapid FM tuning, and from excessive'cone weave'on warped discs that can cause unwanted intermodulation components. It has negligible effect within the audible bandwidth. The 'CUT' position increases this protection and rolisthe bass off below about 50 Hz. This is used where full reproduction of the lowest frequencies is undesirable - such as when rumble causes feedback through floorboards and under high level playback conditions where the possibility of damage is increased. The'OUT'setting removes the Filter and the full range of the loudspeaker is directly connected to the amplifier. This position is onlyfor use with the finest ancilliary equipmentunconditionally stable and highly damped amplifiers, silent turntables with low mass arms isolated from acoustic feedback. The Filter should only be left 'OUT' when this results in an definite improvement, otherwisethe FiIter 'IN' position should be considered normal.

It is importantthat noneof thesethree pre-set controls,'TILT' 'SLOPE' and 'FILTER', are used as 'tone controis'. They provide only subtle forms of adjustment between laboratory settings and those ideal forthe loudspeakers when at their location of use and connected to the equipment eventually driving them. Switching should be carried out at low volume settings. As soon as the optimum settings have been established, by determining the most 'neutral' combination over a wide range of differing source material, the facia plates should be replaced. It is then necessary to re-adjust the preset controls only if either the location of the loudspeakers, or the equipment driving them, is significantly altered. Regular adjustments of balance that may be required between different 

The Reference Standard Professional Monitor Mk. IV loudspeakers are specifically designed as laboratory devices for use in the aid of subjective evaluation of programme and ancilliary equipment. No commercial compromises have been made in their development, nor have aesthetic considerations detrimentally affected design or construction. The result is a truly faithful yet ruthless transducer which provides the engineer with the maximum information regarding the source material being fed into it.

The loudspeakers are supplied in matched mirror image pairs with the drive units clustered inwards to give a skewed polar distribution, away from wall boundaries so that the listener receives the maximum of direct information, less intermingled with reflections. Despite their size, the speakers are designed to be used on stands provided. These ensure that the loudspeakers are supported off the floor, reducing room colouration components. Importantly the stands slightly tilt the speakers back, maintaining a substantially flat response both axially and hemispherically together with proper phase coherence at high frequencies. Finally but interrelatedly, they lift the loudspeakers to the correct listening elevation.

The full transmission line loading incorporates new damping techniques and materials. Initially the enclosure is lined with a dense antidrumming material, the heterogeneous matrix of which provides an optimum deadening interface. Acoustic foam, as used in anechoic chambers, is then 'sculptured' to produce a wedge effect where the maximum surface area is exposed to damp the line, yet presenting the minimum of restriction. The separate midrange line is similarly terminated whilst standing waves are progressively absorbed by long hair wool.

The necessarily complex crossover network is situated behind a removable panel at the bottom of the grill front. As well as proportioning the audio spectrum into the correct phase and amplitude relationship for each drive unit, pre-set controls are provided to equalize the loudspeakers to their acoustic environment. A low frequency filter is incorporated which can be switched to give varying degrees of protection from unwanted near sub-sonic bass cone motion. Two further controls affect adjustment of the energy response in the midrange and treble, each switch function being made fine yet supplying a wide range of configurations.

The advantages of transmission line loading, as pioneered by us, are well known. Extended bass performance is complimented by unusually low colouration. The Reference Standard Professional Monitor Mk. IV exhibits the lowest distortion characteristics of any loudspeaker so far produced. This, together with research in depth into maximum phase congruence, results in a loudspeaker of outstanding neutrality. The professional will particularly appreciate this, enabling decisions about the quality of programme signal to be made without undue allowance for loudspeaker idiosyncrasies.

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NOMINAL SPECIFICATIONS

Dimensions 101 cm (h) x 43cm (d) x 50cm (w)
Overall height on stand 117 cm
Drive Units 30 cm x 21 cm polystyrene bass unit loaded by transmission line 
15 cm plastic cone midrange in separate line
4.5 cm diaphragm high gauss tweeter
2 cm chemical dome super-tweeter
Crossover Electrical four way at 350 Hz, 3 kHz and 13 kHz
Frequency Range 17 Hz to beyond audibility
Frequency Response & See Graphs Distortion Characteristics
Dispersion See Polar Diagram
Controls FILTER : see graphs and text
TILT: +/- 1 dB : 300 Hz to 15 kHz
SLOPE: +/- 1 dB : 2 kHz to 15 kHz
Matching Impedance 4-8 ohms See Graph
Efficiency Measured via Pink 96-98 dB dependant on Control settings Noise at 1 metre for 40 watts
Driving Power Requirements 50-150 watts
Nett Weight (each) 46 kilos
Gross Weight packed (each) 56 kilos
Nett Weight of Stands (each) 2,1 kilos
Gross Weight Consignment 134 kilos (pair with stands) packed
For further information request Technical Data Sheet RSPM IV.

 

Graphs

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