IMF Reference Standard Professional Monitor Mk. IV

Large Monitor Loudspeakers

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IMF stands for Irving "Bud" M. Fried, and these were originally on the market from 1977-1982.These have an amazing pedigree! Read more here. These are in nice condition. Sorry original box, packing, and manual are not included. THESE ARE LOCAL PICKUP ONLY.

Reference Standard Professional Monitor Mk IV 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.

41" x 16 3/4" x 19" wide
104 x 43 x 50 cm
Allow 463 (116 cm) to high on stand

Drive Units
Bass unit 11 3/4" x 8 1/4" flat polystyrene diaphragm loaded by transmission line
mid range unit 6" plastic cone containing in separate line
tweeter 1 3/4 " diaphragm
3/4" chemical dome super-tweeter

Crossover: Electrical four way at 350 Hz , 3 kHz and 13 Khz

Frequency Range: 17 Hz to beyong audibility

Matching Impedence: 4 to 8 ohms

Efficiency Measured via Pink Noise at 1 metre on axis for 40 watts: 96dB (dependant of control setting)

Driving Power Requirements: 50 - 150 watts

Controls: Filter, Tilt and Slope Controls

Net Weight (each): 46 Kg plus 2.1 Kgs for stand

Gross Weight: 122.5 kgs (pair with stands)

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