La premiére fois que je les ai vues, elles se cachaient au fond d'une discothéque. Je me disais que Earth Win and Fire sonnait drôlement bien boosté par une paire de Denon 2800 Pa. Quand j'ai levé les yeux et vu ce qui me décoiffaient,  j' ai tout de suite su que le son studio  du disco n'a rien à envier à une paire de Magnepan reproduisant un quatuor de cordes. L'émotion était là, les cuivres cinglaient et les basses séchent et profondes remuaient toute la salle. Peut ëtre qu'un jour, les auditorium nous passeront autre chose que We get request et les tambours japonais.

La doc d'origine du fabricant,  Le Dieu JBL de la meilleure époque quand Harman Kardon ne l'étranglait pas.

Une simple enceinte 4 voies avec 2 haut-parleurs de grave de 38 cm pour vous taper dans les trippes. Un 2405 dans les aigus, JBL était en avance en ce temps là.

Qui peut encore vous remuer comme cela, une paire de JMF pour obtenir la pêche du son studio.

JBL Professional SériesModel 4355 Studio MonitorFour-way System designed for biamplificationExtremely wide-band linear responsecharacteristicsHigh acoustic output; controlled dispersion patternProvision for mirror-imaging.

The 4355 Studio Monitor

The JBL 4355 is the latest resuit of an engineering study undertaken to create, regardless of cost, the optimum studio loudspeaker for monitoring recording sessions and for final mixdown of master tapes. A four-way System designed for biamplification, it achieves inherently smooth reproduction from 28 Hz to 20 kHz.controlled high frequency dispersion, and exceptional transient performance In addition, the 4355 is capable of wide dynamic range with low distortion and of the high acoustic output required for précise reproduction of the original sounds. It is an indispensable tool, not only for mastering and mixdown, but also for subjective anaiysis of the entire studio recording and reproducing complex.

The two low frequency loudspeakersaredriven independently of the other components in the System Biamplification offers significant performance advantages in termsof reducing dis­tortion, particulàrly at high volume levels thaï would be more likely to overload a single amplifier.

Low Frequency Loudspeakers

Two 380 mm [15 in) low frequency loudspeakers mounted in a ported enclosure provide accurate reproduction and high power handling at very low frequencies The use of two drivers allows twice the power input to the low frequency section, resulting in a 3 dB mcrease in acoustic output Each loud­speaker is driven by a 100 mm (4 in) diameter voice coil fabricated of edge-wound copper ribbon wire, operating in a magnetic field with a flux density of 1.2 T (12,000 gauss). The 8.5 kg (18% Ib) magnetic assembly incorporâtes JBL's unique Symmetrical Field Geometry (SFG) design that reduces second harmonie distortion to inconsequential levels. Careful choice ot suspension éléments, taking into account their interaction with the voice coil motion, results in a driver with tight, controlled transient response and complète freedom from dynamic instabiiities A compilant cône termi-nation allows long excursions and damps spunous reflections traveling within the cône material.

Midrange Loudspeaker

Music fundamentals lying in the région between 290 Hz and 1.2 kHz are reproduced by a 300 mm (12 in) loudspeaker housed in a sealed subehamber and driven by a 100 mm (4 in) edge-wound copper ribbon voice coil. The SFG design of the magnetic structure results in exceptionally low levels of second harmonie distortion The magnetic assembly weighs 9.5 kg (21 Ib) and produces a flux density of 1.2 T (12,000 gauss) in the voice coil gap. The driver achieves high acoustic efficiency and effortless reproduction, even at extrême volume levels.

High Frequency Compression Driver

Reproduction from 1.2 kHz to 10 kHz is accomplished by a massive compression driver energized by a magnetic assem­bly weighing 11.3 kg (24% Ib).The 100 mm (4 in) edge-wound aluminum ribbon voice coil, suspended in a magnetic field of 1.8 T (18,000 gauss), drives an aluminum diaphragm featuring a three-dimensional diamond pattern surround that provides improved high frequency response and increased reliability Proper phasing of the wavefront is assured by use of a phasing plug of die-cast concentric exponential noms. The combination of an extremely powerful, efficient magnetic assembly, edge-wound voice coil, and large yet lightweight diaphragm results in exceptional transient response and dynamic range.

Horn/Lens Assembly

The output of the compression driver is distributed by an exponential horn combined with a slant-plate acoustic lens. The rigid horn casting couples the output of the high fre­quency driver to the acoustic lens without adding audible résonance or distortion, The 11 plates of the lens, set at an angle of 38? operate in a manner analogous to a divergent optical lens, providing controlled propagation of high frequency energy.

Ultra-High FrequencyTransducer

The highest octave of the audio spectrum is reproduced by a compression driver specifically designed for ultra-high frequency reproduction and dispersion. Its 2 kg (4î4 Ib) magnetic assembly develops a flux density of 1.65 T (16,500 gauss) and drives a 44 mm (1 % in) edge-wound aluminum ribbon voice coil The driver uses a ring diaphragm pneu-matically formed of 0.06 mm (0.002 in) aluminum foil stock. Output is directed through a diffraction horn providing 90° dispersion in the plane perpendicular to the diffraction slot while restricting dispersion in the vertical plane to approxi-mately 40? The device maintains response within a tolérance of ±3dBîo20kHz.

Frequency Dividing Network

1 ho low frequency loudspeakers operate to 290 Hz and require an atténuation rate of 12 dB per octave below and above the crossover frequency. Transition may be accom­plished with a JBL 5234A dual channel Electronic Frequency Dividing Network or with oneof several electronic crossovers or filtenng devices commercially available. A crossover card designed specifically for the 4355 is available for use in the JBL5234A.

The midrange, high frequency, and ultra-high frequency drivers are regulated by a high-level passive crossover net­work of the L-C type specifically designed and tested for opération with the transducers of the system. Transition be-tween the midrange loudspeaker and the high frequency compression driver occurs at 1.2 kHz at the rate of 12 dB per octave At 10 kHz, the ultra-high frequency driver is brought into opération at 18 dB per octave. Levai controls are provided.

The enclosure of the 4355 incorporâtes two acoustic cham bers. The two low frequency loudspeakers are housed in a bass refiex chamber which has an internai volume of 265 liters (9.5 ft³). Proper loading to 32 Hz is accomplished by a distributed port consisting of two large curved tubes. The midrange loudspeaker is mounted in a second, sealed sub-chamber, 48 liters (1.7 ft³) in volume and designed to prever acoustical interaction with the low frequency drivers.Thesub chamber also atténuâtes output of the midrange unit below 200 Hz, thus reducing unwanted peaks in total System response.The enclosure is constructed of 25 mm (1 in) stock for maximum rigidity with minimum weight. Joints are carefully fitted and beat treated; the enclosure is architec-turally braced to prevent unwanted résonances, and the interior surfaces are padded to damp spurious reflections and standing waves within the acoustical chambers.