What is stereo?

There are now two system of high fidelity, monophonic (monaural) and stereophonic. Monophonic is a system that starts from one microphone and is fed through a single high fidelity set. Stereophonic is a double system. Two separate microphones are placed at different sides of the orchestra and two different systems are used to keep the two signals or channels separated. Two separate speakers are used, placed on different sides of you room. Stereo is much like 3-D photography, two slightly different sound reach your ears giving you a new dimension in sound.

H.H. Scott '59

JBL L250 (1982)

The L250 is the most advanced loudspeaker JBL has ever built for the home. From the shape of the enclosure to the design  of the level controls. JBL has spared no effort. Overlooked no performance factor necessary to building the most accurate loudspeaker possible.
The L250 will sound as good  as your other equipment will allow. Frequency response is nearly ruler-flat over the whole audible bandwidth. Distortion is held to levels more typical of fine electronics than of loudspeakers. JBL engineers paid particular attention to stereo imaging, so  that it is precise, stable and three-dimensional.

 Form follows, function in the L250's enclosure  The asymetrical shape minimizes diffraction effects, as do the rounded edges. The sloping front baffle puts the drivers in correct time and phase relationship as well. To further assure s stable image, the L250's are designed in mirror-imaged pairs.
An advanced, highly refined version of JBL's high resolution dividing network contributes greatly to the excellent performance. The network is a first-order design with 6dB per octave slopes for the smoothest blending of the drivers. Conjugate circuits level the impedance of each driver, so that actual operation approaches the theoretical ideal.
Instead of conventional level controls, the L250 uses fixed-value, stepped attenuators to give the performance advantages of hard wire while still allowing level adjustments, which are made via high-current bus bars.
The L250 is finished in oiled walnut venner. Four other finishes and six grille colors are available by special order.

 Symmetrical Field Geometry
The low frequency driver of the Lseries loudspeakers incorporate JBL's unique Symmetrical Field Geometry (SFG) magnetic structures. There are two innovations in the SFG design. One is the symmetrical magnetic field around the voice coil gap, which reduces second harmonic distortion below 100Hz. Conventional Designs have an asymmetrical field around the gap, so that the interaction of the field and the voice coil is non linear.  The second SFG innovation is the Flux Stabilizing Ring encircling the pole piece. This reduces the second harmonic distortion above 100Hz. Because the low frequency drivers of JBL loudspeakers have bandwidths extending well above 100Hz, SFG results in both cleaner bass and cleaner midrange.

 High Resolution Dividing Network
Most dividing networks blur musical transients because the large capacitors necessary for high power handling introduce a slight time lag between the input and output signal. (This is called hysteresis.) To improve transient resolution, JBL engineers incorporated circuitry more typical of active high frequency electronics. Small, highly linear 'Bypass" capacitors, wired in parallel with the larger capacitors, enable the network to pass transient waveforms unaltered. These high resolution frequency dividing networks are found in all JBL L Series loudspeaker systems.

System: Four-way floor-standing system
Max. Amplifier Power:  400 watts per channel
Nominal Impedance:  8 ohms
Crossover Frequencies:  400 Hz, 1,500 Hz, 5,000 Hz
Sensitivity:  90 dB SPL
Low Frequency Driver
Nominal Diameter:  360 mm (14")
Voice Coil:  100 mm (4")
Magnetic Assembly:  Edgewound copper
Weight:  8,5 kg (18-5/8 lb)
Lower Midrange Driver
Nominal Diameter:  200 mm (8")
Voice Coil:  50 mm (2")
Magnetic Assembly:  Copper
Weight:  2,7 kg (6 lb)
Midrange Driver
Nominal Diameter:  130 mm (5")
Voice Coil:22 mm (7/8")
Magnetic Assembly:   Edgewound copper
Weight:  0,74 kg (1-5/8 lb)
High Frequency Dome Radiator
Nominal Diameter:  25 mm (1")
Voice Coil:  25 mm (1")
Magnetic Assembly:  Copper
Weight:  0,9 kg (2 lb)
Finish:  Transparent Black Stain, Indian rosewood, Macassar ebony, White oak
Grille Colors:  Brown, Blue, Black, Rust, Tan, Maroon
Dimensions (H x W x D):  1321 x 572 x 362 mm (52" x 22½" x 14¼")
Weight:  68 kg (150 lb)

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