JBL L 150 (1979)

The JBL L150. Capable of live-performance volume levels with true deep bass reproduction and high efficiency, the JBL L150 is a worthy addition to JBL's line of outstanding loudspeaker systems. JBL designed each component of this three-way floor-standing model for maximum power-flat frequency rsponse, controlled dispersion, and extended bandwidth. The newly developed low frequency driver is the product of over two years of intensive research by JBL engineers. The result of this careful engineering is clearly audible: smooth,transparent sound at any volume level, over a frequency range extending from the lowest organ tones to the limit of audibility and beyond. JBL takes as much care with the appearance as with the sound, and the elegant columnar design occupies little floor space and fits comfortably into any room.

Advantages of the Floor-Standing Design.

While bookshelf loudspeakers systems such as the JBL L150 have reached a high degree of refinement, there are a number of significant advantages to the floor-standing design of the JBL L150. Most immediately apparent to the listener is the increased bass performance. The JBL L150 will comfortably reproduce the power of an organ or bass guitar; if the bass information is in the music, the listener will hear it. To accomplish this, JBL engineers utilized both the larger enclosure volume of the floor-standing design and a passive rediator. The bass performance of the L150 is true deep bass, without the artificial boost in the mid-bass region that often substitutes for actual low frequency reproduction. The response of the L150 extends to the lowest octaves and is completely natural in sound with no hollow quality.

Another very audible advantage of the JBL L150 is the placement of the mid range and high frequency drivers at approx. ear level of the listener. Such placement aids in the perception of the sound as being "live", and also reduces the proportion of high and mid-frequency energy that is absorbed by furniture in the room. Although placing a bookshelf system on a tall stand will produce the same effect, the L150 provides much better bass performance and is also more easily integrated visually into a room.

A loudspeaker system should do more than merely reproduce the notes. It should bring the essence of the live performance into the living room. Listen to the L150 and hear what we mean.

Components

Each component od the JBL L150 loudspeaker system is designed and produced to meet the most rigorous standards in the audio industry. The loudspeaker frames are massive cast structures, machined to exacting tolerances. The magnetic assemblies are precisely manufactured oflow-reluctance iron, energized by powerful, high-grade magnets. Voice coils are hand wound and held within one turn of design specifications. Cones are designed from the best possible combination of stiffness, density, and weight.

Low Frequency

The Newly developed 300 mm (12") low frequency loudspeaker produces the powerful bass of the L150. The driver utilizes a stiff, heavy cone, coated with an exclusive damping formulation (the white material on the cone) to give it optimum mass and density. The 75 mm (3") voice coil, formed of cooper ribbon and hand wound on edge, is powered by a 4,7 kg (10,25 lb) magnetic assembly. Beacuse the voice coil is unusually large for a 300 mm driver, the L150 offers exceptional transient response and high efficiency.

The magnetic assembly is the first JBL low frequency design to incorporate a ferrite magnet. Ferrite magnets have many desirable characteristics, but these have been overshadowed in conventional designs by unacceptably high (by JBL standards) levels of second-and third-harmonic distortion. However, after two years of concentrated research, JBL engineers have developed an assembly that solves the distortion problem.

One key to the new JBL design is the Symmetrical Field Geometry (SFG). Accurate reproduction of the audio signal requires that the cone and voice coil move in or out with equal facility. This does not happen in conventional designs because the magnetic field around the voice coil gap is not symetrical; such designs generate large amounts of third-harmonic distortion. JBL's new SFG design greatly reduces this distortion by creating a symmetrical magnetic field on both sides of the gap.

JBL has also devised an innovative solution to the problem of second-harmonic distortion. As the voice coil moves in the gap in a conventional ferrite design, the electrical field produced by the coil (from the audio signal) modulates the flux in the magnetic structure. This in turn affects cone movement and generates from 3% to 5% second-harmonic distortion. JBL engineers found an ingenious solution - the Flux Stabilizer, an aluminum ring surrounding the pole piece. The Flux Stabilizer minimizes this flux modulation and thereby reduces second-harmonic distortion to 0,01% or less.

The low frequency reproduction of this driver is not only powerful, but clean, exhibiting a depth and transparency seldom encountered outside a live performance.

A 300 mm (12") passive radiator extends bass response to the lowest octaves. The passive radiator, essentially a loudspeaker cone with no magnet or voice coil but of a precise mass, takes the place of a large volume of air and allows the L150 to achieve its deep bass in an enclosure of modest size. Similar performance from a conventionally ported system would require a much larger enclosure; a completely sealed (acoustic suspension) design would be much less efficient.

Midrange

The 130 mm (5") midrange driver, housed in an isolated sub-chamber to prevent interaction with the low frequency loudspeaker, delivers clear, undistorted reproduction, even at extremely high volume levels. The combination of a stiff cone and large voice coil (22 mm, 7/8") give this driver exceptionally good transient response, crucial to accurate reproduction. The midrange driver is designed to be more efficient than the low frequency loudspeaker in order to maintain the substantial reserve dynamic range necessary to reproduce high-intensity program peaks without strain or distortion. (This reserve dynamic range is important because most music has far more energy in the midrange than in the bass or treble regions.)

High Frequency

The 25 mm (1") dome radiator produces high acoustic output with exceptional clarity and dispersion. The dome is constructed from phenolic-impregnated linen and combines stiffness with light weight; it is small enough to provide the dispersion necessary for excellent stereo imaging, yet strong enough to produce live-performance volume levels without distorting. Special clamping rings assure linear movement to further aid in distortion-free performance.

Frequenvy Dividing Network

The dividing network receives the signal from the amplifier and allocates each portion to the appropriate driver. The sophisticated network of the L150 utilizes phase-correcting and impedance-leveling circuitry so that the drivers operate through the transition frequencies in a manner approaching the theoretical ideal. All of the network components are mounted on a single large printed circuit board, which improves the already excellent reliability. The driving network of the JBL L150 does its job so well that the listener will never be aware of separate drivers - just the smooth, transparent sound.

Controls for midrange and high frequency output accomodate variations in room acoustic and personal preferences.

Enclosure

A tightly constructed, non-resonant enclosure is important to any loudspeaker system and especially importand to a robust system such as the L150. Therefore, the enclosure panels are made of dense compressed wood, superior to solid wood in its acoustic properties. For maximum strength and resistance to vibration, all panels are cut from 19 mm (3/4") stock. In addition all joints are hand fitted and heat cured. To absorb unwanted resonances, the enclosure is lined with fiberglass. The finish veneer is American black walnut, hand-rubbed to alustrous finish.

Power Capacity

The JBL L150 will produce sound at comfortable listening levels when driven by an amplifier having an output of as little as 10 watts continuous sine wave per channel. However, the L150 combines high efficiency with high power capacity; for the best possible performance, an amplifier capable of delivering up to 300 watts continuous sine wave per channel is recommended. Such an amplifier has the reserve power necessary for accurate reproduction of transients, which can reach momentary peaks equivalent to ten times the average power level.

Specifications

JBL has traditionally refrained from listing data for which no widely accepted test procedures have been establoshed. In the absence of such standards, any laboratory can legitimately produce a variety of values, depending on the conditions selected.

System

Max. Recommended Amplifier Power: 300 watts per channel

Nominal Impedance: 8 ohms

Crossover Frequencies: 1,000 Hz; 4,000 Hz

System Sensitivity: 88 dB SPL, (1W/1m)

Low Fequency Loudspeakers

Nominal Diameter: 300 mm (12 inch)

Voice Coil: 76 mm (3 inch) copper

Magnetic Assembly Weight: 4,7 kg (10¼ lbs)

Flux Density: 1.05 tesla (10,500 gauss)

Sensitivity (Averaged from 100 Hz to 500 Hz, within 1 dB): 89 dB SPL (1W/1m)

Midrange Loudspeaker

Nominal Diameter: 130 mm (5 inch)

Voice Coil: 22 mm (⅞ inch) copper

Magnetic Assembly Weight: 0,74 kg (1⅝ lbs)

Flux Density: 1,4 tesla (14,000 gauss)

Sensitivity (Averaged from 1 kHz to 3 kHz, within 1 dB): 91 dB SPL (1W/1m)

High Frequency Dome Radiator

Nominal Diameter: 25 mm ( 1 inch)

Voice Coil: 25 mm (1 inch) aluminum

Magnetic Assembly Weight: 0,68 kg (1½ lbs)

Flux Density: 1,4 tesla (14,000 gauss)

Sensitivity (Averaged above 5 kHz, within 1 dB): 90 dB SPL (1W/1m)

General

Finish: Oiled walnut

Grille Colors: Brown, rust, camel

Dimensions (W x H x D): 1054 x 432 x 330 mm (41½ x 17 x 13 inch)

Weight (net): 36,4 kg (80 lbs)