JBL are one of the longest established names in speaker design.

Design & Construction

The LSR moniker stands for Linear Spatial Reference, something that is said to deliver greater accuracy at the mix position in a variety of room types. What this translates to in simple terms is an emphasis on more consistent off‑axis sound, ostensibly resulting in a wider sweet spot, and less in the way of coloured wall and ceiling reflections. Apparently, the methodology behind the LSR approach is to take 72 different measurements at various angles right around the speaker, and then to use this data to help engineer the final design.

The low‑frequency transducers are magnetically shielded and have a 1.5‑inch diameter voice‑coil. A problem facing all speaker designers is how to get rid of the heat that builds up in the voice coil, so as to reduce the effects of power compression and the consequent tonal changes at high operating levels. JBL have always paid attention in this area, combining good thermal management with high efficiency, often utilising the cabinet port as part of the cooling system.

Class A/B monolithic power amplifiers are used to drive both the woofer and tweeter, the latter being a damped soft‑dome device (again, magnetically shielded). The tweeter feeds JBL's EOS (Elliptical Oblate Spheroidal) waveguide, shaped to give a dispersion pattern width of ±30 degrees horizontally and ±15 degrees vertically. There's also an elliptical aperture around the tweeter, rather than the more usual circle — which is apparently designed to optimise HF coverage at frequencies above 9kHz.

Audio input is via balanced XLR or quarter‑inch jack and unbalanced RCA phonos, and mains is supplied using the usual IEC power connector, next to which a voltage selector allows 120 or 230V AC operation. HF and LF adjustments are available to the user via horizontal slide‑switches ( LF: ‑3dB, 0dB, +2dB. HF: ‑2.5dB, 0dB, +2.5dB) to compensate for placement and room characteristics, and there's a rotary volume control for setting the input gain. There's no quarter-/half-/full-space switch, so the optimum LF EQ position has to be determined by ear (or measurement). There are standard mounting points for those wishing to wall‑mount the speakers, and a thin foam isolation pad is built into the cabinet base for secure desktop or stand mounting.

Constructionally, the cabinets appear to be made from MDF, with a black plastic-foil finish, and augmented by a moulded plastic front-baffle skin to provide the HF waveguide and the smooth‑edged woofer aperture. Radiused corners improve the look of the boxes and help reduce diffraction. The power light (which is, in accordance with current fashion, blue!) sits between the woofer and tweeter, while the rear reflex-port features a plastic moulded slot, with rounded edges and a series of fins on its lower edge.  The metal rear panel is flush with the cabinet sides and holds all the audio connections, as well as the mains inlet, power switch and voltage selector.