VSEL LS40 linesource speakers
Above, a detail from a shot of the Vox Sound Equipment Limited display at the British Musical Instrument Fair at the Russell Hotel, London, 17th-21st August, 1969. The LS40 linesource speakers are indicated with an arrow.
Vox Sound Equipment Limited (VSEL) LS40 speakers were generally provided with the late-style tilt back frame devised in 1967 or early 1968 by Jennings Musical Industries. A JMI example can be seen on this page, entry for 16th December. As can be seen in the pic above, the side struts pass through and protrude beyond the handwheels on the side.
Previously the side struts of LS40s terminated at the wheel. The advantage of longer ones was that the speakers might be supported better when standing squarely upright. Older LS40s could be extremely unstable when they were bolt upright - they were definitely at their best tilted back.
Below, a set of VSEL LS40s in excellent condition sold by vintage-guitar.de a little while ago. The presence of an XLR connector indicates that units were to be used with valve PA amps.
Solid state PA amps had 1/4" jack sockets. The new linesource units for these were the Focus - see this page.