Refurbishing and analysing a pair of JBL L150A loudspeakers



                               January 2006 ( revised Oct 2006/May 2007)


By way of explanation I remark that most of my 50 years of working ( born London, England 1937, B.Sc.( Elec.Eng), M.B.E, same employee number since 1956 except for a two year spell at Lockheed Aircraft Georgia, in the mid 1960's) has been in the design and engineering of radar and thermal infrared sensors.  As I must eventually find something else to do, I thought I'd collect some of the results of the work and play which I've done most recently.  



(1)  This is intended as an introduction to POVRAY for traditional optical designers who, if they have not already done so, would like to add a truly  'photorealistic'  dimension to their raytracing designs.



The optical design and  evaluation tool, ZEMAX,  presently licenseable from ZEMAX Development Corporation, is one of the most powerful professional tools available for creating and analysing almost any optical sytem.  Typical applications are for imaging optics for cameras, or light manipulation systems such as illuminators, or fibre optic components in communication systems. 

The freeware scene visualisation application POVRAY was originally  created by and for hobbyists, but which over the years of dedication by the POVRAY team of mathematicians and programmers around the world has evolved into one of the most powerful tools for scene visualizations, comparable with and in many ways superior to the professional benchmarks such as 3D-Studio and MAYA.

Although ZEMAX and POVRAY are both programs whose purpose is to show the way light behaves as its energy interacts with natural and cultural objects, their applications were originally very different.   ZEMAX is primarily an optical systems design tool for designing image forming optical systems such as camera lenses.  In its early days  POVRAY was a hobby tool for those with strong artistic imagination, but who are possibly more fluent with mathematics and computers than they are with an artist's paintbrush.  But the introduction by Nathan Kopp of the mathematics of the 'photon mapping'  technique developed by Henrik Wann Jensen  transformed POVRAY from a hobby application into a serious optical analysis tool for professional use.

I've used for many years the OSLO and ZEMAX optical design programs,  and the POVRAY visualisation program, in my job as a concepts and details designer of optical systems.  The aim of this web-site is to extend the use of POVRAY to more users of the traditional  optical design programs. 


                             (2)  A number of designs of apochromatic lenses using modern glasses




This work arose from a desire to buy an eyeball telescope for a holiday visit to  more favourable skies.  It expanded to assesss the possibilities of high performance lenses designed for 35mm and 80mm SLR cameras.  It was expanded in April 2007 to create lenses suitable for the very large CCD focal planes now available for astronomical electronic cameras    

    (3) A collection of images and movies made using POVRAY, Terragen and VistaPro







(4) Loudspeaker modelling

This item is not in the generic field of optical design and engineering.   I placed it here as a contribution to the largely US community of devotees of the JBL  loudspeaker brand and its legacy forum   During the 1960s to 1980s JBL were the US market leaders in loudspeakers for both the high fidelity domestic market  and public entertainment.  By 2002 they had largely withdrawn from the domestic market in the face of severe competition from Eastern and European manufacturers, and now concentrate on the public entertainment market, which is substantially more lucrative, and better matched to their industrial manufacturing capability.

In the item, I describe a programme of repair and analysis and  results of  electrical and acoustic measurements.







Copyright Don Barron 2007