Harbeth M30.2 XD

Had it been possible to bring the combined intellects of Kirke, Shorter and Harwood together, doubtless man-years of painstaking research could have been reduced to months. The no-alternative was a process of sourcing candidate materials under conditions of commercial secrecy and working through them systematically. All fifty or so that met the low-mass requirement but had a range of other properties (including colour) were painstakingly subjected to a series of controlled and standardised excitations to simulate music in a test jig of Harbeth’s design. This obviated the cost and inconvenience of moulding hundreds of alternative speaker cones, assembling them into drive units for measurement and listening, with the risk of overlooking that the best candidate due to the overwhelming practical complexity of the task.

As the months passed, an objective correlation began to develop between the materials under mechanical test, and their subjective sonic signatures. To prove the relationship between physical parameters and perceived sound, suppliers with pilot process plants, including other universities, volunteered to make incremental modifications to candidate materials for Harbeth to analyse and learn from. Typically this involved manipulating the electrical charge that holds molecules together, to tighten or loosen cross-linking chain bonds. As knowledge accrued, the project advanced to the crucial phase: deciding upon the optimum ratio of elements and bulk-blending.

There had been a growing appreciation that candidate materials had distinctive acoustic strengths, and that surprisingly and disappointingly, no one material had optimal audio properties across the entire audio band, as would be needed by a bass-midrange cone.

Conceptually, what was needed was a metal-polymer hybrid: rigid metal for bass punch and softer more forgiving polymer for well damped higher frequencies without the need for cone-doping. The creation of such a material took much more effort.

Assuming such a two-element composite was conceptually feasible, how much of each component would make the perfect cone? The metal-like material could be theoretically blended from between 10% and 90%. With no prior art to draw upon and with four material components, a matrix of possible test blends was proposed, bulk material quantities procured, and experimentation began in small-scale process plant. All samples were carefully archived and subsequently subjected to analysis.

As anticipated, after discarding results from outlying blends, a core group of prospective candidate blends with ideal acoustic performance emerged. It was time to ask the petrochemical industry to manufacture Harbeth’s bespoke plastic compound, in bulk. Much easier said than done.