How special is Harbeth's RADIAL cone material?

Did all of that government-funded BBC-lead research actually result in a driver that remains superior (in the aspects that were/are deemed important by it's intended users) to anything that has followed?

 

Very interesting question.
I've heard both the C7ES2 and latest HL5 using this material. They do have good tonality and realism in the mids, but neither are quite as good as a pair of Vintage Rogers Export Monitors I have. The Rogers is very close to the BBC LS3/6 from which all the later desings including the the HL5 are derived. My Exports are labelled 3/6 in key areas such as the crossover and are very close indeed to the BBC speaker.

Those early BBC based designs of course used bextrene for the cones. Radial would appear to be lighter and better damped which means potentially better sensitivity and no need for damping applied directly to the cone.

So ultimately it probably represents a better material but so much depends on how the driver is loaded and of course the crossover.

 

Something which worries me about such a driver is that (as far as I know) it works by being more flexible towards the outside edge. In most cases a driver cone that flexes causes distortion problems, so I'd be very interested to see distortion plots for some of these drivers. Does anyone have any?

I can also think of another speaker that used such drivers, designed by Harbeth in fact, the funky coloured HHB Circle 5 and and Circle 3.

 

I would have thought that the key to the material ( in fact , any speaker cone material) is the balancing of flexure vs. internal damping. IIRC its this which 'Radial' was developed to specifically address / improve on Bextrene's performance

It's uncontrolled, underdamped/ peaky modes that give audible problems - eg certain metal coned drivers can be awful for this.

 

IIRC the Radial material is plastic (polyprop I think) loaded with glass or acrylic beads.

 

from: Enjoy the Music

 

Not trying to harp on or promote honest, but "Controlled Cone Flexure" was the basis of Jordan's Designs for his spun aluminium cones

contrast this to say the paper Yamamura Churchill cone design with no surround or edge restraint at all (never heard these)