With the aid of distinguished staff at the Cranfield Institute of Technology, Christopher developed a range of 'folding horn loudspeakers.

They were originally developed for 'rock groups' of the time, but so effecient was the design that Christopher found himself, in the early 1970's, developing a set commissioned by the Sidney Opera House.

In addition another variant was used by the then Central Electricity Generating Board to test the ability of the large cooling towers to withstand the 'sonic boom' of low flying fighter aircraft.