In search of perfect sound – introducing Britain’s largest horn loudspeaker

A long black metal tube, slightly tapered and almost 9-foot-long lay on a row of filing cabinets at Blythe House, the Science Museum’s storage facility. The object was pointed out by John Liffen, the Museum’s Curator of Communications, who guided me during a research visit of the collections in 2008. It was all that remained of a mighty horn loudspeaker that was demonstrated in the Museum during the 1930s, John explained. A demolition accident had almost totally destroyed it in 1949.
Now the tube assumed a more fascinating form, like a fossil or a dinosaur bone as we delved into audio archeology.

The story of the horn, researched in great detail by John, sparked an interest in me. Four years later in 2012, on being appointed as the Museum’s first-ever sound artist-in residence, I was given a wonderful opportunity to initiate its reconstruction.

The exponential horn loudspeaker was designed in 1929 by the Museum’s curator of  ‘Electrical Communication’ R. P. G. Denman who also personally built a radio receiver to run in tandem with it. The purpose of this new sound system was to provide the public with demonstrations of the highest quality broadcast sound that was obtainable at the time. Denman saw it as setting a benchmark for audio quality, his aim was, in his words “to provide a standard by which commercial apparatus could be judged”.

The horn measured 27 feet (8.23m) in length with a cross section that curved exponentially from 1 ^1/16 inches (27mm) to a massive 7-foot-1-inch square (2.16m sq.) at the horn mouth. The science and theory of how horns propagate sound had only begun to emerge in the mid-1920s. It was found that a horn with an exponential shape was the most effective means of converting the sound energy from high pressure, low velocity vibrations produced at the narrow end of the horn, into low pressure, high velocity vibrations at its mouth, then radiated into the outside air. However, in order to reproduce the lowest sounding frequencies, this type of horn has to be very long with a correspondingly large opening.

More here

and here