For circular and near circular horns a lens was the most effective means to increase horizontal dispersion without introducing lobe distortion and minimal loss of efficiency. An acoustical lens is the equivalent of the optical lens.
A labyrinth of concave plates is put in front of the horn. Sound from the centre of the horn passes through unhindered. Sound to the sides of centre in the horn, pass through the lens labyrinth, increasing the distance traveled and delayed in time. The sound waves are bent forming a wide horizontal dispersion. The lens improves horizontal dispersion as the frequency increases.
The lens is no longer used. It is large, fragile and expensive. Economic rationalism, not technical performance was and still is its downfall. Also the lens function was not well understood. Its physical appearance does not give an intuitive understanding of its function. Many old 60s - 70s roadie sound engineers believed the lens directed sound downward to the audience sitting in the front row. The lens was commonly referred to as a waterfall effect speaker. Ignorance and miss-understanding was and still is a problem throughout the professional audio industry. |