the areas required for the correct operation of the horn itself all the parts may be produced on site in brickwork or with the use of prefabricated elements the upper wall 12 of the horn may itself constitute a surface that can be walked on as an alternative this upper wall may be overhung by a support cover 14 represented by or forming the floor of a stage the curved walls 13 of the horn extend outwards away from a space 15 of suitable volume in which a driver unit 16 is housed this unit comprises one or more loudspeakers 17 which are arranged in a cabinet 18 fitted with wheels 19 the driver unit 16 can thus be moved in the manner of a trolley to be easily inserted into the dedicated space 15 and be easily removed and transferred as required the horn 10 may be built for example at the base of a screen in a room used for the reproduction of music and speech as is schematically shown in fig4 and 5 or of a concert stage fig4 b in combination with complete low medium high and screen loudspeaker systems respectively the walls 20 of such a room may be covered according to the present invention with a diffusing reflecting absorbing structure 21 which consists of basic modules or panels 22 in a large variety of shapes and materials the structure 21 may therefore be made of bricks may consist in prefabricated modules or even wood panels or wood modules and may.