Sound reproduction equipment and method for reducing the level of acoustical reflections in a room

DETAILED DESCRIPTION It is an object of the present invention to provide an entirely novel method that in a simple manner is capable of reducing the disturbing low-frequency acoustic reflections otherwise occurring in a listening room without the disadvantage of simultaneously creating new disturbance at higher frequencies.
It is another object of the invention to provide a sound reproduction apparatus offering attenuation of annoying reflected sound in a listening room with a simpler construction and improved performance over that available in conventional apparatuses.
The goal of the invention is achieved by way of sampling the sound signal electrically from the equipment used for producing the original sound such as the amplifier feeding a loudspeaker.
The sample signal is processed in order to generate the cancellation signal for attenuating the pressure level of reflections and the cancellation signal thus formed is converted by means of at least one loudspeaker into a cancelling sound in the listening room where the impact of reflections is desired to be attenuated.
According to the invention, the sample signal used for generating the cancellation signal is filtered so as to free the signal from essentially all the sound components that can create a so-called diffuse sound field in the listening room.
The term diffuse sound field refers to a situation in which the sound does not excite a pressure pattern of systematic reflections in the listening room, but rather the sound field is comprised of an incoherent composite waves formed by reflections from a plurality of different surfaces and/or diffraction waves about different objects.
In such a diffuse sound field, each point of the listening room receives waves related to the same original sound but received as a sum of partial waves in different phase and incoherently directed, which makes the behaviour of the interfering wave pattern difficult to predict.
The filtration is advantageously performed before the delaying operation and the setting of the signal phase and amplitude