Method for eliminating room modes, and digital signal processor and loudspeaker therefor

A method for eliminating room modes (Ñ) which form as resonances in a room when a digital user signal (N) is played by a main loudspeaker, characterised by the following steps:

• a. setting up and carrying out characteristic value measurements, by
• i. positioning a main loudspeaker and a correction loudspeaker in a room, for example in a sound studio, wherein these loudspeakers (21, 22) can be two separate loudspeakers or one common loudspeaker;
• positioning a microphone in this room;
• providing a digital signal processor with a signal input for inputting and processing digital signals (A, C, N), a first loudspeaker output and a second loudspeaker output for the main loudspeaker and the correction loudspeaker, which can be combined to form a common loudspeaker output for the common loudspeaker, and a microphone input for the microphone,
• connection of the signal processor, the loudspeaker or loudspeakers and the microphone to sound electronics;
• ii. carrying out a first characteristic value measurement, in which a first transfer function (S(z)), which maps the change in a digital signal (A) after it has been recorded on the microphone on a secondary path (S) which is played via the correction loudspeaker or the common loudspeaker as sound waves, and captured as a digital signal [AS(z)=B], is reproduced by a changeable electronic filter (S′(z)),
• using an LMS(Least Mean Square) module to carry out a numerical gradient method,
• iii. saving this electronic filter (S′*(z)), which thus becomes unchangeable;
• iv. carrying out a second characteristic value measurement, in which a second transfer function (P(z)), which maps the change in a digital signal C after it has been recorded on the microphone on a primary path (P) which is played via the main loudspeaker or the common loudspeaker as sound waves and captured as a digital signal (D) [CP(z)=D], is partially reproduced by a changeable electronic filter (W(z)),
• using the LMS module to carry out a numeric gradient method;
• v. saving the electronic filter (W*(z)), which thus becomes unchangeable;
• b. setting up and using the method with a user signal (N), by
• i. positioning the main loudspeaker and the correction loudspeaker, or the common loudspeaker, at the same locations in the same room as for the characteristic value measurements, with the same sound electronics required for that and connection to the digital signal processor as in step a;
• ii. routing the digital user signal (N) to the first or common output and playing it through the main loudspeaker or common loudspeaker, wherein room modes (Ñ) are formed in the room;
• iii. simultaneously routing this user signal (N) through the last saved filter (W*(z)) in the signal processor and subsequently forwarding it to the second or common output, and
• playing this filtered user signal (Ñ−) through the correction loudspeaker or common loudspeaker with a delay on account of the time (dt) required by the filter (W*(z)),
• iv. through which the room modes (Ñ) of the digital user signal (N) that are still present in the room after the time delay (dt) are eliminated.