Kardioidhögtalare : Jakten efter en väggmonterad högtalare med kardiodstrålning

Wall mounted loudspeakers are becoming more and more appealing to the average home. The disadvantage with these kinds of loudspeakers is that the acoustic flaws of a room, in most cases, get more excited. A company named DLS Svenska AB is keen to find a solution to this problem and the following mission statement, translated from Swedish to English, was handed to the author from their loudspeaker engineer named Mats Andersen:“Mission to investigate, measure and verify the possibility to remove/minimize the effect the closest room boundary has on the sound from wall mounted speakers, or speakers standing close to a wall, using acoustic and electrical solutions. With focus on acoustic solutions. Electric solutions essentially means analog solutions, but also to examine digital solutions (DSP).”Five different prototypes called Chamfer, Plate, Pressient, Toploaded and Type R were developed based on acoustical theories. Chamfer was focusing on edge diffractions. Plate had a wide baffle which would lower the box shadowing. Pressient and Type R were based on microphone technologies and Toploaded used an acoustical mirror. Frequency spectrums for all the prototypes were measured in a room called multi-studio and in an anechoic chamber. By doing this it was possible to identify the problems created by the wall behind the loudspeaker. The polar patterns were measured in the anechoic chamber to investigate if the prototypes had the wanted radiation patterns.The results produced by the experiments in this thesis say that it is possible to minimize the effect the closest room boundary (i.e. the wall behind the loudspeaker) has on the sound from wall mounted speakers. However, it is not possible to remove the effect completely, with the tested acoustical solutions. Electrical solutions were not investigated since it fell outside the author’s educational orientation. Some of the prototypes did not behave as expected. All of the prototypes require further work to be usable for conventional loudspeakers, even those which had good cardioid or half spherical characteristics. Chamfer did minimize the back radiation quite well, but some pretty drastic interference appears when the baffle ends right at a room boundary. Plate did extend the box shadowing to lower frequencies so the reflections would not disturb the midrange as much. The baffle did, on the other hand, create drastic edge diffractions. Pressient did not work at all. It had a system which works in theory but needs more implementation in real life to work properly. Toploaded had more success than the previous prototypes. The acoustical mirror worked very well and the prototype acted as ka goes to zero up to 900 Hz instead of creating minimum and maximum. The theory for Type R works, but it created some acoustical disturbances which make it unsuitable for conventional use.Validerat; 20150224 (global_studentproject_submitter