Acoustics and Hearing

When one listens to music at home, one would like to have an acoustic impression close to that of being in the concert hall. Until recently this meant elaborate multi-channelled sound systems with 5 or more speakers. But head-related stereophony achieves the surround-sound effect in living rooms with only two loudspeakers. By virtue of their slight directivity as well as an electronic filter the limitations previously common to two-speaker systems can be overcome and this holds for any arbitrary two-channel recording. The book also investigates the question of how a wide and diffuse sound image can arise in concert halls and shows that the quality of concert halls decisively depends on diffuse sound images arising in the onset of reverberation. For this purpose a strong onset of reverberation is modified in an anechoic chamber by electroacoustic means. Acoustics and Hearing proposes ideas concerning signal processing in the auditory system that explain the measured results and the resultant sound effects pleasing to the audience.

Résumé
In a good concert hall, a big orchestra can evoke remarkably spacious sounds. The concertgoer is surrounded by the physical sound waves, and out of these waves the subjective sound impressions are created in the listener's head. This biological measuring device organized itself during childhood. With no special effortand quite continuouslyit performs parallel data proce- ing and makes no distinction between complex or simple analysis. Imagine that the orchestra, after complete silence, strikes a load, abrupt chord. In that moment we can watch the immediate response of the hall. The phenomenon is called the onset of reverberation. During this process the l- tener's auditory system has to evaluate the direct sound of each particular - sical instrument along with portions of sound re ected from the walls or the ceiling. If those sound re ections arrive at the listener's ears less than 50 ms later than the direct sound, they are called early re?ections. All these amounts of sound make up such an intricate mixture that the ear is unable to resolve it as a series of separate events. From a favourable seat in the auditorium the listener receives only one complex impression, which can be wide and yet very detailed and appears abruptly in the front. This subjective impression may brie y be named a sound image. Its width and its depth, its facets and the weights or contrasts of its different parts characterize the acoustics of the concert hall and also the orchestra.

Contenu
Head-Related Sound from Two Loudspeakers.- Head-Related Stereophony.- The Hearing Process in Concert Halls.- Powerful Onset of Reverberation.- Definition of Diffuseness.- Theory of Drift Thresholds.- Loudness and Diffuseness.