The directional characteristics of the string instruments depend not only on the frequency, but on the kind of wood and the thickness of the plates. It is necessary, therefore, to measure several violins, violas, violoncellos, and contrabasses and to evaluate an average characteristic for each instrument group and many frequency ranges. The results of such investigations, made in an anechoic chamber, demonstrate the main directions of the sound radiation and the directions of less sound pressure in dependence on the frequency. These characteristics make it possible to discuss the influence of different seating arrangements of the orchestra on the loudness, the harmonic content and the clearness of the transients in a concert hall. The interaction between the room acoustics and the main directions of the instruments is very important for the ratio between direct and slightly delayed sound and reverberation. It is interesting, too, for the construction of reflectors on the walls near the orchestra and under the ceiling.