Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 34 ACOUSTICAL RADIATING SYSTEMS where d = the distance between the center of the mouth of the horn and the reference plane X'O'Z', in centimeters, and X = wavelength, in centimeters. The vectors, having amplitudes Ji, Ai, Az, A^, etc., determined from the directional characteristics and having phase angles ^i, d^, 6s, Oa, etc., determined from equation , are added vectorially as shown in Fig. This method of predicting the directional characteristics assumes that there is n
Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 34 ACOUSTICAL RADIATING SYSTEMS where d = the distance between the center of the mouth of the horn and the reference plane X'O'Z', in centimeters, and X = wavelength, in centimeters. The vectors, having amplitudes Ji, Ai, Az, A^, etc., determined from the directional characteristics and having phase angles ^i, d^, 6s, Oa, etc., determined from equation , are added vectorially as shown in Fig. This method of predicting the directional characteristics assumes that there is no interaction between individual horns which changes the com- plexion of the velocities at the mouth from that which obtains when operating an individual horn. Obviously, this condition is not absolutely satisfied. Apparently, the discrepancy has no practical significance be- 250^ 500<v lOOO'V Fig. , Directional characteristics of the 15-cell cellular horn shown in Fig. in a plane containing the line B-B' and the axis of the center horn. The polar graph depicts the pressure, at a fixed distance, as a function of the angle. The pressure for the angle 0° is arbitrarily chosen. cause it has been found that this method of analysis agrees quite well with experimental results. The directional characteristics of the cellular horn of Fig. are shown in Figs. and Above 2000 cycles the dimensions of the total mouth surface are several wavelengths and the directional character- istics are fairly uniform and defined by the total angular spread. Where the dimensions are comparable to the wavelength the directional char- acteristics become very sharp, as shown by the polar curves for 500 and 1000 cycles. Then, as the dimensions of the surface become smaller than the wavelength, 250 cycles, the angular spread broadens, as is illustrated by the larger spread for the smaller vertical dimension when compared to the smaller spread for the larger horizontal dimensi
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