A blend prepared by milling carbon black and a resin in a ball mill for about 300 hours is used as a paint in printing resistance elements on the miniature electronic circuit. Experimental results on the use of ultrasonic blending in place of the conventional ball mill blending in manufacture of this paint are reported in this paper. The auther classified the phenomena occurring during the blending process into the following three in discussion of the results. a)Pulverization of carbon black Fig. 2 to Fig. 4 are the photographs of carbon black in resin mixed during 2, 120 and 650 hours, respectively. In Fig. 4, particles of 10 microns remain after milling even for 650 hours. The photographs from Fig. 5 to Fig. 7 are results of treatment by ultrasonics for 2, 10 and 30 minutes. Fig. 7 shows the particles pulverized uniformly into a few microns. It proves that the ultrasonic method can disperse carbon black into the resin in a shorter time and better than the ball mill method. Fig. 8 is the graphs of milling time versus resistance value mixed by a ball mill and by a ultrasonics, and the results of treatment by ultrasonics indicate a decrease in the resistance value in a shorter time. b)Depolymerization of the resin Fig. 9 is the curves of milling time versus degradation of DC-996(silicone resin) by a ball mill and by ultrasonics. The viscosity of resin becomes lower in a shorter by ultrasonic method than by a ball mill. Table 1 shows the viscosity change of the various resins treated during 30 minutes by ultrasonics. The most suitable resin(DC-996) for paint recommended by B. L. Davis depolymerize most readily, as well as KR-272. c)Dispersion of carbon black Fig. 10(carbon black in ethyl alcohol), Fig. 11(carbon black in low viscosity resin), Fig. 12(carbon black in high viscosity resin), and Fig. 13(carbon black and inorganic matter in low viscosity resin) are the results of dispersion by the ultrasonic method respectivety. As indicated by the results, the degree of dispersion depends upon the solution, viscosity of resin and the amount of added inorganic matter. In Fig. 14 in which inorganic has been added, resistance becomes smaller with treatment time by ultrasonics.
The influence of Received March flow resistance of fibrous materials on their sound absorption characteristics has been investigated by measuring the flow resistance and the normal incident sound absorption coefficient. To deal with this subject from the point of view of several factors relating to the structure of fibrous materials, glass wool boards of various dimension made by three manufacturers(Table 1), five different non-woven fabrics sold on the market(Table 4), 31 different kinds of cotton fabrics woven out of the same yarn(Table 2)and eight kinds of felt made by a needle punch machine(Table 3)were used as sample. The apparatus shown in Fig. 1 was used to measure the specific flowresistance which is difined by the speed of pressure differential △P(dyn/cm^2) between two faces of a sample and the ratio of current V(cm/sec). The relation between the specific flow resistance R_v(dyn・sec/cm^3) of fibrous materials and V in a range of the low speed can be expressed by the experimental formula Eq. (2), where A_i and B_i are constants decided by the structure and the yarn density of a fabric or the thickness and the bulk density of a glass wool board. A_i can be suggested as a specific flow resistance R_s of the sample. The relation between the specific flow resistance R_vs(dyn・sec/cm^4) and the bulk density D_a(g/cm^3) of a fiber assembly can be given theoretically by Eq. (7). However, as a result of measurement it is evident that the specific flow resistance of the glass wool board of 2. 5cm thick was in proportion to D^<5/3>_a and, in case of thickness of 5. 0cm the power of D_a varied according with the manufacturers, as shown Fig. 3. The relation between the specific flow resistance R_s of glass wool board having the same thickness and the sound absorption coefficient for each frequency is shown in Fig. 6 and 7. Accordingly the absorption characteristics of a glass wool board can be detarmined by measuring the specific flow resistance. The maximum absorption coefficient on the frequency characteristic curve of the viscous resistance type is not affected by the depth of air layer behind the sample. The relation between the specific flow resistance R_s of fibrous materials and the maximum absorption coefficient is shown in Fig. 12. The maximum absorption coefficient of a fibrous material can be obtained from the specific flow resistance by using this curve, whatnever the structure of the fibrous materials may be.
A piston diaphragm is an ideal diaphragm for electoroacoustic transducers such as telephone transmitter and receiver. In order to realize the ideal diaphragm, the concentric part at the center of a circular diaphragm is bent into the form of a cone or a dome. As a result, the concentric part, which is rigid compared with the circumferential part of the diaphragm, performs a piston vibration. So a circular diaphragm with a concentric rigid at the center is adopted as the model of vibration analysis. Steep peak and dip of the frequency response curve are often observed in the neighbourhood of resonace frequency in measuring the displacement of diaphragm. This is explained by the fact that the resonance frequency of symmetrical mode, with which the rigid part at the center vibrates in translational motion and that of unsymmetrical mode with which the rigid part vibrates in rotational motion around the diameter of the rigid part are close to each other. The equation of motion and the boundary condition of the diaphragm of Fig. 1 are given by Eqs. 1 and 2 respectively. A general solution of Eq. 1 is represented by Eq. 3 and the displacement along the circle of radius b is given by Eq. 4. While the displacement along the same circle of Fig. 2 is given by Eq. 5. Comparison of Eqs. 4 and 5 shows that the displacement of translational motion is represented by Eq. 6 and that of rotational motion by Eqs. 7 and 8. The force acting on the boundary element of the rigid part is a uniform transverse force in the case of translational motion and a periodic transverse force with respect to angle θ in the case of rotational motion. Accordingly the boundary conditions along radius b are given by Eq. 13 and Eq. 14. On the basis of the displacements and the boundary conditions, the frequency equations 16 and 17 with respect to symmetrical mode and unsymmetrical mode respectively are obtained. Roots α_<m, n> (m=0, 1) called normal constants are shown in Fig. 3 as a function of β or γ. The relation between normal constants and angular resonance frequency is given by Eq. 18. If 4κ^2/a^2, the ratio of γ or β, is nearly equal to 1, where a is the radius of the diaphragm and κ the radius of gyration of the rigid part, then two steep peaks appear in about the same frequency of the frequency response curve. The diaphrams used in the measurement are simple diaphragms shown in Fig. 4 and that bent into the form of a cone or a dome. The curve(a) of Fig. 5 is the relative displacement of the center point of the rigid part and curve(b) is that of the circumferential point of the rigid part. Comparison of curves (a) and (b) shows that the first resonance corresponds to the resonance of the translational motion of the rigid part and the second resonance to that of the rotational motion. The relative displacement of the diaphragm used in the telephone receiver R-60 is shown in Fig. 9. These measured values are in good agreenment with the computed values.
This paper describes the acoustic design and characteristics of the sound echo chamber, which was recently constructed and taken into service by NET-TV Co. Features of the chamber:(1)In order to be entirely free from outside noise and vibrations, the bulding is isolated from other buildings and the room itself is supported by anti-vibration rubbers. The plan view is shown in Fig. 3. (2)The mortar-walled room has rectanglar shape and 86m^3 in volume. The ratio of length, width and height is fixed to 1:2^<2/3>:2^<1/3> so that a uniform distribution of the axial modes with respect to frequency may be attained. (3)Reverberation time of medium and high sound frequency is adjusted by up and down motion of a curtain hanging in the middle of the room. Adjustment of reverberation time of low sound frequency is done by varying the position and surface area of the motor-driven glass wool blocks placed at the three corners of the room. These adjustments are remotely controlled from the studio control room. Details of variable absorbers are shown in Fig. 5 and Fig. 8. (4)Various tones of echo are obtained by the combination of the places and mixing of four microphones available. (5)In order to improve the diffusion condition of the room, four boards for each of the sizes 910×910mm and 910×1820mm are hung. In order to limit the booming in low sound frequency region, two small pocket resonators having resonace frequencies of 50c/s and 80c/s are placed at the corners. (6)Reverberation characteristics are shown in Fig. 13, 14 and 15 respectively.