US2122587A - Acoustic device - Google Patents

Description

July 5, 1938.

A. s. RINGEL v ACOUSTIC DEVICE Original Filed July 20, 1925 INVENTOR ABRAHAM s. RINGEL BY TORNEY Patented July 5, 1938 UNITED STATES PATENT OFFICE ACOUSTIC DEVICE Abraham S. Ringel, Brooklyn, N. Y., assignor to Radio Corporation of America, a corporation of Delaware 6 Claims.

This invention relates to acoustic devices for use in reproduction of voice, music or other signals. It has for its object also the truer and more exact reproduction, constancy of volume and 5 in general more faithful likeness to the original than heretofore.

It is known that whenever a vibration was impressed upon any vibratile body that there are certain frequencies at which reproduction will be most efiicient while at all others more or less inefficiency occurs resulting in exaggeration of certain tones as well as other undesirable effects. This invention attempts toobviate these difficulties by so arranging the oscillatory member or 15 members that difierent elements of it will respond at their most efficient regions of vibration at different frequencies thereby causing the reproduction to be more uniform and of a more constant volume over a Wide frequency range as well 20 as giving greater sensitivity and efiiciency.

This invention also relates to telephony, telegraphy, and other allied arts. More specifically the arrangements herein disclosed represent what is commonly known as loud speakers or electrical reproducers and the like although it is not intended to limit its use to this particular field. It might as well be used with phonographs and other resonant reverberating systems. It is also useful wherever large amplitudes of vibration 30 are desired at or within the audio frequency range and which should be of constant value. This application is a division of a co-pending application filed by myself and John P. Minton on July 20, 1925, Serial Number 44,735, now Patent 35 No. 1,868,019, granted July 19, 1932.

Other objects and advantages will be apparent upon reading the following disclosure including specification, claims and annexed drawing.

7 The various figures of the drawing show dif- 40 ferent specific details as follows:

Fig. 1 shows a front view of one embodiment of the invention.

Fig. 2 shows a cross section of the adaptation of Fig. 1 along'the lines 2-2.

45 Fig. 3 is a graph of various characteristic curves of this arrangement.

In Figs. 1 and 2, numeral 2| denotes a conical frustrum mounted for free vibration and 22 denotes a similar but smaller frustrum mounted 50 for free vibration. These frustra are formed of some suitable material which combines light weight and rigidity such as paper, parchment, cardboard or other membranous material or light metal such as aluminum or duralumin. A mag- 55 net frame 25 supports at its front two cylindrical members l9 and 2!]. The outer cylinder I9 is set into a suitable opening in av baffle plate 3, which acts not only to support the entire cone system but also as a baflle to prevent sound radiated from the rear of frustrum 2| from mingling too 5 soon with sound radiated from the front thereof. This effect is more important at lower acoustic frequencies than at higher frequencies since at higher frequencies the diameter of the cone itself becomes comparable in value to the wave 10 length of the sound. Thus, at higher frequencies the cone itself tends to behave as a satisfactory bafile in preventing the sound waves emanating from the rear from affecting those emanating from the front face of the cone. For this reason it is not necessary to provide a baille for the inner conical frustrum 22 which is used principally to produce higher frequency sounds. The dimensions of the baffle 3 surrounding the outer frustrum 2| must be comparable to the wave length of the sound waves of lowest frequency that are to be radiated satisfactorily. Baffle 3 may be the front wall of a suitable cabinet which houses in addition a radio receiver or a phonograph using electrical means to reproduce sound waves from its records. Either or both the cylinders |9 and 20 may be completely closed thus confining the sound radiated from the rear of cones 2| and 22 or may have suitable openings 4 to permit the sound to escape into the open air.

The frame 25 is made of magnetic material and may be a permanent magnet or may be magnetized by coils 26 and 52 through which direct current from any suitable source may be passed. Frame 25 is formed with extended portions 29, 30 and 3| which are separated by the gaps. 32 and 33 in which strong or intense radial magnetic fields are produced. Located in these fields are the coils 21 and 28 which are secured to the rear ends of cones 2| and 22 and are designed to carry the signal or voice currents so as to be sensitive to the slightest change in. current. As the current in these coils changes, the magnetic fields associated therewith react with the strong magnetic fields existing in gaps 32 and 33 to cause corresponding vibrations of the cones. It is not intended to limit the method of mounting cones 2| and 22 to the cylindrical members shown as it is obvious that they may be mounted on any suitable support. Numeral 23 denotes a flexible disc with spirally cut holes to give it added resilience and is fastened at its center by means of screw or rivet 24 to the middle pole or magnet 25 and helps to center the vibrating system.

The disc 23 may be made of a very flexible material such as rubber or paper, or may be of metal. In any case, by choosing a suitable material having the desired rigidity for this disc, the vibrating system consisting of cone 22, coil 28 and centering disc 23 may be given a suitable fundamental resonance peak with resultant efficiency of vibration at some intermediate frequency range whose value will be determined by the combined mass of the cone and coil and the degree of stiffness of disc 23 and suspension H and the resistance to mechanical vibration of the complete system. By this means the characteristic curve 2 of Fig. 3 will be obtained, showing the variation with frequency of sound radiated from frustrum 22'. Similarly, the centering device for coil 21 and cone 2|, attached near the small end of cone 2| together with the suspension ll may be selected of the proper degree of stiffness or rigidity, so that when combined with the large mass of the cone 2|, it will produce a fundamental resonance peak at a much lower frequency than that produced by cone 22, as shown by curve I, Figure 3 and thus producing sound efficiently at these lower frequencies. Furthermore, the larger size of cone 2| enables it to radiate lower frequencies much more effectively. As shown in Fig. 2, the frustum 2| may be of such a size that the driving coil connected to its smaller base is larger in diameter than the larger base of the frustum 22. The increased response at the higher frequencies is caused by some higher order of vibration of the cone.

It has been found that due to the larger size and mass of cone 2| its main resonance frequency is lower than that of cone 22. If the apparatus shown in Fig. 2 be analyzed and the characteristics of its conical elements plotted taking the audibility as ordinates and the frequency in cycles per second for abscissas, a set of curves like those shown in Fig. 3 results. Curve I shows the sound characteristics of cone 2!, while curve 2 shows those of cone 22. When these two cones are operated jointly from any common operating means or by the same current passing through coils 21 and 28, the two characteristic curves will be superimposed upon each other giving a resultant represented by curve 3 which shows a smaller percentage of variation and no valleys as a and b, as well as greater sensitivity and broader band of frequencies covered satisfactorily.

While I have shown two vibrating diaphragms or cones, it will be understood that three or more vibrating members may be used in combination in order to make the audibility curve more constant in value over a very wide frequency range. It is not intended to limit the construction to the details shown but any other elements may be used which are well known and the characteristics of which are known to take the place of those shown. The greater the number of elements used and the more diversified their maximum values of audibility are in respect to frequency, the more constant will be the response. This arrangement could also be used with a phonograph or other similar device by attaching a needle or reproducer to the system of cones in a well known manner.

Having thus described my invention, what I desire to secure by Letters Patent is:

1. In combination a cone shape diaphragm, a second diaphragm mounted within the first named diaphragm whereby a compact operating unit is secured and separate means associated with each diaphragm for simultaneously vibrat ing said diaphragms.

2. In combination, two diaphragms of different mass mounted for vibration, means for vibrating said diaphragms simultaneously, a support, and a control member extending between one of said diaphragms and said support, said control member having such a spring factor as to make the diaphragm it controls resonant at a predetermined frequency.

3. An acoustic device comprising a magnet sys tem having a pair of concentric flux gaps, a pair of diaphragms arranged one within the other, a driving coil connected to each diaphragm and means for supporting said diaphragms so that one driving coil lies within one of said flux gaps and the other driving coil lies within the other flux gap.

4:. An acoustic device comprising a magnet system including a central pole piece, an outer pole piece and an intermediate pole piece, said pole pieces being spaced from each other so as to form an inner and an outer flux gap, a pair of diaphragms, a driving coil connected to each diaphragm, a supporting member secured to said intermediate pole piece, one of said diaphragms being flexibly supported from said supporting member so that its driving coil lies within the inner flux gap, and a second supporting member secured to said outer pole piece, the other diaphragm being flexibly secured to said second supporting member so that its driving coil lies Within the outer flux gap.

'5. An acoustic device comprising a pair of diaphragms, each of said diaphragms having the shape of a frustum of a cone, a driving coil secured to the smaller base of each of said frustum shaped diaphragms and means for supporting said diaphragms one within the other, one of said diaphragms being of such a size that its greatest circumferential dimension is smaller than the circumference of the driving coil of the other diaphragm.

6. An acoustic device of the electro-dynamic type comprising a frustum shaped diaphragm, a driving member secured to the smaller base thereof, means for supporting said diaphragm, means for supporting a second diaphragm extending through said driving member and having a smaller diameter than the diameter of said driving member, and a second frustum shaped diaphragm supported from said last mentioned means.

ABRAHAM S. RINGEL.

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