US2109012A - Acoustical device - Google Patents

Description

Feb. 22, 1938. A. E. N LAWRANCE 2,109,012

ACOUSTICAL DEVICE Filed Feb. 27, 1956 2 Sheets-Sheet 1 Feb. 22, 1938 A. E. N. LAWRANCE 1 ACOUSTICAL DEVICE Filed Feb. 27, 1936 2 Sheets-Sheet 2' Patented Feb. 22, 1938 ACOUSTICAL DEVICE Athol Ernest Neville Lawrance, Johannesburg,

Transvaal, Union of South Africa Application February 27, 1936, Serial No. 66,100

8 Claims.

The present invention relates to acoustical devices such as microphones, loud speakers, horns, cabinets, phonographs and musical instruments, and its object is to provide even response and entire non-resonance to sound waves of the different frequencies employed in speech and music.

According to the invention, an acoustical device comprising a channel or tube having a conical, prismatic, cylindrical or like shape and successive longitudinal elements of the device vary in stiffness and form a continuously progressive series embracing the whole cross-sectional periphery of the device.

Embodiments of the invention are illustrated in the accompanying drawings in which:

Figure I shows a speech coil in perspective.

Figure II is a plan view of an unfolded speech coil.

Figure III shows a cross-section of the speech coil of Figure II.

Figure IV shows a modified construction of speech coil.

Figure V shows a cross-section of Figure IV.

Figure VI shows a horn construction in perspective.

Figure VII is an end view of the horn of Figure :VI.

Figure VIII is an end view of a modified construction of horn.

Figure IX is a plan of another horn construction, and

Figure X shows a transverse section of the horn of Figure IX.

Figures XI and XII show other modified forms of speech coil or channel.

Figures XIII to XVI show other modified forms of speech channel.

Referring to Figure I, this shows a speech coil former of cylindrical shape, a portion 2 of which is occupied by a coil of wire 3 to which connections aremade by leads 4 and 5. A speech coil wound on a cylindrical former in this manner may be employed in a moving coil loudspeaker or a moving coil microphone, as is known. The former on which the coil is wound is made of stiff but very light material and comprises successive longitudinal elements which vary in stiffness and form a continuously progressive series embracing the whole cross-sectional periphery of the former. This variation in stiffness may refer to the whole of the former but in\ the arrangement shown in Figure I it applies only to the unwound portion 6. Figure II shows the former unrolled. The portion 2 is the wound portion and the portion 6 is the unwound portion, the successive elements], 8, 9

and I of which vary in stiffness. The variation in stiffness is effected by making these portions of different thickness as shown in Figure 111.

The speech coil is preferably constructed by taking a plain cylindrical or other shaped former, of uniform stiffness around the whole of its cross-sectional periphery comprising the whole area 2, 6 and attaching to the portion 6 successive strips of very thin material, such as tissue paper, by means of glue or other adhesive. The first strip 9, greatest in length viz. of the length of the circumference of the former, is then applied in the manner shown in the drawings. A second strip 8, the length of the circumference of the former is then superimposed and a third strip I, the length of the circumference of the former is then superimposed on the other two. The leads 4 and to the coil of wire are secured to the thickest part I of the former. The use of three separate additional strips has been shown, but any number suitably varying in length may be used. Due to their different thicknesses and mass, the different longitudinal elements of the speech coll have differcut stiflnesses and elasticity and therefore respond differently to the various speech frequencies employed, the result being that the overall response is very even and free from resonance. Owing to the use throughout of extremely thin material for the portion 2, 6 and for the laminatlons superimposed thereon, the speech coil former can be made very light in comparison with known types of speech coil formers.

In the arrangement of Figure IV the portion 6 of the speech coil comprises longitudinal elements of different stiffnesses as before, but in this case the variations in stiffness are produced by corrugations in the different sectors: for example the sector H has only four corrugations; the element 12 has eight corrugations; the element l3 has twelve corrugations and the element I4 has sixteen corrugations; these corrugations all being of the same length, and height as shown in Figures IV and V. Alternatively the difference in stiffness may be produced by making the corrugations lie at an inclination to the direction of the axis of the coil or by making them of different height or length or thickness. It will be noted that the superficial area of each longitudinal element is different, the area of an element with a large number of corrugations being greater than that of an element with a small number of corrugations.

Figure VI shows a horn with a progressive variation of stiffness which is produced by a progressive variation in thickness of the wall of the horn around its'circumference. This variation is shown as being uniform in the drawings but may take place in a series of steps as in the case of the speechcoil. An end view of the horn of Figure VI is shown in Figure VII and it will be noted that the stiffness of quadrant l5 exwill be non-resonant.

ceeds the stillness of quadrant ii, the stiifness oi quadrant l1 exceeds the stiffness of quadrant I5 and the stifl'ness of quadrant l8 exceeds that of ll. Figure VIII shows a similar construction in which the surface of separation between the thinnest and thickest parts of the wall of the horn occurs inside the horn instead of outside. Alternatively, the horn may have a prismatic form so that its cross-section forms a polygon the sides of which vary in thickness and form a continuously progressive series.

Figure IX shows a born with a wall I9 01' uniform thickness, the variations in stiflness in this case being produced by stiffening ribs 20 placed externally, the separation of the ribs being progressively increased around the circumference of the horn as shown in Figure X. Alternatively the stiii'ening ribs 20 can be placed inside. the horn, or the variation in stiflness maybe produced by means of corrugations in the manner described with reference to the speech coil of Figure IV.

Element ll] of Figure 11 and element l8 of Figure VII are both of very thin construction and for this reason will assist in the reproduction of a band of very high frequencies. Similarly element 9 of Figure II and element ii of Figure VII will assist in reproduction of a band of tones of lower frequency than element 10 of Figure II and element It of Figure VII, and so on. Each of the four portions as marked off in the drawings will be resonant to a band of different frequencies and provided such four bands of frequencies are separated and do not overlap one another the device The elimination of resonance from sound channel devices is the principal object of this invention and devices constructed according to the invention show great advantage over other methods in use today.

Figure XI shows an alternative form of speech coil former the cross-section 01' which is an irregular polygon. The sides M, 22, 23, 24, 25, and 26 progressively increase in width and thus form elements which progressively increase in stiffness.

Figure XII shows an alternative form of speech coil former the cross-section of which is a regular polygon. The sides 3i, 32, 33, 34, 35 and 36 progressively increase in thickness as shown and thus form elements which progressively increase in stiffness.

The construction of Figures XI and XII and also a construction of circular cross-section similar to Figure I may also be used as sound channels for conducting sound.

Figures XIII and XIV show loud-speaker horns in which the progressive variation in stillness is obtained in the same way as in Figures XI and XII respectively.

Figure XV shows a rear view of a construction of sound channel which is similar to that of Figure XII but used to form the sides of a cabinet for housing a loud-speaker 40. A progressive variation in the stiffness of the walls of the cabinet is obtained by the use of stifieners 4| 42, 43 and 44 of different thickness; these may be made of wood or more suitably of sound absorbing material.

Figure XVI shows a somewhat similar construction of cabinet for a loud-speaker 40 to Figure XV but in this case the variation in the thickness (and consequently the stifl'ness) of the walls is obtained by building up the walls of varying layers 01' wood or sound absorbing material. The use of ribs, however, progressively spaced, appears advantageous in the construction of wireless cabinets. The principle of this invention also applies in regard to the elimination of resonance and echo from auditoriums and music halls. Many other modifications may be resorted to. without departing from the spirit of the invention, and I desire therefore to claim the invention broadly, limited only by the scope of the appended claims.

I claim:

1. An acoustical device comprising a sound channel the wall of which progressively varies in thickness around its cross-sectional periphery, thereby providing a progressive variation in stifl ness around the cross-sectional periphery of the device.

2. An acoustical device comprising a sound channel the walls of which progressively increase in stiffness around the periphery of each crosssection taken along its axis, from a point of minimum stifi'ness to a point of maximum stiiiness.

3. An acoustical device comprising a tapering sound channel of similar cross-section at each point along its axis, the wall of said sound channel increasing progressively in stiffness around the periphery of each cross-section from a point of minimum stiffness to a point of maximum stillness.

4. An acoustical device for guiding the passage of sound waves through a volume .of air comprising a tapering sound channel of circular crosssection at each point along its axis, the wall of said sound channel increasing progressively in thickness around the periphery of each crosssection from a. point of minimum thickness to a point of maximum thickness.

5. An electro-acoustical device comprising a cylindrical tube having a coil of wire wound thereon, the wall of said tube increasing progressively in thickness around the periphery of each crosssection from a point of minimum thickness to a point of maximum thickness but remaining constant in thickness along any axial section of said wall.

6. An acoustical device provided with a peripheral wall embracing a volume of air and forming an inlet opening and an outlet opening at opposite ends of the axis of said device, said peripheral wall progressively increasing in stiffness around the periphery of a cross-section taken along its axis, from a point of minimum stiffness to a point of maximum stiffness.

'7. An electro-acoustical device comprising a cylindrical tube having a coil of wire wound thereon, the wall of said tube being provided with longitudinal corrugations which are so chosen that said wall progressively increases in stiffness around the periphery of a cross-section taken along its axis, from a point of minimum sti finess to a point of maximum stifi'ness.

8. An electro-acoustical device comprising a cylindrical tube having a coil of wire wound thereon, the wall of said tube comprising a plurality of layers of different widths but of the same axial length so as to cause a progressive variation in thickness around the periphery of a cross-section taken along its axis, from a point of minimum thickness to a point of maximum thickness.

ATHOL ERNEST NEVILLE LAWRANCE.

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