US2458038A - Acoustical apparatus - Google Patents

Description

Jan. 4, 1949.

3 Sheets-Sheet 1 Filed Aug. 29, 1942 Bnventor KMANN Gttomeg 1949- J. E. VOLKMANN ACOUSTICAL APPARATUS 3 SheetsSheet 2 Filed Aug. 29, 1942 4 Summer JOHN E. MILK/v N (Ittorneg J. E. VOLKMANN ACOUSTICAL APPARATUS Jan. 4, 1949.

5 Shee ts-Sheet 5 Filed Aug. 29, 1942 JOHN I 1 0mm??? (Ittorncg Patented Jan. 4, 1949 ACOUSTICAL APPARATUS John E. Volkmann, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application August 29, 1942, Serial No. 456,627

'1 Claims. 1

This invention relates to acoustical apparatus, and more particularly to horn structures for auditorium loud speakers.

It is well known that sound reproduction in the average auditorium or theatre calls for the use of directional loud speakers which give a high ratio of direct to reflected sounds if a high degree of intelligibility is to be obtained. In the early days of sound motion pictures and other similar types of reproduction, the directional loud speakers employed were not uniformly directional with frequency, being more directional at the high frequencies, with consequent distortion in the frequency balance at the seats located on the sides of the front rows. In the development of the art, cellular high frequency loud speakers were later provided which givea more uniform characteristic and overcome the lack of coverage at the side seats in the front of the auditorium. While giving adequate spread for the front seats, the cellular loud speaker arrangement has too great a spread for the more remote seats, with the consequent result of directing too much sound energy to the side walls from which reflections are obtained. In addition, due to the approximately spherical distribution pattern of the cellular loud speaker arrangement, the remote seats suffer some loss in sound level as compared to the front seats.

The primary object of my present invention is to provide an improved horn structure for auditorium loud speakers which will not be subject to the aforementioned disadvantages.

More particularly, it is an object of, my present invention to provide an improved horn structure for loud speakers which will have improved distribution characteristics.

Another object of my present invention is to provide an improved horn structure for auditorium loud speakers which will radiate its energy directly to and uniformly for all parts of the auditorium and with the least waste due to sound radiating beyond the confines of the seating area which, indoors, usually gives rise to unnecessary reflections.

Still another object of my present invention is to provide an improved horn structure for auditorium loud speakers the directional pattern of which can be fitted to the distribution requirements of the auditorium or other seating area or space in which it is to be used.

It is also an object of my present invention to provide an improved horn loud speaker as aforesaid Which is relatively simple in construction and highly efficient in use.

In accordance with my present invention, I

provide a horn structure comprising a plurality of horns, or rows of horns, each associated particularly with a preselected seating area of the auditorium, and each of which is arranged to have a distribution angle corresponding to the angle subtended at the loud speaker by the various rows of seats or seated areas of the auditorium with which each horn row is associated. The several horns or rows of horns, as the case may be, are

contiguous to each other to prevent phase shift and are so arranged that energy per unit area at the seats is made uniform for the entire seating arrangement, the ratio of direct to reflected sounds being maximum since all of the radiated energy is directed to the seats before reaching the Walls. Such a distribution characteristic can be very nearly approximated by stacking several horns in a plurality of rows or layers in pyramid fashion such that the distribution angle of each layer corresponds to the average distribution required by the area to which'the energy is radiated, it being assumed that the energy fed into the throat of each. horn layer is either equal, or preferably in proportion to the respective areas covered by each horn layer. Each row or layer of the pyramida1 arrangement consists of one or more horns arranged to provide approximately a radially expanding cylindrical Wave front, and each row or layer of horns covers a different, preselected area of the auditorium.

In one form of my present invention, the pyramid horn may be of cellular construction with an appropriate number of individual cells or horns in each row, the number of cells in each row decreasing in an upward direction and the individual horns all facing in a slightly different direction so chosen as to provide a cylindrical wave front for each layer of horn cells or approximately a spherical wave front for the aggregate of horns. The distribution angles of the several horn layers are such that a progressively sharper angle of distribution is obtained from the lowermost to the uppermost layer.

In another and preferred form of my invention, a single horn is provided for each row or layer, each of the horns again expanding radially to give a cylindrical wave front and preferably having the same rate of flare, the same throat area, and the same mouth area. However, the angle of flare and the aspect ratio (that is, the ratio of width to height) of the mouth area of each horn differ in each case in a manner to provide horizontal and vertical distribution angles for the respective horns which are progressively sharper as the uppermost horn is approached. With this form of my invention, a wide distribution pattern is obtained such as may be obtained by the use of a cellular or diffuser construction, but without the inherent disadvantages of the cellular construction referred to hereinafter in greater detail. With either form of my invention, the directional pattern of the loud speaker may be custom fitted, so to speak, to the distribution requirements of the auditorium or other space in which it is to be used, or to some particular area thereof which is to be covered. This may be accomplished either (a) by a suitable combination of horns and/or driving units, (b) by positional (that is, phase) adjustment of the horns and/or units, or (c) by a combination of both (a) and (b).

The novel features that I consider character istic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof will best be understood from the following description, when read in connection with the accompanying drawings in which Figures 1 and 2 are diagrammatic top plan and side views of an auditorium with reference to which the principles involved in the present invention are explained hereinafter,

Figure 3 is a top plan view of one form of loud speaker horn structure constructed in accordance with my present invention,

Figure 4 is a front elevation thereof,

Figure 5 is a side elevation thereof,

Figure 6 is a front elevation of another form of horn structure constructed in accordance with my present invention,

Figure 7 is a top plan view of the latter form of my invention,

Figure 8 is a central sectional view of the latter form of my invention taken on the line VIII-VIII of Figure '7, and

. Fig. 9 is a view similar to Fig. 8, but only partly in section, and showing a somewhat different form of horn structure constructed in accordance with my present invention.

Referring more particularly to the drawings, there is shown, inFigures 1 and 2, an auditorium I, such as a theater having an orchestra 3, a balcony 5 and stage 1 at one end above which may be located a moving picture screen or the like 9. Behind the screen 915 a loud speaker H constructed in accordance with my present invention and'described in greater detail hereinafter.

From an inspection of Figure 1, it will be evident that, in order to cover all of the seats in the front portion of the orchestra 3, that is, the seats in the vicinity of the stage I, it is necessary that the loud speaker II should have a relatively wide horizontal angle of distribution A1. If the loud speaker H were to distribute sound over only the angle A1, it is obvious that the seats in the rear of the orchestra and in the balcony would receive a considerable quantity of sound reflected from the walls of the auditorium instead of receiving mostly direct sound, as would the front seats in the orchestra. If, however, the loud speaker II can be made to cover different portions or areas of the auditorium in each of which the seats would receive direct sound, improved results will be obtained. This can be accomplished by providing a loud speaker which will have a different angle of distribution to various parts of the auditorium, as represented by the horizontal angles A2 and As, the angle A2 embracthe uppermost row I6.

ing approximately the mid-portion of the auditorium and the angle m embracing the rear of the auditorium. Thus, it will be seen that the angles A1, A2, and A3 are progressively smaller in the order named.

In a vertical direction, it is also desirable to have the loud speaker I I distribute the sound directly to and uniformly over all parts of the auditorium. This may be accomplished by having various portions of the loud speaker radiate the sound over various distribution angles which cover various areas, such as those embraced within the vertical angles B1, B2, and B3 in Figure 2. Here, again, the angles Bl, B2 and B3 are progressively smaller in the order named, the angle B1 embracing the front part of the orchestra, the angle B: embracing the rear part of the orchestra (and, if necessary, the front part of the balcony as well) and the angle B; embracing the balcony, or at least the rear portion thereof if the angle B2 also embraces the front portion of the balcony.

One form of loud speaker which will accomplish the foregoing results is shown in Figures 3, 4 and 5. This comprises a plurality of contiguous rows l2, I4 and I6 of individual horns l'l stacked on each other in pyramid fashion, as clearly seen in the drawings. The horns ll all have the same rate of flare, the same mouth area, the same throat area, and the same length, and each has, individually, the same angle of flare. Depending on the requirements of the particular auditorium where the horn structure is to be used and on the position of the horns, there may be provided one or more individual horns ll (public address and sound reenforcing loudspeakers are usually overhead or to the sides of the proscenium) in each of the rows l2, l4 and IS, the horns I? each constituting a cell of the horn structure. The axes of the individual horns are angularly related to each other, as is best evident from Figure 4, and the horns are so arranged as to provide approximately a radially expanding wave front. Each layer or row of horns expands radially in a horizontal direction only, so that the wave front provided thereby expands cylindrically. However, the several rows may expand substantially radially in a vertical direction as well, in which case the wave front could be considered as expanding spherically. In any case, the greatest number of horns will normally be in the lowermost row l2 and the smallest number of horns will be in the uppermost row l6. Thus, it is apparent that the several horn rows have different distribution angles which are progressively smaller or sharper from the lowermost row l2 to The several horn layers I2, l4 and It may be enclosed within a suitable casing IS the back of which carries one or more throats II by means of which the several horns l1 may be connected to a single driver 23. Any suitable combination of drivers and throat couplings may, however, be used.

The horn row [2 is directed downwardly and embraces the angle Bl. Since this row requires the widest side-to-side or horizontal distribution angle A1, it is provided with the greatest number of horns. It is obvious that the horn row 11 will therefore cover the front rows of the orchestra adequately and will radiate direct sound thereto. In the row I4, the horns I! are so arranged that they will radiate sound directly to the rear portion of the orchestra. Since this row need only embrace the angle A2 from side to side, a smaller number of horns suflices therefor. The smallest horn row l6 embraces the smallest horizontal dis- The form of my invention just previouslydescribed is open to the objection that the energy radiated by each horn row or layer is proportional to the number of its cells. Consequently, the top layer I6 may not radiate sufificient energy for the remote seating areas in the rear portion of the balcony. To overcome this objection, the form of my invention shown in Figures 6, '7 and 8 may be employed. In this form, each horn layer is constituted by a single discrete horn, thelowermost horn 3i having the greatest angle of distribution from side to side, the intermediate horn 33 having a relatively smaller, angle of distribution from side to side, and the topmost horn 35 having the smallest angle of distribution from side to side. Here, again, the horns 3|, 33 and 35 are contiguous to each other to prevent phase shift and are stacked on each other in pyramid fashion, The three horns 3|, 33 and 35 face in different directions, the horns being so related to each other that when the horn 3| faces downwardly, the horn 33 faces forwardly, and the horn 35 faces upwardly. In each of the horns 3|, 33 and 35, the rate of flare is substantially the same, as are also the areas of the throats and mouths of the respective horns. A single throat member 31 may be connected to the throat ends of the horns 3|, 33 and 35 and connects these horns to one or more suitable drivers 39, only one driver being shown in Fig. 8 for the sake of illustration.

Each of the horns 3|, 33 and 35 is constructed to provide a radially expanding wave front from side to side. However, the angle of flare of each of the horns in this modification differs, as does also the aspect ratio of their mouth areas, that is, the ratio of the width to the height of the mouth. By suitably proportioning the mouths of the horns, appropriate horizontal and vertical angles may be obtained which are progressively sharper from the lowermost horn 3| to the uppermost horn 35. It will be noted, from an inspection of Figure 8, that the axes of the horns 3| 33 and 35 are angularly related to each other in a common, vertical plane. It will also be noted that the angle X between the axes of the horns 3| and 33 is greater than the angle Y between the axes of the horns 33 and 35. These axes may be so located as to provide the coverage for predetermined areas of the auditorium. In one construction, for example, the angle X was approximately degrees and the angle Y was approximately degrees, the horn structure having had an overall length of 23 inches from the mouth of the horn 33 to the rear end of the throat member 31. In the same construction, the horn 3| had a horizontal spread of 120 degrees, and its mouth was four and a half inches high; the horn 33 had a spread of 90 degrees, and its mouth had a height of 6 inches; and the horn 35 had a horizontal spread of 60 degrees, and its mouth had a height of 9 inches. The initial throat area of each horn was one inch high by four inches wide.

Since the directional characteristics of an aggregate of horns at certain frequencies, especially the lowerand mid-range frequencies, depends not only on the directional properties of the individual horns but on the amplitude and phase relations between the horns as well, the directional pattern of the loud speakers herein described can be controlled somewhat by adjusting the lateral and vertical position of the horns relative to each other, as well as by their angular position. Also, with the horns fixed in position, some adjustment of the wave front -(and hence the directional pattern of the wave leaving the loud speaker) can be .obtained by adjusting the phase relation between the driving units, either by acoustical means (spacing, path length, etc.) or by suitable electrical means.

Although I have shown and described two embodiments of my invention, it will be apparent to those skilled in the art that many other modifications, as well as variations in the particular modifications described, are possible. For example, any suitable number of horns may be provided in each row, either with the cellular type of Figs. 3 to 5 or the other type shown in Figs. 6 to 9. It is also obvious that the number of horn rows, the rates of flare, the sizes of the horns, the angles of distribution, and the direction in which each horn or horn row is oriented may be varied to suit the requirements of the particular auditorium or other space or enclosure where the loud speaker is to be used. In certain cases, it may be found desirable to use direct radiators without horns in one or more of the horn rows in place of the horns. Hence, wherever the term sound radiator is used in this specification, it is intended to mean either a direct radiator used without a horn, or the horn itself, as the case may be. Also, in certain cases, it may be desirable to arrange the horns in juxtaposed relation instead of in superposed relation, as in Figs. 6 and 8. Furthermore, in connection with the modification shown in Figs. 6 to 8, the flare of each horn could be either the same or different, as may be most suitable, and a separate driver may be provided for each horn or layer, as shown by the separate drivers 4|, 43 and 45 of Fig. 9, all the drivers being connected to and fed from a common signal source 41 and the power delivered to each driver being either the same or difierent depending upon the distribution required. Other variations will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In sound reproducing apparatus, a plurality of discrete horns arranged in superposed relation with their axes angularly related to each other in a comon plane, said horns thereby all facing in different directions, said horns each having an angle of distribution from side to side which is of different magnitude than that of any other of said horns, each of said horns expanding radially over its said distribution angle, and said horns all having substantially the same mouth and throat areas and substantially the same rate of flare and being adapted to be fed from a common signal source.

2. The invention set forth in claim 1 characterized in that the magnitude of the angle of flare of each of said horns in said common plane is different.

acsaose 3. The invention set forth in claim 1 characterized in that the aspect ratio of the respective mouth areas of said horns differs for each horn.

4. The invention set forth in claim 1 characterized by the addition of a throat member, and characterized further in that the throat ends of the respective horns are all connected to said throat member whereby said member is common to all of said horns.

5. The invention set forth in claim 1 characterized in that the angles between the axes of adjacent horns vary progressively, the angle between the axes of the two lowermost horns being smallest, and the angle between the axes of the two uppermost horns being largest.

6. Sound reproducing apparatus according 'to claim 1 wherein said horns are arranged pyramid fashion and are adapted to be located adjacent one end of an auditorium, each of said horns in association with a preselected and different area of said auditorium, and the distribution angle for each horn corresponding to the angle subtended by the area associated therewith.

7. Sound reproducing apparatus according to claim 1 wherein said horns are arranged pyramid fashion and are adapted to be located adjacent one end of an auditorium, each of said horns in association with a preselected and different area of said auditorium, the distribution angle for each horn corresponding to the angle subtended by the 8 area associated therewith and said distribution angles being progressively sharper from the lowermost to the uppermost of said horns.

JOHN E. VOLKMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,384,612 Gray July 12, 1921 1,684,975 Slepian Sept. 18, 1928 1,768,226 Williams June 24, 1930 1,776,902 Harrison Sept. 30, 1930 1,812,878 Karnes July 7, 1931 1,825,166 Sullivan Sept. 29, 1931 1,871,531 Kellogg Aug. 16, 1932 1,934,932 Lindenberg Nov. 14, 1933 1,992,268 Wente Feb. 26, 1935 2,045,180 Douthwaite June 23, 1936 2,089,391 Marion Aug. 10, 1937 2,127,110 Farrand Aug. 16, 1938 2,135,610 Wente Nov. 8, 1938 2,174,163 Olson Sept. 26, 1939 2,175,833 Farrand Oct. 10, 1939 FOREIGN PA'IE'NTS Number Country Date 20,797 Great Britain 1900

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