US2001089A - Horn - Google Patents

Description

D. G. BLATTNER aoim Filed April 7, 1933 3 Sheets-Sheet 1 FIG.

INVENTOR D. a. BLATTNER' 11 nzronlvsy May 14, 1935. D. s. BLATI'NER HORN Filed A ril 7. 1933 :5 Sheets-Sheet 2 FIG? IN l/E NT OR 0.6. BLA TTNER TORNE Y May 14, 1935. D. s. BLATTNER HORN 3 Sheets-Sheet 3 Filed April 7, 1933 zz zo 27 Ba mvs/vron D. G. BLA TTNER W v M Patented May 14, 1935 2,001,089

UNITED STATES PATENT OFFICE norm David G. Blattner, Mountain Lakes, N. 1.. aslignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 7, 1933, Serial N... 664,891 14 claims. (ci. 181-27) This invention relates to horns and more'par what comparable to the dimensions of the pasticularly to horns suitable for the transmission sages. In this way the radiation resistance of of speech and music such as are used with the horn mouth and hence its low frequency phonograph reproducers and loudspeakers. eiliciency will be made greater than that of a One object of the invention is to provide a single mouth opening having the same area as 5 horn which will give a uniform distribution of the combined area of the openings in the dithe sound energy at all frequencies over a large vided hom, without excessively increasing the area. horn dimensions.

Another object is to increase the eiliciency of A horn made in accordance with this inventhe horn as a sound radiator at low frequencies. tion has a sound field prac i uniform in a 10 It is well known that in conventional loudcommercial sense covering a spread of 90 as sneaker horns thesound waves of low 'frequencompared with 30 for a similar horn of single cies are radiated from all parts of the mouth mouth opening having a sound passage of the of the horn but that as the frequency is insame dimensions and taper.

creased the waves become more and more con- In the drawings: 15

centrated so that the highest frequencies are Fig. 1 shows one form of folded exponential Droiected as a narrow beam with the result horn having its bell portions successively subthat the quality of complex sound, such as divided to reduce the directional effect; music, varies greatly with the position of the Fig. 2 is an elevation, partly in section along ne n the sound field. A much more unlthe line 22 of Fig. 4, of a common commercial 20 form distribution of the sound energy at all he horn showing a relatively inexpensiv r quencies is obtained according to this invention merit of partitions for approximating the enby "ranging in the mouth of the horn vertical, ergy distribution obtained in the horn of Fig. 1; diverging partitions extending back into the Fig. 3 is a view looking into the mouth of the horn far enough to intercept efiectively the horn of Fig. 2 showing the fixed partition walls 25 waves of both high and low frequencies. In for improving the low frequency response; and this way the high frequency waves are conduct- Fig. 4 is a sectional view along the line 4-4 ed to the various portions of the horn mouth of Fig. 2 showing the arrangement of the tapered and projected along with the low frequencies p rtition Wa lsmore uniformly over the desired area. Pref- The more uniform distribution of the high 30 erably, the total cross-sectional area of the horn frequency waves according to this invention, will 7 increases logarithmically at the same rate be more clearly understood by considering first throughout its lengt the fundamental requirements of such distri- It is also well known that if a horn is to be bution and then the manner in 'which these .eflicient for low frequencies down ,to its cut-015i, requirements are met in a practical structure; 35 the horn mouth dimensions should be large in If it were possible to provide a spherical source comparison with the wave length of the cut-off of sound, thatis, a source consisting of a sphere frequency. For the eflicient radiation of the the surface of which has a radial vibratory very low frequencies required in reproducing motion in phase at every point of the surface at 40 high quality music this means that the horn all frequencies, sound would be radiated uni- 40 month should be very large. In commercial de-' formly outward in all directions from the center 8 8118,!!! order to limit costs and space requireof the sphere. If further the vibrating surface ments to reasonable proportions, it is common of the sphere is'traversed by the walls of a pyrapractlce to limit the mouth opening to less than mid having its vertex at the center of the spherev the optimum dimensions. the sound distribution will not be affected there- 4 Applicant has found that, for low frequencies, by. Throughout the space included within the two identical, conventional loudspeakers conpyramid the sound distribution will not be nected in parallel to a source of power will prochanged if. that part of the spherical source duce more sound than one of the speakers opernot intercepted by the pyramid is removed.

ating alone and drawing the same electrical Furthermore, the sound distribution within this 50 power as the two operating in parallel. In acspace will be altered only slightly if the boundcordancetherefore with an important feature of ing walls of the pyramid are removed provided the invention the subdivided passages compristhe superficial dimensions of the spherical seging the horn mouth are separated from each ments within the pyramid are large compared other by partition walls of a thickness somewith the wave length of the radiated sound. 5

From this reasoning it is seen that in order to get the ideal distribution of a spherical source within a region defined by a certain solid angle, it is necessary and sufficient that over a spherical surface having its center of curvature at the vertex of the angle and having an area whose superficial dimensions are large compared with the wave length of sound, the radial motion of the air on this surface'shall vibrate at equal amplitudes and in phase.

Since in practice a horn is driven by a receiver unit in which the diaphragm sets up a plane 'wave in the throat of the horn the problem resolves itself into one of causing the sound waves of all frequencies of interest to emerge from the mouth of the horn in phase on a spherical wave front and with a uniform distribution over a length of are at least comparable to the longest wave length to be transmitted. This condition is approximated by successively subdividing the bell portion of the horn in at least one plane so that the subdivided passages are kept small enough to prevent undue concentration of the higher frequencies in any passage. If the horn mouth is contoured as in Fig. 1 so that the several paths are all of the same length, the sound waves will be projected as a series of separate waves which merge into a single "were :cnforining substantially to the contour of the mouth opening and moving outwardly as if originating at the virtual source In.

The expressions horn throat and horn mouth are used to designate in a general way the portions of the horns adjacent the receiver unit and the mouth opening respectively but since the cross-sectional area of the horn increases at the same rate throughoutits length, there is no definite dividing line between these portions. The horn of Fig. 1 is composed of two sections 36 and 31 and the throat portion may be considered as consisting of the section 35 and possibly a small part of section 31. The horn of Fig. 2 is composed of three sections 38, 39 and 23 and the throat portion may be considered as consisting of section 38 and possibly a part of section 3G.

The central subdividing partition H extends backward toward the receiver unit I2 to a point where the cross-section of the horn is so small that the wave front is substantially planar for all frequencies. As the horn expands the width of each subdivision becomes comparable to the wave length of the higher frequencies and another partition such as 13 is required to prevent undue concentration of these frequencies. These channels are again subdivided as by walls l4 and i5 so that each of the sixteen openings at the mouth of the horn will emit a wave containing all the component frequencies of the sounds being reproduced. It will be understood, of course, that the number of partitions used in any given horn will depend upon the range of frequencies to be covered and the permissible variation from the ideally uniform distribution.

In the horn shown in Figs. 2', 3 and 4 the general principles discussed above have been applied to a commercial structure to approximate the desired distribution without resorting to an unduly expensive construction. The long partitions 2|, 22 divide the entrance to the mouth portion 23 of the horn into three substantially equal parts so that a considerable proportion of the high frequency energy is diverted into the lateral passages 24 and 25. Each of these passages is again subdivided by partitions such as 25 and 21 which divert a part of the high frequency energy to the passages 28 and 29. When the wave front 30 in the central passage 3i reaches the mouth of the horn the wave front in the other passages will be disposed along an are as indicated by the dotted line and corresponding to a virtual spherical sound source 32. While from the standpoint of high frequency energy distribution it is unnecessary to continue the partitions beyond this line of wave fronts, it is sometimes desirable to do so for other reasons. It is much easier to build such a horn with a planar mouth opening as shown and in this way reflection effects are minimized when the horn is located behind a screen as in the usual theater installation.

The proper thickness of the partitions at the horn mouth depends on a number of factors. In general, for a given cut-off frequency, the longer the' horn and the larger its mouth opening, the nearer to its cut-off frequency will the radiation resistance be maintained so that it is quite possible as pointed out above to design the horn to respond satisfactorily to the desired low frequencies without relying on the partitions to increase the low frequency response. When it is desirable from cost and space requirement standpoints to keep the horn as small as possible, the horn length may be less than the quarter wave length of the lowest frequencies to be projected. In such cases a relatively greater low frequency correction is desirable and the thickness of the ends of the partitions should therefore'be a greater proportion of the width of the sound passages as viewed in Fig. 4.

Another important consideration is the required angle of dispersion. For since the total cross-sectional area ofthe passages expands logarithmically at the same rate toward the horn mouth, the thicker the partition walls are made, the greater the angle of dispersion will be for a given horn taper such as shown in Fig. 2. This particular horn has an effective length of about 13 feet and a cut-off frequency of about 60 cycles. The partition walls are 3 inches and the sound passages are 5% inches at the horn mouth so that the partition thickness is greater than one half the spacing between them, or, in other words, the area of the ends of thhe partitions is greater than one half the total mouth opening. This arrangement is found to give a considerable improvement in low frequency response from the cutoff up to about 150 cycles. Since these walls are not intended as resonators, but are used merely to disperse the sound over the required angle, they should be made as rigid as possible as by upright members 33, 34 and 35 or any other suitable means.

What is claimed is:

1. In a horn, a logarithmically tapered throat portion having a single passage and a mouth portion comprising a plurality of diverging sound passages each increasing in cross-sectional area at the same rate as the throat portion.

2. In a horn, a throat portion of logarithmic taper having diverging side walls, a mouth portion having side walls diverging at a greater angle than the side walls of the throat portion, and rigid partitions in the horn mouth extending toward the throat portion and varying in thickness so that the net effective cross-sectional area of the mouth portion increases logarithmically at the same rate as the throat portion.

3. A horn comprising a throat portion having a single 1 a mouth portion of rectangular cross-section and a plurality of diverging non-resonant partitions subdividing the horn so that the net eirective cross-sectional area of the horn increases logarithmically at substantially the same rate throughout its length.

4. A horn comprising a throat portion. 9. rectangular mouth portion, and non-resonant partitions dividing the mouth portion into a plurality of diverging passages, said partitions extending from the mouth or the horn toward the throat portion to a point where the sound waves are substantially planar and increasing in thickness towards the horn mouth.

5. A horn comprising a throat portion and a mouth portion of rectangular cross-section, a plurality of vertically disposed partitions spaced in the mouth portion extending substantially longitudinally of the horn axis, and increasing in thickness towards the mouth of the horn.

6. A horn comprising a throat portion, a mouth portion of rectangular cross-section, a plurality of short and a plurality of relatively longer vertically disposed partitions, the outer ends of all terminating at the mouth of the horn, said longer partitions being interposed at intervals between the shorter partitions and symmetrically disposed with respect to the vertical medial plane of the horn mouth.

7. A horn comprising a throat portion, a mouth portion oi rectangular cross-section, the horizontal dimension oi the bell portion at its mouth being substantially greater than its vertical dimension and a plurality of wedge-shaped partitions extending between the top and bottom walls of the horn and having a total end area at the mouth of the horn greater than one half the area of the total mouth opening.

8. A horn comprising a throat portion, a mouth portion and a plurality of equally spaced and vertically disposed partitions in said mouth portion, said partitions tapering uniformly from their outer and thicker edges to their inner and thinner edges, the thickness of the outer edges of said partitions being greater than one half the spacing therebetween.

9. A horn comprising a throat portion, a mouth portion, a plurality of wedge-shaped partitions tapering from a maximum thickness the mouth of the horn to portion of the horn where the high frequency sound beam substantially iills thehorn.

10. In a horn comprising a throat portion, and a mouth portion each having the same logarithmic taper, a plurality oi. wedge-shaped partitions vertically disposed and dividing the horn into a plurality of sound es having the same logarithmic taper, both the partitions and the sound passages increasing in cross-sectional area toward the mouth opening.

.11. A horn comprising a throat portion, a mouth portion having plane diverging side walls and outwardly curved upper and lower walls, and wedge-shaped partitions extending between said upper and lower walls dividing said mouth portion longitudinally into a plurality of sound passages, a plurality oi shorter wedge-shaped partitions dividing said passages into smaller passages, the end area of the partitions at the mouth opening being approximately one third the over-all mouth area.

12. A horn comprising a throat portion and a rectangular mouth portion having a greater horizontal dimension than vertical, and partitions dividing said mouth. portion vertically into a plurality oi passages, said partitions being substantially non-resonant wedge-shaped members decreasing in thickness from the mouth oi the bell portion toward their inner extremities.

13. In a horn, a longitudinally tapered throat portion having a single passage and a mouth portion comprising a plurality oi diverging sound passages each increasing in cross-sectional area at the same rate as the throat portion, the overall length of the horn as measured through each of said passages and said throat being substantially the same,

14. A horn comprising a throat portion having a single passage, a mouth portion of rectangular cross-section and a plurality of diverging non-resonant partitions subdividing the horn so that the net eflective cross-sectionrl area of the horn increases logarithmically at substantially the same rate throughout its length, which measure through each subdivision is substantially the same.

DAVID G. BLA'I'I'NER.

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