US1849840A - Horn for auditorium sound reproduction - Google Patents

Description

March 15, 1932. E. w. KELLOGG HORN FOR AUDITORIUM SOUND REPRODUCTIQN Filed April 18, 1930 invgfiilqr I Edwardwi Kai iogg 1015 @(ZZQ/ His Attorne 1g.

?atenteel 15 revamps @t lrllela ASS'iG-NOE TQ GENERAL ELEC- NEW "ZOEK HORN FGR AUDITOEIUM SGUHD R EUD'UCTZON Application filed April 18,

M invention relates to horns for loud spea ers, particularly to acoustic horns as used in large loud speakers for sound reproduction in auditoriums, and has for its object F the provision of an improved loud speaker horn of the large curved or coiled type.

It is well known that horns which are bent or curved give inferior sound reproduction as compared with horns with straight axes 10 and with equivalent lengths and cross sections. This distortion eliect is least if the horn is bent or curved near its small end, at which point the cross section ofthe sound wave passage is small, or the walls of the assage are close together. The distortion e ect is greatest if the bend occurs close to the bell oi? the horn, the cross section of the sound wave passage at this point being large the walls of the passage far apart. It is necessary, however, that the curvature of the horn occur close to the large end, or bell portion, in order to comply with the requirement of limited space frequently encountered in loud speaker installations.

In the straight axis horn the wave front expands continuously without encountering any obstructions or reflecting surfaces, and the various portions of the advancing wave front expand approximately equally. In the case of a bend in the sound passage, on the other hand, one edge, of the wave front is released by the recedingwall while the other edge is obstructed by the obliquely placed surface, H the two walls are close together, or less than about a half wave length apart, the two effects largely cancel and the wave front takes the new direction with little dis turbance. But if the walls are farther apart there is no such neutralization, and the vari- 011s portions of the wave front experience reflections in various directions andrphases e 1930. Serial No. 445,487.

horn near the bell. lhe sheet of such a bend is, in effect, to provide a sound passage vented on the side instead of at the end. The pressure release for long waves occurs when the wave front reaches the lower edge of: the opening, which is considerably before it has travelled fully the axial length of the horn. The bending thus shortens the effective length of the horn which reduces its etliciency and causes resonance to occur.

My invention provides means for obviating both of the detrimental efi'ects just described, and secures the acoustic equivalent of a straight axis horn, while permitting bends to be made wherever desired to meet space requirements even though this may mean placing a bend close to the mouth of the horn. Attempts have been made heretofore to comply with the condition of small wall separation of the sound wave passage at that point where the curvature of the horn takes place. lln these prior constructions, however, objectionable distortion of the sound waves still remained, the resulting designs were expensive to manufacture, and further, it was not possible to form the bend within less than a considerable distance from the mouth of the bell.

My invention will be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be set forth in the appended claims.

Referring to the drawing, the single figure thereof illustrates aloud speaker having a horn in which my invention is embodied. lhe figure shows a loud speaker 1, which comprises an acoustic horn-2 and an electroresponsive device 3 for translating electric waves into sound waves. l-his latter device =1nay'be ofany preferred form and in the emclose to the large end 8-,of the horn, that is, close to the mouth of the bell portion thereof.

In accordance with my invention, in order to prevent the interference efiects and reflection losses above described as occurring when the horn is bent or curved, at least a portion of the air column or sound wave passage 7 is divided by a series of substantially parallel partitions into a plurality of air columns or sound wave passages, each of which is of relatively small wall separation throughout its length, measured along the radius of curvature. The dimensions of the passages measured perpendicular to the plane of cross section are not necessarily small since there is no curvature of the passages except in planes parallel to the cross section. The principal requirement in regard to the passage width, measured perpendicular to the section shown in the drawing, is that expansion of the passage in that direction be continuous-and not involve rapid expansion followed by slow expansion. The Wall separation throughout the passages is sufficiently small with relation to wave length to avoid reflection efi'ects at the bends of the passages. In order to construct the respective parallel passages 10 of approximately equal length loops 11 are introduced into those passages which would otherwise be too short, Loops 11' may be formed, as shown in the figure, by increasing the thickness of the partitions 9 to the desired degreethroughout that portion of the sound passage 7 in which the loops are required.

In operation of the loud speaker comprising the above described means for dividing the horn passages 7 into a plurality of passages 10, sound waves from diaphragm 4 proceed through the latter passages without distortion by reason of the comparatively small wall separation inthese passages. Further, the soundwaves in the individual passages arrive at the large or bell end of the horn in phase, by reason of the looping of certain of the passages in such a manner that all of the passages have the same total length. The sound waves on emerging from the several narrow passages unite to form a single wave front travelling in a direction normal to the mouth 80f the horn.

What I claim as new and desire to secure by Letters Patent of the United States is: 1. In a curved acoustic horn, means to divide a portion of the air column therein into a plurality of sound wave passages of 'substantially equal length, said first-named portion including that portion of saidair column which extends through the curved portion of said horn.

2. In an acoustic horn having a bend formed therein adjacent the bell portion thereof, means to divide a portion of the air colunin within said horn into a plurality of sound wave passages of substantially equivaincluding that portion of the air column within said-horn which lies within said bend.

3. In an acoustic horn having a bend formed therein, means including a plurality of partitions mounted within said horn and extending within said bend, said partitions forming a plurality of sound passages of substantially'equal length to prevent distortion of sound waves at said bend.

4. In a curved acoustic horn, a plurality of partitions mounted therein and extending into the curved portion thereof to divide a portion of the air column within said horn into a plurality of substantially parallel passages of substantially equal length each having a relatively small wall separation.

5. In an acoustic horn having a bend formed therein, means to divide the air column therein through aportion of its length into a plurality of sound wave passages throughout said portion of said length of said air column, one of said passages throughlout a portion of said length of said air column being substantially straight and at least one of said passages being looped.

6. In a curved acoustic horn a plurality of partitions mounted therein to divide the air column within said horn through a portion of its length into a plurality of sound wave passages, said partitions being increased in thickness throughout part of their length toform loops in said passages.

It witness whereof, I have hereunto set my hand this 15th day of April, 1930.

EDWARD W. KELLOGG.

CERTIFICATE or CORRECTION.

Patent No. 1,849,840. Granted March is, 1932, m

EDWARD W. KELLOGG.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, lines 87 and 88, strike out the words "throughout said portion of said length of said air column" and insert the same to follow the word "passages" in line 91, same page and claim; and that the said Letters Patent should be read with correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 17th day of May, A. D. 1932.

M. J. Moore,

(Seal) Acting Commissioner of Patents.

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