US1871531A

US1871531A - Sound distribution system for auditoriums

Info

Publication number: US1871531A
Application number: US605710A
Authority: US
Inventors: Edward W Kellogg
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1932-04-16
Filing date: 1932-04-16
Publication date: 1932-08-16
Anticipated expiration: 1949-08-16

Description

Aug. 16, 1932. E. w. KELLOGG SOUND DISTRIBUTION SYSTEM FOR AUDITORTUMS Filed April 16. 1932 Invenbm Edward W KeHogg,

bg W640 Patented Aug. 16, 1932 UNITED STATES PATENT osrica EDWARD W. KELLOGG, OF MOORESI'OWN, 'NEW JERSEY, ASSIGNOR TO GENERAL ELECL TRIO COMPANY, A CORPORATION OF NEW YORK SOUND DISTRIBUTION SYSTEM: FOR AUDITORI'UMS Application filed April 16,

My invention relates to sound production in auditoriums, particularly to the distribution of a desired sound spectrum uniformly to all parts of an auditorium, and its principal object is the provision of improved means for.

and methods of such sound distribution.

Experience in theatre acoustics up to the present time indicates that sound radiation of high directivity constitutes the best means of securing understandability in auditoriums characterized by a considerable amount of reverberation. However, practically all methods of concentrating sound into a beam become less and less effective as the wave length increases. Considering horns as the sound directive devices since they are widely used for thepurpose and appear-to provide the most effective means of securing directive sound radiation, it is to be noted that the larger the horn the lower will be the frequency at which it ceases to be directive. For example, a horn of given shape and having a bell opening two feet in diameter is markedly directive for frequencies above five hundred per second and practically non-directive for frequencies below two hundred fifty per second. A similar horn having an opening four feet in diameter would be directive at two hundredfifty cycles per second and practically non-directive at one hundred twentyfive.

In an auditorium adapted to and arranged for talking picture use the ideal system of distributing sound would be by means of a plurality of horns direct-ed to differentparts of the auditorium, each horn radiating the entire sound spectrum, the intensity .of the radiation fromeach horn being adjusted in accordance with the distance from the horn 'to that part of the audience reached by its beam. In such a multiple horn system it is assumed that the sound shall seem to emanate from the screen rather than from a distributed or multiple source. Such an artensity of direct beam sound to 'all parts of the auditorium and at the same time no sound would be directed to those parts of the audi- 5 torium where there were no listeners, thus minimizing the reverberant'sound in the audirangement would provide nearly equal in-* V 1932. Serial No. 605,710.

torium which isextremely prejudicial to the understanding of speech.

The foregoing ideal horn arrangement for sound distribution in auditoriums is not practicable on account of the number and size of horns required. My invention, however, insures in a simple manner sound distribution results closely approximating those of the above described horn arrangement.

In accordance with my invention one horn or set of similar horns projects directively all of the required sound spectrum to a certain portion of the auditorium and at the same time supplies non-directively a second portion of the auditorium with a band of low frequency sound radiation, and another horn or set of similar horns projects directively to this second portion of the auditorium all of the sound spectrum except the above-men tioned low frequency band.

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

Referring to the drawing the single figure thereof illustrates an embodiment of my invention comprising an arrangement of directive loud speakers or horns in an auditorium for substantially uniform distribution of sound therein.

In the figure the auditorium 1 is considered for convenience in illustrating the invention as comprising two portions, the rear half, for example, of the auditorium con stituting a portion 2 remote from the talking-picture screen 3 and the front half 4: constituting a portion of the auditorium nearer the screen. To project a required sound spectrum to the auditorium 1 in such a manner that the sound shall appear to emanate from the screen 3 a sound source 5 comprising a plurality of sound projectors or loud speakers is mounted in any desired position, as above the screen, to produce this result.

In accordance with my invention, the assembly of sound producers or horns comprises a'horn 6, or a set of similar horns, having a relatively large bell opening 7 for example. four feet by four feet, such a horn or set of horns being adapted to the projection at relatively high sound intensity of the entire required sound spectrum. in order to insure good listening conditions in the portion 2 at the rear of the auditorium the horn or set ofhorns 6 should be so mounted as to be aimed at this rear portion 2. An extension of the horn 6 to forma long visor 8, or a plurality of visors for a set of horns similar to 6, may be provided further to assist in reducing radiation to the ceiling and to strengthen the upper edge of the sound beam which reaches the most remote listeners.

The horns illustrated by arranged as to be directive for all bands of the sound spectrum, being highly directive for high frequencies but considerably less directive for low frequencies. Therefore the listeners in the front or portion l of the auditorium while not in range of the high frequency sound beam from horn or horns 6, nevertheless receive much radiation of the numeral 6 are so low frequencies for which the-horns 6 are Iii;

not highly directive. In order to provide radiation of higher frequencies and therefore to complete the sound spectrum for the listeners in the front or portion 4 of the auditorium I provide an additional sound producer'or horn 9, or set of similar horns, adapted to projectsounddirectively at lower intensity than that projected from horns 6 and so arranged that low frequency radiation, i. e., the band of frequencies correspond ing to the low frequencie supplied to the front portion l from horns 6, is eliminated. Horns 9 are so mounted as to be aimed at the front portion l of the auditorium.

It will be seen therefore that the listeners in the front portion 4 of the auditorium receive efliciently the entire sound spectrum, the low frequencies being supplied from the scattered radiation of larger horns 6 and the higher frequencies from the smaller horns 9. "It is understood that the loss of directivity of a horn or other directive sources as the wave length increases is gradual, and

correspondingly the loud speaker 9 is not to be sharply limited to a definite minimum frequency, but, by Well known principles of design, either of the loud speakers 9 them-- selves or of the electrical circuit which supplies power to them, the loud speakers 9 should be made to give more output at high frequency than at low frequency, the relatlve output at each frequency bein such as to supplement the low frequency sound received in the near part of the auditorium from the larger loud speakers 6, and give a satisfactory balance between high and low frequencies. The term frequency band throughout this discussion and in the appended claims is therefore to be construed as a restricted portion of the audible frequency range, but not as a sharply defined band in which sense the term is sometimes used.

The arrangement of loud speakers in accordance with my invention can be made to provide, throughout an auditorium, sound of more uniform intensity and quality than can be provided by arrangements hitherto employed. For example, non directive sources give excessive loudness close to the source, a single directive source giyes either too much high frequency sound dlrectly 1n front, or too little to theside, and a group of similar units located near or behind the screenand pointing in different directions, apart from the disadvantage of taklng up more space than my arrangement, tend to give excessive low frequency sound in the parts of the auditorium WhlCh are near the source. y

it will be observed that the direction of sound radiation from the sound producing units herein illustrated and described is easily controlled by horns or ba'liies whlch 1n thev case of the high frequency units can be of conveniently small dimensions. The fundamental idea of the sound distribution system for auditoriums in accordance with my invention is the u ilization of scattered radiation of low frequencies for those portions of the auditorium nearer the sound source, suplementing this low frequency radiation with directed high frequency radiation.

What I claim as new and desire to secure by Letters Patent of the United States, is: 1. In a sound distribution system for anditoriums, a sound reproducer adapted to project all of a sound spectrum, and a second sound reproducer adapted to project all of said sound spectrum except a band of fre quencies at the low end thereof, said first reproducer being mounted to projectall of said spectrum to a portion of the auditorium remote from said reproducers and to project a band of frequencies at the low end of said spectrum to a portion of the auditorium near said reproducers, said second reproducer be-,

' ducers being adapted to project directively all of said sound. spectrum except a band of frequencies at the low end of said spectrum to said portion of said auditorium near said reproducers.

3. In a sound distribution system, an auditorium, and a plurality of sound reproducers, one of said reproducers being adapted to project a sound spectrum directively at a relatively high sound intensity to a portion of said auditorium remote from said reproducers and to supply a band of frequencies at the low end of said spectrum to a portion of said auditorium near said reproducers, a second one of said sound reproducers being adapted to project directively at a relatively low sound intensity all of said sound spectrum except a band of frequencies at the low end of said spectrum to said portion of said am ditorium near said reproducers.

4. In a system of sound distribution for an auditorium, the method of radiating; a sound spectrum from a plurality of sound sources which comprises, proiecting the entire sound spectrum to one portion of said auditorium from one of said sound sources, roiecting a band at the low frequency end of said sound spectrum to a second portion of said auditorium from said sound source, and projecting all of said sound spectrum except said low frequency band to said second portion of said auditorium from a second one of said sound sources.

5. In a system of sound distribution for an auditorium. the method of radiating a sound spectrum from a plurality of sound sources which comprises, proiecting the entire sound spectrum from one of said sound sources to a portion of said auditorium remote from said sound sources, projecting by means of the same unit a band at the low frequenc end of said spectrum to a portion of said auditorium near said sound sources. and projecting by means of another unit all of said sound spectrum except said low frequency band to said portion of said auditorium near said sound sources.

6. In a system of sound distribution for an auditorium. the method of radiating a sound spectrum from a sound source which comprises, proiecting directiyely the entire sound spectrum to a portion of said auditorium remote from said sound source. supplying substantially non-directively a band at the low frequency end of said spectrum to a portion of said auditorium near said sound source. and projecting directiyely all of said sound spectrum except said low frequency band to said portion of said auditorium near said sound source.

7. In a system of sound distribution for an auditorium, the method of radiating a sound spectrum from a sound source which comprises, projecting directively at a relatively high sound intensity the entire sound spectrum to a portion of said auditorium remote from said sound source, supplying non-direc tively a band at the low frequency end of said spectrum to a portion of said auditorium near said sound source, and projecting directly at hand. EDWARD W. KELLOGG.