US2239503A - Sound pickup apparatus - Google Patents

Description

April 22, 1941. B. KREUZER 2,239,503

' sourm PICKUP APPARATU Filed Aug. 5, l938 2 Sheets-Sheet 1 6312 701V KQEUZEB Wm W April 22, 1-941. B. KF QEUZER 2,239,503

souun PICKUP APPARATUS Filed Aug. 5, 193a 2 Sheets-She et 2 I00 mooo I) Q I -2 S Q 33 Q fesouslvcw- I00 /QO00 RESPONSE -06 l -907NC/DENCE Patented Apr. 194-1 UNlTED STA'INE'S PATENT OFFICE causes I l soua'n rrcxur arrana'rus Barton KreuenLos Angeles, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application s m 5, 1m, Serial No. may: a claim. (Cl. 179-188) This invention relates to sound-translating devices and particularly to sound wave-to-electrical current translators commonly known as microdirectional type of microphone is generally preferable so as to concentrate on the sounds originating in front of the camera and microphone and to prevent, the unwanted and reflected sounds at the rear or sides of the microphone from being recorded. 7

It has been previously found that the use of a flat baille or sound wave deflector in connection with a pressure-operated microphone will pro-{ vide certain directional effects. That is, the sensitivity of the microphone for sounds originating in front thereof is greater than for sounds originating in the rear. The frequency-response characterlstics of such a microphone, however, is quite variable with the angle ofv incidence of the impinging sound waves. This is particularly true at the middle-high frequencies, such as three thousand cycles. In this frequency range, the responseisquitehighonthestandarddirectional pressure microphone for an angle of zero incidence and falls of! quite rapidly at the higher.

angles of incidence, zero incidence being taken as normal to the diaphragm of the microphone. This condition is particularly undesirable, since it not only provides an unequal frequency re-,

spouse for a particular angle or incidence, but

both diaphragm and ribbon, although Preferable with the diaphragm type.

An object of the invention, therefore, is to make more uniform the frequency-response characteristic of a microphone at a definite angle of incidence.

Another object of the invention is to decrease the variation in the frequency-response characteristics of a certain microphone for different angles of incidence of the sound waves on its diaphra e A further object ofthe invention is to increase I the eflicacy of a directional type of microphone v inPlg. 1;

the variation in frequency response between different angles of incidence is not uniform. Thus,

if a recording or public address circuit were' equalized for a microphone having a particular frequency-response characteristic for zero incidance, the equalization would not be correct for other angles of sound wave impingement.

The present invention, therefore, is directed to an improvement which, although not completeLv eliminating all unequalities in the frequency response for a definite angle or between different. angles of incidence, nevertheless, does flatten these characteristics to produce more uniform response characteristics as well as somewhat reduce the sensitivity at the rear of the microphone. Specifically, the improvement con-- sists of the use of a curved type of baiiie instead of the previous flat type, the invenmn being applicable to any pressure-operated microphone.

with respect to sounds emitting between the front and rear thereof.

Although the novel features which are believed to be characteristic of this invention will be pointed out wtih particularity in the claims appending herewith, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawings forming apart thereof, in which:

Fig. 1 is a partial cross-sectional view of one type of pressure microphone embodying the invention:

Fig. 2 is a plan view of the invention as shown Fig. 3 is another view of the microphone of Figs. 1 and 2 showing the former modification thereof;

- Fig. 4 is a graph of the frequency-response characteristics for the microphone of Fig. 3;

Fig. 5 is a graph of the frequency-response characteristics for the microphone of Figs. 1 and 2; and

Fig. 6 is the legend appriipriate to Figs. 4 and 5.

, Referring now to Figs. 1 and 2, a type of presmicrophone, such as a diaphragm 6 with a coilv portion I positioned between poles of a magnet structure 8. A protective screen 8 is shown bridging the opening in the casing I. Mounted on 'three posts II, II and II, and shown in crosssecticn, is a spherical baifle I! attached to the posts by screws II. There is an opening llin the bailie II comparable in size with'the opening in the casing bridged by the screen Q. Mounted over this opening is a screen 20 held within a ring member 2| fastened to the baflie and microphone by screws IS.

The baiile it, which was found to provide improved results for a microphone having an outer diameter of approximately 2% inches, had an It will also be noted that -microphone, it is shape of the f definite resonance due to the geometry of the baiiie with respect to the impi ing *Iclaim:

said microphone.

microphone and outside diameter of approximately i'inches', a

depth of 7a of an inch, an opening 01' 1 inch, a wall thickness of ,3; of an inch, and a curvature for the outer portion on a radius of 2% inches. This baille, applied to the microphone 4, gave more uniform frequency-response characteristics than the list type of baifle 22, shown in Fig. 3, which had been previously used. This flat baflie had approximately the same diameter as a curved baflie and employed the same screen mounted in the ring II.

To show the improved results between the two types of bames, reference is now made to I'igs. 4,

and 6, Fig. 4 showing measured frequencyresponse curves for the flattype oi baiiie for four 15 paratively flat up to 4,000, the peak coming in the neighborhood of 6,000 cycles. This peak is also .not of the magnitude of the 3,500Jeak in.- Fig. 4. the general nature of the characteristics in Fig. 5 are flatter. That is, the variation in response is more uniform for variations in the angles of incidence up to 90", so that a single equalizing circuit would suflice for all angles. These curves, therefore, actually show the improvement obtained in a sound-tocurrent translating device by the invention as defined in the appended claims.

Although the particular bailie described above is spherical to improve the spherical type; of to be understood that the gen! baille should be such that any or reenforcement of response sound waves be avoided or placed outside the usable portion of the frequency spectrum. Thus, for a certain microphone con figuration, the baille could be made with a wavy contour to further destroy any symmetrical geometry of the baifle with respect to the impinging sound waves.

. 1. In a sound-to eurrent translating device. the combination of a microphone anda baille for said bailie having an inner flat opening therein adjacent said an-outer solid surface portion, the outerv portion conform to the general external curve of. said Portion with an 1 diameter, the outer of saidbaiile being .curved to in said casing for the entranceof sound waves.

to said diaphragm, and a sound wave deflector adjacent said opening having and-inner portion with a screened opening therein and an outer 5 solid surface portion forming a continuation of said inner portion and having a diameteronehalf greater than the diameter of said microphone. a

3. In a sound-to-current translating device; a

spherical pressure type microphone having an opening in one side thereof for the entrance of sound waves, and a spherical baiiie having ailat portion with anopening therein immediately ad- Jacent said microphone opening, the outer surface of said baiile and said microphone having substantially the same curvature-the diameter 01 said baifle being approximately one-half greater than the diameter of said microphone.

4. A sound wave deflector for sound waves being received comprising a circular flat portion having an opening therein, said opening having a diameter of substantially one half that of said flat portion, and being centrally disposed within said flat portion, and a solid surface spherical '25- po tion surrounding said flat portion.

- 5. A sound wave deflector for sound waves being received comprising a substantially flat portion having a plurality of openings therein, said openings extending over an-area having a diameter of substantially one half that of said flat portion and being centrally disposed within said flat portion, and a solid surface second portion forming a continuation of. said flat portion and g of substantially uniform curvature. 1

6. A soundwave deflector for sound waves being. received comprising a substantially flat portion having an opening therein and a second portion forming a continuation of said flat portion.and of substantiafiy uniform curvature, said flat portion being approximatelytwo inches in diameter with a screen covering said-opening, i said opening being approximately one inch in diameter, the diameter of said curved. portion being approximately four inches.

microphone approximately three inches in diameter and a home for said microphone, said banie having an inner portion of approximately two inches in diameter with an opening therein of 5 approximately one inch in diameter and an outer eter and a baille for said microphone, .said baille having an inner-flat portion 'of approximately twoinches in diameter with a fiat screened microphone and having a diameter greater than opening therein 01' approximately one inch in the diameter of said microphone. diameter, and an outer curved portion f D- 2. In a 'sound-to-current translating degice, proximately four inches in diameter, the outer the combination or a pressure type microphonehaving a casing and -a diaphragm tor the impingem'ent of sound waves thereon, an

portion of said baifle having a curvature on a BARTON -7. In a sound-to-current translating device, a

radius of approximately. two and one-halt inches.

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