US2299342A - Electroacoustical apparatus - Google Patents

Description

Ust. 20, 1942. v H. F. OLSON 2,299,342

` ELECTRO-ACOUSTICAL APPARATUS Filed Nov. 30, 1939 2 Sheets-Sheet l //V VE /V 70,6

Oct. 20, 1942. H. F. oLsoN ELECTROACOUSTICAL APPARATUS 2 Sheets-Sheet 2 Filed Nov. 30, 1939 rra/e445),

' horizontal plane,

Patented Oct. 20, 1942 UNITED4 STATES PATENT OFFICE l 2,299,342 ELECTROACOUSTICAL APPARATUS Harry F. Olson, Haddon Heights, N. Yto Radio Corporation of America, a

of Delaware J., asslgnor corporationV Application November 30, 1939, Serial No. 306,954

`l1 Claims.

usually very small, being the difference between a person standing o r sitting down. The same is true of an orchestra where the level of the instruments does not vary appreciably from an average horizontalfffplane. As a consequence, there is no point in employing a nondirectional microphone which piclm up sound from all directions and therefore picks up sound reflected by the ceiling and floor. For this reason, the bidirectional velocity microphone has been employed'almost exclusively for sound collection in radio broadcasting. When oriented to pick up sound in radio broadcasting, the velocity microphone does not pick up sound from the ceiling or door. However, in a horizontal plane, the velocity microphone also varies as the cosine of theangle of the approaching sound wave. In other words, in the plane of the ribbon of a velocity microphone, the pickup is zero.

This

into corresponding feature of the velocity microphone is' useful for balancing orchestras, for eliminating unwanted sound, etc.

v In certain types of six-able to pick up sound in al1 directions in a it being extremely important, to eliminate sounds from the ln other words,` it is very at the saineV time, doors and ceiling.

sound collection, it is deprovide an improved microphone as aforesaid which hasadirectional characteristic independent of the frequency of the sound picked up thereby.

It is also an object of my present invention to provide an improved line microphone as above described which is compact in construction,-

easily portable, and highly efficient in use.

According to one form of my present invention, the system consists of a number of vertically extending pipes or tubes of equal length with their pickup ends open and arranged on a line. 'Ihe pipes are equipped with progressive bends so that their open ends will lie progressively nearer a ribbon element or the like to which the pipes are coupled and forming the sound transmitteddown the pipes acoustic paths from the opening of each pipe to the ribbon element are, however, the same in each case because the pipes are all of equal length. The ribbon element is terminated in a damped pipe which constitutes an acoustical resistance. Sound waves travelling in a horizontal plane will reach the open, or pickup, ends of each of the pipes substantially simultaneously, and, since the pipes rare all of equal length, they will reach the ribbon element simultaneously and in phase.

According to another form of my invention, it is not necessary to use pipes and a ribbon element as above described, but several sound wave salt or condenser units which are arranged vertically one above the other in suitably spaced relation and which are coupled to a common coudcsirable that the microphone which picks up the f sound shall have a relatively sharp directional characteristic which discriminates against undesirable sounds, but which will pick up all the desired sound in a predetermined plane throughout a 360 angle, and itis the primary object oi.' my present invention to provide a novel microphone which will accomplish this result.

More particularly, it is an object of my present invention to provide an improved directional microphone which is especially suitable for use in radio broadcasting, sound reinforcing systems, etc., where it is desirable to have maximum pickup in substantially a predetermined plane, but no pickup, or at least a minimum of pickup, 'outside of this plane.

Another object of my present invention is to ,55

' made long. The length of pling circuit connected to a suitable amplifier.

To render either of the above-described systems independent of frequen it is possible, in the case o1' the iirstdescribed modification of my present invention, to provide several lines of different lengths, the high frequency lines being made short and the low frequencyllines being the lines should be inversely proportional to the frequency to obtain uniform directional characteristics, and the output of each line is fed through a lter system which discriminates against different frequencies within a preselected range, so that the output of'each line is allocated to the proper frequency band. In the case of the second modiiication described above, suitable filter circuits may be coupled to certain ones of the pickup devices, the several filter circuits being effective which is used for trans-l electrical variations. The

.the modification of my Figure 1 is an elevation of one form of my invention as set up for use,

Figure 2 is an enlarged view thereof, partly in section, and with the coverremoved,

Figure 3 shows the directional of this microphone,

Figure 4' shows a modificationof my invention, Figure 5 shows a variation of the first form of my invention by means of which uniform re-1 sponse for all frequencies is obtained.

Figure 6 is a wiring diagram illustrating a filter system thatmay be employed in connection with invention shown in Figcharacteristic ure 5.

Figure '1 shows the response curve of the system shown in Figure 4, b`ut arranged with a Afilter system such as shown in Figure 6, and y Figure 8 shows a modification of the system shown in Figure 4,' but arranged with a filter system to provide uniform response for all frequencies.

Referring more particularly to the drawings, wherein similar reference characters designate corresponding parts throughout, I have shown, in Figs. l and 2, a microphone comprising a hollow base or pedestal I carrying a casing or the like 3 in which is mounted a vibratiie member or ribbon 5 arranged to operate in a suitable magnetic field and adapted to convert acoustical energy into electrical energy in tending vertically from are coupled to the upper 5 are a plurality or pipes 1, 9, II, rounded by and cover or casing I1. which base I.

The pipes 1, 9, II, I3 and I5 are all of the same length, but the pipes 9, II, I3 and' I5 are provided with uniformly progressively varying bends I0, I2, I4 and I5, so that the open ends of all of thepipes lie along a straight line with the pickup ends of the pipes 5, II, I3 and I5 successively nearer the ribbon element 5 than is the pickup The lower surface of the ribwell-lmown manner. Exthe casing 3 so that theysurface of the ribbon I3 and I5, the pipes being surenclosed within a perforated issupported on the mize reflection at the junction or casing 3, particularly when the acoustic impedance of the ribbon 5 is small compared to the acoustic resistance offered by the pipe I9. In this respect, the construction of my present microphone is similar terminated in an acoustical re from a sound source to one of open-ended tubular elements vdirection from a to that disclosed and application Serial No. 1938, now Patent No. i941.

of the order of six to eight feet. Since the sound path from the opening of each of the pipes 1, 9. II, Il and I5 to the ribbon 5. is constant, it is apparent that sound travelling in a horizontal source to one side of the microphonewhich is substantially equidistant from all of the pick-up points will strike the pickup end of each tubular element Aat the same time and will therefore be conducted simultaneously to the f the ribbon 5 transforming' the sound which travels down the tubular elements electrical variations or pulsations. The directional characteristic of this microphone is shown in microphone coinciding with the axis of the threedimensional curve shown in Fig. 3, and it will be noted that the directivity of the microphone isl conned tov a plane normal to the microphone axis.

. In the modification of my invention shown in Fig. 4, instead of employing the tubes 1, 9, II, I3 and I5 for picking up the sound, I employ a plurality of pickup devices 2| to 28, inclusive, which are arranged vertically along a line in spaced relation to each other and which are suit- -ably supported on the base or `pedestal I, the

devices 2I to 28 being substantially equidistant side of the microphone. The pickup devices 2| to 28 may comprise small Rochelle salt units, condenser units, Aor the like,

and they are connected in parallel relation, their outputs being coupled to a suitable amplifier (not shown) by means (of a coupling transformer 29 which may be housed within the base I. The operation of this form of my invention is, in general, the same as that described above insofar as the simultaneous picking up of the sound by all of the units and its conversion into electrical energy is concerned.

The two modifications'of my invention thus far described have characteristics which vary with frequency, becoming relatively sharp at the higher frequencies. 'This, in general, is an undesirable characteristic. To overcome this objection, I provide the modifications shown in Figs. 5 and 8.

In the modication shown in Fig. 5, I-provide 'three ribbons 3|, $3 and 35 on the base land couple to each of them three separate lines 4I, 45 of tubular elements, each similar to that described above in connection with Fig. 2, However, the lines 4I, 43 and 45 vare made progressively longer, the line 4I being shortest and being effective for the higher frequencies, the line 45 being longest and effective for the lower frequencies, and the line 43 being of intermediate length and effective for the intermediate frequencies. The lengths of these lines should be inversely proportional 'to the frequency to obtain uniform directional characteristics. and the outputs of the lines are fed to a lter system such as yshown in Fig'. 6. This filter system may include, in connection with each line and its associated ribbon, a coupling transformer 41 across the secondary of which is connected a capacitance i and inseries with which there may be provided an inductance 5I and a second capacitance 5l. The values of 58 and the inductance 5I will be different in each case, of course, and all of the circuits are connetted together to a common output circuit, as

The over-all height of this microphone may be Fig. 3, the axis of the the capacitancesls and sociated with said member and arranged to di- .rect acoustical waves to shown. Thus, the output of each of the lines 4|, 48 and d5 is limited to a relatively narrow fr quency band shown, respectively, by the curves 6i, 63 and 55 of Fig. 7. In this way, the over-all directional characteristic of the microphone can be made independent of the frequency.

Similar arrangements may be provided for the modidcation shown in Fig. 4 to make the length ot the line inversely proportional to the frequency, as in the case of the modication Just previously described. To this end, there may be provided in circuit with certain of the devices 2| to 28 (for example, the devicesY 2i, 22, 23, 2E, 2l and 2t) inductances li, l@ and l5, each of diierent value. This arrangement will provide a response characteristic for the system like that shown in Fig. '2.

Although I have shown and described several embodiments oi my invention, it will be apparent to those skilled in the art that many. other modiiications are possible. I therefore desire it to be understood that ll do not wish to limit myself except insofar as is madenece'ssary by the prior art and by the spirit of the appended claims.

I claim as my invention: 1. In combination with a source of acoustical energy, a line microphone including a plurality of pickup elements all arranged on a single line and an output membercoupled to said elements,

said elements being so constructed and arranged relative to said source and said output member that the energy picked up by each of said elements in a predetermined plane is delivered to said output member simultaneously and in phase.

2. A line microphone comprising, in combination, a plurality of pickup elements all displaced along a single line and adapted to pick up acoustical energy simultaneously in a predetermined.

plane, means for converting said picked' up energy into' electrical variations, and meansior simultaneously conducting the energy picked up by each of said elements to said means in phase.

3. In electroacoustical apparatus, the combina- I tion of a member adapted to be actuated by acoustical waves, and a plurality of tubular elements associated with said member and arranged to direct acoustical waves to said member, said tubular elements being of equal length and having their ends open and all arranged on a single line.

4. In electroacoustical apparatus, the combination of a member adapted to be actuated by acoustical waves, a plurality of tubular elements associated with said member and arranged to direct acoustical waves to said member, said tubular elements being of equall length and having their ends open and all arranged on a single line, and certain of said tubular elements being provided with bends therein whereby their open ends lie closer to said member along said line the open endsof certain other of said ele i ments.

5. In eectroaooustical apparatus, the combination of a member adapted to be actuated by acoussaid member, said tubular elements being of equal length and having their ends open line, and certain of said tubular elements being provided with bends therein of progressively varying length whereby the ends of said bent elements lie at different distances from said member along said line. 6. In electroacoustical apparatus, the combination of a member adapted to be actuated by acoustical waves, a plurality of tubular elements associated with said member and arranged to direct acoustical waves to said member, said tubular elementsY being of equal lengthY and having their ends open and all arranged on a single line, and means providing an acoustical resistance terminating said member.

7. In electroacoustical apparatus, the combination .of a base, a member mounted on-said base and adapted to be actuated by acoustical waves, a plurality of tubular elements associated with one surface of said member and extending upwardly therefrom, said tubular elements being of equal length and having their ends open whereby they are adapted to pick up acoustical waves and direct them to said member simultaneously and in phasesaid open ends all lying along a single line, and a tubular member associated with the other surface of said first-named member, said tubular member being housed Within said base 'and being iilled with a material, constituting an acoustical resistance.

8. The invention set forth in claim 7 charac- 'tei-ized by the addition of a perforated casing carried by said base and surrounding Said tubular elements.

9. In electroacoustical apparatus, the combination of a plurality of line microphones each comprising, in combination, a member adapted to be actuated by acoustical Waves, a plurality of open-ended tubular elements associated with one surface of said member and arranged to direct acoustical waves to said member, the tubular elements of any one of said microphones being of equal length but being of dierent lengths in each line and the open ends oi the tubular elements of each microphone all lying, respectively, along a separate, single line, and means coupled to the opposite surface of each of said members providing an acoustical resistance terminating said members.

tical waves, a plurality or tubular elements as- 10. 'The invention set forth in claim 9 characterized by the addition of a hollow pedestal and characterized further in that said members are mounted on said pedestal with said tubular members rising upwardlyv therefrom. andcharacterized further in that said acoustical resistances include pipes enclosed with said pedestal. 1l. The invention set forth in claim 9 characterized by the addition of electrical frequenuy discriminating circuits coupledto each of said members, each oi' said circuits being eiective over a diilerent range.

HARRY F. OLSON.

and all arranged on a singleV

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