US2070867A - Tuning apparatus - Google Patents

Description

Feb. 16, 1937. v. H. SEVERY 2,070,867

TUNING, APPARATUS I Filed Dec. 4, 1935 5 Sheets-Sheet l WZ Zor-AC .Jveky Feb. 16, 1937. v. H. SEVERY TUNING APPARATUS Filed Dec. 4, 1935 5 Sheets-Sheet 2 Vic-for H Jez/ezy ama Feb. 16, 1937. v. H. SEVERY TUNING APPARATUS Filed D60. 4, 1935 5 Sheets-Sheet 3 Wafer- H Severy Feb. 16, 1937. v SEVERY 2,070,867

TUNING APPARATUS Filed Dec. 4, 1935 5 Sheets-Sheet 4 m] A lawn!" Feb. 16, 1937. 2,070,867

V. H. SEVERY TUNING APPARATUS 5 Sheets-Sheet 5 Filed Dec. 4, 1935 Patented Feb. 16, 1937 U N] T-ELD STA sPATENT -o-F2F.-1-cE TUNING APPARATUS VictorH. Severy, Glendale, Calif. Application December 4, (1935; Serial .-No..52,794

Claims.

This :invention relates to tuning apparatus,

"and while:features of the invention may beemployed'fontuning musical instruments of different kinds, the invention is intended to be particularly usefulintuning reed instruments. In the present specification the invention is described as;applied to the'tuning of harmonicas. :At7present, the tuning of harmonicas isaccomplished with considerable difiiculty, and requires the servicesof a highly paid expert.

.The general object of this inventionzis to provide 1 tuning apparatus of simple construction, which can be employed for tuning harmonicas or similarinstruments, or for voice testing.

In the; preferred form of the apparatus, it involves the use of a gang of test vibrators, which are graduated to vibrate at slightly different frequencies individually, one of the testvibrators having a natural frequency which is the same as that of the reed of the instrument 'that is to be tuned. The other test vibrators are in two sets, one set of which is graduated individually "to vibrate at slightly higher frequencies, and the other set of which has its individuals constructed to vibrate at slightly lower frequenciesithan that of the reed that is to be tuned.

One of the objects of this invention is to pro vide simple means for eifecting the vibration of these test vibrators, and for indicating the relative activity of the same as induced by the vibra- -tion of the reed that is to be tuned; also to provide a test box of simple construction and involving the use of simple means for eifecting the vibration of the test reeds, and for adjusting the tuning apparatus.

=A- preferred embodiment of the invention is described in the following specification, while the broad scope of the invention is pointed out in the appended claims.

In the drawings:

.Figure l isaside elevation of the table carrying theapparatus,--and also illustrating two adjacent banks of test boxes, but omitting the .banks of test boxes beyond the .banks illustrated.

Fig. 2 is a longitudinal section through one of the test boxes illustrated inFig. 1, and further illustrating details of its construction, and also the construction of a means for effecting the vibration of .the' test vibrators asinduced-by the vibration .ofithereed that is tobe tuned. .In .this view certain parts are broken away and shown partially. inelevation.

Fig. 3 isua longitudinal section taken about ki on the line 33 of Fig. 2,1 and: particularly illustrating the translating devicefor effecting the vibration of the test vibrators andthe arrangementofjthe test vibrators,'which enablesthem to cooperate with a screen to' indicate visually to -10 the tuner whether the reed being tuned isflator sharp,

Fig. 14 is: a diagrammatic view of; the =forward end of the gang of test vibrators :as viewedr-in :elevationifrom the-curved line 4-4 .of Fig. 3. 1 5

In other words, this;view,.as farsasthe test vibrators are uconcerned, is adeveloped elevation.

This view also illustrates a portion of-xtheelectro- .mechan-ieal translating apparatus that cooper- .atesrwiththese test vibrators.

Fig. 5,-is a vertical section taken in the same plane as-FiguZ, but upon an enlarged scale, and .this view is a ifragmentary one, which particularlyillustrates the manner "of mounting thetest vibratorsfor effectingtheiradjustment toenable them to cooperate one screen operating asa visual indicator.

Fig. 6 isa front elevation of one ofthe screens employed in tuningthe reed, and indicating the location-of reflected light beams on. the screen when the reed is in. perfect tune.

Eigfllis a View similar to Fig. 6, but indicating the relation of reflected light beams on theindicator screen when the reed isflat; that is. tosay, when-theperiod of vibration of the reed is too;. low.

Fig. Bis-a diagrammatic view indicating the wiring arrangementand the general relation of .the apparatus embodied in the invention.

.In employing the apparatus embodying this 49 invention-to tunefthe'reeds v of a harmonica the creed 'plateis mounted in asuitable holder, and the reed toebetuned isset in vibration. Through the agency of the vibrating reed, impulses are developed in a circuit having the same frequency as the frequency of the'reed in its natural vibration. This impulse current is then amplified to .produce an amplified current, which is in circuit with a'translating device operatingtoproduce sympathetic vibrations in a test vibrator device. so

This test vibrator deviceincludesa gang of test vibrators, which are graduated to vibrate at frequencies slightly above and slightly below the frequency of the reed that is being tuned. One. of the test vibrators, preferably the one in the mid be tuned.

vibration or frequency the same as that of the reed if in tune. In front of the tuner a screen is placed, upon which beams of light are reflected from the test vibrators, and the light projected on the screen becomes more elongated when the reed reflecting the light is vibrated. In this way the screen operates as a visual indicator to indicate which test vibrator in the gang is vibrated in harmony with the reed that is to In this way the tuner determines whetherthe reed to be tuned is fiat or sharp, and he then performs an operation'upon the reed to reduce its frequency or to increase its frequency, as the case may be, to bring the reed into tune.

In the present instance, the vibration of the reed to be tuned is preferably effected through the agency of pneumatic means preferably including a suction box in which a partial vacuum is maintained. The means for holding the reed plate and the suction box, forms the subject matter of my copending application, Serial No. 51,369, filed November 25, 1935, and that application also includes a detailed description of the means for removing a slight amount of material from the reed to change its frequency.

Referring more particularly to the parts, I indicates a table for supporting the apparatus, and toward the rear of this table a plurality of test boxes 2 are provided, said test boxes being arranged in vertical banks and horizontal tiers.

The reed plate, the reeds of which are to be tuned, is set up in a holder 3 near the front of the table, and the reeds, such as the reed 4 indicated in'Fig. 1, are exposed at the forward face of this holder. Beneath the holder 3 a suction box 5 is provided, and associatedwith the suction box there is a valve 5a corresponding to each reed 4, which can be opened by depressing a button 6 and actuating lever 6a to apply suction to the reed 4 to effect its vibration. The suction box also includes a pick-up diaphragm I that becomes vibrated by the vibrating air in the suction box, and this develops impulses in a circuit within acable 8 that leads to amplifying apparatusJ9. From this amplifying apparatus 9 a cable If! leads off to carry circuits leading to the test boxes 2. Referring particularly to Figs. 2 and 3, each test box is provided at its rear end with a translating device I l including electro-mechanical means [2 actuated by amplified electric impulses to vibrate a tongue [3 that is in contact at its end with a tip M on a diaphragm I5, which may be of the usual conical form. In this way, the conical diaphragm I5 is caused to vibrate at the same frequency as the impulses in the circuit passing into the electro-mechanical means 2. The diaphragm I5 is preferably located in a substantially horizontal position, but slightly inclined upwardly to correspond with the inclination of the test box (see Fig. 2). The space under the diaphragm l5 constitutes an air chamber 16 having a bottom wall I! that forms an angle with the plane of the diaphragm, so as to form an opening l8 facing toward the opposite end or forward end of the test box. In this opening l8 a gang of test vibrators l9 are mounted, said vibrators being preferably mounted in an are as indicated in Fig. 3, the center of which is located toward the front end of the box and preferably at the location of a source of illumination, such as an electric lamp 20. These test vibrators are provided with means enabling them to reflect a beam of light onto a screen 2| at the front of the box (see Figs. 6 and 7). For this purpose each alongside of each other on the screen 23.

' illustrated in Figs. 6

2,070,867 dle of the gang of test vibrators, has a period of I vibrator, as indicated in Fig. 5, is provided with an opening 22 in the upper end of the same, to which a small reflector or mirror 23 is mounted. Thismirror is preferably mounted in place by means of a shim 24 of cork, which is secured to the mirror and to the vibrator by Canada balsam, or similar material.

There is a test box corresponding to each reed that is to be tuned, and by reason of the adjustability of the reeds I9 individually, they can all be placed in a position such that the beams of light indicated by the lines 25, will be thrown This screen may be made of translucent paper, but preferably is made of frosted glass or similar material. In order to enable the test vibrators to be individually adjusted in this way, I prefer to mount each vibrator securely. in a head 26 formed on the upper end of a rotatable spindle 21 mounted in a socket 28 in a base or block 29, and each spindle 21 is provided with a set screw 30 for rigidly securing it in place. Each head 25 is provided with a short handle 35 for rotating it into its proper adjusted position.

The middle test vibrator of the vibrators it, has a predetermined frequency of vibration, which is the same as the true note that should be produced by the reed that is being tuned. When the diaphragm I5 vibrates at a certain frequency, the reed in the gang of reeds that has the same frequency of vibration, will be more activated by the vibrations of the air in the air chamber I6 than its adjacent reeds. The effect of this is and 7 If the reed is in perfect tune, the middle beam of light on the screen will be greatly elongated, as illustrated bythe dotted lines 32 in Fig. 6. Each screen has a scale suchas illustrated in Figs. 6 and '7, with the letter F toward the left, and the letter S toward the right. If the reed being tuned is fiat, for example, the appearance of the longest beams of light on the screen will not be as illustrated in Fig. 5, but will have the appearance indicated by the dotted lines 33 in Fig. 7, indicating that the vibrator to the left of the middle vibrator is being vibrated in sympathy with the diaphragm l5, and this would indicate that the reed being tuned is slightly flat. The tuner will then remove some of the material from the reed to increase its frequency of vibration. For this purpose, at the front of the table, abrading or cutting tools 34 and 35 are provided, which are mounted just in front of the reed 4. By operating the handle 36, either one of these tools 3 3 or 35 may be advanced to remove a small quantity of material from the face of the reed. When applying these tools to the reed, the reed is backed up by a slide 3'! controlled by a handle 38. All of this mechanism is illustrated in detail in my prior applica-- tion, Serial No. 51,369, filed November 25, 1935.

The base or blocks 29 are all mounted on insulation 39 on a base rail li and the back end of the translating device 5! is supported on a suitable bracket ll. In addition to this, each test box is insulated from all the other test boxes by means of insulation 62 (see Fig. 2), thereby preventing interference.

In order to prevent direct light from the lamp 20 from impinging on the screen 2|, each test box is provided with a shield 23 projecting rearwardly from the forward wall, as indicated in Fig. 2. i

The walls of each test box are provided with ventilating openings 24 covered by guards 45,

trol I by: means :noti illustrated, andawhichiforms no a part ofLthis invention.

The translating device I I includes remover-e49 in theform oLarconical plate vorfiispiderfi'havirrg a pluralityofcopenings J mthrouglrit (see :Fig.7:3)

and this:coverihasaafforwarmsextensionri I ,iz whibh extends out :to :thevopening I 8 sat theriorwand side OfIthetaiNchamber. I6. LThisrzcover isformed I with a rfiange n52 -:*extending ,zaround tits rnmargin, which is; secured; in place in zanysrsuitable :manner, as by means :of :sscrews 153.

1 One of the advantages :of l -vibrating a the .test

vibrators :19 "through: the agency :01 the rair in the air chamber I6,1is-rthat :great saccuracyiris Lpossible lin ithe. frequency ,of the a test vibrators, due to theiact'athat Ltheyr'are :not .Jmder :the: in- 1 fluencee of magnetism.

It has rbee-nt found :that such vibrators whichfare aunder magnetic ainfluence, tendito :change their 'pitch slightly, :liue to magneto striction. Wthem suchztestxvibratorsrare vibrated through the -:use-' ofselectromagnets, it is found that: magnetism Iloadsi the :vibratorzif 1 the magnet isz'placedrnear athe center 1.01 :lower apart "of the vibratorgwvhich naturally lowerstheipitch.

Vibratinga the test vibrators through the: agency of :Jthe air; remainslinvariable, and the slightsad- -justments o! theitest vibrators rthat-areznecessary iorvcastingi the: beamsfof light :onithescreen 2 I udonot substantially: afiectrtheifrequencycof the "vibrator.

called to: Fig.14pwhichl illustrateszthe; test vibrators .In :this :connection, :attention is I9 :mounted in slots "54T'i11 :the grating cor? face plate55 of the air :chamber rI-Ii. :In.:order:t0

preventvany possibility f rthe vibration not one test vibrator afiecting any tother lvibratorsiimthe gang, their bases '29vare :separatedffrom each otherby'vibration insulation :56, zsuchrasrsoft yrubber; cork, similar material.

In Fig. 8 I illustrate diagrammatically tithe general arrangement :-of r, the apparatus rand ing. ,In this diagramril and v 58sin'dicatethepower circuit wires, eandtthe "wire ':connects: up with two conductors: or wires 59:.anda6ll v-leading"respectively, to: anamplifying switch 6I :zand 1a mower switch- 62. From theramplifying switchw I TB, conductor 63 leads .OVCIt'O' an amplifieri'fikandcoutput conductorsi65 and .6 6; lead ".ofiiirom'r this: am-

Jplifier, the "wire ":65 :passing over ":to ::a multiple :switch 61 with aauotatable arm 68 "capable :of

making contact with any 70118 .:of ';twenty rcontacts '69. Each of these contacts 569 .CQIIBSDOIIdS to a test box. From each icontact $69 ea "wire 111 extends over to' a corresponding" testrboxi to r conmeet up with the translating device II or the same. The returnwires' 'IFfrom thetranslating devices connect :up to ma "return 'i'trunk wire 12, which is'connectecl to the-wire' GB. Between the wire 66 and the 'wire 'liia voltmeter V is-connected by ashunt'l3 including a switch'fl. The wires 15 and "16 that "connect the -"diaphragm" 1 into the circuit, lead' to a*preamplifier 11,:-one side of which is'connected bywires 'l8sand19 to one endof the amplifier Ii I"Isa-cooperatewith a balancing circuit atihis-end -"6f' the"amp1ifier carried through wires 80- and- 8 I, and including a variable resistance82. When-thepower sivitch 62 is closed, current flowsthrough the wire 83- to a converter 84,-being connected 'at'a terminal 85 cooperating :with the terminal that' is connected to the wire 8l that leads ofidromthe -iine mire s58. iThe iwire 981 a connects to the terminal rl aaratzonezendrofthe amplifier':64,;.and the coopaerating: terminal 89;is:connected to theaforesaid wireit3tthat leadsto the amplifier switchli I. p The :lamp;Zlllsmonnectedzupjinto alamp circuit 90,

zincludingzabattery:orr-source of E. vM. F. i 9 I ,:and ctheiswitchrifl for lightingzthe lamp .whenever .deesired.

iThe ageneralzmode of operation of the apparaitusiwillrnom'be described. Therreed platesof the iharmonicathatpis.toibertuned, isLset up in the J-holder 3.1so1that the reeds 4 are in theposition .indicatedixin'l igzl. *Thetunenthen depresses a -plungerr'6, which opensa valve 5a-to draw air iinto "the suction "box -5 past the ;ree'd 4.

causes thexreed towibrateyand the reed of course, vibratesiat its-ownnatural frequency. The vibration oi?thisreed setstheair in the suction box m vibration and causes the diaphragm I to vibrate at the same'frequency as the air. The :vibration of 1 the "diaphragm 1 causes 1 impulses in thecircuit wires"|5,"16,at the samefrequency asthe reed. These impulses are'preamplified in the-preamplifier ll and amplified in the amplifier -64, so= that -amplified impulses pass through the translating device "I I, which has been put into the circuit "by means of the multiple switch 6'l. Theactivating-Of thetranslating device causes ifi'brations of its diaphragm I5, and the vibra- =tions of this diaphragmare imparted to the air in'thewair chamber I6. The vibration of the air in this -air chamber I6 imparts vibrations to the test vibrators I9 and, of course, the'test vibrator lthat is mo'st nearly in tune with the reed, will become most active in its vibrationya-nd if it happens 'to be in tunegthis -will" be indicated to the tunerby lookingupon the-screen 2|, where the conditions illustrated in.Fig.'6, will occur; that is to say, the light bands of maximum length will 'beat the middle of the scaleoi the-screen. If the reed is not-in'tune, "a'band of light having the"most-=elongation,will be to one side or the other-of the-middle of thescreen. Kit is to the "right, it' will indicate that'the reed is sharp, and if it -is" to the left. itwill indicate thatthe reed is flat. For -example,=as indicated inFig. '7, the elongation-of the bandjustto the left of the central=bandas=indicated in dotted lines, wouldin- "dieate that-the ree'd is flat. *Having ascertained 'whether'the-reedis flat or sharp, the tuner then usesthe abradingior cutting: tools 34 or to bring" the "reed into tune. If the reed is flat, it *wi1l 'be**necessarytotake off'a small amount of material towardtheiree'end of thereed by using thecutting 'or abrading instrument 34, and vice :versa.

It is understood-thatthe embodiment of the invention described herein is only one of the many embodiments this invention'may takaand 'I'*do-not wishtobe limited in the practice of the inventionynor in the claims, tothe particular --embodiment'set forth.

'By reason of the insulation 56'-'ior theindi- -vidual'test vibrators, it will be "evident that no interferencecan occur between them.

Itis evident 'that-this apparatus can be em- :ployed for testing thetrueness of'a vocal note by having the singer sing the note'so as'tovi- Pirate-diaphragm 1.

"tric*circuit=at'the samefrequehcy as that of the This vibrator to be tuned, means for developing-an electric current from the first-named circuit 'i'n which the said impulses are amplified, a translating devicereceiving said current for translating the impulses of: the amplified current into audible notes, a gang of graduated test vibrators vibrated sympathetically by the said audible notes, and having predetermined natural. frequency, said test vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned and including other test vibrators having natural frequency respectively, above and below that of the said note, and means for indicating the relative activity of the test vibrators actuated through the agency of the translating device.

2. In tuning apparatus for tuning a musical instrument having vibrators, means for vibrating the vibrator that is to be tuned, an-electric circuit, means for developing impulses in theelectrio circuit at the same frequency as that of the vibrator to be tuned, means for developing an electric current from the first-named circuitin which the said impulses are amplified, a translating device receiving said current fortranslating the impulses of the amplified current into audible notes, said translating device having an air-box, the air in which is vibrated at a frequency the same as that of the translating device as induced by the amplified electric current, a gang of test vibrators having predetermined natural frequency including one Whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned and including other test vibrators having natural frequency respectively, above and below that of the said note, and means for indicating the relative activity of the test vibrator actuated through the agency of the translating device.

3. In tuning apparatus for tuning a musical instrument having vibrators, means for vibrating the vibrator that is to be tuned, an electric circuit, means for developing impulses in the electric circuit at the same frequency as that of the vibrator to be tuned, means for developing an electric current from the first-named circuit in which the said impulses are amplified, a translating device receiving said current for translating the impulses of the amplified current into audible notes, said translating device including a diaphragm vibrated by the impulses of the amplified current to reproduce the note corresponding to the frequency of the vibrator that is to be tuned, an air chamber. adjacent the diaphragm, the air in which is vibrated at the same frequency as the note from the diaphragm as induced by the said amplified current, a gang of graduated test vibrators having predetermined natural frequency to be vibrated sympathetically by the air vibrations in the air chamber, said test vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned, and including other test vibrators having natural frequencies respectively, above and below that of the said note, and

means for indicating the relative activity of the test vibrators actuated through the agency of the translating device.

which the said impulses are amplified, a translating device receiving said current for translating the impulses of the amplified current into audible notes, said translating device including a diaphragm vibrated by the impulses of the amplified current to reproduce the note corresponding to the frequency of the vibrator that is to be tuned, an air chamber adjacent the diaphragm having a wall inclined to the plane of the diaphragm so as to form an opening into the air chamber located toward one edge of the diaphragm, a gang of graduated test vibrators mounted in the said opening and having predeterminednatural frequency, to be vibrated sympathetically by the air vibrations in the air chamber, said test vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned, and including other test vibrators having natural frequencies respectively, above and below that of the said note, and means for indicating the relative activity of the test vibrators actuated through the agency of the translating device.

5. In tuning apparatus for tuning a musical instrument, the combination of means for vibrating thevibrato-r that is to be tuned, an electric circuit, means for developing impulses in the electric circuit at the same frequency as that of the vibrator to be tuned, means for developing an electric current from the first-named circuit in which the said impulses are amplified, a test box corresponding to the vibrator of the instrument that is to be tuned, a translating device receiving said amplified current for translating the impulses of the amplified current into audible notes, said translating device including a diaphragm located adjacent one end of the test box, and including an air chamber adjacent the diaphragm, a gang of graduated test vibrators vibrated sympathetically by the said audible notes and each'having a predetermined natural frequency, said test vibrators disposed in an arc having its center adjacent the other end of the test box, said test vibrators including a test vibrator whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned, and other test vibrators having natural frequencies respectively, above and below that of the said note, a screen located at the end of the test box remote from the translating device, reflectors on the test vibrators, and a source of light for reflecting beams from the said reflectors onto the said screen to indicate the relative activity of the test vibratorsinduced through the agency of the translating device.

6. In tuning apparatus for tuning a musical instrument, the combination of means for vibrating the vibrator that is to be tuned, an electric circuit, means for developing impulses in the electric circuit at the same frequency as that of the vibrator to be tuned, means for developing an electric current from the first-named circuit in which the said impulses are amplified, a test box corresponding to the vibrator of the instrument that is to be tuned, a translating device receiving said amplified current for translating the impulses of the amplified current into audible notes, said translating device including a diaphragm located adjacent one end of the test box, and including an air chamber adjacent the diaphragm, a gang of graduated test vibrators vibrated sympathetically by the said audible notes and each having a predetermined natural frequency, said test vibrators disposed in an arc having its center adjacent the other end of the test box, said test vibrators including a test vibrator whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned, and other test vibrators having natural frequencies respectively, above and below that of the said note, a screen located at the end of the test box remote from the translating device, reflectors on the test vibrators, a source of light for reflecting beams from the said reflectors onto the said screen to indicate the relative activity of the test vibrators induced through the agency of the translating device, and means for mounting each test vibrator to enable the same to be adjusted to regulate the position of the light beam from the same on the screen. a

'7. In tuning apparatus of the kind described for tuning a musical instrument having vibrators, a translating device including a diaphragm with electrical means for vibrating the same to produce musical notes, a gang of graduated test vibrators vibrated at the frequency of the note produced by the diaphragm, said test vibrators each having a predetermined natural frequency, said vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned and including other test vibrators having natural frequencies respectively, above and below that of the said note.

8. In tuning apparatus of the kind described for tuning a musical instrument having vibrators, a translating device including a diaphragm with electrical means for vibrating the same to produce musical notes, a gang of graduated test vibrators vibrated at the frequency of the note produced by the diaphragm, said test vibrators each having a predetermined natural frequency, said vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned and including other test vibrators having natural frequencies respectively, above and below that of the said note, said test vibrators being disposed in an arc and carrying reflectors.

9. In tuning apparatus of the kind described for tuning a musical instrument having vibrators, a translating device including a diaphragm with electrical means for vibrating the same to produce musical notes, a gang of graduated test vibrators vibrated at the frequency of the note produced by the diaphragm, said test vibrators each having a predetermined natural frequency, said vibrators including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned and including other test vibrators having natural frequencies respectively, above and below that of the said note, said test vibrators being disposed in an arc and carrying reflectors, and means for mounting the individual test vibrators for rotation about an axis extending in the same general direction as the plane in which the test vibrator extends to enable the direction of a reflected beam from the reflector to be regulated.

10. In tuning apparatus for tuning a musical instrument having vibrators, a translating device having a diaphragm with electrically operated means for vibrating the same to develop vibrations in the diaphragm corresponding to the frequency of electrical impulses imparted to the same, an air chamber formed adjacent the diaphragm and having a wall in a plane inclined to the plane of the diaphragm so that an opening in the air chamber is formed adjacent one edge of the diaphragm, a gang of test vibrators mounted in the said opening and disposed along an are having its center remote from the translating device, said gang of test vibrators being graduated to vibrate at predetermined natural frequency and including one whose natural frequency is that of the note to which the vibrator of the instrument is to be tuned, and including other test vibrators having natural frequencies respectively, above and below that of the said note, a reflector carried by each test vibrator, and means for mounting each individual test vibrator to enable the same to be adjusted to regulate the direction of a beam reflected from its reflector.

VICTOR H. SEVERY.

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