US1666058A - Sound projector - Google Patents

Description

Patented Apr. 10, 1928.

UNITED STATES ELWOOD GBISSINGER, OF BUFFALO. NEW YORK.

SOUND PROJECTOR.

. Application filed December 11, 1923, Serial No. 679,911. Renewed November 5, 1997.

My present invention is closely related to that claimed in my copending application an amplifier for phonographs, but certainfeatures of the projector will be found useful in connection with telephone receivers and other vibratory sound producers and also in connection with other sources of sound particularly where, as in the case of human speech and music, the sounds comprise a wide range of frequencies, and particularly where it is desired to faithfully reproduce a multiplicity 'of sets of waves or complex waves of many frequencies, simultaneously.

A s ecific object of my invention is to provi e an air column associated at one end with the diaphragm of the phonograph reproducer and at the other end communicating with the open air, in which the air cola umn will be a suitable medlum for develop-.

ment, expansion of wave front, and ,projecting into the open air, sound waves having a wide range of hysieal lengths, including sound waves of which the quarter wave length is long and requires great length of air column, and also short waves of the higher frequencies, the quarterlengths of which may be two inches or less.

In my device the waves from the tone arm or other source, discharge directly into primary expansion conduit in which the wave front is immediately afforded rapid but guided expansion in one dimension, with little or no expansion in the other dimension. This primary expansion conduit discharges through'a slot-like outlet into a projector portion in which there is rapid but guided expansion in the other dimension. The primary expansion conduit" may have its non-divergent walls somewhat converging towards its outlet, and the projector portion should have its non-divergent walls converging toward its outlet.

I am able to start the primary expansion in one dimension directly at the outlet of the tone arm, and this conduit may be curved to almost any desired extent in the direction of its thinness, without danger of serious phase displacement for the short length waves. The sound beam from the outlet of the primary expansion conduit is turned abruptly through the desired angle and into the terminal or projector portion, the arrangement being so ordered that the main beam preferably crosses the plane of the vertical mouth of the projector at a.

sharp angle. This abrupt turning is in the direction of the thinness of the sound beam and is preferably by high an le reflection. However,vv the widening con uit may be curved in the direction of its thinness through an arc of degrees or more if desired.

In the preferred form, the wide thin sound beam projected from the slot-like outlet of the widening conduit is caused to impinge successively upon two high angle reflectors and is then permitted guided but wide angle expansion in avertical direction. Care should be taken to keep thedh mensions of the throat through which the main beam is finally projected, as narrow as may be Without cho ing the exit of said main beam. In practice I have found that this dimension, the distance from the bottom reflector to the roof at the nearest point, may be not very much greater, and referably less than the inlet slot from whic the primav beam is projected, although this seems to be partly an energy problem and the .desideratum seems to be to have the beam fill the throat without choking it.

It will thus be seen that the only part of my air column in w'hichthe cross-section is big enough to afford opportunity -for dephasing' reflections, and diffusions is the wide angle terminal portion and here only very acute angle reflections can occur and practical use proves that such as occur are advantageous rather than otherwise. a

The above principles are ca able of em bodiment in many specifica ly different forms, but I have selected for illustration herein a form in which all of the walls are very thick and are of dense stiff wood, preferably spruce. A spring metal widening conduit is sometimes desirable in connection with present day records, particularly those v the accompanying drawings, in which-:-

Figure 1 is a vertical section along the central axis of the sound amplifier and projector on the line 1 -1, Fig. 2, showing diagrammatically the path of the main beam and also a part of the,forward diffusion thereof near the mouth of the projector.

Fig. 2 is a section on the line 2-2, Fig. 1, indicating diagrammatically the angles of diver ence incidence, reflection and crossing of t e flanks of the sound Waves, the paths of the primary expansion and right angle reflections being projected on a plane, for this purpose. These'drawings are intended to indicate approximate sizes as well as the proportions of the parts in-onedesirable embodiment of my invention; The scale for, Figs. 1 and'2 is indicated above Fig. 1.

In these drawings the .invention'is shown as adapted for a cabinet type of phonograph.

The top of the cabinet which carries the tone arm and other operating parts of the phonograph also carries the primary expansion conduit 10 and the reflectors 24, 25

and the secondary-expansion or projector portion 26, 27, 28, which opens through the side of the cabinet. Y

The tone arm or other source of sound discharges at 16 directly into the upper end of the air column which extends continuously throughthe primary and secondary expansion conduits to the outer air.

The conduit walls are all of very thick spruce, includingthe walls 10, '10", 10 and 10 of the widening conduit. Theangular divergence of walls 10 and 10 is approximately indicated on Fig. 2. These walls are all at least one inch thick except the wall 10*, the lower end of which is preferably thin in order to bring the widening conduit inproper relation to the reflector 24, withont blocking the reflected beam from 25. Vibration of this thinner portion, however, is prevented by providing piers 10, preferably of wood. These are firmly glued between 10 and 10", the'surfaces being drawn into most intimate engagement while the glue is wet by means'oftension screws 10 These screws, preferably pass freely through holes 10' in piers 10 withoutengagin the sides of said holes. This leaves the en sur faces of the piers freer to take and maintain the desired position under the clamping of the conduit are stress of the screw; also unequallateral ex pansion or contraction of the Wood cannot take effect directly on the screw.

The terminal portion of the conduit, ineluding reflectors-24 and 25 and the side walls 28 are also one inch spruce. The length of the lower plate 26 is such that it is particularly liable to vibrate under the acoustic stresses set up by proper functioning of the projector as a Whole. Hence I prefer to make the thickness of this plate greater, say 1% inch. The same tendency to vibrate is found in the roof plates 27 and 10*, but these are so massively backed in the present construction that vibration is minimized, if

not eliminated.

vents their being selectively resonant to one frequency, even for such slight vibration as they may be capable off.

By referenceto the scale on the it will be seen that the inlet from the tone arm or other source is about 2 inches in diameter. Then for the'next 11 inches or so through the primary expansion chamber, the air column has a front-to-rear contraction to say 1 'inches, while the lateral widening. in the same distance is 13 inches to 14 inches. The next 3 inches measured along the axis of the main beam, follows the reflection path, and is contained in a portion of the projector which actually measures only about 1 inches from front'to rear. The path of the beam from the second reflection out to the mouth of the projector is about 7 inches to 10 inches though the shortest dis tance to themouth is say 6 inches. The final expansion in the vertical direction is also limited as to angle, being preferably between top and bottom walls diverging at an les less than 90, preferably about 60 to 0.

drawings,

the face of the cabinet is preferably the same or slightly less than'that of the slot outlet of the primary expansion conduit.

The waves emerging'from the conduit 10 are diverging on a spherical wave front and It results that v the angle. is considerable. when the end walls of the terminal portion parallel, as in my said application Serial No. 484,240, a substantial part of each flank of the main beam will impinge upon said wallsand will be thencc reflected out o the mouth of the projector. In most cases t e thus deflected flanks of the beam will tend to converge toward crossing points far beyond the mouth of the projector and practically the angles are insuflicient for effective lateral diffusion of the sound on each side of the direct beam. I have found, however, that improved acoustic effects, accom anied by adequate lateral diflusion may be 0 tained by converging the end walls as shown in Fig. 2 of this case.

to be a further advantage due to confining There seems the waveslaterally (a sort of reveisel of flank diffusion), probably because the vertical expansion permitted in this part of the conduit is extremely rapid'and if the side walls are outwardly diverging-or even parallel, sounds of less than average volume appear not to till the mouth of the projector.

The convergence of the sidewalls of the projector need not be more than, say, degrees, that is, 10 degrees inward toward the axis, for each wall. The increase in angles of incidence of each flank of the beam, will be multiplied by two for the angles of reflection of each flank, and by four for the angles of intersection of the reflected flanks. In the proportions indicated in Fig. 2 about half of the wave front will be deflected by the sides. The extreme flanks will cross each other at obtuse angles well inside the projector and all the crossing points will be at acute angles to the plane of the mouth of the projector. It may be that. the situation is analogous ofthe human mouth 1n slnglng,

-' where the trained artist seems to focus the sound practically in front of the lips rather than far backin the mouth or throat. However thatmay be, with. the construction shown, sounds of average intensity appear to ditl'erent times.

originate at or near the mouth of the proto respond to a wide rangeof frequencies.

In Fig. 1 the dotted lines and arrows indicate in a suggestive though more or less inadequate manner the path of the main beam. through the reflectingprojector and also with less degree of completeness some of the forward diffusion from thefront face Z- "m of the mam beam and also the face n'o. The curved lines m--r and o-1' represent the wave fronts of these diflusions. These varioussets of lines indicate that the main beam and all of the stronger portions ot the forward diflusion, cross the plane of the mouth oft-he projector at comparatively high angles and at different angles andv at Thus the curvature of the wave front and its non-simultaneous passage of points where backward reflection might occur'exists not only with reference to the d mensions illustrated in Fig.2, but also with; reference to the other dimension illustrated in Fig.1.

.As I have indicated herein and also in my patent aboye referredto. spring metal walls for any part ofthe widening conduit or prtqector are desirable, or even tolerable,

only as'a means for restoring to some kinds of music, some 'of the brilliant ualities which have been lost in the recording and reproducing operations. Nevertheless, for speech and certain other records and for more perfect records which will doubtless become available in the future, and for telephone and radio reproduccrs, perfectly faithful undistorted amplifications may be found highly desirable. For such undistorted amplification I find that the walls of the widening conduit as well as of the projector should be very stiff and at the same time very light, so that. tendency to sympathetic vibration will be avoided and such as may occur will be of the higher frequencies. To this end the quality of the material used should be very stiff and light as to quality, while the construction should be as solid as possible. For this purpose the best material which I have been able to find up to the present time, is boards or timbers of well seasoned s ruce. Probably the thicker the timber is the, etter it would be, but experience shows that the above named thickness of an inch or two is practically sufficient for the walls of the widening conduit and the projector. In this connection it will be noted that throughout the widening conduit the exterior walls are almost as thick as the sound beam which is confined between them.

While I prefer the right angle reflectors 24, 25 turning the waves emerging from the slot outlet of widening conduit 10, through angles totaling 180 degrees, it will be found that curved or partly curved and partly plane deflectors can be used, as for instance, semi-cylindrical surfaces having an axis parallel with the slot outlet, centering at or near ion the point 7, as indicated in dotted lines on Fig. 1. Curved surfaces of less angular are or less-radius or struck froma more remote center, are usable butless desirable. Where the conduit 10 is vertical, instead of inclined at a 45 degree angle, a single reflector maybe used to turn the waves through the 90 degree angle, instead of two reflectors for the 180 degree angle, and such single refiector may be either'plane or curved, or

partly plane and partly curved. These and other similar modifications are based on my above explained principle that where th widening conduit is kept thin as compared with the phase lengths of the waves of the higher, frequencies necessary to good "reproduction. the conduit may be curved in the.

direction of its thinness. without great losses and without danger of serious phase displacement for the short lengths (high frequency) waves.

"My invention correctness of my theorieswith re erence to it and in so far as I have stated theories4-it.

has been forthe purpose of indicating or accounting for novel results, -Whether correct or not, thev will be found useful ashvpotheses to assist those skilled in the art when does not depend upon the seeking to apply one or more of my novel principles to new conditions or purposes.

In my prior application above i eferred to, I have described heavy stiifwallsfor the widening conduit. W'hile certain claims of said prior application are broad enough to cover this feature, the specific claims of said prior application are limited to the form in which the widening conduit has spring walls adapted to add a brilliant quality to the reproduced sounds, but the specific claims for the widening conduit with the thick stifi' walls are necessarily reserved for this separate application.

I claim: I i

1. A sound amplifying conduit for expanding the wave fronts of complex sound waves, said conduit being solidly"'constructed of thick, prising a portion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension along widely diverging. lines and other walls nearly parallel w th each other, arranged to guide said Waves in the other dimension, thereby forming athin sound beam with widely divergentflanks and a deeply curved wave front; and, as a continuation thereof, a projector portion having walls diverging at an angle permitting guided but rapid expansion of said beam in said second dimension, one of said latter walls being integral with one of said nearly parallel walls" and, in combination therewith one or more 5 piers rigidly secured near theoutlet of said nearly parallel walls.

2. A sound amplifying conduit for expending the wavefronts of complex sound waves, said conduit being solidly constructed ofthick, stifi, light material, and comprising a portion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension alon widely diverging lines and other walls near y parallel with. each other, arranged to guide said waves in the other dimension, thereby forming a thin sound beam'with widely divergent flanks and a deeply curved wave front; and, as a continuation thereof, a projector portion having walls diverging at anangle permitting vgiiided but rapid expansion of said beam in said second dimension,-'oiie of said latter walls being integral with one of said nearly parallel walls and, in combination therewith one. or more piers rigidly secured nearthe outlet of said nearly parallel Walls,

said piers being elongated in I a direction parallel'with he direction of the sound waves impin ing thereon.

3. Asound amp ifying conduit for expanding the wave-fronts. of complex sound wavespsaid conduit being solidly construct.-

ed of thick, stilf, light material, and. coin prising a portion having Walls arranged to I permit guided andlimited butrapid expanstifl, light material, andcoin sion of the wave front in one dimension alon widel diverging lines and other walls near y para lel with each other, arranged to guide said waves in the other dimension, thereby forming a thin sound widely divergent flanks and a deeply curved wave front. and, in combination therewith one or more piers rigidly secured near the outlet of said nearly parallel walls) 4. A sound amplifying conduit for expinding the wave fronts of complex sound ii aves, said conduit being solidly construct-. ed of thick, stifi', light material, and comprising a portion having walls arrangedto permit guided and limited but rapid expansion of the Wave front in one dimension along widely diverging lines and other walls nearly parallel with each other, arranged to guide said waves in the other dimension,

thereby forming a thin sound beam with e sound waves imbeam with 70 a direction parallel solidly conalong widely diverging lines and other walls I nearly parallel with each other, arranged to guide said waves in the other dimension, thereby forming a thin sound beam with widely divergent flanks. and a deeply curved wave front; and, as a continuation thereof,

a projector portion having walls diverging at an angle permitting guided but rapid expansion of said beam in said second dimension, one of said latter Walls being integrals with one of said nearly parallel walls and, 1l0

in combination therewith one or more piers rigidly' 'sccure'd near the outlet of said nearly parallel Walls. 4

6. A sound amplifying conduit for expanding the wave fronts of complex sound no waves. said conduit being solidly constructed of thick, stifi; light material, and comprising a portion havin walls arranged to permit guided and limi ed but rapid expansion of the wave frontin one dimension along widely diverging lines and. other walls nearly parallel with each other, arranged to guide said waves in the other dimension,- thereby forming a thin sou'nd beam with widely divergent flanks and a deeply curved .125 wave front; and, as a continuationthereof,

a projector portion having, opposite wallsdiverging at an angle permitting guided but rap d expansion of said beam in said second.

dimension, and other; opposite walls a lao neeepes ing a ortion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension along widel diverging lines and other walls nearly para lel with each other, arranged to guide said waves in the other dimension, thereby forming a thin sound beam with widely divergent flanks and a deeply curved wave front; and, as a continuation thereof, a projector portion having opposite walls diverging at an angle permitting guided but rapid expansion of said beam in said second dimension, and other opposite walls arranged to confine and deflect inward the divergent flanks of said beam, said deflecting walls of the projector converging toward the mouth of the projector at substantial angles, whereby said diverging walls are of substantially decreasing width toward the mouth of the projector.

" thereby 8. A sound amplifying conduit for expanding the wave fronts of complex sound waves, said conduit being solidly constructed of thick, stifl, lightmaterial, and comprising a portion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension along widely divergin lines and other walls nearlyparallel wit each other, arranged to guide said waves in the other dimension, thereby forming a thin sound beam with widely divergent flanks and a deeply curved wavefront; and, as a continuation thereof, a projector portion having opposite walls diverging at an angle permitting guided but .rapid expansion of said beam in said second dimension, one of said latter walls being integral with one ofsaid nearly parallel oppositewalls, and other walls arranged to con-v fine and'deflect inward the divergent flanks of said beam.

9. A sound amplifying conduit for expanding the we've fronts of complex sound waves, said'conduit being solidly constructed of thick, stiff, light material, and comprising a portion having walls arranged to per mit gpided and limited but rapid expansion of the wave front in one dimension along widely divergin lines and other walls nearly parallel with each other, arranged to guide said. waves in the other dimension, forming a thin sound beam with widely divergept flanks and a deeply Eurved wave front; and, as a continuation thereof, a projector portion having opposite walls diverging at an angle permitting guided but rapid expansion of said beam in said second dimension, one of said latter opposite walls being integral with one of said nearly parallel walls, and other walls arranged to confine and deflect inward the divergent flanks of said beam and, in combination therewith one or more piers rigidly secured near the outlet of said nearly parallel walls.

10. A sound amplifying conduit for expanding the wave fronts of complex sound waves, said conduit being solidly constructed of thick, stiff, light material, and comprising a portion having walls arran ed to permit guided and limited but rapid expansion of the wave front in one dimension along widely diverging lines and other walls nearly parallel with each other, arranged to guide said waves in the other-dimension,

thereby forming a thin sound beam with widely divergent flanks and a deeply curved wave front; and, as a continuation thereof, g a projector portion having opposite walls diverging at an angle permitting guided but rapid expansion of said beam in said second dimension; one of said latter opposite walls being integral with one of salt] nearly parallel walls, and other walls arranged to confine and deflect inward the divergent flanks of said beam and, in combination therewith one or more piers rigid-' 1v secured near the outlet of said nearly parallel walls, said piers bein elongated in a direction parallel with the direction of the sound waves impinging thereon. a

11. A sound amplifying conduit for expanding the wave fronts of complex sound I waves to a desired outlet area, said conduit comprising a primary expansion (portion having walls arranged to permit gui ed and limitedbut rapid expansion ofthe wave front in one dimension along widely diverging lines to a width reater than that'of the outlet, and other wal s arranged to guide the waves in the other dimenslon, to form a thin sound beam with widely divergent flanks and a deeply curved wave front; and a secondary expansion portion or projector having opposite walls divergin at an angle permitting guided and limited ut rapid expansion of said beam to the desired area I in said second dimension, and other 0 posite walls arranged to confine the i v'ergent flanks of said beam in said first dimension and to deflect them toward each other. I Y

12. A sound amplifying conduit for expanding the wave fronts of complex sound waves to a desired outlet area, said conduit comprising a primary expansion por tion having walls arranged to permit guided and limited but rapid expansion of the wave -front in one dimension -along widely diverging lines to a width greater than that of the outlet, and other walls arranged to guide the waves in the other dimension, tofform a thin sound beam with widely divergent flanks and a deeply curved wave front; and a secondary expansion" portion or projector having opposite walls diverging at an angle permitting guided and limited but rapidexpansion of said beams to the desired area in said second'd'imension, and

"- other opposite walls arranged to confine the divergent flanks of said beam in said first comprising a primary expansion portion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension along widely di-v verginglines to a width greater than that of the outlet, and other walls arranged to guide the waves in the other dimension, to form a thin sound beam with widely divergent-flanks and -a deeply curved wave front; and a secondary expansion portion orprojector having opposite walls diverging at an angle permitting guided and limited but'rapid expansion of said beams'to the desired time in said second dimension, and

other opposite walls arranged to confine the tdivergent flanks-of "said beam in said first dimensionfand to deflect them toward each other at angles predetermined withv respect to the width and depth of the projector portion to'caus'e the lines of reflection of said flanks to cross each other and diverge at highangles, within the mouth of the projector, yet clearing-the edges of the convergerit walls at the mouth'of the projector. 14. .A sound amplifying conduit for. ex-

'fp'andingjthe wave fronts of complex sound waves to a desired outlet area, said conduit Y guided and limited but rapid ex 'ansion of i being solidly constructed of thick, stiff inateria and comprising a primary expanslon portion having walls arranged to .permit the wavefront in one dimension-a on .wide- 1y diverginglines to a desired widt and other walls" arranged. relatively parallel v to guide the waves in the other dimension,

thereby forming a thin sound beam with widely divergent fianksiand a deeply curved wave front; means for deflecting said beam through a wide angle in thedirection of its thinness; and a secondary expansion portion or projector havin wallsdiverging' at any anglepermitting ided and limitedbut rapid expansion of said beams to the des red area in said second dimension.

15. AL sound amplifying conduit for ex- I panding the .wave fronts of complex sound waves to-a desired outlet area, saldconduit being solidly constructed of thick," ti-fi ma.-

nceaoce other Walls arranged relatively parallel'to guide the Waves in the other dimension, thereby forming a thin sound beam with. widely divergent flanks and a deeply curved wave front; and a secondary expansionportion or projector having walls diverging at an angle permitting guided and limited b t rapid expansion of said beams to the desired area in said second dimensioin one of said latter walls extending reverse-1y 'at a very acute angle to said relatively parallel walls and having a substantial portion of its length integral with one of them.

16. A sound amplifying conduit for expanding the wave fronts of complex sound Waves to a desired outlet area, said conduit being solidly constructed of thick, stifi' material and comprising a primar expansion portion having walls arrange to permit guided and limited but rapid expansion of the Wave front in one dimension along widely diverging lines to a desired width, and other walls arranged relatively parallel to guide the-waves in the other dimension, thereby forming a thin sound beam with widely divergent flanks and a deeply curved wave front; and a secondary expansion portion or projector having walls diverging at an angle permitting rapid expansion 0 said beams to'the desired area in aid second dimension, one of said latter walls extending reversely at a edge of'said integral wall against sympa thetic vibration.

- 17. In the combination specified by claim 14, the further in the expanded sound beamto said diverging walls for expansion in the other dimension.

18. In the combination specified by claim 14 the further feature of arranging the feature .of'a plane reflector parts so that the sound beam is projected along'one of the diverging walls of the mouth of the projector. 19.,In the combination specified by claim projector for directing, the laterally guided and limited but 14 the further feature of having the .projector directed upward so that the emerging sound waves areprojected upward and at considerable angles to the plane of the mouth of the projector for the purposede; scribed. 4

20, A. projector. solidly constructed .of thick, stifi material and comprising two high angle reflecting surfaces .on the same side of the projector, the second reflector 1,eee,oss

duit leading thereto, solidly constructed of thick, stiff material and having two opposite approximately parallel walls for a considerable distance backward from the reflector, said sound reflecting surface being rigidly secured in fixed angular relation with the outlet of said expansion conduit.

22. A sound amplifier comprising a primary expansion conduit leading downward from the tone arm solidly constructed of thick, stifl material and adapted to expand the sound waves rapidly in one dimension without substantial expansion in-th'e other dimension to project a relatively wide thin sound beam,'in combination with a plane reflector arranged to deflect said sound beam in the direction of its thinness and a second plane reflector in receiving relation to the first reflector and arranged to reflect said sound beam through a further angle in the same direction.

23. A primary expansion conduit solidly constructed of thick, stiff material, having opposite walls diverging in one dimension much more than in the other dimension to project a relatively thin sound beam,in combination with a projector having two adjacent reflcctors at a high angle to one another on the same side of the projector.

24. A sound projector solidly constructed of thick, stiff, light material and comprising a thin flat expansion conduit, rapidly diverging to great width as compared with its thickness, its thickness being less than 2 inches, the conduit being curved in the direction of its thinner dimension and discharginginto a shorter conduit having "a wide expansion angle in the direction of said thinner dimension.

25. A sound amplifying conduit for expanding the wave fronts of complex soun waves to a desired area, said conduit comprising a primary expansion portion having walls arranged to permit guided and limited but rapid expansion of the wave front in one dimension along widely diverging lines; and a secondary expansion portion wherein sai walls converge in the latter dimension to confine and deflect inward the divergent flanks of said beam, the length and angle of the convergence of said converging portions being predetermined with reference to the widthv and angle of the'divergence of said diverging port-ions so that said converging portions intercept and deflect'toward each other approximately one-half the wave front projected from said primary expansion portion, while the total cross-sectional area continues increasing throughout.

26. In a method of sound wave amplification the step of expanding sound waves between substantially non-vibratory walls, causing their expansion in substantially one dimension only, then expanding them again in substantially another dimension only.

27. A method of sound wave amplification within confining channels whose walls are designed and constructed to reduce the effect of vibration, comprising the steps of first expanding the waves in one dimension in one stage, and then in a succeeding stage expanding them in another dimension only.

28. In a method of sound wave amplification the step of expanding the sound waves between sensibly non-vibratory walls, causing their expansion in substantially one dimension only, deflecting them in the direction of their thinness and then expanding them again in substantially another dimension only between sensibly non-vibratory walls. p

29. A method of sound wave amplification in confining channels whose walls are sufficiently rigid to be substantially non-resilient to audible vibrations, comprising the steps of causing at least two distinct and successive stages of expansion, one stage in which the waves are expanded in one dimension,.deflected in the direction of their thinness, and then after such deflection a succeeding stage in which the waves are expanded in another dimension only.

30. A method causing substantially uni-dimensional expansion only of the waves in successively different dimensions through conduits sensibly non-vibratory.

31. A method of sound wave amplification comprising expanding the waves in a channel whose walls are suflieiently rigid to be d substantially non-resilient to audible vibra tions, causing at least two distinct and successive stages of expansion, first expanding the waves substantially in one dimension only, then deflecting them in the direction of their thinness, and then expanding the waves d substantially in another dimension only in a succeeding stage.

Signed at Buffalo in the county of Erie and State of New York this 8th day of December, A. D. 1923.

ELWOOD GRISSINGER.

" "too of amplifying sound waves

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