US920387A - Acoustic lens. - Google Patents

Description

D. PBTRI-PALMEDO.

ACOUSTIC LENS.

APPLIUATIQN MLHD AUG.

Patened May 4, i909.

2 SHEETS-SHEET 14.

D. PETBl-PALMBD.

ACOUSTIC LENSk APPLwATIoN Hmm AUG.1,19a.

` 920,387. Patented May 4,1909.

2 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

DAVID IITRI-IALMIIDO, Ul" 110150K EN, NEW JERSEY.

ACOUSTIC LENS.

Specification of Letters Patent.

Patented May 4, 1909.

Application led August 11, 1908. Serial No. 447,922.

mitting and recording sound as embodied in' various contriviinces now in general use such ns telephones, phonographs, graphophones and the like. ln all these a iparatus the sound waves originated bythe human voice, musical instruments or other sources are made to inipmge upon an elastic diaphragm or membrane which is set into vibrations thereby. The vibrations of the diaphragm are then used either to make` impressions on a soft cylinder or plate by means` of a stylus as in the various sound recording apparatus in use, or to cause secondary currents to he induced in an electric circuit, for the tran*- mission of sound as inthe telephone. El order that the vibrations of such a membrane be sul'liciently violent to be used for recording with a stylus or to generate sulfi- "ciently strong secondary'currents in a telephone, the source of sound must be Very close to the membrane. This is at host an inconvenience in telephone apparatus, and a positive liiiii'lraiice in phonographic work such as for instance the recording of orchestral and vocal music, and even speech.

In making phonograph records it has been the general practice to use simple funnel shaped horns of various diameters and lengths presumabl for the purpose/of condensing'the soun waves emanating from the source. Funnels of relatively ,great length and small diameter are thus used for` concentrated sources such as the voice of an individual speaker or singer oran individual instrument; and funnels of relatively small length and large diameter for dispersed sources of sound Vsuch as the instruments Vof an orchestral band, the combined voices of a `f iiartet,l orchorus of singers, and the like.

he presumption that bysuchfunnel shaped horns sound waves can be condensed and made to produce true records is erroneous. I have, in carrying out the work of making records for teaching foreign languages with the aid 'of the phonograph demonstrated the fact that good clear records can be produced only bythe speaker keeping his mouth close lering the funne to the diaphragm, with just a small mouth piece for an intermediate apparatus. The use of funnel shaped horns of any kind in an kind ol phonographie and tele )lionic wort produces reiiection of the sound waves from the walls of the funnels in such a manner that the inajorit of the waves originally cnl/are finally lost vibrating at right angles to the walls and only those waves do actual work on the diaphragm that enter the funnel at or about the center and suller no, or but slight refiection froml theV wall of the funnel, so that as good or bad re-V sults may he accom lished with horns of small diameter, and t ie use of large funnels is useless, and more than that, injurious to the production of true records, because tllose sound waves that are strongly reflected and iinally vibrate back and forth within the funnel, not only fail to'do useful work but set up so called "standing waves, and creato! vibrations of the horn itself resulting in cx'- tianeous sounds known'in the technical langiuage of the art as barrel tones, metallic spunds, and the like.`

It is the purpose of this invention to do alway with the erroneous method of us' f nnel shaped horns. To this end Icollec t ie sound waves and condense them in a manner analogous to the collection and concentration of light w'aves by means of lass' lenses. I do not, however, make use o the pro )crt 'of refraction, this rescnting practica di `culties, but `that o reflection only. For this purpose I have constructed `an acoustic lens consisting ol' a screen composed of a series of concentric truncatedcones of varying angularity, and by means of these I divide up the total quantity of sound waves coming from the source toward the dia- :hragm into a series vof sound wave cones hat, after having suffered but one reflection in passin through the screen of concentric truncate cones are directed toward the dia hragm, all as will be fully described herc-y ina ter in connection with the accompanying drawings in which: y Figure 1 represents in central longitudinal section such an acoustic lens,4 embodying in desirable forni the present improvement, and Fig. 2 is a yertical cross section of the saine on linc 2, 2 Fig. 1. i

[n the drawing a are concentric truncated conical members or rings of various a ilarity held in place relatively to each o er by cross wires b of which two or more may los phragnu the an ularity ol the concentric outside shell or horn c as shown 1n dotted some convenient manner on a stand or other purposes but has been dexjised for instance 'concentric truneated'conical members of vaz be d. The whole screen thus coniposed of iiile rings a may be held in )ositlon at a y certain distance from the drap nagm by an in 1or it may be mounted in `fixtureenabling it to bey laced at a proper distance from the diap uagm. The construction of this `acoustic lens or screen is as follows: assuming for the sake oi' sim licity that the source is so far away from t e recording diaphra m that the sound waves traveling towar it may be practically rearded as parallel, as indicated by the thin otted line w in Fig. if such waves fw impin e upon the screen they will be reflecte as shown in Fig. 1, toward the diarings being of t e proper magnitude, and become smaller and smaller as the rings be# come smaller in diameter, that is, located more closely to the center ol the screen. At the very center of the screen the last concentric ring assumes the shape ol' a cylindrical tube oi a diameter' equal tothe opening of the diaphragm holder. The lengths ol` the concentric rings or truncated cones and the distances between them is such that the area covered by the sound waves dellected by one individual ring will not exceed in width the d" meter ol' theo )ening in the diahragm holifer, as clearly s lou-n for example y the areaol sound wares w, wf, impingmg on the ring' a or the arca 'w"w, impinging on the ring a". 'l`o carry this system to its logical conclusion and to avoid wares entering the space behind the screen without being properly reflected and illus to causo interferences, it even becomes heccssary to insert now and then baille plates, as' shown for instance atcl and d* in Figli.

The acoustic lens for condensing sound as above described may be'applicd for various or the manufacture of records and it has been the endeavor to produce records from which, uponftlie re n'oduftion ol the sound emanates same in a nll, clealy'melodims and harmonious tunc without any foreign, disagreeable or shrinking sounds. t

I claim as my invention:

1. An acostic lens comprising a series vof rions lenith spaced from one another, each member eing successively tapered to a less extent than ltsouter member. f

'.2. An acoustic lens, com n'isin a series of concentric truncated conical mem )ers spaced from one another and ol' various length so that their edges lie in a curved surface on each side, each member being successively tapered to a less extent than its outer member. A l i An acoustic lens, com rising a series ol' concentric truncated conical)members spaced fronrone another and ol various length so `that their edges lie in a curved surface on each'side, and means for holdingI the conical members in their relative positions, each member being snccessivel \Y tapered lo u less extent thun its ontcr member.

4. An acoustic. lens, comprising a series ol concentric truncated conical members spaced from one another and ol' various length so that their edges lie in n cin-wd san-face on each side,'and means for holdingl the conical members in their rclatiw positions, and nn outside tapering horn or shcLl, each member being successively tapered to a less extent than its outer member.

5.' An acoustic lens, comprisin;r a series ol' concentric truncated conical members spaced from one another and oi' various length. so that. their edges lic in a curved surface on' each side, and means for holding the conical members in their relative positions, euch member being siucessvely tapered to a less extent than its cuter member, and a cylindrical member constituting the innermost member of saidlcns.

6. An aconst lens, comprising a Series of diaphragm.

Signed at New York, N. Y., this 10th das4 of fitngust, 1908` DAVID lElRI-PALMEEDO.

Alrlfitncsses: O

LUDwiG K. BHM, JACOB LL DLAMOND.

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