US1827994A - Loud speaker - Google Patents

Description

Patented ct. 2K0, 1931 UNITED STATESA PATENT OFFICE :rorm rar-.cron mrow, or WHITE nuns, NEW Yonx, AssrG'NoE 'ro amro con.- romrroN or AMERICA, A conPoaA'rroN or Enawm LOUD ySPEAKER plantation-med :une 1s, m8. serial No. sans.'

The invention relates to devices for producing sounds by electric current and has for its principal object to improve the quality of sounds emitted and to increase the intensity {5} thereof. Amore-specific object of the invention is to provide an acoustic ldevice from which sounds will be emittedfrom the front part'of the diaphragm onl y,

Still another object of t e invention is to "'4 provide an acousticA device in which the sound will be emitted from the front part of the diaphragm only, any tendency to interference between sound waves from the front and l `rear of the diaphragm being overcome.

.15j It .is Well known' that the construction of man types of acoustic devices of the loud spea er typ? forms a fairly large cavity behind the v1 rating diaphragm and it is often necessary or desirable to enclose 'this cavity by the casing of the device., This closed cavity has 'certain undesirable effects on the intensity and quality of sound emitted for several reasons.' In the rst place under certainA yconditions sound energy may flow from both sidesot the diaphragm thereby theoretically at least, reducing by one half the' useful sound energy, as of course, ordinarily only the sounds emitted b the front part of the diaphragm are use ul.' Another bad eiect of such a closed cavity may be traced to the casing itself which may have sufficient resiliency to cause it to vibrate in sympathy with the vibrating lcolumn of air entrapped in it. This will give the effect of a second sound source and sound waves'from it will naturallfy interfere more or less with. waves emitted omthe front part of thediaphra therecausing distortion and lessened intensity. Still another eifect'resides in the action of the vibrating column of air on the diaphra itself. The column of air set in motion y therear face of the diaphra will of course be reflected by the walls of t e enclosing casing and there will be certain frequencies at which strong resonant effects willbe obtained thereby increasing the amplitude of the diaphragm vibrations. At certain other frel quencies the entrapped air inthe casing may be reflected in the correct phase relationship `to exactly oppose the vibration of the diawith a modified form of lining.

phra m, thereby cuttin down its amplitude of v1 ration considerab y. While these effects are more noticeable at certain frequencies than at others it is obvious that they will 4waves from the rear of the diaphragm being reflected from the Walls of the casing and therefore, no tendency to resonant edects. This material also, if properly chosen, will prevent the passage of sound waves through it and, therefore, obviate any tendency of the casing itself to vibrate. The sound emitted by the device so constructed will, therefore be free from distortion and greatly increas in intensity, giving a faithful loud reproduc-` tion of the original sound.

The invention is illustrated, by way of example, in the accompanying drawings in whichv Fig. 1 illustrates the operating mechanism of a loud speaker constructed in accordance with the invention.

Fig. 2 is a sectional view on line 2-2 of Fig. 1 showing the construction of the lined .casing Wall, and

Fig. 3 is a cross section of a casing Wall Referring to Fig. 1, the operating mechanism of a loud speaker of a Well known type is showncomprlsing a base 1 on which is mounted a support 6, to which is fastened the operating mechanism of the loud speaker. The operating mechanism comprises a permarient magnet 3, held in place on'the support 6 by the clamp 5. The vibrating armature 7 isl suitabl supported as shown and the o eratino' coi 4 is mounted on the armature and foastened to the vibratory cone 9 100 by means of the r'od' 8.' The cone 9 has iianges provided at its outer ed e which are fixedto flexible ring 10, clampe in place bctween the clampin rings 11. The outer or operative surface o the cone 9 communlcates with the sound duct l2 which may be joined 49 will' then, of course, reproduce the sounds which originally caused the undulations of current in the, coil 4.

The undesirable effects noted above are obviated in the device shown in the igure bg lining the cavity behind the diaphragm Wit sound absorbing material shown at 13. This, as pointed out above, prevents any resonant effects due to the presence of the closed chamber and also prevents any vibration of the casing 2, permitting it to act as a secondary sound source.

It has been found that a felt lining as shown in Fig. 2 will eliminate all the undesirable eiects but in order to obtain substantially perfect operation of the diaphragm, this felt would have to be of considerable thickness, probably an inch, which ordinarily would make the apparatus too bulky. It should' be noted however, that a much thinner lining of felt or absorbing material will substantially improve the operation of the device and it is not always necessaiy to make a covering of this thickness.

ig. 3 shows a modication of a lining for the casing which is not unduly bulky and which gives substantially the same results as a felt lining an inch thick. The shown in Fi re 3 comprises a layer of le foil 202 which is attached to the casing 201, and a layer of felt 203 which covers the layer of lead foil. rI`he layer of lead foil may be about 5 mils thick and the layer of felt may be about l; of an inch thick. It has been found that this gives substantially perfect operation of the device from an acoustical point'of view and that it is rnot so bulky as to make it objectionable from the manufacturing standpoint. The lead foil in this case forms a substantial rigid barrier which transmits and reflects sound waves ve rly, if at all, thereby making a thif ligger of felt unnecessary.

The device is illustrated and described in connection with a loud speaker having a completely enclosed cavity behind its diap and this is the application in which the inveneiects which it is' designed to prevent.

tion is most effective and will nd its use as, in this case the undesirable e'ects pointed out above will be at their maxima. The device, however, is not limited to this specific case' as it can be equally well a p lied to 70 a cavity behind the diaphra whic is only partially enclosed and coul even be applied to an 'open diaphragm in which objects in the vicinity would tend to cause any ofthe While I have shown the device in several very specific modifications, it is obvious that many other methods of puttin it into effect will readily occur to those ski ed'in the art'. The modications described should therefore be taken in an exemplary andv not in a limitin sense as I intend to be limited only as in icated by the scope of the -following claims.

I claim:

l. An acoustic device comprising a sound emitting element, operating mechanism and supporting means therefor and a covering comprising a layer of non-vibratory metallic material and a layerof sound absorbing material on said supporting means.

2: An acoustic device comprising a sound emitting element, operating mechanism and supporting structure therefor and a covering comprising a layer of lead and a layer of kfelt f on said supporting structure.

3. An acoustic device comprising a vibratile element, a casing enclosing the s ace at the rear of said element and a lining or said casing comprising a layer of non-vibrator? `metallic material and a layer of sound absorbing material.

4. An acoustic device comprising a vibratile element, a casing enclosin the s ao'e at the rear of said element and a ming or saidC casing comprising a layer of lead and a layer of felt. l

5,. An acoustic device com rising a vibratile diaphragm,a casing enc osing the space at the rear of said diaphragm anda soundabsorbing lining for said casm 6. An acoustic device comprisin a vibratile diaphragm, means formin a su antially enclosed air space in bac of said diaphragm, and a layer of fibrous material positioned in said' enclosed air space for reducing the 'damping action of the entrapped air on said diaphragm.

. 7.- An acoustic device comprising a vibratile diaphragm, means for preventing com- "12 f munication between the rear and the front of said diaphragm, and additional means positione'd at the rear of said diaphra for'preventin the sound waves radi from the rear o said diaphragm 'from substantially '125 affecting said dia hragm, said additional means consisting o a layer of fibrous sound absorbing material. 8. An 'acoustic device com rising a vibratile diaphragm, a casing en sing the space 43.,

saam

at the rear of said dia h and forming a substantially closed all!)l prgt, and acoustic damping material positioned in said air ace for preventin the sound waves radiated gom the rear of sald diaphragm into said substantially closed air pocket from applying a damping action to said diaphragm, said acoustic damping means comprising a layer of felt applied to at least la substantial portion of said casin v 9. An acoustic evice comprising: conical diaphragm, supporting means at e edge of said diaphragm, a structure to which said supporting means is attached, said structure forming with said supporting means and said diaphragm a substantially enclosed air space, and damping material positioned within said air space for reducing the reaction of the entrap ed air in said air space against said 20. dia ragni,fsaid-dampingmateria1"consist:

ing of a: layer of fibrous material secured in back of said diaphragm.

10. An acoustic device com rising a vibratile diaphragm, a casing su antiall 'enclosing the space at the rear of sai diaphragm, means for securing said diaphragm to and directly mounting said diaphragm inl said casin and vibration dampingmaterial positione within the enclosed space.

3 11. An acoustic device comprisin a conical diaphragm, structure substantial y encompassing the rear of said conical diaphragm, and a layer of sound absorbing materlal positioned within said structure.

12. An acoustic device comprising a conical diaphra m, structure encompassing the rear of said iaphragm, and a layer of felt within said structure.`

JOHN PRESTON MINTON. c

Images