US 1878088 A
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Sept. 20, 1932. Q ZW|KKE`R 1,878,088
ACOUSTIC APPARATUS FlQd NOV. 1, 1929 2159.1 175,2 zfvzjg,5
INVENTOR comms,v zvxxsn BY 7 l M1144/ lATTORNEY Patented Sept. 20, 1932 UNITED STATES .PATENT OFFICE CORNELIS ZWIKXER, OF EINDHOVEN, NETHERLANDS. ASSIGNOR T RADIO CORPORA- i TION OF AMERICA, A CORPORATION OF DELAWARE ACOUSTIC APPARATUS Application led November 1, 1929*,.Seria1 No. 404,088, and in the Netherlands December 4i, 1928.
It is known to directl sound waves by 'According to the invention, first the sound means of a horn or trumpet intoa definite di-i. radiating area is reduced and then the sound rection. It has been found that a vertical angle of a sound beam which is thus directed and radiated is inversely proportional to the cross sectional area of the mouth opening of the trumpet. The larger the said lmouth opening is the smallervis the angle of the radiated beam and the more strongly directed muis`l the sound. It has been stated, that this relation only holds good when the trumpet matches the sound source to such an extent that al1 the air particles in the mouth of the trumpet vibrate with the same amplitude. When use is made for example 'of a diaphragm whose diameter is small in'comparison with the length of the trumpet and with the diameter of its mouth opening, it may be assumed that all of air particles in the mouth opening of the horn really vibrate with the same amplitude. When using, however, a diaphragm whose diameter is large in comparison with the dimensions of the trumpet, the said diaphragm is liable to exertsa cer- 26 tain directional eifectand to radiate a divergent sound beam. lWhen a trumpet -badlyf` `matches this diaphragm the airparticles in the mouth of the trumpet which arelocated within the beam radiated by the diaphragm 30 Will vibrate lmore strongly than the particles located outside the said beam. In this case only part of the mouth opening comes into consideration for the angle of the` beam emitted by the trumpet and the diaphragm. The said angle will consequently be larger than would be expected from the trumpet opening and the sound will consequently be directed less strongly. Consequently, if one wants to direct the sound waves issuing from a diaphragm which as to its diameter can no longer be said to be small relatively to the horn or trumpet opening one wishes to use, one is obliged. to take horns, or trumpets of great length. yThese horns are very expensive and extremely unsightly. The invention has for its object tofsuggest a method which lallows of directing sound waves strongly without? necessitating abnormal dimensions of the trumpet or hornrequired to obtain 4the directional eii'ect.
is directed by means of a trumpet or horn which surrounds the said reduced area. The sound radiated by the reduced area can be directed with the aid of a short and strongly diverging horn without any risk that air particles in the mouth opening of the hornvibrate unequally. Infact, the vsmall sound radiating area may be considered as a vibrating point which radiates 1n every direction vthe samex quantity of sound. The sound radiating area can be reduced by means of a trumpet or horn whose concave side is turned towards the sound source.
In the device according to the invention the sound radiating area is first reduced and then' the sound Waves are directed by means of a trumpet or horn which surrounds the reduced area. According to the invention this device may consist of two funnel shaped parts whose throats open into each other. Either V or both of the two funnel shaped parts may be formed as a horn.
The invention will be more clearly understood by referring to the accompanying drawing which represents by way of example some embodiments of the invention. In the drawing:
Figure 1 represents a horn shaped loudspeaker;
Figure 2 shows a loudspeaker comprising a horn and a diaphragm which relatively to the said horn has large dimensions;
Figure 3 represents a loudspeaker Whose ldiaphragm has the same dimensions as that of Figure 2 but whose sound trumpet is longer than the horn represented in Figure 2;
Figure 4 shows a soundtrumpet according to the invention used in conjunction with a located in the mouth opening vibrate with:
the same amplitude. This will usually be the case When the diameter of the diaphragm 11 y is small in comparison with the dimensions of the trumpet.
Figure 2 represents a combination of a diaphragm-12 with a horn 13 in lwhich the dia? phragm has larger dimensions owing to which it has already a certain directional ecct Which i-s indicated by the diverging beam 14. i If the horn 13 badly matches the diaphragm 12, as is shown in Figure 2 the air particles in the mouth of the trumpet Which are located in the zone g will vibrate more strongly than the particles located outside the said zone i. e. in the zone h. In this case, only the portion g of the mouth opening will princi ally come into consideration for the angle ci) the beam radiated by the trumpet and the diaphragm.
In order to avoid this, one must use a trumpet or horn which is better suited to the diaphragm 12, for example the trumpet 15 represented in Figure 3. When comparing Figures 2 and 3, one will observe that the mouth openings ot the horn 13 and of the trumpet 15 have the same diameters but that the trum pet 15 is much longer than the horn 13.
Figure 4: represents a sound trumpet which consists of two funnel shaped parts 20 and 21 Whose throats 22 and 23 open into each other. The concave side of the funnel shaped part 2O is turned towards the sound source 24. The sound radiating area of the said sound source may be considered the surface of the diaphragm 25. This sound radiating area is reduced by the trumpet 20 to the area of the throat opening 23 of the funnel shaped part 21. The sound radiated by the area 22 is directed by means of the short, strongly diverging trumpet 21. All the air particles in the mouth opening of this trumpet will vibrate with the same amplitude so that a strongly directed beam will be radiated. Vhen comparing the Figures 3 and 4, one observes that the mouth opening of the trumpets 15 and 21 are equal but that the length Z of the trumpet 15 is much greater than the length Z of the sound trumpet according to the invention. 4
Figure 5 represents a mode of realization in which the twol funnel shaped parts are formed as a horn.
In Figure 6 Aonly the directing funnel shaped part and in Figure 7 the reducing funnel shaped part, are Jformed as horns.
r-I`hese sound trumpets are eminently suited to exert a strongly directional effect on the sound issuing from a loudspeaker having a large diaphragm, such for example as loudspeakers With diaphragms having diameter of 10 centimeters and more.
y A loudspeaker comprising a conical diaphragm having a large surface, a sound am.- plifying body having an opening which is smaller than the said diaphragm and comparable in size with the other dimensions of the body to make a good amplifier of sound, and a sound directing body interposed between said diaphragm and said sound amL plifying body, said sound directing body having a. shape such that its end which is'associated with the diaphragm has an opening that is larger than the diaphragm and its end which is associated with said sound amplifying body has an opening that is smaller than the opening in said sound amplifying body whereby the largerend of said sound directing body is outof contact with said diaphragm and the smaller. end of said sound directing body is out of contact With the sound amplifying body.