US2826259A - Concussion protection for loudspeakers - Google Patents

Description

March 11 1958 A. w. PAGE CONCUSSION PROTECTION FOR LOUDSPEAKERS Filed Aug. 4, 1952 J N V ENTOR.

ARTHUR W. PAGE BY 8 g 2 E V fi/zar'kzey United States Patent CONCUSSION PROTECTION FOR LOUDSPEAKERS Arthur W. Page, Red Bank, N. J., assignor to the United States of America as represented by the Secretary of the Army Application August 4, 1952, Serial'No. 302,634

2 Claims. Cl. 181-31) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental pur-- poses, without the payment of any royalty thereon.

This invention relates to loudspeakers and particularly to loudspeakers having a movable diaphragm provided with an external driving means. More particularly, this invention relates to a mechanical means for blastproofing the diaphragm of a loudspeaker.

Loudspeakers are well known in the art and usually comprise a diaphragm in the form of a cone, tapered or corrugated to provide certain acoustical effects and including a driving means, usually electromagnetic and commonly in the form of a thin cylindrical coil, rigidly attached near the apex of the cone and coaxial to the cone. This voice coil is free to move in a strong magnetic field supplied by an electrodynamic or permanent magnet. The cone is resiliently mounted, near the apex and around its base, to a fixed support coupled to the magnet.

The cone is made of light, relatively thin materialusually some form of paperand is only strong enough to be driven by the light force of the voice coil. The cone has a relatively large area exposed to the air and is inevitably exposed to blast or pressure waves wherever such may exist. Therefore, a pressure wave of any intensity may tear the fragile cone out of its mountings.

It is an object of this invention to provide a blastproof, cone-type loudspeaker.

It is a further object of this invention to provide a means for protecting the diaphragm section of a loudspeaker against shock.

It is a further object of this invention to provide perforated plates on either side of a loudspeaker diaphragm for protection against excessive excursion of the diaphragm. Other objects of the invention will become apparent from the specification and claims.

Certain obscure types of loudspeakers have been suggested, as in the patents to Rice 1,631,646 and Gueritot 1,523,262, where the diaphragm and voice coil have been combined in a unitary cone structure. These are impractical by modern standards due to the limited size of diaphragm, the cumbersome and ineffective magnetic structure and the uncertain acoustical quality. These types of speakers are almost unknown today and since they do not teach or refer to blastproofiug in any way, they do not, even broadly construed, provide a practical solution to the problem solved by applicants device. These speakers will fall in the general class of driver units for horns that have such small diaphragms that blastproofing is not generally requisite.

In the drawings Fig. 1 shows a cross sectional view through the conical axis of a typical loudspeaker blastproofed according to the invention. The mounting of the cone, voice coil and protective plates is shown but the magnetic structure, since it is well known in the art, has been omitted to simplify the drawing.

Fig. 2 is a view of a standard loudspeaker, such as Fig. 1 would appear as a complete unit.

Referring now to Fig. 1 the cone shaped diaphragm 10 is seen mounted at its base in the ring structure 12 and near its apex by another ring structure 14 through a supporting spider 16. The spider is a highly compliant structure allowing a considerable freedom of movement in the direction of the axis of the cone while holding the cone rigid in lateral directions.

The voice coil 18 is in the form of a thin cylinder and I is rigidly attached near the apex of the cone. Magnetic: structures such as are well known in the art would sun round this voice coil and be a part of the rigid structure of the loudspeaker, including the rings 14 and 12, seen to better advantage in Fig. 2. The base of the cone includes a corrugated ring 20 or other means, relatively more compliant than the rest of the cone, to allow the main portion of the cone 10 to move, in response to the voice coil, in an. axial direction.

The excursion of the cone to the rear is limited by mem-- ber 22 and the excursion of the cone to the front is limited by member 24. These members are thin plates which: need be of only sufiicient thickness and strength to withstand the pressure of the diaphragm and the shock wave.. The plates would be of any rigid material such as metal: or fiberboard and should be as light as practical to avoid adding unnecessary weight to the speaker and should be non-magnetic to avoid interference with the voice coil field. Both of these plates are formed to follow the configurations of the diaphragm as closely as possible so that the diaphragm in its extreme excursion will seat itself evenly against these retaining structures.

The outer structure 24 has perforations 26 to allow thepassage of normal sound waves generated by the voice coil. and the element 22 has the perforations 28 to relieve the; back pressure of the diaphragm. The sound pressure is. also to some extent relieved by the openings 27 and 29 near the apex of the cone. These perforations should be of a large enough size and of sufficient number to pass sub stantially all of the normal sound pressure of the diaphragm. At the same time, their diameter, spacing and number can be chosen to produce certain desirable effects by their inherent filter action. These retaining plates 22 and 24 can be supported by ring 12 along with the rigid structure of the loudspeaker and separated and uniformly spaced from the diaphragm 10 by gaskets 30 and 32.

The two conductors to the voice coil may be brought out in a conventional way across the spider 16 or they may be brought out along the surface of the cone 10 to terminals 34 and 36 at any convenient points along the outer rim of the loudspeaker.

Fig. 2 shows a rear view of the loudspeaker with outer rim 112 corresponding to ring 12 of Fig. 1, and the inner rim 114 rigidly supported by braces 116 and attached to the magnetic structure 115. The retaining plate 122 with its perforations 128 can be seen from this view.

The foregoing describes a preferred embodiment of this invention. Any number of mechanical variations of loudspeaker structure, shape of cone, driving elements, etc, will be obvious to those skilled in the art.

What is claimed is:

l. A loudspeaker comprising a diaphragm mounted to permit a normal excursion thereof between a first and second position, and means for limiting abnormal excursions of said diaphragm comprising a first, perforated, nonmagnetic retaining wall having a shape which is congruent with one surface of said diaphragm situated in the vicinity of said first position, and a second perforated, non-magnetic retaining wall having a shape which is congruent with the other surface of said diaphragm situated in the vicinity of said second position.

2. A loudspeaker having a resiliently mounted diaphragm of substantially uniform thickness, said resilient;

Patented Mar. 11, 1958 mounting: permitting va;normal"excursion of said diaphragm between a firstand.secondeposition, .and-meansfor preventing abnormal excursions of said diaphragm comprising a first, perforated, non-magnetic retaining structure having; onev-surface. shaped substantially like said diaphragm- .and closely spaced: from. one. surface of said" diaphragmin said:fi1'St.positiOI1',.and;a; se'eonct-perforat'ed, nonmagnetic. retaining structure having one surface sha'ped substantially like sa'id diaphragm and closely spaced from the otherr.surface='of'said diaphragm in said-second-posi- References Cited in the file of this patent tion, whereby said diaphragmis 'prevented' from moving beyonditsnormal excursion;

UNITED' -STATES PATENTS Stewart Apr. 1, Burch Aug. 26, Wegel Sept. 12, Evans Mar. 20, Marlow -Apr.-. 1 1, Gersch June 20, Olsen-er a1; Oct. .23;

FOREIGN PATENTS GreaLBritain Dec. 27,

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