US2642948A - Portable radio with a bass-reflex cabinet - Google Patents

Description

Jue 23, 1953 H. F. oLsoN ETAL 2,642,948

PORTABLE RADIO WITH A BASS-REFLEX CABINET Filed May 28, 1948 Patented June 23, 1953 PORTABLE RADIO WITH A BASS-REFLEX CABINET Harry F. Olson, Princeton, and John Preston,

Metedeconk, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application May 28, 1948, Serial No. 29,845

3 Claims.

This invention relates to radio receivers, and more particularly to a sound system for personal radio receivers.

The term personal radio receiver, as used herein is intended to designate a complete radio receiver with self-contained power supply and of such physical dimensions that it can be carried in the pocket.

Small, personal, radio receivers are, at present, decidedly inferior to the average table model set with respect to fidelity. This restricted fidelity is inherent with personal receivers by reason of the fact that, if the receiver itself is to be small, the loudspeaker used with the receiver must be reasonably small; and the smaller the loudspeaker used, the lower will be the acoustical output in the low-frequency range due to loss of coupling between the diaphragm and the air.

The primary purpose of our present invention, therefore, is to provide a sound system for personal radio receivers which will increase the acoustical output of the receiver.

In accordance with our present invention, we have provided an improved personal radio receiver in which the arrangement of component parts has been altered to allowthe use of a horn and phase-inverter acoustical system. The personal radio receiver of our present invention has a cover which is hinged to one end of the top wall l of the housing enclosing the component parts of the receiver. An opening is provided in the top wall adjacent the end to which the cover is hinged, and a loudspeaker is mounted behind the opening. The cover has a panel extending perpendicularly from each of two opposite side edges thereof so that the cover, panels and top wall together form an acoustical horn for sound waves emanating from the loudspeaker. Each of the panels is slidably received in slots in the top wall of the housing thereby permitting the horn to be collapsed by moving the cover in close proximity to the top Wall While the panels are received within the housing. Another opening is provided in an end wall of the housing remote from the opening in the top Wall, and is of a size to constitute a bass reiiex opening for sounds emanating from the reverse side or back of the loudspeaker diaphragm, the space within the housing acting as a phase inverter. The cover, in addition to forming part of the acoustical horn for the receiver, also carries a loop antenna therein. Thus, we have provided an improved, compact, personal radio receiver having greater acoustical eiliciency and more output power than commercial personal radio receivers in use at the present time..

2 The novel features of our invention, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following detailed description of two embodiments thereof, when read in -connection with the accompanying drawing, in which Fig. 1 is a front elevation view of one embodiment of a personal radio receiver constructed in accordance with our present invention showing the cover raised to an open position,

Fig.\2 isa cross section view of the personal radio receiver shown in Fig. 1, taken on the line 2-2 of Fig. 1, the component parts of the receiver being omitted,

Fig. 8 is a View similar to Fig. 1 but with the cover in a closed position,

Fig. 4 is a diagrammatic representation of the acoustical circuit oi the sound system of the personal receiver of our present invention,

Fig. 5 is a graph showing the comparative responses of a personal radio receiver1 constructed in accordance with our invention, and a conven tional, commercial receiver of the same size, both receivers using like loudspeaker units, and

Fig. 6 is a View similar to Fig. 1 but illustrating a modification of a personal radio receiver in accordance with our invention.

Referring more particularly to the drawing, there is shown in Figs, 1 through 3, a personal radio receiver I according to one embodiment of our invention and including radio apparatus of any suitable or conventional type. Pursuant to our present invention, however, the arrangement of component parts in the receiver has been al= tered to allow the use of a horn 3, and to accom modate a loudspeaker 5 Within a cabinet or housu ing 1, keeping in mind simplicity of design and compactness.

Referring to Fig. 1, the housing or casing 'I includes a top wall 9, a bottom wall II, two end Walls I3, I5, and two side Walls (only one side wall I1 being shown in the drawing). A cover I9 is mounted on one end 2| of the top wall 9 by means of a hinge 23. Two panels 25, 21, preferably made of stii or rigid material, extend perpen dicularly from opposite side edges 29, 3I of the cover I9 and are slidably received in openings oi slots (not shown) in the top Wall 9 so that when the cover is in its closed position (that is, when it is positioned parallel with and adjacent to the top wall 9, as seen in Fig. 3), the panels 25, 21 will be positioned inside of the housing adjacent and parallel to the side walls. The top wall 9 is also provided with an opening 33 near the end 2I to which the cover I9 is hinged, and a loudspeaker 5 is mounted inside the housing i behind the top wall opening 33. It will thus be seen that the cover I9, panels 25, 2l, and top wall 9 together form an acoustical horn 3 for sound Waves (repn resented by arrows 35) produced by one side (the front) of the diaphragm of the loudspeaker 5 when the cover is raised to an open position, as shown in Fig. l.

An opening 37 is provided in the end wall i3 of the housing 'i which is remote from the loudspeaker. The interior 3Q of the housing will then 'function as a phase inverter for sound waves (represented by arrows di) produced by the opn posite side or back of the loudspeaker diaphragm, and the opening 3'? will function as a bass renex opening for these sound waves.

It will thus be seen that we have provided an improved Ysound system for personal radio receivers consisting of a combination horn and phase inverter. The acoustical circuit of the vibrating system is shown in Fig. 4 in which:

P=4driving pressure of the loudspeaker,

M1=inertance of the diaphragm and voice coil of the loudspeaker,

CA1=acoustic capacitance of the diaphragm suspension system,

M2=inertance of the base reflex opening,

wuz-:resistance of the base reliex opening,

CAz=acoustic capacitance of the receiver housing,

ZAH=impedance of the quadripole of the horn (impedance of the coupler between the throat and mouth of the horn),

M3=inertance of the mouth of the horn, and

vus-:resistance of the mouth of the horn.

The horn used in the sound system of our presn ent invention may have a parabolic, and exponential, a conical, or any other suitable rate of flare, there being little difference in results achieved in practice between any of these horns due to the small size of the hor-n. It is well known by those persons skilled in the art that, in small horns of thisA type, the acoustical output drops off below 800 cycles. Therefore, by employing a combina tion horn and phase-inverter system and adjusting the constants so that the particle velocity in the base reflex opening is in phase with the output of the horn, it is possible to maintain uniform output down to e5() cycles, the cutoff frequency of the phase inverter system.

A comparison of the response frequency characteristics of the sound system in the personal receiver of our present invention using a combination horn and phase inverter loudspeaker with that of the sound system in a conventional, commercial receiver having the same cu'bical content, both using a conventional, direct radiator loudspeaker of the same size, is shown in Fig. 5 of the drawing. Referring to Fig. 5, the solid black line represents the characteristics of our combination horn and phase inverter system, while the broken line represents the characteristics of loudspeakers of most conventional, commercial receivers. These characteristics were taken under the same conditions of input, environment and microphone distance and show that the combination horn and phaseinverter sound system of our improved receiver are, on an average, 8 to 10 db greater than the sound system of the ordinary commercial receiver over a range of frequencies from approximately 400 tov 2000 cycles.

The cover i9, in addition to its function of forming part of the acoustical horn of the rei ceiver, also carries a loop antenna 43 enclosed therein. In order to keey the Q of the loop as high as possible, the top wall 9 of the housing I is made of l-lbf copper plate. The Q of the loop may be dened by the equation Where L=inductance of the loop, r=resistance of the loop, and f=frequency vReferring to Fig. 6 of the drawing, there is shown a modification of our invention applied to a personal radio receiver similar to that shown in Figs. 1 through 3. In this modication, the housing l is provided with apertured top and end walls 9', I3', i5 similar to the top and end walls t, I3, l 5 of the modification shown in Figs. l through 3. The loudspeaker il is mounted inside of the housing i behind the aperture or opening 3l in the end wall i3. rlhe opening 31" functions to transmit sound waves (represented by arrows 35') produced by the front side of the diaphragm of the loudspeaker 5. The opening 33 in the top Wall 9 is remotely situated from the end wall i3 and functions as a bass reflux opening for the sound waves (represented by arrows lli) produced by the opposite or rear side of the loudspeaker diaphragm.

The personal radio receivers of both modifications are provided With screens in front ofthe openings for preventing dust or other foreign matter from entering the interior of the housings, as for example the screens ll, 47 in the openings 33, 37 respectively, and the screens t5', il in the openings 33', 37' respectively. C0ntrol knobs for the radio receiver components or apparatus may also be located on the end wall, as for example the knobs 39, 5| shown on the end Wall i3 of the modification illustratedby Figs. l through 3, or they may be arranged on the top wall nearthe mouth of the horn, as for example, the knob 49 shown in the modification illustrated by Fig. 6 of the drawing.

It will readily be seen by those skilled in the art that we have provided an improved sound system for personal radio receivers which has many advantages over sound systems employed in conventional personal radio receivers of the same size in use at the present time. While we have shown but two modifications of our invention, various other modifications and changes will no doubt, readily suggest them-selves to those persons skilled in the art. Therefore, we desire that the particular form of our invention described herein shall be considered as illustrative and not as limiting.

What is claimed is:

l. A sound system for a personal radio receiver comprising a housing including at leasty one wall substantially closing an aii` chamberspace, said housing having a pair of openings therein remotely spaced from each other, a sound translating unit including a diaphragm mounted behind one of said openings for vibratory movement and closing o the air chamber space behind said one opening from the atmos phere, said diaphragm having one surface fully exposed to the atmosphere through said one opening and its other surface fully exposed to said air chamber space, the dimensions of the other of said openings being so small that it functions as a bass reiex opening, and an acoustical horn mounted on said housing in relation 5 to one of said openings for transmitting sound Waves emanating therefrom, said horn being constituted of a hinged cover for said housing, side pieces extending from opposite edges of said cover, and a wall of said housing.

2. A sound system according to claim 1 characterized in that said acoustical horn is associated with said one opening, and further characterized in that said air chamber space and-said horn are so dimensioned that the particle velocit? in said bass reflex opening is in phase with the output of said horn.

3. A sound system according to claim 1 characterized in that said acoustical horn is associated with said bass reflex opening, and further characterized in that said horn and said housing are so dimensioned that the particle velocity in said one opening is in phase with the output of said horn.

HARRY F. OLSON. JOHN PRESTON.

References Cited in the le of this patent UNITED STATES PATENTS Number Number Name Date Cisco July 5, 1927v Harrison Oct. 29, 1929 Baumann Dec. 31, 1929 Fisher May 20, 1930 Thuras July 26, 1932 Coumbopolous Aug. 1, 1933 Jefferis Nov. 21, 1933 Olson Dec. 17, 1940 Kellogg June 16, 1942 Reid Jan. 23, 1951 FOREIGN PATENTS Country Date France Aug. 6, 1931

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