Tweeter Bidirectional Radiating

The present invention relates in general to loudspeaker systems and more particularly concerns novel apparatus and techniques for efficiently and economically reproducing sound with relatively compact inexpensive apparatus.

The internationally known BOSE 901, 601, 501, 301 and 201 loudspeaker systems embody principles for simulating in the home sound of the character heard in the concert hall by providing, inter alia, a good balance of reflected and direct sound. U.S. Pat. Nos. 4,133,975 and 4,266,092 describe the BOSE 301 loudspeaker system having a woofer mounted on a front panel and a tweeter mounted on an angled panel beside the woofer, both drivers radiating into the listening area only from the front surface of each driver. Crossover or transition network means couple electrical energy from an input terminal pair to the woofer and tweeter so that the woofer and tweeter radiate energy over a common frequency range.

It is an important object of this invention to provide an improved loudspeaker system.

According to the invention, there is cabinet means for supporting loudspeaker drivers. First loudspeaker driver means supported by the cabinet means is for radiating sound energy to the front over a first frequency range and has a first polar response. Second loudspeaker driver means comprising a tweeter supported by the cabinet means is for radiating sound energy over a second frequency range mostly higher than the first frequency range from one surface inward and from the other surface outward. Preferably, radiation from the first surface is inward and forward and that from the rear surface is rearward against a reflecting surface. The second loudspeaker driver means is preferably an openbacked tweeter mounted on an angled baffle of the cabinet means free from obstruction to both the rear and the front to allow radiation to occur from both surfaces.

Numerous other features, objects and advantages of the invention will become apparent from the following specification when read in connection with the accompanying drawing in which:

FIGS. 1, 2 and 3 are a diagrammatic representation of a stereo loudspeaker system according to the invention positioned along the rear wall of a room illustrating the forward and inward radiation of the tweeter, the rearward and outward radiation from the tweeter back surface, and the combination of tweeter radiation and woofer radiation, respectively;

FIGS. 4 and 5 are front and side views, respectively, of a loudspeaker cabinet according to the invention;

FIG. 6 is a view through section 6--6 of FIG. 4;

FIGS. 7 and 8 are front and rear view, respectively, of a tweeter according to the invention; and

FIG. 9 is a view through section 9--9 of FIG. 7.

With reference now to the drawing and more particularly FIG. 1 thereof, there is shown a diagrammatic representation of a stereo system according to the invention in a room 10 adjacent a rear wall 11 that intersects left and right walls 12 and 13, respectively. Left loudspeaker cabinet 14L and right loudspeaker cabinet 14R each have a woofer 15L, 15R and a tweeter 16L, 16R located nearer to the left and right walls 12 and 13, respectively, than to woofer 15L and 15R, respectively. Loudspeaker cabinets 14L and 14R are arranged as the mirror images of each other with the axes of tweeters 16L and 16R aligned along the length of forward radiation indicating patterns 17L and 17R, respectively. Each tweeter 16L, 16R, is mounted on a baffle to provide a desired low frequency tweeter response, typically by cancellation of sound pressure front to back around the tweeter baffle starting at 2 KHz and will be down 20 dB at 500 Hz. Each baffle-mounted tweeter is oriented at an angle and displacement relative to the axis of each woofer 15L, 15R to provide a preferred balance of outward radiating energy to inward radiating energy so that about 60% of the energy first reflects off a wall before entering the listening area while about 40% enters the listening area directly and perferred acoustic coupling to the woofer to provide a smooth midrange response. Each baffle-mounted tweeter is practically surrounded by open grill which provides an acoustically transparent cabinet allowing unobstructed sound to travel from the enclosure in a controlled pattern. High frequencies from each tweeter are directed inward for improved localization as represented by patterns 17L and 17R and outward for an improved spatious stereo image as represented by patterns 18L and 18R shown in FIG. 2.

The outward firing energy represented by patterns 18L and 18R is reflected off sidewalls 12 and 13, respectively, to provide a broad sound source that extends beyond loudspeaker cabinets 14L and 14R while enhancing stereo separation throughout the listening area.

Referring to FIG. 3, there is shown the stereo system of FIGS. 1 and 2 according to the invention with the representations of the forward-inward radiation 17L, 17R, outward-rearward radiation 18L, 18R, and woofer patterns 19L, 19R. The result is a quality of sound that approaches concert hall realism with proper stereo separation perceived from nearly any seating position in the room.

Referring to FIGS. 4, 5 and 6 there are shown front, side and sectional views, respectively, of a cabinet according to the invention. The cabinet includes a front panel 21, side panel 22, rear panel 23, front angled panel 24 and rear angled panel 25, top panel 26 and bottom panel 27. Front panel 21 is formed with an opening 31 for accommodating a woofer, such as 15L, 15R. Front angled panel 24 is formed with an opening accommodating port tube 32. Rear panel 23 is formed with an opening 33 for accommodating a terminal panel.

An angled tweeter baffle 34 is formed with an opening 35 for accommodating a tweeter, such as 16L, 16R. The angle between tweeter baffle 34 and the front edge of bottom and top panels 26 and 27 is typically 67.degree. so that the axis of tweeter opening 35 with the front panel is substantially 33.degree.. The tweeter diameter is about three times the width of the baffle portion adjacent the horizontal diameter of tweeter opening 35.

Referring to FIGS. 7, 8 and 9, there are shown front, rear and sectional views, respectively, of a tweeter according to the invention. The tweeter comprises a basket 41 attached to front plate 42 with a magnet 43 sandwiched between front plate 42 and back plate 43. Frame 41 supports spider 43" which carries voice coil 44 to which the center of cone 45 is attached. Dust cover 46 covers the center of cone 45. The edge of cone 45 is fastened to the edge of frame 41 by pad ring 47. Frame 41 also carries on its rear terminal strip 51 with tinsel 52 connecting the voice coil leads to terminals on terminal strip 51. Frame 41 is formed with a number of openings 53 that allow high frequency energy to radiate to the rear.

The invention has a number of features. The angled tweeter baffle directs high frequency energy both forward and inward and rearward and outward for reflection to achieve advantages noted above. The angled side panel carrying port tube allows port tube 32 to clear the rear of a woofer, such as 15L, 15R while creating additional volume for the woofer. The port is vented into this volume before air hits the grille cloth which would cause a noise and cloth flapping. Only the right cabinet has been shown in FIGS. 4-6, it being understood that the left cabinet is the mirror image of the right cabinet.

There has been described novel apparatus and techniques for providing a loudspeaker system characterized by exceptional realistic sound reproduction with a compact relatively inexpensive structure. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concepts. Consequently, the invention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed by the apparatus and techniques herein disclosed.