EP0155266B1

EP0155266B1 - Loudspeaker structure

Info

Publication number: EP0155266B1
Application number: EP19830903131
Authority: EP
Inventors: Henry Oliver Wolcott
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-09-06
Filing date: 1983-09-06
Publication date: 1991-03-20
Also published as: DE3382223D1; EP0155266A1; WO1985001176A1; EP0155266A4

Abstract

An up-firing woofer loudspeaker (12) is mounted atop a truncated pyramidal enclosure (1). A down-firing tweeter (5) is aligned above the woofer. A sound-reflecting sphere (4) is disposed between the woofer and the tweeter. When the sphere is aligned therebetween omni-directional sound is radiated in both horizontal and vertical planes. When the sphere is positioned to the rear a hemispherical pattern is obtained. This pattern is desirable when the loudspeaker structure is positioned against a wall. Ducted ports (3) or a folded horn (20) within the enclosure enhance very low frequency sound.

Description

This invention pertains to electro-acoustical transducer structures, particularly the acoustic aspects thereof.
The use of both a "woofer", or base notes only transducer, and a "tweeter", or treble notes only transducer, have constituted high-fidelity wide-range loudspeaker structures for some time. The acoustic performance of the system, as judged at the listener's ears, determines the pragmatic results. The better this performance, the more nearly a lifelike effect of "live" performers is obtained;i.e.,"realism".
SoundSpan Speaker Systems, of B.I.C/AVNET, Westbury, N.Y., employ three transducers; a woofer pointing ("firing") downward, a mid-range transducer employing a horn, and a treble transducer also employing a horn. These transducers are positioned coaxially one above the other in the order recited; the latter two transducers firing upward.
By factual analysis, an omnidirectional sound pattern is presumably obtained, but it is not seen how this pattern could be obtained vertically as well.
The sound-emitting elements being stacked coaxially vertically, an away-from-the-wall placement of the loudspeaker would be required to give the intended omnidirectional lateral sound fidelity. However, if placed against a wall the backwardly-directed sound conflicts with the direct sound, and an irregular amplitude vs. frequency characteristic occurs.
Williams, Jr. in United States patent 4,200,170, discloses a "Pyramid Speaker Assembly", having two vertically aligned four-sided pyramids and one cone loudspeaker firing downwardly upon the lower pyramid.
An alternate embodiment merely doubles the structure vertically and employs two identical cone loudspeakers.
A further alternate embodiment assembles two of the initial structures, with one of them inverted, so that two cone loudspeakers are employed, one up-firing and one down-firing.
The four-sided pyramid causes a four-leaf clover horizontal dispersion of sound. The vertical pattern of the loudspeaker is not enhanced.
Typically, tweeters are not employed at all, save for a further embodiment in which a tweeter is disposed off-axis but "- in alignment with a ridge -" of a pyramid. This causes a two-only (opposed) cloverleaf for the high frequencies involved.
It is seen that a uniform omnidirectional pattern for either woofer or tweeter sound is not attained.
The numerous sharp edges in the sound field are expected to give an uneven amplitude vs. frequency characteristic because of acoustic diffraction.
Westlund in United States patent 3,819,006, discloses a three-globe (sphere) structure, each having an identical loudspeaker within a globe, plus a spaced concave reflector that is elongated to serve the plural globes.
The acoustic structure and functioning thereof is quite the opposite of the present invention and cannot suggest the same. Standing waves occur within the globes.
In general, the art has been wont to combine plural loudspeakers, up to six per unit of a stereo pair of loudspeakers, typically by merely firing the sound outward from the cabinet that supports the loudspeakers, but does not shape the sound pattern thereof.
Still others partially or totally enclose loudspeaker units in an enclosure that "colors" the sound by having a predominant resonant frequency. This causes the sound to have the characteristic of a particular musical instrument, rather than a uniform characteristic of amplitude vs. frequency that is suited to reproduce all musical instruments and voice with fidelity.
US-A-3500953 discloses a loudspeaker structure in which a cone loudspeaker in an enclosure is directed upwardly at a curved surface, whose orientation affects the distribution of radiated sound. FR-A-2163600 discloses a loudspeaker structure having a fixed sphere whose vertical axis is colinear with a speaker axis, and whose loudspeakers are of the cone type.
According to the invention as defined in claim 1 at least one up-firing woofer is surmounted by a sound-reflecting sphere, which, in turn, is surmounted by a down-firing tweeter having a dome radiator, with the sound waves thereof impinging upon the same sphere.
This configuration provides omni-directional sound, both horizontally and vertically.
According to the invention by moving the sphere rearwardly a hemispherical horizontal and vertical pattern is obtained, such as is desirable if the loudspeaker structure is to be placed against the wall of a room.
One embodiment includes a downwardly extending horn within the structure housing the woofer. The horn is front-firing. It is folded.
A truncated plural-sided pyramid is employed to house the woofer. No two sides thereof are parallel. The sides are stiffened to prevent acoustic vibration.
Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which:
Fig. 1 is a perspective view of the loudspeaker structure showing the disposition of the principal components.
Fig. 2 is a perspective view of an alternate embodiment of the loudspeaker structure in which a base horn is utilized.
Fig. 3 is a vertical sectional view of the structure of Fig. 2 along lines 3 - 3, showing the construction of the folded base horn, in section.
Fig. 4 is a fragmentary perspective view of the base of Fig. 1, in which an auxiliary baffle radiator (ABR) is employed.
In Fig. 1, the slant of all of the sides of truncated pyramid 1 is typically 1 in 6, i.e., for each 6 centimeters (cm) of height the surface is inwardly inclined 1 cm.
Within nominal limits of two or three to one, the structure of this invention can be embodied in different sizes. The criterion is determined by the acoustic parameters, which must be properly inter-related. This is further set forth below.
A typical size for the base pyramid is 70 cm high, with a width at the bottom of 54 cm and at the top of 40 cm. The base pyramid is supported incrementally above the floor on four feet, elements 2, each having a height of approximately 9 cm.
The bottom of the base is closed by a rigid surface 10 that is inclined with respect to the horizontal truncated surface top, typically with a slant of 2 in 6. Acoustic ports, preferably three ducted ports 3, are provided. These are hollow cylinders extending into the interior volume of the base, typically being 9 cm in diameter by 15 cm in length.
The edges of the top of the base pyramid are rounded with an approximately 2 cm radius to prevent sharp-edge acoustic diffraction.
Physical support for sphere 4 and tweeter 5 is provided by typically four vertical members, as metal angles 6. These extend from the bottom of base pyramid 1 to a four-arm spider 7 at the top of the structure. Part way up two horizontal members 8 are individually fastened to an adjacent pair of vertical angles 6 to support sphere 4 at the extremities of a horizontal diameter thereof. Preferably two hollow rods that are internally threaded at each end pass through holes in the sphere and receive screws that slide in slot 9 in the horizontal member for the support of the sphere. This allows a forward and back adjustment of the position of the sphere.
Angles 6 each have a quarter-round wood inner surface to provide a rounded surface for preventing acoustic diffraction. Of course, rounded metal tubes may be substituted for angles 6 to prevent acoustic diffraction.
The embodiment of Fig. 1 has four woofers, 12, 12', 12", 12'", symmetrically disposed in the upper surface of the truncated base structure 1. These are electrically connected in parallel and are the equivalent of one large woofer. Each of the four may have a diameter of approximately 15 cm, and be the long-throw type TP165F, of which Peerless Audio Manufacturing Corp. is a manufacturer. The acoustic range is from approximately 30 hertz to 5,000 hertz.
Tweeter 5 has a 3 cm dome radiator and an external diameter of approximately 12 cm with a vertical cylindrical length of 3 cm. The central circular portion of spider 7 is also approximately 12 cm so that edge acoustic diffraction is minimal. The four arms of the spider are each approximately 3 cm high by 1.5 cm thick. The inventive effort is to minimize any structure around the tweeter, so that it approaches the effect of being suspended in vacant space. The tweeter range is from 1 kilohertz to 20 kilohertz, and may be the soft dome type of Audax, of France,, type HD13D34H.
The relative placements of the woofer, sphere and tweeter are determined by acoustic considerations. The structure of this invention allows a large advance in acoustic fidelity by maintaining coherency in amplitude and phase of the sound over the whole range of sound reproduced, and in all directions from the loudspeaker.
It will be realized that when a given sound involves audio frequencies that are emitted by both the woofer and the tweeter, these frequencies must reach the ear of the listener at the same instant of time; otherwise a "mushiness" occurs.
The inertia of the larger moving system of the woofer is greater than that of the smaller moving system of the tweeter. Accordingly, when a step function waveform, such as from tap dancing, is impressed upon both loudspeakers the sound is emitted first from the tweeter and second from the woofer. Although the interval between the two sounds may be only a fraction of a millisecond, the effect is discernible. The effect can be eliminated by spacing the tweeter farther from the sphere than the woofer, in the present novel structure.
The difference in the spacing is determined by the dynamic characteristics of the two speakers involved. It is constant for those speakers. Thus, the vertical position of the sphere can be fixed for a given pair of speakers. For the speakers previously identified, the vertical position is 29 cm from the diaphram of the tweeter to the center of the sphere and 25 cm from the woofers to the center of the sphere. Considering the reflection areas on the sphere for the tweeter and the woofer, this amounts to 2.58 cm difference in path length. If this was not taken into consideration, at the cross-over frequency of 2000 hertz a phase difference of 54° would exist. This is undesirable for impulse sounds.
Loudspeakers are invariably operated in a room, such as the living room of a family residence. Under such conditions the sound heard by a listener is that directly from the loudspeaker, and that reflected from the walls, ceiling and floor of the room.
Although it may not be generally known, acoustic testing carried on by the inventor prior to the invention of the present loudspeaker structure revealed that although the direct sound from the usual loudspeaker might have a smooth amplitude response characteristic as a function of frequency, that characteristic from the sides of the loudspeaker had numerous "hills and valleys" and was the very opposite to a smooth response. The same was true for the characteristic from the rear of the loudspeaker, usually with a different set of hills and valleys.
In a room all of these sounds reach the listener, giving a jumbled response that belies realism and naturalness of the sound. Such a response may be accepted by a listener, as what has always been heard from a loudspeaker. However, once the clarity and realism of a superior response has been heard the advance in technique is readily appreciated.
Superior response is obtained with the present loudspeaker by virtue of the reflection of sound from both tweeter and woofer from a single sphere. Two directional patterns are available, depending upon the placement of the sphere with respect to the loudspeakers.
For placement of the loudspeaker structure away from a wall in a room, such as might occur in a large room, a uniform spherical pattern in both horizontal and vertical planes is desired and is secured by locating the sphere coaxially with respect to both the tweeter and the woofer. In most high-fidelity sound reproduction, a stereophonic ("stereo") signal sound source is provided and two of the present loudspeaker structures are used, spaced one from the other by a few meters.
When the loudspeaker structure(s) are to be placed against a wall of a room it is desirable to limit the horizontal sound directional pattern to a hemisphere; i.e., to the free space in front of the wall.
This is accomplished by moving sphere 4 rearwardly a distance of 5.4 cm in the present embodiment. In this position the vertical axis of the tweeter impinges upon the surface of the sphere at an angle of 45°. Because the remainder of the sphere above the 45° point is an obstruction, the sound from the tweeter cannot radiate backward toward the wall.
The upper audio frequencies in the woofer range, such as at the crossover frequencies, typically from 1,000 to 3,000 hertz, are given some directivity by the position of the sphere, similar to the tweeter frequencies. However, low audio frequencies, such as 100 hertz and below, are notoriously non-directional, but this does not affect the performance of the loudspeaker structure of this invention.
Certain modifications of the structure of this loudspeaker may not be made and still retain its performance.
The positions of the woofer and tweeter may not be interchanged. When up-firing, the sound from the tweeter reaches the ceiling of the room and destroys the otherwise "point source" of the loudspeaker structure as previously described. Also, the base truncated pyramid must then be inconviently above the sphere, and floor loading of the base frequency ports is absent.
Another undesirable modification is to position the ducted ports 3 on a side of the truncated enclosure 1, rather than at the bottom. Measurements show that a loss of low frequency response occurs, amounting to over 30% of the lower limit response over that obtained with the ports in the bottom of the truncated enclosure. The greater phase lag of the low frequencies out of the bottom ports because of the greater distance from the woofer is believed responsible for the improvement.
Substitution of an auxiliary baffle radiator (ABR) may be made in the bottom of the truncated enclosure with results approaching those obtained with the ducted ports 3. The ABR is a flat resiliently mounted stiff diaphram, in this instance about 30 cm in diameter, 11.
The sphere is typically hollow and of glass, or an equivalent very hard substance, such as ceramic or a glass-like plastic. Wood and similar soft substances are not satisfactory. With translucent glass or equivalent, a light-emitting element,such as light bulb 30, can be contained within the sphere and the same thereby illuminated. Music-controlled lamps may also be utilized.
While the true sphere is a preferred shape, this may be modified to an elongated "sphere", having the major axis vertical. This accomplishes functioning according to this invention by reason of providing increased extreme side projection when in the recessed position with the loudspeaker structure against a wall due, to the acoustic geometry involved.
An example of another preferred embodiment of the subject invention is shown in Fig. 2.
A distinguishing feature is an internal folded horn in the base truncated pyramid 21, having a forward-opening mouth 20.
A single large woofer 22, such as the type LR1280C of Professional Audio Systems, a California corporation, is disposed in the top horizontal surface of the truncated pyramid base. The downward emission of sound therefrom passes through horn 20, while the upward emission of sound passes to sphere 24, which typically is the same as prior sphere 4.
Four fully-cylindrical external tubing members 26 extend from the bottom of pyramid 21 to above the same for supporting sphere 24 and tweeter 25. The latter is supported by metal spider 27.
The woofer-sphere-tweeter relationship is as before. To illustrate the two prime positions that the sphere can occupy, forward and back; sphere 4 is shown in the back position, while sphere 24 is shown in the forward, or vertically coaxial position.
The top edges of truncated pyramid 21 are rounded with a 3 cm radius to prevent sound diffraction, as has been previously explained.
Typical dimensions for the embodiment of Fig. 2 are; for the truncated pyramid, 77 cm high, 69 cm on a side at the bottom, and 43 cm on a side at the top. The tweeter is 53 cm above the top surface of the truncated pyramid, and is 30 cm above the center of the sphere, which is again 36 cm in diameter.
As before, spider arms 27 are of minimal cross-section and the diameter of that structure around the tweeter is not greater than that of the tweeter itself.
The opening of horn 20 extends totally across the bottom of truncated pyramid 21 and is 30 cm high by 65 cm wide in the embodiment of Fig. 2.
The horn is formed of baffles within the truncated pyramid, as shown in Fig. 3. When thus formed the length of the horn is approximately 215 cm.
First baffle 35 is disposed at a downward slant of approximately 12° to the horizontal closely below the frame of woofer 22. The baffle extends 75% of the distance from the front surface of the truncated pyramid base.
Second baffle 36 is disposed horizontally and extends 70% of the distance from the rear surface of the base.
Third baffle 37 is disposed at a downward slant of approximately 15° to the horizontal and extends 65% of the distance from the front surface of the base.
These baffles extend completely from side to side of the base and are securely fastened thereto by glue or equivalent means.
Additionally, stiffeners 41, 42, 43 extend from the rear corners at an approximate angle of 30° from the vertical and are fastened to horizontal stiffeners 38, 39, 40 respectively. The latter are centrally located, side to side, and are individually rigidly attached to baffles 35, 36, 37, respectively.
The baffle and stiffener structure is typically fabricated of dense particleboard 1.2 cm thick, while the truncated pyramid base is 2 cm thick. An inner lining of the truncated pyramid base of "soundboard"; i.e., a fiber board that is loosely packed, is desirable.
Also, it is desirable but not mandatory, to install five formed curved elements 45 of a sound-reflecting material, such as fiberglass, in the several sharp corners existing between the baffles and the front and rear of the truncated pyramid base. These provide a desirably relatively smooth inner surface for the horn chamber.
The truncated pyramids illustrated herein have square bases. These are typical, but not essential, to the acoustic functioning of the invention. By geometrical definition a pyramid may have a triangular, square or polygonal base, and these variants may be herein employed.
An electro-acoustical transducer structure is, of course, a definitive term for a loudspeaker structure. The input is electrical, the output is acoustical, and the transducer is the device that accomplishes the transformation of energy from one form to the other.
Hardwood cross-braces 47 and 48 may be employed to give acoustic stiffness to base 1.

Claims

An electro-acoustical transducer structure, comprising
(a) at least one woofer (12,22) oriented to emit sound vertically upwardly;

(b) a sound reflecting sphere (4,24) disposed above the woofer (12,22),

(c) a tweeter (5,25) disposed above the sphere and oriented to emit sound vertically downwardly,

(d) a base enclosure (1,21) of approximately truncated pyramidal shape with no two sides parallel,

(e) wherein the sphere (4,24) has a location with its vertical axis colinear with the axis of at least the tweeter or offset in a horizontal direction from the axis of at least the tweeter or is adjustable to such an offset location, and

(f) the tweeter (5,25) has a dome radiator.
A transducer structure according to claim 1 wherein said woofer (22) and said tweeter (25) are coaxial.
A transducer structure according to claim 1 having a plurality of woofers (12) arranged symmetrically about a vertical axis which is coaxial with the tweeter axis.
A transducer structure according to any one of claims 1 to 3 in which said sphere (4,24) is rearwardly offset by approximately 30% of its diameter with respect to the tweeter axis.
A transducer structure according to any one of claims 1 to 4 which additionally includes a folded horn (20) within said base enclosure (21) having its exit aperture in the front of that enclosure.
A transducer structure according to claim 5, in which said folded horn (20) is formed of plural baffles (35,36,37), each disposed against alternate opposite sides of said base enclosure (21) and extending approximately 70% across the interior space of said base enclosure, and each said baffle includes a centrally located stiffener (38,39,40) that extends fully across the interior space of said base enclosure.
A transducer structure according to claim 6, which additionally includes curved elements (45) fitted into each corner formed by a said baffle and a side of said base enclosure against which said baffle is disposed, to form a curved interior path for said folded horn at each said corner.
A transducer structure according to any one of the preceding claims, which additionally includes means (2) to incrementally elevate the bottom of said base enclosure above a floor, and plural ducted acoustic ports (3) disposed in the bottom of said base enclosure.
A transducer structure according to claim 8, in which said bottom (10) is inclined at an angle to a surface supporting said at least one woofer (12).
A transducer structure according to claim 8 or claim 9, in which the number of plural ducted acoustic ports is three.
A transducer structure according to any one of claims 1 to 7 which includes an auxiliary baffle radiator (11) disposed in the bottom (10) of said base enclosure.
A transducer structure according to any one of the preceding claims which additionally includes plural vertical members (6,26) each having a rounded surface, means to fasten said vertical members to said base enclosure, means (8,28) to fasten said sphere to said vertical members, and means (7,27) to fasten said tweeter to said vertical members.
A transducer structure according to any one of the preceding claims, wherein said sphere (4,24) is of light permeable material, and a light-emitting element (30) is disposed within said sphere to illuminate the external surface thereof.