LOUDSPEAKER SYSTEM

Abstract: The disclosure relates to an audio signal reproduction system having one or more of the following features: (1) a loudspeaker having (a) a flat frequency response and (b) a predetermined power response; (2) two loudspeakers adapted to be positioned relative to one another so that they reproduce a stereophonic image substantially independent of the listener's position along a listening line spaced from the loudspeakers and nonintersecting a line extending between the two speakers; (3) an improved cross-over network having a substantially constant input impedance as a function of frequency; (4) a power sensor for sensing the power applied to a transducer so that audio signals are transmitted over a first signal path through the system when the sensed power is above a predetermined minimum level, and over a second path when the sensed power falls below the minimum level; (5) a power monitoring circuit to prevent a loudspeaker driver from being overdriven; and (6) a circuit for substantially balancing the signal energy levels between two audio chan­ nels over a long period of time.

Description: The present invention relates to a loudspeaker system comprising a plurality of loudspeaker drivers for producing sonic signals in response to electrical driving signals, at least two of said loudspeaker drivers each producing sonic signals substantially within the same frequency range, means for mounting said loudspeaker drivers in a predetermined spatial array so that at least two of said drivers producing sonic signals substantially within the same frequency range are angularly spaced with respect to one another about a central axis, and modifying means for modifying the phase responses of at least two of said loudspeaker drivers producing signals substantially within the same frequency range relative to one another so that said array of loudspeaker drivers produces a combined predetermined radiation dispersion pattern arround said central axis in response to said electrical driving signals. Unless described otherwise, a term 'frequency response' shall be used hereinafter to refer to the frequency response of a loudspeaker in one direction whereas the term 'power response', unless described otherwise shall refer to the amplitude response of a loudspeaker averaged 360° around the vertical axis of the loudspeaker in an anechoic chamber. Conventional loudspeakers typically have a low frequency speaker driver (a 'woofer'), a mid-frequency speaker driver and a high frequency speaker driver (a 'tweeter') all mounted on a front panel of a speaker cabinet so as to radiate in the direction of a major or prime axis, the latter being adapted to be direction oriented in the directional of the listening area. These conventional loudspeakers typically exhibit radiation dispersion patterns (unless otherwise described, the term 'radiation dispersion pattern' as used herein shall mean the power radiated by a speaker as a function of the angle about the vertical axis of the speaker) and frequency responses which are strongly variable functions of the horizontal angular position of the listener relative to the speaker cabinet of each loudspeaker. Generally, the lower the frequency of a sonic signal generated by the loudspeaker, the longer the wavelength and the greater angular dispersion of the sonic signal. These conventional loudspeaker systems generally are designed so that radiation generated along the prime or major axis of radiation propagation of the loudspeaker, i.e., typically in the direction in which the speaker drivers face, oriented typically towards the listener, will be such that the on-axis frequency response is flat. However, off angle responses, i.e., positions other than on the front axis of the speaker, have an uneven frequency response. As a gross generalization it can be said that signals below about 500 - 600Hz will be substantially omnidirectional becoming less so as the frequencies increase from about 20Hz to the 500 - 600Hz limit. The signals generated by the midrange drivers are substantially half omnidirectional at the lower frequency limit of about 500 - 600Hz of the midrange frequencies, while becoming less so with increasing frequencies to the upper limit of 8KHz. The signals of the tweeter become more closely unidirectional as the frequency of the signal increases from 8KHz to the 20KHz. Another approach in speaker design is to provide a power response in which the average power propagated into the listening area over all directions is substantially constant as a function of frequency. Signal attenuation averaged over all horizontal directions is therefore frequency independent. However, when the actual power radiated is measured in any one direction the power propagated can vary substantially as a function of angular position about the vertical axis of the loudspeaker. Thus, in conventional loudspeaker designs, there is a trade-off between a flat on-axis frequency response and a flat average power in the listening area. More recent loudspeaker designs have attempted to provide both in a single design. These designs, however, utilize relatively expensive, unusual speaker drivers (such as Walsh drivers) to make a flat on-axis frequency and flat power response simultaneously possible. From the DE-C 975 222, a loudspeaker system is known using four loudspeaker drivers arranged in a common plane and being driven by electrical signals via means for modifying the phase response of at least two of said loudspeaker drivers. The resulting radiation dispersion pattern of the four loudspeaker drivers may be changed from circular to kidney-shape in predetermined directions by modifying the phase responses of the individual loudspeaker drivers. This radiation dispersion pattern only may be maintained over a narrow frequency range unless special loudspeaker designs having a constant radiation dispersion pattern with frequency are used. The FR-C 24 07 635 does show a loudspeaker system wherein three loudspeaker drivers of different frequency range are disposed in each surface of a truncated pyramid of triangular cross section. This loudspeaker system cooperates with a reflecting wall to obtain a desired radiation dispersion pattern which also is not constant with frequency. It is an object of the present invention to provide an improved loudspeaker system utilizing state of the art electromagnetic loudspeaker drivers and having a preselected radiation dispersion pattern as well as a substantially flat on-axis frequency response and a substantially flat power response. This object is achieved by a loudspeaker system as set out in claim 1. Advantageous and preferred embodiments and developments of the loudspeaker system according to the present invention are set out in the subsidiary claims. In accordance with an embodiment of the present invention, a loudspeaker system comprises at least two loudspeakers each having a predetermined radiation dispersion pattern such that when properly oriented with respect to one another they can produce a stereophonic image substantially independent of listener position along a listening line spaced from both loudspeakers and non-intersecting with a line extending between the two loudspeakers. This loudspeaker system reproduces a stereophonic image within a predefined space such that the perception of the image by the listener is substantially independent of the listener's position along a listening line spaced from the two loudspeakers and non-intersecting with a line extending between the two loudspeakers. The loudspeaker system comprises at least two loudspeakers. Each loudspeaker includes a plurality of loudspeaker drivers for producing sonic signals in response to electrical driving dignals, means for mounting the loudspeaker drivers in a predetermined three-dimensional array at least some of the loudspeaker drivers of the array being angularly spaced with respect to one another about the vertical axis of the loudspeaker and means for modifying the frequency and phase responses of at least some of the loudspeaker drivers of the array of loudspeaker drivers of the array so that the array of loudspeaker drivers produces a combined predetermined power dispersion pattern and a substantially flat frequency response at all positions around the vertical axis in response to the electricla driving signals. The radiation dispersion patterns of the two loudspeakers complement one another when the loudspeakers are in a mutually preselected orientation with respect to one another s that the loudspeakers produce the stereophonic image in response to the electrical driving signals substantially independent of the listener's position within the predefined space along a listening line spaced from the loudspeakers and non-intersecting a line extending between the two loudspeakers. In the drawings the same numerals are used to refer to like parts. Fig. 1 shows the front view of a typical prior art loudspeaker having a woofer, a mid-range frequency speaker and a tweeter; Fig. 2 shows a cross-sectional view taken along line 2-2 in Fig. 1; Fig. 3A and 3B respectively show a simplified radiation dispersion pattern at two different frequencies for a typical woofer; Fig. 4A and 4B respectively show typical radiation dispersion patterns at two different frequencies for a typical mid-range speaker and a typical tweeter; Fig. 5 graphically illustrates the power output of a typical prior art loudspeaker, such as shown in Fig. 1 and 2, as a function of frequency wherein the on-axis frequency response is constant; Fig. 6 graphically illustrates a simplified plot of the power output of a loudspeaker as a function of frequency so that the power output is substantially constant; Fig. 7 shows a front view of a preferred embodiment of a loudspeaker made in accordance with the present invention; Fig. 8 is a cross-sectional view taken through the woofers taken along line 8-8 in Fig. 7; Fig. 9 is a cross-sectional view taken through the mid-range speaker drivers along line 9-9 in Fig. 7; Fig.10 is a cross-sectional view taken through the tweeters along line 10-10 in Fig. 7; Fig.11 is designed to show typical radiation dispersion pattern of the tweeters of the preferred embodiment of the present invention at relatively high frequencies; Fig.12 shows the radiation dispersion pattern of the tweeters of the preferred embodiment of the present invention at relatively low frequencies; Fig.13 shows a plan view of a stereophonic loudspeaker system of the prior art to illustrate the concept of stereophonic imaging and the problems of the prior art; Fig. 14 is a plan view of a loudspeaker system including at least two speakers for creating a stereophonic image substantially independent of listener position along the listening line; and Fig.15A to 15C is a schematic diagram of the preferred embodiment of the modifying means formed by a cross-over network utilized in the present invention. Referring to the prior art loudspeaker of Fig. 1, the typical loudspeaker 10 includes a woofer 12 for generating sonic signals generally within a low-frequency range, typically between about 20Hz and 500Hz; a mid-range speaker 14 for generating sonic signals generally within a midfrequency range, typically between about 300Hz and 3 KHz; and a tweeter 16 for producing sonic signals within a range of about 2 KHz and 20KHz. As shown in Fig. 2, the three different types of speakers are typically vertically mounted, on above the other on the front panel 18 of the speaker cabinet so that the prime axis or direction of radiation propagation is in front of the loudspeaker. As shown in FIG. 3A, the woofer typically produces almost an omnidirectional radiation dispersion pattern for low-frequencies, for example, between 0 and 100Hz for a 30,5cm (12 inch) woofer, while a less omnidirectional radiation pattern at higher frequencies of the output of the woofer, e.g., between about 200 and 500Hz. Similarly, the mid-range and tweeter speakers provide radiation dispersion patterns as shown in FIGS. 4A and 4B, wherein FIG. 4A is the lower frequencies of each of the speakers, while FIG. 4B illustrates the dispersion pattern of the higher frequencies of the speaker. As shown, the dispersion pattern of FIG. 4A is typical of a 10cm (4 inch) mid-range speaker at 2 - 3 KHz, while the radiation dispersion pattern of FIG. 4B is typical of such a tweeter speaker at 10 - 20KHz. When this particular type of prior art speaker is designed to provide a flat frequency response the amplitude of the power output of the speakers along the prime axis of propagation is generally flat as a function of frequency as shown in FIG. 5. However, as shown in FIG. 5, the radiation dispersed in directions other than the prime axis will not be constant as shown. Accordingly, another approach in speaker design is to provide a flat power response into the listening area. Specifically, the speaker is designed so that the energy radiated into the listening area averaged overall direction is flat with respect to the frequency range within which the speaker radiates sound. The average power output of such a prior art system is shown in FIG. 6 as having a flat response. However, as shown, the power output in any one particular direction may not be flat such as the on-axis radiation curve as well as the off-axis radiation curve. Accordingly, in these conventional prior art loudspeaker systems there is a trade-off. A loudspeaker system can be designed to have a flat on-axis frequency response resulting in a power curve which is not flat as shown in FIG. 5, or a system can be designed to have a power curve which is flat resulting in an on-axis response which is not flat as shown in FIG. 6. In accordance with the present invention, a loudspeaker system is designed to provide both a flat frequency response and a radiation dispersion pattern which can be easily predesigned without necessarily resorting to the use of unusual speaker drivers. The preferred embodiment of the present invention comprises ordinary electromagnetic loudspeakers, angularly spaced relative to one another about the verical axis of the loudspeaker cabinet and includes means for modifying as a function of frequency, the phase and amplitude of the driving signals fed to each loudspeaker driver so as to obtain a substantially flat power and on-axis frequency responses. More particularly, as shown in FIG. 7, the preferred embodiment of the loudspeaker system includes a loudspeaker cabinet 28, including suitable baffle structure (not shown) for supporting four woofers 32A, 32B, 32C, and 32D mounted substantially in the same horizontal positions, equidistant from and at 90° intervals about the vertical axis 26 of the loudspeaker. Similarly, four mid-range speakers 34A, 34B, 34C, and 34D are mounted substantially in the same horizontal positions, preferably above the respective woofers 32, equidistant from and at 90° intervals about the vertical axis 26, as shown in FIG. 9. Finally, six tweeters 36A, 36B, 36C, 36D, 36E and 36F are mounted substantially in the same horizontal positions, preferably above the midrange speakers, equidistant from and at 60° intervals about the vertical axis 26, as best shown in FIG. 10. The front of loudspeaker 28 is defined by the positions of speakers 32A, 34A, and 36A. The front of the loudspeaker defines the direction of propagation of the prime axis of the loudspeaker. In accordance with the present invention each of the woofers 32, midrange speakers 34 and tweeters 36 each may be any type of speaker which is known in the art. Preferably, each of the speakers is of the electromagnetic type, each woofer being a conventional 25,4cm (10 inch) speaker. By controlling the frequency and phase responses of each woofer 32, mid-range speaker 34, and tweeter 36, the desired frequency response and power dispersion pattern are achieved. Specifically, the responses of the auxillary speakers, woofers 32B-32D, mid-range speakers 34B-34D, and tweeters 36B-36F are used to complement the responses of the main speakers 32A, 34A and 36A to provide an overall flat frequency response and a preselected radiation dispersion pattern: Thus, when the main speaker drivers 32A, 34A and 36A are omnidirectional at a particular frequency, the response required from the auxiliary speaker drivers may be such as to reduce the omnidirectionality of the main driver (by radiating substantially out-of-phase) then producing the preselected radiation dispersion pattern. When more energy is radiated by the main driver at another particular frequency along the prime axis than radiated in off-axis directions, the auxiliary drivers begin to fill in for the overall dispersion characteristics. In this manner, one can tailor the amplitude and phase response of each speaker so that the system frequency response is flat in any direction, but the overall radiation dispersion pattern conforms to a preselected pattern. This is illustrated by FIGS. 11 and 12, wherein FIG. 11 shows the response of each tweeter at a relatively high frequency, while FIG. 12 shows the response of each tweeter at a relatively low frequency. More particularly, in FIG. 11 at the higher frequencies each tweeter will generate its radiation substantially within an approximate 60° angle symmetrical about the direction of propagation of radiation from the driver, indicated by the corresponding arrow 40 so that the radiation dispersion pattern of each tweeter 36 is substantially the same as indicated by the patterns 42 to produce an overall radiation dispersion pattern 44. On the other hand, at the lower frequencies generated by the tweeters as shown in FIG. 12 the main driver 36A will generate the dispersion pattern indicated by the pattern 46A which is more omnidirectional than the pattern 42A. Thus, the adjacent drivers 36B and 36F need to contribute less, and therefore would produce patterns similar to 46B and 46F, respectively. In a similar manner, the dispersion patterns produced by the drivers 36C, 36D, and 36E produce the varied dispersion patterns 46C, 46D, and 46E which combine with the other dispersion patterns 46A, 46B, and 46F to provide the overall dispersion characteristics substantially similar to the dispersion pattern 48. Thus, by varying as a function of frequency the amplitude and phase of the driving signals provided to the tweeters, the overall radiation dispersion pattern including patterns 44 and 48 can be determined in a similar manner for all of the frequencies generated by the drivers 36. In a similar manner by controlling as a function of frequency the amplitude and phase of the driving signals to the mid-range speakers 34A-34D and the woofers 32A-32D the overall radiation dispersion patterns can be made substantially similar to patterns 44 and 48 throughout the entire frequency range of the loudspeaker, e.g., 20Hz - 20KHz. Where it may be desirable to radiate greater power from the loudspeaker in one direction than, for example, another, the overall radiation dispersion pattern can be easily modified by varying the particular phase and power responses of each of the main and auxiliary speakers. Thus, a particular array of loudspeaker drivers (a minimum of two) can be made directional by a combination of their relative locations to one another, and by controlling as a function of frequency, the phase and amplitude of the driving signals used to drive the loudspeaker drivers. In accordance with one aspect of the present invention, in the preferred embodiment, the specific radiation dispersion patterns of each of a pair of separate loudspeakers can be developed such that a stereophonic image can be created between the loudspeaker systems substantially independently of a listener's position within a listening area along a listening line spaced from the loudspeaker systems and non-intersecting with a line extending between the loudspeaker systems. This will be more evident by the following description with respect to FIGS. 13 and 14. Referring to FIG. 13, conventional prior art loudspeakers 10 can, for example, produce constant average power outputs. If the power output of each speaker 10 is approximately the same then a listener positioned approximately equidistant from each speaker 10 along a listening line L₂ , parallel to a line L₁ extending between the two loudspeakers, the listener will perceive an apparent stereophonic image (the apparent location of the source of the sound as heard by the listener) approximately in the center between the two speakers, as indicated by the point I. With the conventional prior art system shown in FIG. 13, the listener receives information from the speakers which includes amplitude and phase. Various certain phase delays occur between the left and right speakers. A small interaural phase delay occurs as one moves closer to one speaker than the other. Thus, should the listener move along the listening line L₂ in a direction toward either one of the loudspeakers 10, the stereophonic image will no longer be perceived and at some point all of the sound will appear to come from one speaker 10 only. In accordance with the present invention, two speakers 28A and 28B are designed to each produce radiation dispersion characteristics such that the stereo image I will appear to be in the same location regardless of the listener's position along the listening line L₂, as well as substantially any other position in the listening space except those positions between the two loudspeakers, although best results ae achieved if the listener is positioned at a distance greater than one-quarter the distance between the two speakers 28A and 28B. In this regard, therefore, the listening line L₂ can be defined as any line spaced from the loudspeakers 28A and 28B so long as it does not intersect the line L₁ between the two loudspeakers. In order to achieve this, it has been determined that in addition to having a flat frequency response in substantially all directions, each speaker should have a radiation dispersion pattern in which a greater power output will be provided along the prime axis of the speaker at each frequency than in other directions, so that the radiation dispersion pattern at each frequency will be substantially oval as shown in FIG. 14. In particular, two loudspeakers 28A and 28B are preferably oriented so that the prime axes of radiation propagation 50A and 50B (the prime direction of radiation propagation of each of the main speaker drivers 32A, 34A and 36A of each loudspeaker) of each loudspeaker is directed toward the opposite speaker so that the prime axes are aligned with one another, and define the line L₁, If both speakers receive the same amount of power, the stereo image I will be created in the center between the two speakers. However, because of the predesigned radiation dispersion pattern of each speaker, as the listener moves along the listening line L₂, the sound intensity from the nearer loudspeaker is reduced, while that from the further loudspeaker is increased, thus, the stereo image will still appear to be generated from the same point I between the two speakers. In order to provide the radiation dispersion pattern similar to the type shown in FIG. 14, the preferred cross-over network utilized with each of the speakers is shown in FIGS. 15A-15C. This preferred network is further designed to provide a substantially flat input impedance as a function of frequency so that any audio amplifier (not shown) of sufficient power can be utilized. More particularly, referring to FIG. 15B, the input signal from any power amplifier of sufficient power is provided to the two input terminals 100 and 102. Terminal 102 is connected to system ground, while terminal 100 is connected to the woofer network section shown in FIG. 15A, the mid-range network section shown in FIG. 15B, and the tweeter network section shown in FIG. 15C. More particularly, the terminal 100 is connected in FIG. 15A to the inductor 104, which in turn is connected through capacitor 106 to system ground. Inductor 104 is also connected through each of the inductor 108, resistor 110, and capacitor 112 to the speaker connection 114. The latter in turn is connected to the main woofer driver 32A, driver 32A being suitably grounded. Inductor 104 is also connected through resistor 116 to one plate of capacitor 118. The other plate of capacitor 118 is in turn connected to the speaker connection 120. Inductor 104 also is connected to resistor 122, which in turn is connected to inductor 124. The latter is connected to connector 120. Inductor 104 is also connected through each of the inductor 126 and capacitor 128 to inductor 124. The speaker connection 120 is in turn connected to both of the side woofer drivers 32B and 32D, the drivers being suitably grounded as shown. Finally, the inductor 104 is connected to each of the resistors 130 and 132. Resistor 130 in turn is connected to one plate of the capacitor 132, the latter having its other plate connected to the speaker connection 134 and inductor 136. Inductor 136 is in turn connected to system ground. Resistor 138 in turn is connected through inductor 140 to the speaker connection 142 and to one of the plates of capacitor 144, the latter having its other plate connected to system ground. The speaker connections 134 and 142 are connected to the two input terminals of the rear woofer speaker driver 32C. Referring to FIG. 15B, terminal 100 is connected to the input inductor 150, which in turn is connected to one plate of capacitor 152. The other plate of capacitor 152 is connected to system ground. Inductor 150 also is connected to one plate of capacitor 154, the other plate being connected to the remainder of the mid-range network section. Specifically, capacitor 154 is connected through conductor 156 to system ground and directly to the speaker connection 158. Connection 158 is in turn connected to the main mid-range speaker driver 34A, the latter being suitably grounded. Capacitor 154 is also connected to the resistors 157 and 162. Resistor 157 is in turn connected through capacitor 159 to the speaker connection 160. Resistor 162 is connected through inductor 164 to the connection 160. Connection 160, in turn, is connected to each of the side mid-range speaker drivers 34B and 34D, the drivers each being suitably grounded. Capacitor 154 is also connected in a similar manner to each of the resistors 166 and 172. Resistor 166 is connected through capacitor 168 to the speaker connection 170. Resistor 172 is connected through inductor 174 to connection 170. Connection 170, in turn, is connected to the rear mid-range speaker driver 34C which in turn is suitably grounded, as shown. Referring to FIG. 15C, the terminal 100 is connected to one plate of capacitor 180 of the tweeter network section. The other plate of capacitor 180 is connected to the remaining network section for the tweeter drivers 36A through 36F. More particularly, capacitor 180 is connected through inductor 182 to system ground. Capacitor 180 is also connected to the speaker connection 184 which, in turn, is connected to the front tweeter speaker driver 36A, the latter being suitably grounded, as shown. Capacitor 180 is also connected to two resistors 186 and 192. Resistor 186 is connected through capacitor 188 to the speaker connection 190. Resistor 192 is connected through inductor 194 to the connection 190. Connection 190 is connected to each of the tweeter speaker drivers 36B and 36F, the latter drivers being angled 60° to either side of the driver 36A. Drivers 36B and 36F are suitably grounded as shown. Capacitor 180 is also connected to resistors 196 and 202. Resistor 196 is connected through capacitor 198 to the speaker connection 200. Resistor 202 is connected through inductor 204 to connection 200. The latter, in turn, is connected to each of the tweeter speaker drivers 36C and 36E, each of the drivers being displaced 120° to either side of the main driver 36A and suitably grounded, as shown. Capacitor 180 is also connected through resistor 206 to the capacitor 208, which in turn is connected to the speaker connection 210. Capacitor 180 is also connected through inductor 212 to connection 210. Speaker connection 210 is connected to the rear tweeter speaker driver 36D displaced 180° from the main speaker driver 36A and suitably grounded as shown. Preferably, the components of the cross-over network sections shown in FIGS. 15A-15C have the following values shown in TABLE A, although it will be appreciated that these values may vary depending upon the specific speaker drivers used and the type of radiation dispersion pattern desired. In TABLE A each inductor is indicated with the prefix L, each resistor is indicated with the prefix R and each capacitor is indicated with the prefix C. The inductors are given in values of henries, with MH indicating millihenries, the resistors are given in values of ohms, and the capacitors are given in values of farads, with uf indicating microfarads. The cross-over network shown in FIGS. 15A, 15B and 15C thus control the amplitude and phase, as a function of frequency of each of the driving signals. applied to the speaker drivers. As shown in FIG. 15A, the main woofer speaker 32A will receive most of the bass signal which passes through the woofer network section and thus functions as the main speaker driver. On the other hand, the rear woofer speaker 32C is driven by a driving signal which is largely out of phase with the speaker driver 32A. The portion of the network including resistors 130 and 138, capacitors 132 and 144, and inductors 136 and 140 for driving the rear woofer speaker driver functions as an all-pass network. At low frequencies the capacitors will function essentially as open circuits and the signal is transmitted across the driver in one direction. However, at high bass frequencies, the capacitors will function essentially as short circuits and the driving signal transmitted to the speaker driver 32C is in the opposite direction or 180° out-of-phase. The mid-frequency portion of the bass signal will be applied to speaker driver 32C in a combination of both. It therefore should be appreciated that by controlling the amplitude and phase of the driving signal, as a function of frequency, for each of the speaker drivers the cross-over network will essentially shape the radiation dispersion pattern for the woofers 32A-32D, for the mid-range speakers 34A-34D, and for the tweeters 34A-34F. With the particular values set forth in TABLE A the stereophonic image I of FIG. 14, created between the tow loudspeakers 28A and 28B will be substantially independent of the listener position along the listening line L₂. Adjust the amplitude relative to the listener location so that the apparent location remains unchanged. Thus, due to the contoured radiation dispersion pattern provided, as the listener moves closer to one loudspeaker 28 the volume drops with respect to the closer speaker, while it increases with respect to the more distant speaker. It should be appreciated that each loudspeaker 28 and the cross-over network of Fig. 15A - 15C can be designed to provide any type of radiation dispersion pattern by rearranging the positions of the speaker drivers and/or modifying the components of the cross-over network. For example, where a loudspeaker is used against a wall or in corner the wall and corner will function as acoustic reflectors so that the radiation dispersion pattern should be modified to account for these reflections and the pattern should conform to the predetermined pattern in the particular position the speaker is placed. However, the frequency response should always be made to be substantially independent of the angle about the vertical axis in any direction within the listening area.

Claims: A loudspeaker system comprising a plurality of loudspeaker drivers (32A-32D, 34A-34D, 36A-36F) for producing sonic signals in response to electrical driving signals, at least two of said loudspeaker drivers each producing sonic signals substantially within the same frequency range; means (28) for mounting said loudspeaker drivers (32A-32D, 34A-34D, 36A-36F) in a predetermined spatial array so that at least two of said drivers producing sonic signals substantially within the same frequency range are angularly spaced with respect to one another about a central axis (26); and modifying means (104-144, 150-174, 180-212) for modifying the phase responses of at least two of said loudspeaker drivers producing sonic signals substantially within the same frequency range relative to one another so that said array of loudspeaker drivers produces a combined predetermined radiation dispersion pattern (44, 48) around said central axes in response to said electrical driving signals, characterized in that said modifying means (104-144, 150-174, 180-212) modify the frequency and phase responses of said at least two of said loudspeaker drivers (32A-32D / 34A-34D / 36A-36F) by modifying the amplitude and phase of the electrical driving signals applied to each of said drivers as a function of the frequency thereof so that a flat response is obtained. A system according to claim 1, characterized in that said modifying means (104-144, 150-174, 180-212) modify said frequency and phase responses of said loudspeaker drivers so that the frequency response of said array is substantially independent of the position of a listener about said central axis (26). A system according to claim 1 for defining a stereophonic image within a predefined space, said system comprising at least two loudspeaker arrays, characterized in that the radiation dispersion patterns of said two loudspeakers (32A-32D / 34A-34D / 36A-36F) producing sonic signals substantially within the same frequency range complement one another so that when said loudspeaker arrays (28A, 28B) are positioned within said predefined space in a preselected orientation, said loudspeaker arrays reproduce said stereophonic image within said predefined space in response to said electrical driving signals substantially independent of the listener's position within said predefined space along a listening line (L2) spaced from the loudspeaker arrays (28A, 28B) and nonintersecting a line (L1) extending between said loudspeaker arrays. A system according to claim 3, characterized in that said modifying means (104-144, 150-174, 180-212) modify said frequency and phase responses of said loudspeaker drivers of said loudspeaker arrays so that the frequency response of said array of each loudspeaker is substantially independent of the position of a listener within said predefined space along said listening line (L2). A system according to claim 4, characterized in that said frequency response is substantially flat. A system according to claim 4 or 5, characterized in that said combined radiation dispersion pattern of each of said arrays (28A, 28B) is such that a greater power output is provided along the line (L1) connecting said arrays than in other directions, said combined radiation dispersion pattern being substantially oval in shape. A system according to any of the claims 3 through 6, characterized in that each of said loudspeaker arrays (28A, 28B) includes a prime axis (50A, 50B) along which more energy is propagated than in any other direction, and in that said loudspeaker arrays are in said mutually preselected orientation when said prime axes (50A, 50B) are aligned and directed toward one another. A system according to claim 7, characterized in that said loudspeaker drivers are electromagnetic. A system according to claim 8, characterized in that said means for mounting said loudspeaker drivers includes support means (28) for supporting said drivers producing sonic signals substantially within the same frequency range in substantially the same plane normal to said central axis (26). A system according to claim 9, characterized in that said support means (28) of each said loudspeaker array supports said loudspeaker drivers producing sonic signals substantially within the same frequency range substantially equidistantly from the corresponding central axis (26). A system according to claim 10, characterized in that said support means (28) of each said loudspeaker array supports said loudspeaker drivers producing sonic signals substantially within the same frequency range in a substantially equiangularly spaced-apart relation around the corresponding central axis (26). A system according to claim 11, characterized in that said plurality of loudspeaker drivers of each said loudspeaker array include at least two groups of drivers, each of the loudspeaker drivers of one group producing sonic signals substantially within the same first frequency range and each of the loudspeaker drivers of the other group producing sonic signals substantially within the same second frequency range at least in part different from said first frequency range, and said means (28) for mounting said loudspeaker drivers includes support means for supporting the loudspeaker drivers within each of said groups of each loudspeaker in substantially the same plane normal to the corresponding central axis (28) of said loudspeaker array. A system according to claim 12, characterized in that said modifying means include a cross-over network (104-144, 150-174, 180-212) for modifying as a function of frequency, the amplitude and phase of the electrical driving signals applied to each of said drivers of each loudspeaker array. A system according to claim 12, characterized in that said loudspeaker drivers of one of said groups of each loudspeaker array is axially spaced along the corresponding central axis (26) from said loudspeaker drivers of said other group of that loudspeaker array. A system according to claim 14, characterized in that said first frequency range is below said second frequency range. A system according to any of the claims 11 through 15, characterized in that said plurality of loudspeaker drivers of each said loudspeaker array includes at least one group of woofers (32A-32D), at least one group of mid-range speakers (34A-34D) and at least one group of tweeters (36A-36F), and in that said means (28) for mounting said drivers of each of said loudspeaker arrays includes means for supporting said woofers of each said loudspeaker array each in a first axial position equiangularly spaced about and equidistant from said central axis (26) substantially within a first plane normal to said axis, means for supporting said mid-range drivers of each said loudspeaker array each in a second axial position equiangularly spaced about and equidistant from said central axis (26) substantially within a second plane spaced from and parallel to said first plane, and means for supporting said tweeters of each said loudspeaker array in a third axial position equiangularly spaced about and equidistant from said central axis (26) substantially within a third plane substantially parallel to and spaced from said first and second planes, said second plane being disposed between said first and third planes. A system according to claim 16, characterized in that said plurality of loudspeaker drivers of each said loudspeaker array includes four woofers (32A-32D), four mid-range drivers (34A-34D) and six tweeters (36A-36F).

Inventors: DAVIS, MARK F.
Applicants: MILLS-RALSTON, INC.
Application year: 1984
Main classification: H04R1
IPC codes: H04R3, H04R1, H04R5