Sound direction system

This invention provides a sound source system capable of producing a desired coverage pattern with high SPL that may be steered towards a desired listening area. The sound source system may provide an array of sound sources where the coverage pattern and SPL may depend on the height, width, and depth of the assembled array. Adding height and width to the array may narrow the vertical and horizontal coverage patterns that are projected, respectively. To maintain a substantially constant coverage pattern, a frequency shading techniques may be used to keep the height of the array constant relative to the wavelength. Adding depth to the array may provide greater SPL with minimal effect on the coverage pattern because array's height and width have not changed. The sound source system may also coherently sum in the main lobe and provide substantial off-axis rejection. This may be done using an end-fired related principle where each sound source in the array may be delayed proportional to its delay distance. The delay distance for each sound source may be the shortest distance between the sound source and the reference plane. This allows the sound source system to provide a desired coverage pattern with a desired SPL.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention provides a sound source system capable of producing a desired coverage pattern with a high sound pressure level that may be steered towards a desired listening area.

2. General Background and State of the Art

In sound reinforcement applications, a sound source that produces an effective high sound pressure level (SPL) may be desired at low frequencies. This is often accomplished by forming an array of sound sources that are stacked together to increase the SPL. As each of the sound sources in the array generate sound, they add to generate a main lobe of sound energy, and depending on how the array is configured, other side lobes of sound energy may be generated as well. The main lobe and the side lobes of sound energy form a coverage pattern of sound energy that has increased SPL on axis, however, the main lobe of energy may become excessively narrow and the side lobes may be undesirable.

As the array increases in size, the coverage pattern may become narrower. For example, a taller array will generally have a narrower vertical coverage pattern than a shorter array. And a wider array will generally have a narrower horizontal coverage pattern than a narrow array. This narrowing may be desirable in some instances, but it can also limit the number of low-frequency sound sources that can be effectively added to an array. This can be a problem where a wider or more consistent coverage pattern is desired without the detrimental effects of lobing, where there are dips and peaks in the response. Excessive narrowing may also occur when using a large curved array of speakers. In addition, an array may be inefficient and may not provide a great deal of useful off-axis attenuation—that is rejection directly behind the array. Therefore, there is a need for a sound source system that is capable of directing the coverage pattern with high SPL at low frequencies without the problem of narrowing the coverage pattern.

SUMMARY

This invention provides a sound source system capable of producing a desired coverage pattern with high SPL that may be steered towards a desired listening area. The sound source system may provide an array of sound sources where the coverage pattern and SPL may depend on the height, width, and depth of the assembled array. Adding height and width to the array may narrow the vertical and horizontal coverage patterns that are projected, respectively. To maintain a substantially constant coverage pattern, a frequency shading techniques may be used to keep the height of the array constant relative to the wavelength. Adding depth to the array may provide greater SPL with minimal effect on the coverage pattern because array's height and width have not changed. This allows the sound source system to provide a desired coverage pattern with a desired SPL.

The sound source system may also coherently sum in the main lobe and provide substantial off-axis rejection. This may be done using an end-fired related principle where each sound source in the array may be delayed proportional to its delay distance. The delay distance for each sound source may be the shortest distance between the sound source and the reference plane. Based on the respective delay distance for each sound source, a processor may delay the audio signal for each sound source by dividing the delay distance by the speed of sound. With such delays, the sound energy from each sound source may be aligned normal to the reference plane, creating a coherent lobe of energy from the array that is normal to the reference plane. For steering, the reference plane may be rotated vertically relative to a given angle that causes the main lobe of energy from the array to be directed at that given angle.

A variety of array configurations may be developed for a particular application by trading off height, width, depth, and delay settings in the array. For example, an array may include four or more dual-sound source elements that may be steered at an angle between 0 and −90 degrees from the reference axis that may be horizontal. The steering may be accomplished by delaying each low frequency sound source element back to a reference plane that is normal to the direction that the array is steered. The resulting sound energy is pushed forward, coherently summing in the direction of aiming and minimizing energy directed off-axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Driving a group of sound sources with signals delayed relative to a common physical reference may provide a relatively high directivity of sound.FIG. 1illustrates two sound sources100and102that have a delay distance106apart along an axis104that is in the direction of the aiming108.FIGS. 2A through 2Dillustrate the effect on the sound pressure level (SPL) as a function of degrees off-axis as the spacing between the two sound sources increases. If the front sound source's signal102is delayed corresponding to the sound propagation time within the space106between the two sound sources100and102, then there may be coherent summing in the direction108of the array. If the delay distance106of the two sound sources100and102is chosen to be ¼ of a wavelength, then at that frequency there may be a null behind the array. This is the result of the forward sound source being delayed ¼ wavelength added to the physical separation of ¼ wavelength. The energy directly behind the array may be offset ½ wavelength creating a null at that single frequency. With two element or sound source array, this null change may be useful attenuation for about half an octave or so centered about that frequency.

When multiple sound sources are used in an end-fired configuration, the length of the array may determine its low frequency useful limit, while the resolution or the delay distance106of the sound sources may determine its useful upper limit. These upper and lower limits may be when the side lobes or off-axis attenuation are less than about 6 dB relative to the main lobe. For example, at the lower limit, approximately 6 dB of off-axis rejection may be provided when the length of the array is approximately ¼ wavelength. At the upper frequency limit, the side lobes may remain 6 dB less than the main lobe when the resolution or spacing of the sound sources is less than approximately 0.4 to 0.5 times the wavelength.

FIG. 3illustrates an array with five sound sources:302,304,306,308and310. The spacing312between two sound sources may be 1 foot apart so that the overall length314of the array is about 4 feet. In this example, the aiming direction316may be in the direction of the axis318.FIGS. 4A through 4Dillustrate the effect on SPL as a function of degree off-axis as the frequency increases from 70 Hz to 450 Hz. At 70 Hz the array is approximately ¼ wavelength as illustrated inFIG. 4A, the array provides approximately 6 dB off-axis attenuation, and may be less at lower frequencies. As illustrated inFIG. 4D, at 450 Hz, where the 1 foot spacing of the array is about 0.4 times the wavelength, the side lobes remain suppressed by at least 6 dB. As illustrated inFIGS. 4B and 4C, intermediate frequencies of 140 Hz and 280 Hz are also shown to help describe the polar characteristics of the array. Accordingly, a multiple-element end-fire array may produce substantial off-axis rejection. Note that the main lobe may have a relatively flat on-axis polar response throughout much of its effective coverage area with a relatively steep polar cut-off. Increasing the number of elements may provide greater off-axis rejection, however, the main lobe directivity may also increase.

A three-dimensional array may be created by adding elements to give height, width and depth. Depending on the height, width, depth and resolution (delay distance), the three-dimensional array may have certain desirable characteristics. For example, a variety of arrays may be configured so that the coverage area may be narrow, while coherently adding power. The array may also use frequency shading to create a single lobe of sound energy at a desired power level and polar pattern that is appropriate for the application. Frequency shading techniques may be used to substantially maintain the ratio between the height of the array and the wavelength so that the coverage pattern may be more constant. Other frequency shading techniques known to one skilled in the art may be used to provide a more consistent coverage pattern.

FIG. 5illustrates a sound source system500capable of providing a main lobe506of sound directed along a vector510from a reference point R to a point V. A main lobe may have a useful coverage pattern where the sound energy is within certain dB from the maximum sound energy. For example, sound energy that is at least 6 dB within the maximum sound energy may describe the main lobe. That is, if the maximum sound energy at point P is 60 dB then sound energy that is at least 54 dB at point N may describe one of the boundary point of the main lobe506. The main lobe506may have a height angle α and a width angle φ that provides suitable height and width that defines STWX with the point V at about its center to cover the area where the audience is situated.

The vector510may be formed between groups of sound sources formed along a first plane502and a second plane504. The vector510may also be substantially normal to a reference plane512. The sound sources in the first and second planes may produce the lobe506. A portion of the first plane502may include a rectangular array ABCD of sound sources. For example, a sound source F may be a part of the array. A portion of the second plane504may include a rectangular array JKLM of sound sources. These arrays ABCD and JKLM may be symmetrical so that the sound source F in the array ABCD may correspond to the sound source H in the array JKLM.

The dimensions of the lobe506may be expressed with reference to a coordinate system511, where lines AB and JK may be parallel to the y-axis, and lines AD, BC, JM, and KL may be parallel to the z-axis. Angle θ between the line AB and the projection AE may reflect the arbitrary orientation of the vector510with respect to the y-z plane. In other words, point E may be any point along the lines BC and CD. The projection AE may be substantially aligned with the vector510so that the projection AE may be normal to the reference plane512as well.

Each sound source in each array may receive the full power and frequency spectrum, however, each sound source may be delayed generating sound depending on the geometry of the array. For example, the appropriate delay between sound radiating from a reference sound source at point A and the sound radiating from sound source F may be proportional to a delay distance between point A and point G (AG); where point G may be defined as the intersection of a projection AE of the vector510onto plane502passing through point A. A line FG may be perpendicular to the projection AE at point G. The location of the sound sources H in the second plane502may be symmetrical to the location of the sound source F in the first plane502, so that the delay distance for the sound source H relative to point J may be same as the delay distance AG for the sound source F. With the delay being the same, the two sound sources F and H may be driven from the same signal or amplifier.

A single plane of sound sources may also be used where the vector510may appear in the plane as the sound sources. Sound sources may be arranged in any number of planes in any relationship to the vector510. There is no requirement that more than one sound source be located in the same plane. Sound sources may also be arranged so that there are more than two planes, however, an approximation of a plane may be used to simplify the design of suitable delays. When sound sources are arranged in two planes as inFIG. 5, the first and second planes502and504may be parallel to each other, but they may also intersect one another. The line of intersection may include reference point R or may be any distance to the rear of reference point R. The planes502and504may also be parallel or within a few degrees of being parallel to the vector510.

The plane502may include any number of sound sources. These sources may be arranged in a grid-like array having regular spacing in both directions, parallel to AD and parallel to AB. The spacing along AD may be different than the spacing along AB. A portion or all of the sound sources in the plane502may be symmetrical to the sound source arranged in plane502.

FIG. 6illustrates the plane502with twenty sources, where each sound source may be identified by its respective row and column numbers. For example, the source611is at point A in row 1 and column 1; and source634is at row 3 and column 4. Each delay may be determined in part by a line segment beginning at the source and intersecting at a right angle the projection604along the vector510as discussed above forFIG. 5. The delay at the source611at point A may be zero. For the source621, the segment651intersects projection604at point “a.” The delay distance A-a may be proportional to a delay for the source611. For source631, the segment652intersects projection604at point “b.” The delay distance A-b may be proportional to the delay for the source631. For source612, the segment653intersects projection604at point “c.” The delay distance A-c may be proportional to a delay for the source612. For source641, the segment654intersects projection604at point “d.” The delay distance A-d may be proportional to a delay for the source641. Other delays for sources622,632,613,642,623,633,614,643,624,634,615,644,625,635and645may be determined in a similar manner with reference to intersection points “e”-“s.”

When the reference plane602is common with a particular source, sound may be reinforced along the vector510by generating sound from that particular source. For example, sound at time t1at point A may represent a wave front tangent to the reference plane602containing point A. At time t2, the wave front may have traveled to point “a,” and therefore the reference plane602may include the line segment651. The sound radiating from source621reinforces the wave front when the same signal that was radiated at time t1is radiated at time t2from source621. In other words, sources611and621may be driven from the same signal, provided that the signal at source621is delayed a time equal to the difference between time t2and t1where the difference is the time it takes for the wave-front from the reference plan602to travel the delay distance to the line segment651for the sound source621.

The way the sound sources are arranged in an array may affect the two angles α and φ at a given frequency. With reference to vector604, increasing the number of sound sources perpendicular to vector604may reduce the height angle α. With reference to coordinate system511, increasing the number of sound sources in the x-axis or width may reduce the width angle φ. Increasing the number of sound sources along vector604may increase the total output of the sound power level in the lobe with relatively small affect on the two angles φ and α. The two angles α and φ may vary throughout the operating frequency range of the sound source system because at higher frequencies where the wavelengths are smaller, the size of the array may effect the coverage pattern of the two angles φ and α.

For more consistent coverage pattern throughout the bandwidth, a frequency-shading technique may be used. This may be done by reducing the effective height of the array as the frequency increases to maintain the effective height of the array with respect to wavelength. That is, a more consistent coverage pattern may be maintained by keeping the effective height of the array inversely proportional to frequency. InFIG. 6, the effective height654may be the distance between two lines656and658that intersect the two outermost sound sources615and641and are parallel to the projection604. The array620may be divided into many sections such as an inner section650and the outer section652. The inner section650may include sound sources that are within a predetermined distance from the projection604such as611,621,612,622,613,623,633,624,634,635, and645. The outer section652may include sound sources that are outside of the predetermined distance such as631,641,632,613,642,614,643,615,644, and625. As frequency increases, the effective height of the sound source may be reduced by only operating the sound sources in the inner section650so that the effective height of the array may be inversely proportional to frequency. Similar frequency-shading technique may be used for more consistent horizontal coverage pattern throughout the frequency range or bandwidth. The projection604may be centered within the inner section so that the main lobe of sound energy may be centered along the desired direction where it is aimed.

A variety of frequency-shading techniques may be used for more consistent vertical coverage pattern. One way is to use a low-pass filter for the sound sources in the outer section652, and using a high-pass filter for the sound sources in the inner section650. Frequency shading may be also accomplished through other filtering techniques.

Increasing the number of sound sources along the vector604may also increase the amount of off-axis rejection. InFIG. 5, point O may be on the rear side of point R aligned with the vector510, and if the distance between points O and R is substantially similar to the distance between points P and R, the SPL at point O may be more than 18 dB right than at point R. This means that a system designer may predict the direction and degree of off-axis rejection.

FIG. 7illustrates a method700for providing a sound lobe from the sound source system500. The vector510may be defined from the reference point R along the central axis of the desired sound lobe (702). A reference plane512may be translated (704) or moved along the vector510starting from the reference point R. The reference plane512may be substantially perpendicular to the vector510. A delay for each of the sound sources may be defined (706) as proportional to the delay distance corresponding to each sound source. Translating (704) and defining (706) may be repeated for each sound source. If more consistent coverage pattern is desired (708) then frequency-shading technique (710) may be applied. To provide the sound lobe, each sound source may be driven according to its respective delay from an audio signal source (712). A variety of factors may determine the number and position of the sound sources such as desired polar characteristics, existing equipment, budget constraints, desired power level, analysis, measurements, or tests. The sound sources may be arranged arbitrarily in space at any known coordinates.

FIG. 8illustrates a sound source system for directing sound from numerous sound sources, each sound source being driven with a signal that is delayed relative to a time reference. An audio system800may include an audio signal source802, delay elements814-820, frequency-shading elements822-830, amplifiers804-812, and sound sources502including sources611-645. An audio signal source may include any circuit that provides an audio signal to the sound source system. The signal may include analog audio frequencies unmodulated signal or any conventional modulated signal. The signal may be digitized for any conventional digital communication such as a processor for digital signal processing, or formatted in packets for network communication. For example, the audio signal source802of conventional construction may include any program source such as a microphone, instrument pickup, prerecorded media, and audio portion of a video signal to provide a signal AP on a line803.

An amplifier may include any interface circuit for providing a drive signal to a sound source. For example, amplifiers804-812may be conventional amplifier adapted to receive and provide analog audio drive signals to the sources502. Amplifiers802-812may also receive digital signals and include conventional digital to analog conversions to provide analog drive signals to sources502. For example, each amplifier may drive one or more sound sources such as conventional sound sources, or sometimes referred to as transducers or drivers. A sound source may include any sound source, transducer, or sound source that modulates the medium such as the air surrounding the sound source to emit audible sound. A sound source may include any conventional configuration of one or more sound sources, horns, cavities, ports, and sound treatment materials.

A delay element may include an analog or digital circuit that provides an output signal corresponding to an input signal with a delay as discussed above. For example, delay elements814-820may include a digital to analog converter or receive a signal AP in a digital format; a storage device having sufficient capacity to support delay without loss of signal resolution; and a digital to analog converter for providing an output analog signal to the amplifiers804-812. A series of analog storage devices may also provide delay such as charge-coupled devices. The amount of delay may be programmed manually, by initialization, or dynamically via a conventional digital processor (not shown) coupled to each delay element.

The frequency shading elements822-830may be located before the respective sound sources611-645. For example, inFIG. 8, the frequency shading elements may be located between the delay element and the amplifier. A variety of frequency-shading techniques may utilize low and high pass filters or other filtering techniques.

The audio signal source802may provide a signal AP to an amplifier804that drives the sound source611of the sources502. The signal emitted by the sound source may be used as a time reference. The signal AP may be delayed via delay element814a delay21corresponding to a row 2 and column 1 for the sound source621with reference to the delay distance A-a. For example, for the sound source621, the delay21may be A-a (meters) divided by the speed of sound in ambient air, approximately 340 m/s adjusted. Similarly, the delay31corresponding to a row 3 column 1 may use the delay distance A-b to calculate the delay31.

The sources502may be sources that are in the plane ABCD (611-645) as well as sources in the plane JKLM and other planes (not shown) or combination of both planes. The audio system800may include additional delay elements, and amplifiers to drive additional sound sources. When signals to drive a number of sound sources are substantially similar in delay time, a common delay signal may be used for those particular sound sources. In such a case, if an amplifier is capable of driving multiple sound sources, a common amplifier may be used to drive the common sound source elements. For example, when the plane504includes an array corresponding to the array in the plane502in the number and position of the sound sources, a pair of corresponding sound sources (including a reference pair) may share the output of an amplifier. In other words, 40 sound sources (20 per plane) may be driven from 20 amplifiers and 19 delay elements.

FIGS. 9 and 10illustrate a sound source element910incorporating two sound sources913and915that are mounted on a base920. Each sound source913and915may include an electromagnetic motor914and916and a cone919and917. The base920may include a cavity912enclosed in conventional enclosure materials such as wood and may be empty or filled with conventional sound treatment materials such as spun glass fibers. Each cone919and917may define a portion of the cavity912and emits sound from the rear (outer) surfaces924and926of the cones919and917, respectively, so that the electromagnetic motor for each of the two sound sources face away from each other.

With the electromagnetic motors914and916facing out into the atmosphere, heat from the motors914and916may be more readily dissipated. Two cones919and917may also be moved closer together because the two electromagnetic motors914and916do not take up any space in the cavity912. Moving the two cones919and917as close as possible yet providing enough volume in the cavity912for the two sound sources913and915to work properly may allow the array to provide broader horizontal coverage or width angle φ.

Sound sources913and915may be driven in phase to modulate the total volume of the cavity912. The cones919and917may face each other along the axis of cylindrical symmetry918. The volume of the cavity912may also be designed to support a desired frequency emitting capability of the sound sources913and915depending on whether larger, smaller, or mixed sizes of sound sources are used. Sound sources may have a cone diameter in the range from about 4 inches (101.6 mm) to about 36 inches (914.4 mm) for operating between 20 Hz and about 2000 Hz. In particular, the sound source element910may have 12-inch (304.8 mm) diameter cones and operate between 60 Hz and about 250 Hz. For 12-inch (304.8 mm) diameter cones, the spacing930between the outer ends of the cones919and917may be between about 0.2 and 0.3 times the wavelength at the left operating frequency of about 250 Hz. With the spacing930between the two cones, a broader horizontal coverage or width angle φ of at least about900may be provided up to the cross-over frequency.

FIGS. 11 and 12illustrate a module1110incorporating multiple sound source elements910arranged in a column. The sound source elements may be coupled to each other in any manner. For example, the module1110may include three sound source elements1114,1116and1118arranged in a column. Axis of cylindrical symmetry may be shown for each source1115,1117and1119. The module1110may be capable of operating in any orientation.

FIGS. 13 and 14illustrate a sound source element1310incorporating two sound sources1313and1315side by side into a base1308. Each sound source1313and1315may include an electromagnetic motor1316and1320, and a cone1319and1317, respectively. Two cavities may be formed between the base1308and the two sound sources1313and1315, where the divider wall1326separates the two cavities. Each cone1319and1317may define a portion of the cavities1312and1314, respectively, and emits sound from the rear (outer) surface of the cone. With the electromagnetic motors1316and1320facing out into the atmosphere, heat from the motors1316and1320may be more readily dissipated into the atmosphere. Alternatively, with separate cavities1312and1314, the motors1316and1320may be inside of the cavities1312and1314.

With the two sound sources1313and1315being side by side, the delay distance to a reference plane may be different for the two sound sources. Accordingly, the two sound sources1313and1315may be delayed independently corresponding to its respective delay distance.

When the sound source element1310is used in close proximity to other sound source elements, a portion of the exterior1308may serve as a baffle to partially isolate the cones1317,1319from other sound source elements. The cones1319and1317may operate on their respective axes1318and1322. The volume in the cavities1312and1314may be designed to support a desired frequency emitting capability of sound sources1313and1315depending on the size of the sound sources that are used. Sound sources may have a cone diameter in the range from about 4½ inches (12.7 mm) to about 36 inches (914.4 mm) for operation in the frequency range from about 920 Hz to about 1400 Hz. In particular, the sound source element1310may have 15-inch (381 mm) diameter cones and operate between about 50 Hz and about 250 Hz. And for about 15-inch (381 mm) cones, the spacing1328between the two axis1318and1322for the two cones1319and1317may be about 17 inches (431.8 mm).

FIGS. 15 and 16illustrate a sound source element1510incorporating two sound sources1513and1523into a base1508having a trapezoidal side cross-section. The sound source1513may include an electromagnetic motor1514and a cone1515that are within its respective cavity1512. The sound source1523may also include an electromagnetic motor1524and a cone1525within its cavity1522. The base1508may separate the two cavities1512and1522with a divider wall1530. The base1508may have two ports1518and1528formed on a side of each of the cavities1512and1522, respectively. The ports may be designed to extend the frequency response of each sound source1513and1523. Sound sources may have a cone diameter in the range from about 8 inches (293.2 mm) to about 36 inches (914.4 mm) for operation in the frequency range from about 20 Hz to about 300 Hz. In particular, sound sources1513and1523may have 18-inch (457.2 mm) diameter cones and operate between about 25 Hz and about 125 Hz.

FIGS. 17 and 18illustrate a sound source system1710incorporating four columns and three rows of the sound sources. The sound sources on the side1750may represent the sound sources in the plane504, and the sound sources on the side1752may represent the sound sources in the plane502. Each sound source element may have a pair of sound sources facing each other on an axis such as1720. There may be twenty sound sources in sound source system1710:1712A,1712B (not shown);1712C,1712D (not shown);1714A,1714B (not shown);1714C,1714D (not shown);1714E,1714F (not shown);1716A,1716B (not shown);1716C,1716D (not shown);1716D,1716F (not shown);1718C,1718D (not shown);1718E and1718F (not shown). Columns1714and1716may be implemented with the sound source system1110as illustrated inFIGS. 11 and 12. Columns1712and1718may be implemented as versions of the sound source system1110not fully populated, or two high sound source system910ofFIGS. 9 and 10. A separation between adjacent sound sources may be provided to minimize sound conducting from one sound source to another. Alternatively, any conventional sound treatment material may be used between sidewalls to isolate adjacent sound sources.

The sound source system1710may be capable of directing sound in a wide variety of sound lobes. As illustrated inFIGS. 17 and 18, along the y-z plane, the vector1704may be generally defined by an angle φ. As generally defined inFIG. 5, values of angles θ, φ, and á may depend on the sound source diameter, horizontal spacing between the two sound sources (e.g.,1712A to1712B), vertical spacing between the two sound sources (e.g.,1712A to1712C0, intended mechanical durability, accommodation for sound source wiring, and provisions for heat dissipation amount other factors. For example, angles θ and á may be approximately 90° throughout the operating frequency range. In addition, frequency-shading techniques may be used to provide a more consistent coverage pattern throughout the bandwidth. This way, the sound source system1710may incorporate a number of low-frequency sound sources together to form an array in a compact manner and may be configured in a variety of ways to create arrays for different applications.

FIG. 19illustrates a diagram representing the assembly or array1710capable of steering at an angle between 0° and −90° from the reference axis1900. The array1710may steer by delaying each LF sound source back to a reference plane1702that may be normal to the vector1704that the array is being steered. Put differently, the delay distance1902for each of the sound sources in the assembly1710may be the shortest distance between the sound source and the reference plane1702. The resulting sound energy may be pushed forward, coherently summing in the direction of aiming and minimizing energy directed off-axis.

The horizontal space between sound sources such as1718E and1718F may be minimized so that the horizontal polar may be kept wide. Horizontally, the array may behave like a pair of sources that are spaced apart.FIGS. 20A through 20Dillustrate that the array1710may be steered at an angle of 35° with polar responses from 125 Hz to 250 Hz. Note that the desired coverage area, from 0° to −90° in this case, is covered smoothly with one contiguous energy lobe. A large amount of off-axis rejection is also shown inFIGS. 20A through 20D. The combination of even response in the seating area and a large amount of off-axis energy attenuation may improve the quality of the low-frequency sound. That is, the energy from each sound source may sum coherently in the direction it is aimed and exhibits little, if any, phase shift or anomalies throughout the main energy lobe. For example, a twenty-sound source array may develop 112 dB SPL continuous at 100 feet.

The array1710may be steered in other directions as well depending on the application. For example,FIGS. 21A and 21Billustrate polar responses for 0° and −50° at 200 Hz. The array1710may be expanded or reduced depending on the power and directivity requirements for the system. A greater number of sound sources allows for a greater degree of off-axis rejection and provides greater SPL levels. For higher power and wider vertical coverage, the array may be kept relatively small in that direction. Conversely, a taller array may provide a narrower vertical coverage pattern. Because of the orientation of the sound sources, the array may have a left frequency as the sound sources start to exhibit higher directivity. A closed box with a small volume may be needed so that the spacing between sound sources may be minimized. This allows the array1710to have a working frequency range of about 65 Hz to about 250 Hz, and may be suitable for use in an indoor arena.

Each of the sound sources in the assembly1710may utilize the audio system800, as illustrated inFIG. 8, for providing a lobe having a central axis along the vector510. The vector510may be designed to begin at any convenient reference point, such as at the acoustic center of the sound source1712A. In reference toFIGS. 9 and 10, the acoustic center may be the center of cavity912at the left side array element position1712A. If sources are driven in pairs, then ten drive signals may be needed, where nine maybe delayed. After choosing a direction for the vector510suitable for a particular operation of the audio system800, a delay may be determined for each of the delay elements depending on the geometry of the sound source system. For example, for an angle Θ illustrated inFIGS. 5,6,18and19, the sound sources may be driven with delays corresponding to delay distances as follows:1712A-B, no delay; delay distance for1712C-D per A-a; delay distance for1714A-B per A-c; r4; delay distance for1714C-D per A-e; delay distance for1714E-F per A-f; delay distance for1716A-B per A-g; delay distance for1716C-D per A-i; delay distance for1716E-F per A-j; delay distance for1718C-D per A-m; and delay distance for1718E-F per A-n.

FIGS. 22 through 24illustrate a sound source system2210capable of providing a wide horizontal coverage using the sound source1310as described inFIG. 13. The assembly2210may provide at least a 90° horizontal and 90° vertical coverage patterns between its working bandwidth of about 60 Hz and about 250. For example, sound source system2210may include a left-side array2204having four sound sources2224through2227; and an right-side array2202having four sound sources2228through2231. As illustrated inFIG. 24, a truss member2240may be used to couple the right and left arrays2202and2204such that the electromagnetic motors face one another. This allows the motors to radiate heat more readily, and allows the spacing or the width between the left and right arrays to be flexible so that a desired horizontal coverage may be provided. For wider horizontal coverage, the spacing between the left and right arrays may be narrowed, and conversely, for a narrow horizontal coverage, the spacing may be widened.

The sound source system2210may be capable of directing sound by creating a major lobe with definable polar characteristics. The sound lobe vector2226may be directed at any angle φ from about 0 to about 360° in the x-y plane. Again, the design issues and the geometry of the assembly2210may affect the angles φ and α in sound source system1710. All of the sound sources in the assembly2210may be operated, or a portion of the sound sources may be operated for different angles φ, α and output of SPL.

The sound source system2210may utilize the audio system800for providing a lobe having a central axis along the vector2226. The vector2226may be designated to begin at any convenient reference point such as between the first and second arrays on a vertical axis2212passing through the acoustic center of sound source2224A.

Two different sound sources may be driven in pairs when the delay distance between the two sound sources and the reference plane is substantially the same such as symmetrically positioned sound sources in the parallel arrays2202and2204. One non-delayed drive signal and seven delayed drive signals may be used. After choosing a direction for the vector2226, delays may be determined and set in the delay elements. Diameters for all of the sound sources in the sound source system2210may be 15 inches (381 mm). Alternatively, sound sources2224A,2224B,2227A, and2227B may be 18 inches (457.2 mm) and sound sources2225A,2225B,2226A and2226B may be 12 inches (304.8 mm).

FIGS. 25 and 26illustrate a sound source system2510having sound sources particularly suited for larger diameter sound sources. Sound sources2512-2522may be of the type described with reference to sound source1510inFIGS. 15 and 16. The sound source system2510may provide two parallel but offset arrays of sound sources. Array2502may include sound sources2512,2516, and2520. Array2504may include sound sources2514,2518, and2522. Each array may include six sound sources and six ports. Delay for each sound sources in the two arrays2502and2504may be proportional to the delay distance for each sound source where the delay distance may be the shortest distance between a reference plane and the sound source. The reference plane2562may be normal to a vector2560where the sound lobe is aimed at from the sound source system2510. With the offset arrangement of the sound sources in the two arrays2502and2504, each of two sound sources may have a different delay distance relative to the reference plane. As such, where a pair of sound sources has a delay distance, it may be delayed by a delay element. Hence six drive signals may be used, each with a different delay.

The delay distance for each of the sound sources may be calculated based on the vector2560that originates between sound sources2514A and2514B. The delay distance for each sound sources may be proportion to the shortest distance from the sound source to a plane2562that is normal to the vector2560.

The larger spacing of the sound sources may be acceptable in the sound source system2510because the wavelengths are longer. For example, the wavelengths may vary from approximately 8 to approximately 32 feet. Accordingly, the shadowing effect of the boxes may not be a problem due to the longer wavelength. The array may be forward-steered at the angle desired by delaying each sound source back to a plane normal to the direction aiming. Due to the geometry of the array, the main lobe may look slightly different at different steering angles. The sound source system2510may have a greater off-axis rejection when steered downward due to the increase in apparent array length.FIGS. 27A through 27Dillustrate a polar response to a six-element array at an aiming angle of 40° down that is suitable for a typical arena. These FIGS. illustrate that the array2510covers evenly between 0° and −90° and that it is effective at steering and off-axis rejection.

FIGS. 28 through 29illustrate a sound source system2810having a plurality of planes of sound sources. In this example, the sound source system2810may have four planes of sound sources with two inner planes2802and2804, and two outer planes2800and2806. The two inner planes of sound sources may be made up of the sound sources elements910as illustrated inFIGS. 9 and 10. Each of the two outer planes may be made up of the sound source elements1310as illustrated inFIGS. 13 and 14or the sound source elements1510as illustrated inFIGS. 15 and 16. For example, the two inner planes may include 12-inch (304.8 mm) sound sources and the two outer planes may include 15-inch (381 mm) and/or 18-inch (457.2 mm) sound sources. The sound source system2810may include a base2840for supporting all sound sources elements; and for hanging the sound source system2810.

The sound source system2810using delays as discussed above may generate a sound lobe along a vector2864that may originate at any point. For example, the vector2864may originate at a point2862at angle θ from the reference axis2820. For a more consistent horizontal coverage pattern, the two inner planes that are closer together may be driven with the upper frequency band, and the two outer planes that are spaced further apart may be driven with the lower frequency band. This may be done using frequency shading techniques discussed above.

FIGS. 30 and 31illustrate a sound source system where two arrays3002and3004are positioned angled next to each other so that the first ends3006and3008are closer than the second ends3010and3012. This means that the sound sources near the first end are closer to each other than the sound sources in the second end. With the sound sources near the first end being closer, these sound sources may provide wider coverage pattern at higher frequencies. With the sound sources near the second end being further apart, these sound sources may be driven with lower frequencies because wider spacing in the second end has less affect on the polar characteristics at the lower frequencies. This may be accomplished through frequency-shading technique where the sound sources near the first end are driven with higher frequencies and the sound sources near the second end are driven with lower frequencies. More than two arrays may be positioned angled next to each other in horizontal and/or vertical directions to provide a more consistent coverage pattern in both directions using frequency-shading techniques as well.