Methods and systems of vibrating a screen

Screen vibration systems are provided that can vibrate theater screens using acoustical, electromagnetic, or another type of energy while reducing the presence of image artifacts that may otherwise be visible as result of vibrating the screen. In one example of a screen vibration system, the system includes a screen, a permanent magnet mounted to the screen, and a magnetic source positioned with respect to the permanent magnet and uncoupled from the screen. The screen is moveable in response to a changing magnetic field from the magnetic source.

TECHNICAL FIELD

The present disclosure relates generally to the field of displaying images and, particularly but non-exclusively, to enhancing displayed laser images.

BACKGROUND

Shaking display screens can enhance displayed images on the screen. Projecting an image on a stationary screen using a coherent light source such as a laser light source can result in visual artifacts (known as speckle) in the image area. By shaking the screen surface on which an image is projected, speckle artifacts can be reduced or eliminated. To ensure speckle is reduced over all of the image area on the screen, all of the screen area is shaken. It can be desirable to have more than one point or source of screen vibration to achieve vibrating all of the image area of the screen. Screens can have a large surface area composed of a material, such as vinyl, that absorbs sufficient vibration energy imparted to the screen that the screen requires multiple vibration locations.

Using multiple sources to vibrate the screen, however, can introduce problems.

SUMMARY

In one example, a screen vibration system is provided. The screen vibration system includes a screen, a permanent magnet mounted to the screen, and a magnetic source positioned with respect to the permanent magnet and uncoupled from the screen. The screen is moveable in response to a changing magnetic field from the magnetic source.

In another example, is method to vibrate a screen is provided. A permanent magnet is mounted onto the screen. An electromagnet is positioned across from the permanent magnet. An electric current to the electromagnet is controlled to successively repel and attract the permanent magnet to cause the screen to vibrate.

In another example, a system to vibrate a screen is provided. The system includes a first actuator and a second actuator. The first actuator is positioned behind the screen at a first location for moving the screen at the first location based on a first electric signal. The second actuator is positioned behind the screen at a second location for moving the screen at the second location based on a second electric signal that is uncorrelated with respect to the first electric signal.

In another example, a method for vibrating a screen is provided. A first electromechanical acoustic actuator and a second electromechanical acoustic actuator are positioned behind the screen. The first electromechanical acoustic actuator is driven using a first electric signal. The second electromechanical acoustic actuator is driven using a second electric signal that is de-correlated with respect to the first electric signal. The screen is caused to vibrate by the first electromechanical acoustic actuator and the second electromechanical acoustic actuator.

In another example, a method for reducing speckle artifacts is provided. A screen is vibrated by a screen vibrator. Information about a projected image on the screen is captured using a sensor. An amount of speckle artifacts present in the projected image on the screen is determined from the captured information. A signal to a controller that drives the screen vibrator is controlled in response to comparing the amount of speckle artifacts to a predetermined threshold.

In another example, a system to vibrate a screen is provided. The system includes an electromechanical acoustical actuator with an open baffle. The electromechanical acoustical actuator is uncoupled from the screen in an operational setup. The system also includes a controller to provide an electrical signal to the electromechanical acoustical actuator for causing the electromechanical acoustical actuator to output energy to displace air that is (i) in front of the electromechanical acoustical actuator and (ii) between the electromechanical acoustical actuator and the screen. The open baffle is configured for preventing displaced air behind the electromechanical acoustical actuator from affecting the screen.

In another example, a system is provided. The system includes a screen for displaying an image, a laser projector to project the image toward the screen, at least two vibrator assemblies positioned to vibrate the screen, and a controller to control the at least two vibrator assemblies using uncorrelated control signals.

DETAILED DESCRIPTION

Certain aspects, features, and examples of the present disclosure relate to a screen vibration system that can vibrate a theatre screen using acoustical, electromagnetic, or another type of energy while reducing the presence of image artifacts that may otherwise be visible as result of vibrating the screen.

Screens supported by a screen support structure can have a mass in the order of a couple hundred or more kilograms. One approach to shaking the screen is to distribute vibrating sources that can shake the screen over the area of the screen. Applying a small amount of energy to each of the vibrating sources can collectively shake the whole screen.

One challenge can include moving the screen in a way that does not create screen distortion artifact visible by someone in the audience. A screen distortion artifact can be a local physical distortion that is visible on the screen surface and that is inconsistent with other areas of the screen surface. A screen with a high-gain coating on its surface can be susceptible to slight local distortions where a discontinuity in the screen's perceived gain can be recognized when the screen is poked or pulled by devices intended to vibrate the screen. Creating a local physical distortion in the screen position can cause the light reflection of the distorted portion of the screen surface to appear to be inconsistent with light reflected from areas of the screen without the local distortion. Deformations in the screen surface can appear as luminance distribution distortions.

A screen without a vibration system can have a surface profile that is the screen's natural resting state surface profile. A screen can be equipped with a vibration system that does not distort the screen surface profile from its natural resting surface profile. The screen vibration system can avoid exerting a biased force on the screen when the screen vibration system is inactive or not powered on. When the screen vibration system is actively vibrating the screen, the average displacement position of the screen can be the same position of the screen in its natural resting state.

To reduce speckle artifacts, the screen vibrations can avoid creating large screen displacements that can otherwise be visible to a viewer. Displacements can be limited to small amounts in such a way that the screen displacement variation can be un-noticed to the viewer but the displacement can be sufficient to cause speckle artifacts to be reduced or eliminated. The displacement amplitude of the screen to reduce speckle can vary. For example, the amplitude of the screen displacement can be greater at the location of the screen vibrator, but at a distance further away from the screen vibrator the screen displacement can be less and still reduce speckle artifacts. The frequency of the screen displacement can be above a certain level to avoid the displacement becoming easily perceptible. But the higher the frequency of the screen displacement, the more audible the vibration system may become. There can be a limited range of frequencies and amplitudes of screen displacement that can provide an optimum tradeoff of speckle artifact reduction with minimizing audience perceptibility of the screen being displaced and possible audible noise from vibrating the screen. The range of screen displacement frequencies can be within a range of 10 Hz to 35 Hz, although speckle reduction can still occur using displacement frequencies outside of the range.

The screen surface can be designed to vibrate by making physical contact, for example from behind the screen, with a mechanically vibrating surface. In other examples, the screen is shaken using a non-contact approach. An example of the non-contact approach can be by an acoustical component with an electromechanical acoustical transducer or actuator, such as a loudspeaker, being placed behind the screen and in close proximity to the screen. When the acoustical transducer is activated with a low frequency signal, the transducer can displace the air directly behind the screen to induce screen movement with the same frequency by which a transducer is moving. The acoustical transducer can have a moving cone or diaphragm to displace the air. The frequency of the signal to the acoustical transducer can be above or below the maximum hearing range of a human to avoid audible detection by the audience. The acoustical transducer vibration system can allow the screen surface to rest in a natural state profile when the transducer is not active and can allow the screen to be displaced equally in the two directions when the transducer is active.

FIG. 1shows one example a system for screen vibration. The system includes an actuator104that can receive a signal from a power supply106. The actuator104is positioned behind a screen102. The actuator104can displace the air directly behind the screen102to displace the screen102with a frequency of the signal from the power supply106. In some examples, the actuator104is an acoustical actuator.

In another example, an electromechanical acoustical actuator is fit with a baffle to vibrate a screen.FIGS. 2A to 4Bare examples of different baffles fitted to the actuator104that is positioned to face the screen102. The actuator104can be placed a distance from the screen102that is in the range of a one-quarter inch to twenty-four inches. Adding a baffle can cause the air between the screen102and the actuator104to be influenced by a surface of the actuator104that is facing the screen102to maximize screen displacement. When the actuator104moves air, the air on one side of the actuator104experiences a positive compression and the air on the other side of the actuator104experiences a negative compression. The displaced air on the two sides of the actuator104can be of opposite polarity or 180 degrees out of phase. Displacements of air with opposite polarity that interact can have a net effect of reducing or canceling the net displacement of air. Having a baffle restrict the opposite polarity of displaced air at the surface of the actuator104not facing the screen102from influencing the air at the screen102can prevent an undesirable reduction in air displacement at the screen102. Beyond the baffle, the displaced air from the front and the back of the actuator104can interact and can cause partial or full cancellation at locations further away from the actuator104and baffle, such as locations at which an audience viewing the screen can be located.

FIG. 2Adepicts a cross-sectional side view of a baffle250. The baffle250can be a plate that separates any displacement of air towards the screen102caused by the front of the actuator104from interacting with the displacement of air that occurs at the back of the actuator104. The surface of the baffle can be positioned parallel to the screen102and normal to an acoustical axis of the actuator104. The acoustical axis can be a centerline along the direction that air is being displaced by the actuator104. The actuator104can be an acoustical transducer of a configuration used in an acoustical loudspeaker such as an electromechanical transducer with a cone or other diaphragm moved electromechanically.FIG. 2Bdepicts a perspective view of the actuator104and the baffle250. The face252(i.e., the side facing the screen102) of the baffle250and the actuator104is shown inFIG. 2B. The baffle250can be a stiff material or a dense material to prevent air displacements from flexing the baffle, further reducing any interaction between displaced air in the front and in the back of the actuator104. The baffle250can be rectangular, circular or another shape suitable for a specific implementation.

FIG. 3Adepicts another example of a baffle360by cross-sectional side view. The baffle360is tubular, the face362is shown by perspective view inFIG. 3B, to separate the displacement of air that occurs between front of the actuator104and the back of the actuator104. The acoustical axis of the actuator104can be parallel to an axis of the tubular baffle360and at a right angle to the screen102. The opening of the baffle360can be positioned to face the screen102. The actuator104can be an electromechanical transducer with a cone. The baffle360can be a stiff material or a dense material. The cross-sectional shape of an opening of the baffle360can be rectangular, circular, or another shape suitable for a specific implementation. The baffle360can extend behind the actuator104. In other examples, the baffle360can extend in front of the actuator104or the baffle360can extend behind and in front of the actuator104.

FIG. 4Adepicts by cross-sectional side view another example of a baffle470that includes a plate474and a tubular (or other shaped) structure476extending from the plate474.FIG. 4Bdepicts a perspective view of baffle470and actuator assembly104that can be in a face direction472toward the screen.

The open baffles described above can allow for vibrating an area of the screen102that is in close proximity to the actuator104with little cancellation effects yet allowing cancellation effects of the propagating low frequency air disturbances to occur at distances beyond the baffle mounted to the actuator104.

Another approach to vibrate a screen can include positioning a magnetic source in close proximity to the screen in which a magnetic force can be used to repel and attract an element attached to a back surface of the screen.

FIGS. 5 and 6depict an example of screen vibration using permanent magnets. Mounted onto the screen102is a batten504with an element506that can interact with a permanent magnet512a. The permanent magnet512ais mounted to a motor shaft510and the permanent magnet512acan be rotated by the motor508with power from a power supply106. If the element506is a permanent magnet with a North/South orientation, as shown, the rotating permanent magnet512acan push the element506outwards when the North pole of the permanent magnet512ais oriented towards the element506. When the permanent magnet512arotated to be oriented with the South pole positioned next to the element506, the element506can be attracted towards the permanent magnet512a. If the element506is metal that can be influenced by a magnetic field such as iron instead of a permanent magnet, the element506may only move towards the permanent magnet512aregardless of the North or South orientation of the magnetic field facing the element506. The screen displacement may be only in one direction, e.g., towards the permanent magnet512a. Having the element506as a permanent magnet, however, may be useful if the average screen displacement over time is desired to be close to the natural rest position of the screen. The frequency with which the element506moves in and out can be directly proportional to the speed at which the permanent magnet512arotates. The rotational rate can be adjusted using the power supply106to the desired frequency of vibration. The screen102, when displaced outwards from the permanent magnet512a, may have less displacement from the rest position of the screen102when the screen102is displaced towards the permanent magnet512a. The system can compensate for the difference by reducing the length of the permanent magnet512afor the portion that attracts the element506such that the outward and inward displacements are equal to achieve equal inwards and outwards screen displacement. When the screen vibration system is not active, the permanent magnet512acan be positioned as shown inFIG. 6such that its influence on the element506is minimized and the screen102remains in a natural rest position.

FIG. 7depicts an example of a screen vibration system that uses a stationary electromagnet system. A coil720of wire is positioned on a core722and is oriented such that the end of the core722is directed towards the element506. If the core722is of a material, such as iron, that is influenced by a magnetic field, a small amount of electrical current can be made to pass through the coil720by power supply106to create a magnetic field that can repel or attract the element506. When the current through the coil720traveling in the reverse direction, the magnetic field can become opposite than before and can attract the element506instead of repelling (or repel instead of attracting, depending on setup). The screen displacement that results from forcing the element506to move by the magnetic field can displace the screen102in either direction.

The screen102, when displaced outwards from the electromagnet formed by the coil720and core722, may have less displacement from a rest position than when the screen102is displaced towards the electromagnet. This difference can be compensated for by increasing the electric current to the coil720such that there is more current going through the coil720when the coil720repels the element506than when the coil720is attracting the element506. The current can be shaped into an asymmetrical waveform to provide a screen displacement that is equal in both directions from the rest position of the screen102. One approach is to measure the screen displacement profile for a given signal waveform to the electromagnet and determine how the input signal is to be modified to provide the desired screen displacement. The modified waveform is then applied to the electromagnet to confirm the desired displacement profile has been achieved. A range finder sensor can be used to measure the screen displacement. Another approach to creating an asymmetrical waveform is to add a direct current bias in the amount that achieves an average screen displacement that is the same as the natural rest position of the screen.

Changing the magnetic field in the system inFIG. 7can influence the element506associated with the screen102. If the frequency of the changing magnetic field increases, the force exerted by the changing magnetic field may not be able to overcome the combined inertia of the screen102, the batten504, and the element506to make the screen102follow the changing magnetic field. If the maximum frequency that the vibration system (e.g., the magnetic system) is able to influence the screen102is too low, the inertia of the screen102, the batten504, and the element506can be reduced to raise the upper limit at which the screen102can be vibrated. Using more powerful electromagnets and electromagnetic drivers can also increase the upper limit at which the system is able to vibrate the screen102. Screen tension may also be a factor in that the more tension there is on the screen102, the amount of force needed to displace the screen102is greater. Reducing screen tension can help increase screen vibration displacement and increasing the screen vibration frequency. But too much reduction in screen tension can lead to other screen surface artifact problems such as screen sag.

When no current is passing through the coil720inFIG. 7, only the attractive magnetic force present can be from the element506to the core722. This may create a slight residual force on the element that can pull the screen102slightly towards the core722. One approach to reducing the residual force is to move the core722and coil720further away from the element506and use a higher electric current in the coil720to increase the magnetic field to compensate for the increased distance. Another approach can include changing the material from which the core722is made to a material that is not influenced by a magnetic field. Examples of these types of materials include plastic, aluminum and air. When a material that is not influenced by a magnetic field is used for the core722, more current may be needed to achieve the same magnetic field strength compared to a core that is made from iron. The number of turns of wire used in the coil720can be increased to achieve a higher magnetic field. The coil720can be placed closer to the element506when a core that is not influenced by a magnetic field is used.

FIG. 8shows an example of a screen vibration system with a controller806to control electrical current through an electromagnetic device that includes a coil820and a core822. The magnetic flux path through air gaps can be significantly reduced to allow more efficient energy transfer from the actuating device (i.e., the coil820and the core822) to a permanent magnet806and a batten804on the screen802. Where there is more efficient magnetic coupling, the magnetic field can be more contained to provide better energy transfer to the screen102and can be performed by configuring the permanent magnet806on a screen batten804and the electromagnetic core822to form a more complete loop or closed, loop with reduced air gap for the magnetic fields to pass through. The electromagnetic core822can be made from a metallic material that is influenced by a magnetic field. The metallic material may have a high relative permeability characteristic. Examples of metallic materials that have a high relative permeability can be ferromagnetic metals such as iron or Mu-metal. The air gaps in the magnetic flux path may be limited to the shorter paths between the ends of the core822and the permanent magnet806. Energy efficiency of the vibration system can be improved by configuring the electromagnetic core and the permanent magnet on the screen batten so that there are no large air gaps at the open ends.

The elements506,806described above can each be mounted in a batten504,804to distribute the repelling and attractive forces exerted on the element506,806over a larger area of the screen102. For example, the length of the batten504,804can be one foot to two feet long and one inch or more wide. For a screen with only a horizontal curvature and no vertical curvature, one or more battens can be mounted vertically on the back of the screen. The battens can be made of a light yet stiff material, such as balsa wood, carbon fiber, or a composite material. The element506,806can be mounted on the surface of the batten504,804or recessed in the batten504,804. The batten504,804can be fastened to the screen102by adhesive that does not cause a deformity or a stain on the screen102to occur. The side of the batten504,804towards the screen102can be black in color such that it is not visible if the screen102is perforated. Perforated screens may be used, for example, where audio loudspeakers are positioned behind the screens and the presentation sound can pass through the openings in the screen material.

FIG. 9shows the locations of a possible batten distribution of battens932mounted onto a screen930. The larger the screen the more battens can be used or needed.

A suitable power source can be used to power each coil for the locations where battens are located over the screen. One approach is to use one power source that powers all of the coils so that all of the coils vibrate at the same frequency and in phase. The screen vibrations, however, may have the same frequency and phase relationship, which can result in localized standing vibration wave patterns distributed over the screen. Standing wave vibrations may not be effective at reducing speckle because a component of the displaced screen is not moving and therefore may be unable to reduce speckle artifacts.

One approach that may be used to reduce or eliminate standing vibration waves is to power or drive each of the coils with a separate source such that each source generates random signals that are uncorrelated (also referred to as “de-correlated”). The random signals can be random in amplitude and in frequency, similar to pink or white noise. If the signal is random in amplitude and not in frequency, or random in frequency but not in amplitude, there may still be a standing component in the interactions of the waveforms from different sources. The signals from each of the vibration sources can be de-correlated in amplitude and in frequency. For example, each of the coils can be driven with a signal that has a different amplitude, frequency, and phase relationship than signals used to drive the other coils to reduce or eliminate the conditions that lead to standing waves or having a component of a standing wave.

FIG. 10schematically depicts an example of a coil driver configuration for a screen vibrations system. Each of the coils 1-n1050,1052,1054,1056can be electrically connected to an actuator driver power supply1040. The actuator driver power supply is configured (such as by being designed) to have channel outputs1042,1044,1046,1048to provide a signal for each coil. Each channel can be configured with its own frequency source in which the frequency source is a random frequency source, such as a pink or a white noise source. The bandwidth of the frequency source can be such that there are frequency components in the 20 Hz to 30 Hz range so that when the frequency source is filtered with a 20 Hz to 30 Hz bandpass filter there is signal content.

FIG. 11shows a block diagram of system1100for outputting a signal on an output channel that is uncorrelated with other channels. Each of the channel outputs1042,1044,1046,1048inFIG. 10from the actuator driver power supply1040can be fed by separate systems within the actuator driver power supply1040, an example of one of which is shown inFIG. 11. The frequency source1160can be a DSP or other type of signal processor in which a range of random frequencies can be produced, such frequencies corresponding to pink noise or white noise. A bandpass filter1162can filter the signal from the frequency source1160to remove unuseful portions of the signal for the screen vibration coil is used. A screen vibration range can be 20 Hz to 30 Hz, but it is not limited to this range. The filtered source signal is amplified with an amplification circuit1164so that the signal level is appropriate for the screen vibration coil. Each channel can have its own frequency source so that the signal from each channel can be uncorrelated. The same driver configuration can be used to drive other actuators in place of the coil720and the coil820, inFIGS. 7 and 8respectively, such as the actuator104or motor508.

Certain examples of screen vibration systems disclosed here can be retrofitted onto existing theatre screens, including screens in theatres in which the projection system image light source has been changed from a non-coherent light source to a coherent light source, such as a laser light source.

To optimize speckle artifact reduction, a screen image monitoring system and feedback loop can be set up to adjust the amount of vibration or alter a vibration parameter applied to the screen vibrator.FIG. 12shows a system that can be used to optimize speckle reduction in a theatre. A theatre screen1202may have a number of screen vibrators1212a-cpositioned behind the screen and that are controlled by a control unit1214. The control unit1214can provide de-correlated drive signals to each of the vibrators1212a-csuch that the screen1202is vibrated by each vibrator and the screen vibrations can be de-correlated with respect to each other. When a projector1204is projecting light through the projection lens1206onto the screen1202, a sensor1208, such as a camera, can capture the projected light on the screen1202. The captured image can be stored within the sensor1208or in a separate unit1210. The separate unit1210can also process the camera image to analyze and determine or quantify the amount of speckle in the light on the screen1202. The information from the separate unit1210can be communicated to the control unit1214, which can provide the drive signal to each of the screen vibrators1212a-c. The sensor1208can be located in the projection booth with the projector1204or the sensor1208can be positioned outside the projection booth such that the sensor1208is not required to view the screen1202through the booth window1216. The separate unit1210can be on its own or part of the sensor1208, part of the projector1204, or part of the control unit1214.

The process to optimize reducing speckle can be performed by projecting light onto the screen1202from the projector1204. Projected light can be a projected pattern or it can be just one color projected over the whole screen area. For example, the light projected onto the screen1202can be blue, red, or green. The optimization can be performed for one color, such as green light, in which speckle artifacts are known to be more apparent or the optimization can be performed to ensure speckle artifacts reduction is optimized in consideration of all light colors. The optimization to reduce speckle can be performed before a day of shows or scheduled to reoccur over a longer period of time. The sensor1208can be a camera that captures the projected light pattern intended for speckle reduction. The captured image could be processed and analyzed for the amount of speckle present by the separate unit1210. The amount of speckle can be determined globally for the screen1202or the speckle can be determined for more localized areas of the screen1202, such as the screen areas influenced by the vibrators1212a-c. Based on predetermined criteria as to the amount of speckle that is acceptable compared to the amount of speckle present, the control unit1214can be influenced by the information from the separate unit1210to change the signal to the vibrators1212a-cto achieve the speckle reduction required.

An example of a process1300to reduce speckle artifacts is shown as a flow chart inFIG. 13. The process1300is described with reference to the system diagram shown inFIG. 12, but other implementations are possible. In block1302, the image light on the screen1202is captured with the sensor1208. In block1304, the separate unit1210processes the captured image for speckle artifact analysis. Processing the captured image for speckle artifact analysis may include low-frequency filtering of the image to further isolate speckle artifacts. In block1306, the separate unit1210determines the amount of speckle artifacts present on the screen1202from the processed information. In block1308, a comparison of the present amount of speckle artifact is made with a threshold level. In decision block1310, further action is determined based on this comparison. If the present amount of speckle does not exceed a threshold, no further adjustment is required as in block1312. If the present amount of speckle exceeds acceptable limits, then a corrective adjustment to be applied to one or more of the screen vibrators1212a-cis determined in block1314. One or more of the screen vibrators1212a-creceives the corrected vibration signal and the screen1202is vibrated with a corrective adjustment to the screen vibrator(s) in block1316. The process1300ofFIG. 13can be repeated to determine if the corrective adjustment has reduced the amount of speckle to within the predetermined threshold limit. If, after a predefined number of iterations of the process1300, the amount of speckle is not reduced to within the predetermined threshold limits, the condition can be flagged. When flagged, other factors such as repositioning of a screen vibrator can be considered. Re-positioning can be performed manually or with a vibrator system as described inFIG. 14that is automated.

Screen vibrators may need to be repositioned over time to maintain an optimum distance between the vibrator and the screen. A vibrator or vibrator assembly that is hard mounted to the screen frame or other connection point may not be adjustable to accommodate changes in distance between the vibrator and the screen that may occur over time or with a change in temperature and humidity.

An adjustable configuration1400shown inFIG. 14has a vibrator assembly1414with a baffle1450and can be mounted onto a movable portion1402of a platform assembly where the stationary portion1404of the platform assembly is mounted to the screen structure (not shown). The platform assembly can have a motor or actuator1406that can be commanded to move the movable portion1402of the platform to move the vibrator assembly1414closer or further away from the screen102. The vibrator assembly1414and baffle1450may be replaced with a non-acoustical electromagnetic actuator assembly, examples of which are described inFIGS. 5, 7 and 8.

In another configuration, the distance between the vibrator and the screen can be adjusted by mounting the vibrator assembly so that it can move, slide or pivot small distances closer or further away from the screen. By controlling with a motor or actuator the amount of move, slide, or pivot of the vibrator assembly with respect to the screen, the distance between the vibrator and the screen can be adjusted. A pantograph mechanism may also be employed to allow the vibrator assembly to be repositioned with respect to the screen while maintaining a constant angular relationship with the screen.

In the automated adjustment system shown inFIG. 14, a distance sensing device1408can be mounted on the vibrator assembly1414to determine the distance1410that the vibrator assembly1414is from the screen102. The distance sensing device1408can be an ultrasonic distance sensor or a distance sensor that utilizes alternate distance sensing technology. A processor within the controller assembly1412can be used to receive distance information from the distance sensing device1408and determine whether or not the vibrator assembly1414is within the acceptable distance range from the screen102. If the distance1410is not acceptable, the processor commands the motor driver in the controller assembly1412to make the actuator1406move the movable portion of the platform with the vibrator assembly1414attached until it is within an acceptable distance range between the vibrator assembly1414and the screen102. If the vibrator assembly1414remains in the acceptable distance range from the screen102, the processor may command the controller assembly1412to hold the current motor position.

Each screen vibrator can be configured to be automatically adjusted between the screen and the vibrator. In another example, only the screen vibrators in screen locations where there is a greater tendency for the distance between the screen and the vibrator to change over time. For example some portions of the screen can experience more sag with time than other portions of the screen and therefore the vibrators positioned with portions of the screen experiencing more sag can be configured so the distance between the vibrator assemblies and the screen can be adjusted. In one configuration, vibrators positioned at the lower portion of the screen can be vibrators in which their distance to the screen can be adjusted.

In another example, the position between the vibrator and the screen can be optimized in a screen tuning process. For example, the system inFIG. 12can be designed by configuring screen vibrators1212a-cto be adjustable vibrators of a configuration described inFIG. 14. The controller assembly1412can be configured to receive information based on the amount of speckle from the separate unit1210or the control unit1214inFIG. 12. In a screen tuning process, the information received from the separate unit1210or the control unit1214can be commands to change the distance between the vibrator and the screen to optimize reducing speckle and minimize the amount displacement in the screen vibration. The speckle reducing optimization and screen tuning process can occur as part of a daily system calibration, or before each presentation or during a presentation or as required.

In another example, the signal from the distance sensing device1408, on the vibrator assembly1414inFIG. 14can be provided to the control unit1214ofFIG. 12to control the amplitude of the signal to the corresponding vibrator by the control unit1214to maintain a screen vibration that compensates for changes in distance between the vibrator and the screen.

In an alternate configuration where multiple screen vibrators are used and are all driven by substantially the same non-decorrelated signal, standing wave artifacts can be minimized by keeping each screen vibrator a certain distance away from adjacent screen vibrators, such that the respective vibration displacement waves have minimal interference with one another. The distance between each screen vibrator can also be as close as needed to ensure there are no areas on the screen that do not receive the adequate amount of vibration but not too close of a distance to create visible standing waves that form as a result of the interference of the two waves from the two adjacent screen vibrators. Where a screen vibration speckle reduction feedback loop is being used, the global speckle artifact reduction can be optimized for a common vibrator drive signal. Optimization can also include adjusting the amplitude of the drive signal to a different level for each screen vibrator even though all the vibrators are driven at the same frequency.