Abstract:
A wireless audio amplification system for classrooms and the like includes a system that allows for advanced listening and learning audio tools. The invention combines radio frequency and infrared technologies into one integrated system. A microphone includes a radio frequency receiver and an infrared transceiver. The microphone transmits voice signals to an audio amplifier unit that includes a radio frequency transceiver and an infrared transceiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is entitled to the benefit of U.S. provisional patent application No. 60/875,769, filed Dec. 18, 2006. Such application is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates to an audio amplification system particularly suitable for use in classrooms and the like. 
     BACKGROUND OF THE INVENTION 
     In large rooms such as school classrooms, lecture halls, auditoriums, theaters and the like, there is often a need for audio amplification of a speaker&#39;s remarks. Not only do individuals in the back rows of seats need to hear the speaker clearly, but these audio amplification systems can also be used for other purposes. For example, in today&#39;s classrooms many audio systems are used in order to enhance each student&#39;s learning experience, including: paging, audio enhancement for television, overhead projectors, and microphone systems for teachers. These audio systems are frequently wireless. This type of system gives the speaker great freedom to walk about the room or stage to work on a blackboard, operate audio-visual equipment and the like. The microphone transmits a wireless signal to a receiver/audio amplifier unit located within the room, and the amplifier sends an amplified signal (usually by wire) to speakers mounted within the room, typically near the back. 
     Currently, there are two main types of technologies available for wireless audio amplification systems: FM Radio Frequency (RF) systems, and Infrared (IR) systems. Both systems have advantages and disadvantages as described below: 
     Radio Frequency (RF) 
     A typical prior art “pure” RF system is shown in  FIG. 1 . As used herein, “pure” means that only one signal transmission mode is used, in this case RF. In  FIG. 1 , a teacher in a classroom carries or wears a microphone  102  that broadcasts the teacher&#39;s voice by RF signals. The signals can propagate throughout the room, through objects in the room such as blackboards  104 , and even beyond the room. The signals are picked up by an RF receiver  108  mounted somewhere in the room, amplified and then sent to wired speakers  110 ,  112 . Outside light, such as from windows  106 , does not interfere with signal transmission. Since the signals can penetrate the walls of the classroom, if the teacher leaves the classroom and forgets to turn off the microphone, the teacher&#39;s voice will still be heard by students in the room. 
     Some typical advantages of a “pure” RF system include: (1) The RF signal is normally able to be received from anywhere in the room. (2) The RF signal does not require line of sight contact between transmitter and receiver. Thus, for example, a teacher could walk behind a blackboard and still be heard by the students. (3) Signal strength is usually strong and can be transmitted/received through walls, up to a determined area. (4) Only one receiver is needed because of the signal strength and the ability of the RF signal to bounce/reflect off some objects. (5) The receiver can be placed in any area of the room, and does not need to be in a specified place. 
     Disadvantages of a “pure” prior art RF system include: (1) An RF Microphone is limited to the number of channels (frequencies) that can be selected. (2) A different channel must be used for each room, and the user must manually set the channel on the microphone to match the receiver&#39;s channel in each particular room. (3) The RF signal does not stop at the classroom walls. Thus, the signal can often be inappropriately received in other classrooms or when the teacher leaves the classroom. For example, if the teacher leaves the classroom, does not turn off the microphone and is speaking, the signal is still being received inside the classroom that is set to the same frequency, and the audio voice is being transmitted through the speakers. This becomes a problem when the teacher is speaking and does not want the students in the class to hear his or her ongoing conversation outside the classroom. (4) There must be some synchronization between the microphone and the receiver. (5) Radio interference is often a problem. (6) Students are sometimes able to change the channel without the knowledge or permission of the teacher. 
     Infrared (IR) 
     A typical prior art “pure” IR system is shown in  FIG. 2 . The only signal transmission mode used in this case is IR. A teacher  100  in a classroom carries or wears a microphone  102  that broadcasts the teacher&#39;s voice by IR signals. The signals can generally propagate throughout the room, but only by line of sight. They cannot propagate through objects in the room such as blackboards  104 , or beyond the room. The signals are picked up by one or more IR receivers  120 ,  130 ,  140  mounted within the room, amplified and then sent to wired speakers  110 ,  112 . For large rooms, or if there is bright ambient light, such as near windows  106 , then more than one IR receiver may be needed. If ambient light is extremely bright, such as from direct sunlight, then the IR signal could be completely interrupted. 
     Infrared systems have some advantages. Since IR light cannot go through walls, a facility can install and use the same type of system in multiple rooms without causing interference. Also, when a teacher leaves the receiver&#39;s area (such as a classroom), the teacher&#39;s microphone will automatically shut down because interrupting the direct line of sight between transmitter and receiver will cause signal contact to be lost. In this way, the teacher does not need to be concerned about making inappropriate remarks outside the classroom that could be heard by students in the classroom. 
     Disadvantages of a “pure” prior art IR system include: (1) Line of sight contact is required between the transmitter and receiver. Therefore, for example, the receiver must be installed in the ceiling or high on the wall and cannot be covered or obstructed. (2) Even though an IR signal can be reflected off walls, the signal strength may be weak or choppy in areas near windows where there is much light, and in areas behind or near a blackboard which can absorb the light. (3) Since IR light cannot penetrate walls, a classroom with an “L” shape or other unusual shape, or a classroom that has interior partitions, needs multiple receivers that usually must be installed into the ceiling, which can be time-consuming and expensive. (4) Usually the receiver&#39;s control panel must be placed in an accessible area, and not mounted in the ceiling with the receiver. (5) IR systems typically require a fair amount of power to transmit the IR signal. Thus, for example, a portable microphone with an IR transmitter needs a large battery, or a number of small batteries, that must be replaced frequently. 
     Because of the above-mentioned disadvantages of prior art “pure” RF and “pure” IR audio systems, a need exists for a wireless audio amplification system that maximizes the advantages and minimizes the disadvantages of RF and IR systems. 
     SUMMARY OF THE INVENTION 
     To meet the aforementioned need, a wireless audio amplification system for classrooms and the like has been developed that combines the advantages of both RF and IR technologies, and minimizes the disadvantages of each. 
     In one embodiment, the invention comprises an audio amplification system that includes: 
     (a) an audio amplifier including a microprocessor, a radio frequency transceiver, an infrared transceiver, an antenna, amplification electronics and at least one speaker; 
     (b) a wireless microphone including a microphone head, a radio frequency transceiver, an infrared receiver, a microprocessor and an antenna; whereby 
     (c) the audio amplifier is configured to transmit infrared signals to the microphone containing a channel code representative of a particular transmission channel, and the microphone unit is arranged to transmit radio frequency signals representative of audio signals to the audio amplifier over the particular transmission channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the invention will now be described with reference to the drawings of certain preferred embodiments, which are intended to illustrate and not to limit the invention, and in which like reference numbers represent corresponding parts throughout, and in which: 
         FIG. 1  is a block/pictorial diagram of a prior art wireless audio amplification system using “pure” RF signal transmission; 
         FIG. 2  is a block/pictorial diagram of a prior art wireless audio amplification system using “pure” IR signal transmission; 
         FIG. 3  is a block/pictorial diagram of a wireless microphone unit used in the wireless audio amplification system of the present invention; 
         FIG. 4  is a block diagram of an audio amplifier unit used in the wireless audio amplification system of the present invention; 
         FIG. 5  is a block diagram of an alternative embodiment of the microphone unit of  FIG. 3 ; 
         FIG. 6  is a block/schematic diagram showing major electrical components on a microprocessor circuit board for use in the audio amplifier unit of  FIG. 4 ; 
         FIG. 7  is a block/schematic diagram showing major electrical components on a microprocessor circuit board for use on the circuit board of  FIG. 6 ; and 
         FIG. 8  is a block/schematic diagram showing major electrical components on a microprocessor circuit board for use in the microphone unit of  FIG. 3 ; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a preferred embodiment, the audio system of the present invention includes two major components: (1) an audio amplifier unit  200  ( FIG. 4 ) that includes both an IR transmitter and an RF receiver/transmitter; and (2) a microphone unit  300  ( FIG. 3 ) that is capable of receiving an IR signal and receiving and transmitting an RF signal. 
     Some advantages of this combined IR/RF system include the following: (1) Because IR light cannot go through walls, a facility can have the same system in multiple rooms without causing interference. (2) Since IR light needs direct point of view contact between transmitter and receiver, the microphone automatically shuts down when that contact is lost for a specified period of time. Thus, when the teacher leaves the receiver&#39;s area (classroom), the teacher&#39;s voice can no longer be heard. (3) Since the microphone can receive IR signals but only transmits signals in RF, less power is required, namely fewer batteries, at the microphone. (4) The RF signal is normally able to be received from anywhere in the room. (5) The RF signal does not require line of sight contact between transmitter and receiver. Thus, for example, a teacher could walk behind a blackboard and still be heard by the students. (6) Signal strength is usually strong and can be transmitted/received through walls, up to a determined area. (7) Only one receiver is needed because of the signal strength and the ability of the RF signal to bounce/reflect off some objects. (8) The receiver can be placed in any area of the room, and does not need to be in a specified place. 
     A block diagram of a preferred embodiment of the audio amplifier unit  200  is shown in  FIG. 4 . The amplifier includes a microprocessor board  210  coupled to an RF transceiver  220 , an IR transceiver  230  and an antenna  250 . Other conventional audio amplification electronics (not shown) is also contained within the amplifier and coupled to at least one speaker  240 . The audio amplifier can be mounted on a ceiling or wall and can be controlled via RF, IR or wired remote control, or it can be used as a desktop unit with knobs and buttons for control. The audio amplifier typically will be powered by wired classroom electricity. 
     A block diagram of the microphone unit  300  is shown in  FIG. 3 . A microphone head  330  is mounted to a housing containing an RF receiver  310 , an RF transmitter (not shown), an IR receiver, a digital signal processor (not shown), a control button  340 , a vibrator/buzzer  350  and an auxiliary input  360 . The microphone also includes an antenna (not shown) and conventional electronics needed for audio microphone operation. 
     System Operation 
     In operation, the audio amplifier  200  ( FIG. 4 ) sends an IR digital signal through the IR transceiver  230  that includes a channel code, channel number or network ID, e.g., channel number  5 , representative of a particular transmission channel. Bluetooth, direct-sequence-spread-spectrum or other technologies may be used. The channel number associates itself with the frequency or frequencies that are pre-programmed in the microphone and the audio amplifier. 
     The microphone  300  ( FIG. 3 ) has an IR receiver  320  that is capable of receiving the appropriate channel number or synchronization code from the IR transceiver  230  and the microphone adjusts its frequency accordingly to match the frequency of the audio amplifier. When the microphone is taken to another classroom, the microphone will receive a different channel number from a different audio amplifier, and will adjust itself accordingly to match the audio amplifier in that classroom. One of the advantages of such a system is that one microphone can be used in any classroom without the need of manual channel selection. 
     In another embodiment of the invention, the audio amplifier periodically and rapidly sends digital data that includes the channel number, for example 100 messages sent per second. The microphone does not have to receive the signal continually. However, if after a period of time, for example, 5 seconds, the microphone does not receive a channel number, the microphone assumes that the teacher may have left the room. The microphone can provide an audio noise alert, a vibrate alert, or automatically shut off (depending on the preferences of the teacher) to notify the teacher that he or she may still be transmitting an audio signal. 
     During normal operation, the microphone synchronizes itself to the same frequency as the audio amplifier and transmits an RF signal representing the audio signal from a teacher, student, or any other electronic device that is connected to the microphone via an auxiliary input  360 . The RF signal that is sent to the audio amplifier can be in a single frequency, using frequency hopping, spread spectrum, and/or audio compression in order to allow for multiple microphones to operate simultaneously in the same room. 
     In case of single carrier or frequency hopping operation, the RF transceiver needs to find a clear frequency or hopping pattern that does not disturb other neighboring rooms. This may be accomplished implicitly using a Bluetooth implementation. In this way, the channel number may be transmitted clearly to the microphone or other devices. 
     Another advantage of such a system is that many classrooms already use a paging/intercom system in existing classes. Because the audio amplifier of the present invention already includes an RF transceiver module  220 , the audio amplifier can easily work with existing wireless paging/intercom systems, which can eliminate the need for wired paging and intercom systems in the classroom. Also, in a large classroom, the RF signal can cover and transmit to the entire room without the use of multiple receivers. 
     In another embodiment, the microphone  330  can be fashioned as a type of gooseneck device. This embodiment is shown in  FIG. 5 . This device is a long, thin and flexible gooseneck device that has a microphone head on one end coupled to a unit containing an electronic transmitter and other components on the opposite end. The microphone head and transmitter are detachable from the long gooseneck cord and can attach to each other making the device suitable for use as either a handheld, lapel, or pendant unit. 
     A more detailed discussion of the electrical components of a preferred embodiment of the present invention follows. Reference is made to  FIGS. 6 ,  7  and  8 . 
     Audio Amplifier Board ( FIG. 6 ) 
     The audio amplifier board is the main board of the system, and the last point before the audio signal reaches the speaker(s). This board&#39;s detector  19  acts as the tool that notifies the speaker  21  which sounds the students will be hearing, either the intercom paging or auxiliary inputs. The board is powered by a power supply that outputs an appropriate level of power, such as 5v. The audio amplifier board includes the following components:
         Four inputs (elements  3 ,  5 ,  7  and  9 ), each coupled to its own individual volume control (elements  2 ,  4 ,  6  and  8 , respectively)   Four pre-amplifiers ( 11 ,  12 ,  13 ,  14 ), each coupled to an input ( 3 ,  5 ,  7 ,  9 ), respectively.   A mixer  15  that receives signals from the pre-amplifiers ( 11 ,  12 ,  13 ,  14 ) and generates one output to an amplifier  16 .   A master volume control  1  that controls volume for the amplifier  16 .   An RF interface board  10 , which is an important component of the system that is coupled to and mounted on the audio amplifier board (see discussion below).   A detector  19  that is coupled to the amplifier, a transformer  17  and a relay  20 . The detector measures signal voltage from the transformer  17  and amplifier  16 . Depending on priority, the detector  19  controls relay  20 , which controls which device (either an amplifier or the intercom) will gain access to one or more speakers  21 . If the detector  19  detects a signal that comes from an external paging or intercom system, the detector, which connects to master volume control  1 , will shut off the volume to the amplifier  16  to allow the paging on the intercom to take priority.   A relay  20  that allows the detector  19  to select which signal will be sent to the speaker  21  (either a signal from transformer  17  or a signal from amplifier  16 ). Relay  20  gets instructions from detector  19 . It acts as the switch to connect either the intercom or amplifier  16  to the speaker  21 .   The speaker  21  outputs sound received from either the Intercom or the microphone audio.   Line Out  22  allows a connection with another system (another board), and it also connects to the mixer  15 .   Transformer  17  has an Intercom line that comes in to the transformer. It connects to Relay  20 .   A D/C to D/C Power Supply  18  is the power source for the board.
 
RF Interface Board ( FIG. 7 )
       

     The RF Interface board is coupled to and preferably mounted on top of the audio amplifier board ( FIG. 6 ). It is connected to the audio amplifier board so that all devices using the RF or IR signals can have access to the speakers controlled by the audio amplifier board. The RF Interface board includes the following components: 
     RF Transceiver  400 
         Receives wireless RF signals and sends them to a processing unit  410 . Signals can be received from either a wireless RF microphone head  330  of microphone  300  (see  FIG. 3 ) or from an auxiliary input  360  on the wireless microphone.   Sends and receives audio signals from an external intercom system (not shown).       

     IR Transmitter  430 
         Transmits IR signals to the IR receiver on the microphone. These signals include but are not limited to channel codes or channel numbers as received from the processing unit  410 .       

     Processing Unit  410 
         The main processor of the system that is responsible for selecting the RF channel to perform audio compression and decompression as needed.   Connected to and controls an interface unit  440  and another interface unit  450  as needed.   Sends signal to the IR Transmitter   Can read information from a memory, such as an EEPROM  420 , as needed.       

     Interface Unit  440 
         Converts digital signals to analog signals.       

     Interface Unit  450 
         Converts analog signals to digital signals.       

     EEPROM  420 
         Non-volatile memory   DSP  410  writes data to and receives data from the EEPROM memory
 
Wireless Audio Microphone Board ( FIG. 8 )
       

     The wireless audio microphone board controls the audio of the microphone  501  (see also  FIG. 3 ). When a teacher, for example, is speaking, the voice is sent through an RF transceiver  503  on the microphone board to the RF transceiver  400  on the RF interface board ( FIG. 7 ) and then to the audio amplifier board ( FIG. 6 ), which transmits the voice through the speakers  240  in the room ( FIG. 4 ). The wireless microphone board also receives room address information from the IR transmitter  430  on the RF interface board ( FIG. 7 ), so that the microphone and the receiver are set to the same channel frequency. The major components of the wireless audio microphone board are as follows: 
     Microphone  501 
         Connects to a module  510  containing an amplifier and an A to D converter.       

     Processing Unit  502 
         The main processor of the microphone board.   Receives a digital signal representing the voice from the A to D converter module  510 .   Receives channel code (channel selection signals) from an IR receiver  512 .   Controls the RF transceiver  503  for the information sent and the frequency being used.   Receives digital data from an A to D converter  511  representing a signal received from an auxiliary input  509 .   Capable of performing audio compression and decompression as needed.   Can send a control signal to the audio amplifier board ( FIG. 6 ) via RF. The processing unit  502  will receive the control signal via switches SW 1 , SW 2 , SW 3 .   Controls LEDs that represent battery status.   Controls a vibrate/buzzer to give notification to the teacher as needed.   Receives signals from a low voltage detector (LVD)  506  that monitors the status of the battery.       

     RF Transceiver  503 
         Wireless signal receiver/transmitter.   Connects to processing unit  502 .       

     Plug for Charging  504 
         Input for charging the battery from an external power source.       

     Battery Charging Monitor  505 
         Monitors and gives enough charge for the battery.       

     LVD (Low Voltage Detector)  506 
         Tells processing unit  502  that the battery charge is low.       

     Vibrate Indicator  507 
         Informs the user if he or she is out of IR reception range.       

     One or More Batteries  508 
         For power.   Connected to battery charging monitor  505 .       

     Auxiliary Input  509 
         Connects to a mobile device (e.g., DVD, VCR, or MP3 player)       

     Amplifier +A to D Converter Module  510 
         Gets input from microphone  501  and converts analog signals to digital audio signals.   Amplifies the audio voice signals.   Connects to processing unit  502 .       

     A to D Converter  511 
         Gets input from the auxiliary input  509  and converts analog signals to digital signals.   Connects to processing unit  502 .       

     IR Receiver  512 
         Receives data for channel frequency selection.       

     Although only one embodiment of the present invention has been expressly disclosed, it is, nonetheless, to be broadly construed, and not to be limited except by the character of the claims appended hereto.