Abstract:
An audio distribution system in one embodiment includes a master device, a powered speaker unit, and an expander device. The master device has an output port for receiving a cable carrying an electrical power signal along with a digital audio signal. The speaker unit includes a first port for receiving the electrical power signal and the digital audio power signal, and a second port for sending the signals. A digital-to-analog converter in the speaker unit converts the digital audio signal to an analog audio signal, and a speaker driver uses the signal to produce sound. The expander device is electrically connectable to the second port of the speaker unit for providing electrical power to one or more further speaker units. In another embodiment, the invention provides a master mixer device and a speaker unit. The master mixer device includes a digital signal processor for receiving and separately processing a speech channel having digital audio containing speech content and a music channel having digital audio containing music content. In an embodiment a powered speaker unit employing a class D amplifier for reproducing sound is further disclosed. A digital power link in port is provided in the powered speaker for receiving a cable carrying a digital audio signal and electrical power.

Description:
[0001]     This application includes material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office files or records, but otherwise reserves all copyright rights whatsoever.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates in general to the field of audio distribution systems for distribution of audio announcements and/or music throughout buildings or outdoor spaces, and in particular to a digital power link audio distribution system wherein audio is distributed digitally and converted to analog at remote points in the system.  
       BACKGROUND OF THE INVENTION  
       [0003]     Audio distribution systems are used in airports, convention halls, restaurants, other buildings, and outdoor spaces to distribute announcements and/or music. Such systems typically include a mixer/power supply which receives audio from audio sources and feeds a 70v or 100v audio signal to remote passive speakers throughout a building or other space.  
         [0004]     Various disadvantages are associated with prior audio distribution systems. Installation of such systems is complex and subject to errors in wiring, which may result in faulty or out-of-phase connections at one or more of the remote speakers. Such systems are also subject to signal loss when long runs of speaker wire are utilized to connect speakers, particularly those at the far edge of the system. Wiring utilized for such systems may suffer from corrosion when the system is installed in an outdoor or otherwise humid environment.  
         [0005]     Furthermore, prior audio distribution systems suffer from poor intelligibility of voice announcements which are broadcast over the system. Such intelligibility problems have been addressed by providing outboard or plug-in DSPs, but such solutions are complex to install and use.  
       OBJECTS AND SUMMARY OF THE INVENTION  
       [0006]     It is therefore an object of the invention to provide an improved audio distribution system.  
         [0007]     It is a further object of the invention to provide an audio distribution system which overcomes one or more limitations associated with the prior art.  
         [0008]     In an embodiment, the invention provides an audio distribution system having a master device, a powered speaker unit, and an expander device. The master device includes an output port for receiving a cable which carries an electrical power signal from a power supply along with a digital audio signal. The speaker unit includes a first port electrically connectable to a cable for receiving the electrical power signal and the digital audio power signal, a second port electrically connectable to a cable for sending the electrical power signal and the digital audio signal, a digital-to-analog converter for converting the digital audio signal to an analog audio signal, and a speaker driver for using the analog audio signal to produce sound. The expander device is electrically connectable to the second port of the speaker unit for providing electrical power to one or more further speaker units.  
         [0009]     In an embodiment, the invention provides a master mixer device and a speaker unit. The master mixer device includes a digital signal processor for receiving and separately processing a speech channel having digital audio containing speech content and a music channel having digital audio containing music content. A cable carries both an electrical power signal and a digital audio signal from a port on the master mixer device to a port on the speaker unit.  
         [0010]     In an embodiment the invention provides a powered speaker unit employing a class D amplifier for reproducing sound. A digital power link in port is provided for receiving a cable carrying a digital audio signal and electrical power. A digital power amplifier uses pulse-width-modulated digital signals to switch an output power amplifier device, thereby generating an analog audio signal. A speaker driver receives the analog audio signal and reproduces sound in accordance therewith.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments as illustrated in the accompanying drawings, in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention.  
         [0012]      FIG. 1  shows a diagram illustrating an audio distribution system of the invention in one embodiment.  
         [0013]      FIG. 2  shows a block diagram illustrating electrical aspects of a master mixer/power adapter in accordance with one embodiment of the invention.  
         [0014]      FIG. 3  shows a block diagram illustrating electrical aspects of a speaker unit in accordance with one embodiment of the invention.  
         [0015]      FIG. 4  shows a block diagram illustrating electrical aspects of an expander power converter in accordance with one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0017]     With reference to  FIG. 1 , an audio distribution system  10  in one embodiment includes a master mixer/power converter  20  which includes a series of audio inputs  21  for receiving audio signals from a microphone  30  and/or other audio sources  40 . The audio sources  40  may include sources of music content such as, e.g., a satellite radio receiver, a CD player, a radio tuner, an internet radio receiver, a digital audio player, or the like. In this respect, the audio inputs  21  may be analog inputs, digital inputs, or a combination thereof. The audio sources may be separate from the master mixer/power converter  20 , as shown in  FIG. 1 , or may be integrated therewith.  
         [0018]     The master mixer/power converter  20  includes a digital power link out port  33  ( FIG. 2 ) for outputting digital audio and power over a network cable  50 , which may comprise, e.g., CAT5 or CAT5E cable or other similar twisted-pair network cabling terminated at each end with an RJ-45 connection. This cable and termination connections. Transmitting audio data in digital form across such twisted-pair cable provides resistance to radio-frequency interference over conventional speaker cables, and its RJ-45 connectors can be used to quickly connect the various components of the present system without the risk of improper wiring. The use of common networking cable with RJ-45 or similar terminations in the present system reduces the chance of connection failure and/or inadvertent disconnection and facilitates making connections between various components of the system by consolidating wiring into a single connector. One or more of the four twisted pairs of conductors within the network cable  50  may be used to carry the digital audio signal, and one or more of the remaining pairs may be used to carry power. The digital power link out port is discussed in further detail below with reference to  FIG. 2 .  
         [0019]     With continuing reference to  FIG. 1 , the network cable  50  connects output port  33  ( FIG. 2 ) of the master mixer/power converter  20  to speaker unit SU 1 . As will be seen in more detail below, speaker unit SU 1  can be daisy chained with additional speaker units SU 2 -SUn using additional network cables. In an embodiment, each speaker unit comprises a DSP, a digital-to-analog converter, an audio power amplifier, a ceiling-mounted speaker, and suitable digital power link in and out jacks. One example of a suitable digital power link in and out jack is an RJ45 female jack, however, any suitable jack may be used. As described above, the network cable  50  connects the digital power link out jack on the master mixer/power converter  20  to a digital power link in jack in speaker unit SU 1 . A second network cable may connect the digital power link out jack in speaker unit SU 1  to a digital power link in jack in speaker unit SU 2 . A third network cable may be used to connect the digital power link out jack in speaker unit SU 2  to a digital power link in jack in speaker unit SU 3 , and so on until a maximum number of speaker units has been reached.  
         [0020]     A maximum number of speakers may occur as a result of a number of factors, for example, but not by way of limitation, the amount of power consumed by the daisy-chained speakers may not provide enough power to operate another speaker. Another example, also intended to illustrate and not to limit the invention is that the length of cable between the speaker units is sufficiently large that the power or audio signal remaining is too weak to travel further.  
         [0021]     When the maximum number of speaker units has been reached (or the maximum cable length would be exceeded by adding another speaker unit, the system can be expanded to include further speaker units by use of one or more expander power converters EX 1 , EX 2  that serve to refresh the power and/or digital audio signals. Each expander power converter EX 1 , EX 2 , also includes digital power link in and out jacks. The digital power link in jack in the expander power converter EX 1  connects via cable to the digital power link out jack in the last speaker unit in the chain, SUn, and the digital power link out jack in the expander power converter EX 1  connects via cable to the digital power link in jack of the next speaker unit SU 9  in the chain. This daisy chaining is continued until a maximum number of speaker units has again been reached, at which point a second expander power converter EX 2  is connected at the end of the chain to allow further speaker units to be added.  
         [0022]     In addition to the digital power link out port, which outputs both digital audio and power, the master mixer/power converter  20  may include one or more link out ports which output digital audio but do not provide power. The link out port may be connected via a network cable  52  to a remote expander power converter EX 3 , which outputs both digital audio and power to a further chain of speakers.  
         [0023]      FIG. 2  shows a block diagram illustrating selected electrical aspects and functionality of the master mixer/power converter  20 . A digital audio receiver  21  and a digital audio transmitter  23  are provided for respectively receiving digital audio inputs and transmitting digital audio outputs. In an embodiment, the digital audio receiver  21  and digital audio transmitter  23  receive and transmit two channels of digital audio, shown in the figures as two lines, and designated herein as a speech channel and a music channel. As an example, and without limiting the scope of the invention, the digital audio receiver  21  and digital audio transmitter  23  may receive and transmit, using AES/EBU digital audio inputs and outputs as is know in the art. Analog audio inputs  29  are provided for receiving analog audio from sources such as a microphone and line level analog audio sources. In one embodiment, analog audio inputs  29   a  are designated as part of a speech channel, whereas analog audio inputs  29   b  are designated part of a music channel. There is, of course, nothing that limits the speech channel to speech, nor that prevents speech from being reproduced over the music channel. Similarly, the music channel may have any combination of inputs, and need not have any music at all. As will be discussed in more detail below, the speech channel and music channel may be handled differently within, or outside the master mixer/power converter  20 , and it is thus it may be beneficial to provide the two channels.  
         [0024]     A remote volume control input (not shown) may be provided for remotely controlling volume levels output by the speaker units. In an embodiment, one or more link in inputs  31  may be provided for connecting the master mixer/power converter  20  to other system components, including additional master mixer/power converters, in a daisy-chain manner to add functionality and/or provide additional inputs. One or more link in input ports  31  may also be provided for receiving audio input from digital sources rather than from other master mixer/power converters.  
         [0025]     An analog-to-digital converter  37  converts the analog signals from analog inputs  29  to digital format. In an embodiment, the conversion provides at least two channels of digital audio output—a first channel, designed a “speech channel”, may be used for speech from sources such as microphone  30  ( FIG. 1 ), and a second channel, designated a “music channel”, may be used for music or other audio content, from other audio sources  40  ( FIG. 1 ). As discussed above, these channels are not limited to a specific type of content. A digital signal processor  27  receives the digital audio, including the speech channel and the music channel, from the analog-to-digital converter  37 . The digital signal processor  27  may also receive two or more digital audio channels from the digital audio receiver  21 . In an embodiment, the digital audio receiver  21  provides a speech channel and a music channel to the DSP  27 .  
         [0026]     The digital signal processor  27  applies digital processing, such as equalization and compression, to the digital audio signal. The digital signal processor  27  in one embodiment provides at least two channel processing. In an embodiment, the speech channel of the digital audio signal is processed in accordance with equalization and/or compression algorithms which are selected to improve the intelligibility of the content transmitted on the speech channel. For example, the digital signal processor may, when processing the speech channel, cause frequencies in the speech-typical mid band to be emphasized, and may cause frequencies in the low band, and/or frequencies outside of those associated with the human voice, to be attenuated. The digital signal processor may, when processing the speech channel, apply a relatively high level of compression to the speech channel to reduce the bandwidth used by the channel. In an embodiment, the digital signal processor allows the speech channel to be adjusted in volume level independently of the music channel. In an embodiment, the digital signal processor  27  may apply to the music channel different equalization and/or compression algorithms which are appropriate for non-speech audio such as commercial music. For example, without intending to limit the scope of the invention, low frequency response may be enhanced in the music channel to provide improved bass response. In an embodiment, no equalization or compression is applied to the music channel, while the speech channel is processed to improve intelligibility of voice content. In an embodiment, no equalization or compression is applied to the speech channel, while the music channel is processed to enhance music content. In an embodiment, the music channel is slightly or significantly attenuated when the speech channel is in use.  
         [0027]     The output of the digital signal processor  27  is received by a digital audio transmitter  23 , which formats the digital audio signal for output over a network cable via a digital power link out port  33  and/or a link out port  35 . The digital power link out port  33  and the link out port  35  supply such digital audio signal to one or more pairs of twisted conductors in an ethernet cable or other network cable appropriate for transmission of digital signals. In an embodiment, the digital power link out port  33  and the link out port may comprise, e.g., RJ-45 female connectors.  
         [0028]     In addition to the digital audio signal, the digital power link out port  33  supplies electrical power from the regulated power supply  25  over the connected network cable. The power is conducted from the regulated power supply to the digital power link out port  33  to which the network cable is connected. The power may be, e.g., at 48V DC, or other voltage appropriate to drive an audio power amplifier at the speaker unit(s) connected in the daisy chain manner as described above. In an embodiment, the regulated power supply  25  receives A/C power from an A/C in jack or plug, and sends DC power to pins of the digital power link out jack  33 . While the power to the digital power link out jack  33  could be AC power, using AC power may cause interference that may prevents the digital audio signal from being transmitted in the same cable. In an embodiment, power is supplied to two or more pins of the digital power link out jack  33 . In an embodiment where RJ45 jacks are used, power is supplied to four pins of the digital power link out jack  33 , the speech channel is transmitted on two pins of the digital power link out jack  33  and the music channel is transmitted on two pins of the digital power link out jack  33 . In an embodiment where RJ45 jacks are used, power is supplied to six pins of the digital power link out jack  33 , and the speech and music channel are multiplexed on two pins of the digital power link out jack  33 . The pairs of conductors carrying the power signal may all carry power at the same voltage, or may carry power at different voltages. Thus, for example, power may be supplied over the network cable to the audio power amplifier of the speaker units at a relatively high voltage sufficient to drive the amplifier, and may be supplied over a separate pair to the DSP of the speaker units at another, lower voltage.  
         [0029]     In an embodiment, the regulated power supply further provides power to the various components and circuits of the master mixer/power converter  20 , e.g., the digital audio receiver  21 , the analog-to-digital converter  37 , the DSP  27 , and the digital audio transmitter  23 .  
         [0030]     In one embodiment within the scope of the invention, one or more of the pairs of conductors may be used to transmit control signals and/or data signals other than digital audio to the speaker units. For example, such pair or pairs may be used to transmit one or more of the following: volume control signals, equalization or signal processing settings, digital video, data from a computer&#39;s network interface card, or other signals.  
         [0031]     In an embodiment within the scope of the invention, multiple digital power link out ports are provided to support further chains of speaker units, and each such chain may transmit content which is the same as or different than that of the digital power link out port  25 .  
         [0032]      FIG. 3  shows a block diagram illustrating electrical aspects of a speaker unit SU in accordance with one embodiment of the invention. A digital power link in port  59 , which may comprise, e.g., an RJ-45 jack, receives digital audio and power signals from a preceding component in the chain. Such preceding component may be, e.g., the master mixer/power converter  20  ( FIGS. 1 and 2 ), another speaker unit, or an expander/power converter EX 1 , EX 2  or EX 3  ( FIG. 1 ).  
         [0033]     The digital audio and power signals received at the digital power link in port  59  are both passed to the digital power link out port. In one embodiment, either of the digital power link ports can be used for the input of the cable carrying power and audio, and the other can be used as the output to daisy-chain the power and audio signal to additional speaker units. Thus, in an implementation of the invention, the two ports may be interchangeable. This simplifies the installation of the system, and greatly reduces the possibility that the speaker units will be mis-wired when installed. The power signal received at the digital power link in port  59  is also provided to the power circuits  63  for powering the internal electrical components of the speaker unit.  
         [0034]     A digital audio receiver  61  receives the digital audio signal from the digital power link in port  59  and provides a digital audio signal to a digital signal processor  53 . At this point, the digital audio signal in one embodiment includes both the speech channel and the music channel. In an embodiment, the digital signal processor  53  performs a digital sum of the speech channel and the music channel, and then a digital crossover function on the summed speech channel and music channel splitting it into high frequency and low frequency components. Thus, the digital audio signal which is output from the digital signal processor  53  contains two audio channels. This digital audio signal may be in pulse-code-modulated (PCM) form, or other digital audio format.  
         [0035]     In an embodiment, the digital signal processor  53  may perform equalization on the speech channel and/or on the music channel prior to summing the channels. In an embodiment, the equalization may be configured for the speaker individually, and may be configured to accommodate acoustics or ambient noise local to the speaker. This type of flexibility permits a speaker situated above a marble floor, for example, to be equalized differently, on a per channel basis, than a speaker situated above a carpet or other acoustically absorptive surface.  
         [0036]     A Pulse-Width-Modulation (PWM) controller  51  receives the two channels of digital audio from the digital signal processor  53  and converts each channel to a PWM signal comprising a train of pulses whose width varies in accordance with frequency of the encoded audio. Two PWM signals are thus output from the PWM controller  51 . As shown in  FIG. 3 , these are designated PWM-LF (low frequencies) and PWM-HF (high frequencies). The PWM signals are used to drive a Class D digital power amplifier  57 .  
         [0037]     The Class D digital power amplifier  57  utilizes the PWM signals to switch an output power amplifier device on and off to provide an amplified analog signal. The output power amplifier device may be, e.g., a power MOSFET. In one embodiment, the Class D digital power amplifier  57  is a multi-channel amplifier operating at 20 watts per channel or more.  
         [0038]     In an embodiment, the digital power amplifier may be set up for bi-amplification of the speech channel and the music channel. That is, the high-frequency components of those channels may be amplified separately from the low-frequency components. Each of the two separately amplified analog signals may be used to drive one or more speaker drivers  65 ,  65   a . In an embodiment, the low frequency signal is used to drive a speaker driver  65 , for example, but not by way of limitation, a 6.5″ woofer with 20 oz. magnet, while the high frequency signal is used to drive a speaker driver  65   a , for example, but not by way of limitation, a 1″ horn-loaded silk dome tweeter. The speaker unit as shown in  FIG. 3  may be provided in a single speaker enclosure or other unit. In one embodiment, the speaker unit is a ceiling mounted speaker, and the speaker drivers  65 ,  65   a  are downward-facing. In an embodiment, the speaker unit may be a wall-mounted speaker that is either recessed into a wall or surface-mounted to the wall, or even a free-standing speaker such as a floor-standing speaker or bookshelf type speaker. Although speaker drivers  65 ,  65   a  are shown separated, as will be apparent to one of skill in the art, the smaller speaker driver  65   a  may be situated within the perimeter of larger speaker driver  65 .  
         [0039]     In an embodiment (not shown), the digital signal processor  53  and PWM controller  51  output out a single signal comprising both the high and low frequency components, rather than outputting two separate signals. Amplifier  57  may thus amplify only the single signal, and outputs a single signal to a single full-range speaker (not shown.) Notably, the equalization of the speech and music channels can be achieved prior to the combination of the two into a single signal.  
         [0040]     As will be appreciated by those of ordinary skill in the art, the speaker unit as described above can be used advantageously in audio systems other than the audio distribution system described hereinabove. For example, the speaker unit can be used in conjunction with a digital output of any audio source to provide a powered speaker which avoids signal loss, particularly where long cable runs are employed between the audio source and the speaker unit. The use of highly efficient class D amplification provides a powered speaker with very low power consumption which can be powered via cabling which is also used to transmit digital audio to the speaker.  
         [0041]      FIG. 4  shows a block diagram illustrating various electrical aspects of the expander/power converter EX 1  which is used to expand a daisy chain of speakers once the maximum number of speakers in the chain has been reached. The expander/power converter as shown may also be used to add remote speakers or daisy chains of speakers, as shown at element EX 3  in  FIG. 1 , or may be used as an alternative to the master mixer/power converter where only a limited number of analog inputs and processing are required. A digital audio receiver  121  and a digital audio transmitter  123  are provided for respectively receiving digital audio inputs and transmitting digital audio outputs, such as AES/EBU digital audio inputs and outputs. Analog audio inputs  129 , which may be, e.g., a mini stereo ⅛″ TRS jack or a pair of RCA jacks, are provided for receiving analog audio from sources such as such as a DVD player, CD player, or the like. A link in input  131  may be provided for connecting the expander/power converter EX 1  to the last speaker unit in the chain SUn ( FIG. 1 ) or other upstream system components such as the master mixer/power converter.  
         [0042]     With continued reference to  FIG. 4 , in one embodiment, an analog-to-digital converter  137  may be provided to convert the analog signals from analog inputs  129  to digital format. A digital signal processor  127  receives the digital audio from the analog-to-digital converter  137 , and receives digital audio from the digital audio receiver  121 . The digital signal processor  127  may apply digital processing, such as equalization and compression, to the digital audio signal in a manner similar to that described above with reference to the functions of the DSP in the master mixer/power converter  20  ( FIG. 1 ). The analog inputs  129  may be treated as a speech channel or as a music channel by the digital signal processor  127 . Note that an EX 1  need not include analog inputs  129 , nor ADC  137 .  
         [0043]     The output of the digital signal processor  127  is received by a digital audio transmitter  23 , which formats the digital audio signal for output over a network cable via a digital power link out port  133  and/or a link out port  135 . The digital power link out port  133  and the link out port  135  supply such digital audio signal to one or more pairs of twisted conductors in an ethernet cable or other network cable appropriate for transmission of digital signals. The digital power link out port  133  and the link out port may comprise, e.g., RJ-45 female connectors. In addition to the digital audio signal, the digital power link out port  133  supplies electrical power from the regulated power supply  125  over the connected network cable in much the same manner as is described above in connection with the digital power link out port  133  of the master mixer/power supply. In one embodiment, the regulated power supply  125  receives AC power from an A/C in jack or plug, and sends DC power to six pins of the digital power link out jack  133 . This DC power signal is used to power further speaker units SU 9  through SUn′ ( FIG. 1 ) downstream from the expander/power converter EX 1 .  
         [0044]     Thus, an audio distribution system has been described which provides a plug-and-play architecture that facilitates installation and use of the system. While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.