Abstract:
An audio load box to test multiple audio channels using selectable loading for each channel. A resistive load is switched into the signal path of each audio channel before audio tests are conducted. The resistive load can be a single resistor or resistors in parallel. The multi-channel audio load box with selectable loading can provide greater flexibility, reliability and accuracy for tests, for example inter-channel phase measurements and crosstalk.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    An audio load box provides a fixed load configuration for an audio channel during audio functional testing. The audio load box can accommodate multiple audio channels in one audio box fixture. Devices Under Test (DUTs) have their audio channel outputs terminated in a fixed load impedance to maximize power transfer or to match specified measurement conditions. 
         [0002]    An example of such a measurement condition is when a power amplifier is tested to deliver an output voltage at the current drawn by a the loudspeaker. In this instance, the loudspeaker is replaced by a load, i.e. resistor of a fixed resistance, either 2, 4 or 8Ω. 
         [0003]    Alternatively, the DUT to be tested may be a receiver for a home theater, an audio power amplifier or a DVD player, or one of hundreds of other devices that require audio testing. 
         [0004]    Current in-car infotainment systems provide more than just audio entertainment, they add information and services useful to drivers for safety, communications and navigation. Sophisticated infotainment systems are equipped with the latest digital audio and video services, GPS and communication systems such as Bluetooth and WLAN. 
         [0005]    Increasing integration of audio and information systems built into vehicles has led to a demand in sophisticated audio testing systems. 
         [0006]    An audio channel can comprise two wires. A signal path of the audio channel is the path a signal takes from one wire through a load and returns through the second wire. Alternatively, the second wire can be a ground wire. 
         [0007]    Presently on the production floor or in the R&amp;D lab, an audio load box, comprising multiple channels with non-selectable or non-variable resistive loads, provides limited freedom to test an audio system during production or research. As described above, a load in a multiple channel audio box is fitted with a fixed resistive load value. In some instances, the resistive load can be manually reconfigured by physically removing the resistive load and replacing it with another value, making the audio load box a quasi-selectable load box. 
         [0008]    Inter-channel phase measurements and crosstalk are audio engineering tests that are measured in relationship to a reference waveform. The reference can be a signal at a different point in the system, or a related signal in a different channel in the system. It is possible that the reference channel or the channel under test has a different loading resistance value. 
         [0009]    When performing inter-channel phase and crosstalk tests, the quasi-selectable load box described above can create inefficiencies. It can lead to improper test conditions and inconsistent results, and consequently creates a scenario where reproducing results can be a daunting task. 
         [0010]    Unfortunately, present audio load box offerings do not cater to the testing requirements of contemporary audio testing systems. A void in the industry is a multiple channel audio box with a selectable or variable load for each audio channel. 
         [0011]    Audio testing facilities desire an audio load box design that can be customized. This can comprise testing additional channels and with a higher power rating for the load and selecting load values for each channel. 
         [0012]    Accordingly, a need exists to test an audio system comprising multiple audio channels using selectable loading for each audio channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram describing a multi-channel audio load box with selectable loading within an audio testing system; 
           [0014]      FIGS. 2A-B  are schematic drawings of the audio load box with selectable loading; and 
           [0015]      FIG. 3  is a flow chart describing the operation of the audio load box with selectable loading in an audio test. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The description herewith details a multiple audio channel load box with selectable or variable load settings for each audio channel. A multi-channel audio load box with selectable loading (“selectable load box”) enables an audio test engineer to conveniently and efficiently test a multi-channel audio system with a variety of load settings. The selectable load box can improve repeatability and speed of testing in an R&amp;D laboratory or on a production line. The selectable load box can also aid in conducting tests requiring simultaneous channels with different loads. 
         [0017]      FIG. 1  is a block diagram describing a selectable load box  105  within an audio testing system  101 . 
         [0018]    Input ports  103  comprising six audio channels are fed into the selectable load box  105 . Output ports  107  comprising six audio channels are also illustrated in  FIG. 1 . The output ports  107  can be connected to an audio analyzer (not shown). 
         [0019]    Selectable (or programmable) load devices  111  in the selectable load box  105  are used to simulate an actual speaker load. For example, high power load settings can be resistors of value 2, 4 and 8 Ohms with a power rating of 40 Watts. Meanwhile, the low power load settings can be 100K, 47K and 10K Ohms with a power rating of 2 Watts. 
         [0020]    The selectable load box  105  comprises a switching matrix unit  109 . The switching matrix unit  109  provides a switching platform. The switching platform actuates a load device from within the selectable load devices  111  to simulate a load for an audio channel. 
         [0021]      FIG. 2A  is a schematic drawing of the selectable load box  105 . The schematic illustrates 6 audio channels with 3 load settings apiece. The six audio channels comprise four channels  203  of selectable load devices with fixed load values and two channels  205  of selectable load devices with variable load values. The variable load devices can be load devices that are removable (and replaceable) or can be load devices with an adjustable resistance value setting. For example, the resistors for the variable load devices can be a combination of fixed value resistors which are, 100K ohm (+/−5%), 47K ohm (+/−5%) and 10 ohm (+/−5%). 
         [0022]    The four audio channels  203  have 4 mm speaker plugs and XLR connectors as input and output ports respectively. The three load devices are connected by individual switches. For example switches S 10 , S 11  and S 12   217  connect the two wires of audio channel  211 . Examples of switches are mechanical relays, electronic relays and reed switches. The switches  217  can be part of the switching matrix unit  109 . 
         [0023]    In audio channels  203  the load resistors  221  are configured with 4, 8 and 8 Ohms of varying wattage. In audio channels  205 , the load resistors are configured with variable resistor values to provide design flexibility to an operator. The operator can add values of resistance or wattage for specific application as required. 
         [0024]    The switches in each audio channel, for example the switches S 10 , S 11  and S 12   217  of audio channel  211  can be applied individually or in a parallel combination to achieve a desired load and power rating. For example, parallel combinations of the resistor loading of the audio channel  211  can produce resistor values with a larger power rating. The switches can be controlled manually or through the switching matrix unit  109  as part of a larger test system. 
         [0025]      FIG. 2B  is a schematic diagram illustrating a design of an audio channel  251  using a single switch  253 . The audio channel  251  is one of many audio channels in the audio box  105 . When the switch  253  is actuated, a load device is inserted between the audio channel wires. The switch  253  can be controlled manually or through the switching matrix unit  109  as part of a larger test system. 
         [0026]      FIG. 3  is a flow chart describing the operation of the selectable load box  105  during an audio test. Block  310  describes connecting audio channels to the input  103  and output  107  ports of the selectable load box  105 . Block  320  describes selecting a load resistance value for each audio channel. This is achieved by making a selection through the switching matrix unit  109 . The selection can comprise more than one load device if permissible, creating a parallel combination from the individual load values. Block  330  describes performing the audio tests on the audio channels. 
         [0027]    While the embodiments described above constitute exemplary embodiments of the invention, it should be recognized that the invention can be varied in numerous ways without departing from the scope thereof. It should be understood that the invention is only defined by the following claims.