Nexo NXAMP4X1 User Manual

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Nexo NXAMP4X1 User Manual Manual pdf 67 page image

APPLICATION NOTE: DRIVING THE SUB FROM THE AUX SENDApplication Note: Driving the Sub from the AUX sendIt is quite common to use the AUX send of a mixing desk to drive the Sub section of a PAsystem. This gives the mixing engineer more flexibility to set the level of its subbassrelative to the main PA, apply special effects, use a different EQ on the Sub…However, italso rises some serious issues for the performance & safety of the system (mostly timealignment).What is the phase relation between the AUX and MAIN output of your Desk?At NEXO, when we align systems, we take great care to have an optimum phase alignmentfrom one octave above to one octave below the crossover frequency point. By doing so, weensure that both drivers are working perfectly together and providing the best efficiencypossible. It is then up to the user to adjust the delay on the NXAMP4x1 to match thephysical path difference of the different systems. It is thus possible to get a well adjustedsystem, even without measuring instruments.If you choose to drive the Sub from the AUX, you feed the NXAMP4x1 with two signalscoming from different sources. If those two sources (MAIN output & AUX send) are notexactly in phase, you are introducing a delay –without knowing it- into the crossoverbetween your main system and your sub. Without the proper measurement tools, you willnever be able to tune the system as it should be.Why it is unlikely the AUX and MAIN have the same phase?• Signal paths are likely to be different; any filter modifying the bandwidth and EQ ofthe signal is also affecting the phase.Example: a 24dB/oct high pass filter set at 15Hz is only affecting amplitude of thesignal by 0.6dB at 30Hz but the phase shift is 90°!! At 100Hz we can still measure25° of phase shift• Should you want to restrict the bandwidth with a low pass filter, you can introducea phase difference of up to 180° (completely out of phase) at the cross over point• If the signal is passing though any digital equipment you are adding between 1.4msand 2.2ms (around 70° phase shift at 100Hz) due to the converter delay only! Theadditional delay due to the processing itself (look ahead compressor, delay…) canbe quite importantAt the end of the day, if you have not measured both outputs in the actual configurationyou can be 90% sure that you won’t get the correct phase alignment that you would havehad if the NXAMP4x1 was fed by a single source.Consequences of badly aligned systemsMis-aligned systems have less efficiency: i.e. for the same SPL you will be obliged to drivethe system harder, causing displacement & temperature protection at lower SPL than aproperly aligned system. The sound quality will decrease. The reliability will decrease as thesystem is driven harder to achieve the same levels. In certain situations you may evenneed more speakers to do the same job…PAGE 67 OF 80