Nexo GEO M1210 System Manual
Also see for GEO M12 Series: User manual
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SYSTEM CHECK ALIGNMENT GUIDELINES Page 67/907.3 Driving the MSUB18s from the AUX sendIt is quite common to use the AUX send of a mixing desk to drive the Sub section of a PA system. Thisgives the mixing engineer more flexibility to set the level of the subbass relative to the main PA, applyspecial effects, or to use a different EQ on the Sub. However, it also raises some serious issues for theperformance & safety of the system (mostly time alignment).At NEXO, great care is taken to design optimum phase alignment from one octave above to one octavebelow the crossover frequency point. By doing so, drivers are working perfectly together and providingthe best efficiency possible. It is then up to the user to adjust the delay on the NEXO TD Controllers tomatch the physical path difference of the different systems. It is thus possible to get a well-adjustedsystem, even without measuring instruments.If MSUB18s are driven form an AUX output, NXAMPs are fed with two signals coming from differentsources. If those two sources (MAIN output & AUX send) are not exactly in phase, delay is introducedinto the crossover between the GEO M12 array and the MSUB18s. It is then mandatory to use propermeasurement tool to optimize phase response.Why is it unlikely that AUX and MAIN outputs have the same phase?• Signal paths are likely to be different; any filter modifying the bandwidth and EQ of the signalis also affecting the phase.Example: a 24dB/oct high pass filter set at 15Hz is affecting amplitude of the signal by only0.6dB at 30Hz, but the phase shift is 90°!! At 100Hz we can still measure 25° of phase shift.• Limiting bandwidth with a low pass filter can introduce a phase difference of up to 180°(completely out of phase) at the cross over point.• If the signal is passing through any digital equipment, between 1.4ms and 2.2ms is beingadded (around 70° phase shift at 100Hz) due solely to the converter delay! The additionaldelay due to the processing itself (look ahead compressor, delay…) can be quite importantas well.If both outputs are not measured in the actual configuration, it is very likely that phase alignment will notbe correct.Consequences of badly aligned systemsMis-aligned systems have lower efficiency: i. e. for the same SPL the system will have to be driven harder,activating the displacement & temperature protection at lower output levels. Both sound quality andreliability will decrease as the system is stressed.Precautions & ChecksBefore using the AUX of a mixing desk, ensure that MAIN and AUX outputs are in phase;Always apply identical EQ or processing on both channels, so that the phase relationship will not bealtered;Never add additional low pass filtering on the SUB or high pass filtering on the main system;Inverting polarity on one channel should always result in a massive difference near the crossover point.If that is not the case, the system is no longer aligned.7.4 Recommended installation tools and equipmentTape measure – should be 30m/100ft in length and be of durable fibre material. Have one per arrayavailable to speed up the installation process.Spirit level – used to ascertain the trueness of the surface from which the angle measurements originate.Rangefinder measuring device – either a Disto type laser measure or an optical laser rangefinder can beused. Devices such as the Bushnell ‘Yardage Pro’ sports rangefinders provide sufficiently accuracy andare easy to use. They have the additional advantage of working very well in bright sunlight. |
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