NEXO NXAMP 4X1 Owner's Manual - Yamaha Commercial Audio

BLOCK DIAGRAM DESCRIPTIONProtectionsThe NXAMP4x1 TDcontroller will limit the user gain adjustment to a group of channel inspecific case such as cardioids setups (for example on CD18 setup, gain is linked betweenfront and rear loudspeaker).Each channel has its own simulation and protection process. Each audio channel contains acombination of controlled gain stages (let's call them VCA’s as in our analogue circuitry).These VCA's are embedded into complex composite structures in order to change theirbasic operation into frequency selective attenuation. This operation is similar to that of avoltage controlled dynamic equaliser (VCEQ).Each VCEQ and VCA is controlled by the synthesis of several signals issued from thevarious detection sections. That synthesis is in fact the envelope of those signals, with anoptimised release and attack time for each VCEQ and VCA (depending on its frequencyrange and the cabinet selected).One or several of the protections below can be used depending on the setup chosen.Source signals for protection algorithms (25)Signals coming from amplifier output voltage/ current, processor output, and status fromamplifier are all sources that will lead to protection system implementation.Displacement control (7) (8) (9)The amplifier output voltage sense input signal is sent to a shaping filter producing a signalwhose instantaneous amplitude is proportional to the voice coil excursion (this is Globaldisplacement block (7)). This signal, after rectification, is compared to a preset thresholdmatching the maximum usable value, as determined from laboratory measurements. Anypart of the signal exceeding the threshold is sent to the VCEQ control buffer while theVCEQ acts as an instantaneous limiter (very short attack time) to prevent displacementfrom overriding the maximum permissible value.Another set of VCEQ (this is first displacement block (8)) is used to protect the loudspeakerfrom an excessive displacement in the next worst displacement frequency area (thisusually is 3 dB bellow the global displacement protection area). In case of band passcabinets, we need another set of VCEQ (this is first displacement band pass block (9)) toprotect from another peak of secondary displacement.All these VCEQs have separate shaping filter, separate action filters for VCEQ, and separateRatio, Attack and Release time.Mechanical stress control (10) (11)Whereas some frequency areas are dangerous at high level due to excessive displacementof the loudspeaker (see above), there is another area where the displacement of theloudspeaker is minimum, but then the mechanical stress on the cone during large inputsignals is maximum.To protect from overstressing the loudspeaker, VCEQ process can also be used in thesePAGE 33 OF 80