Nexo GEO D - Manual (Page 69)

NEXO NX242 D IGITAL C ONTROLLER FOR GEO D AND GEO SUB Page 69/97
The Physio control voltage acts independently on the VCA with its operation threshold slightly (3 dB)
above that of the temperature limiter and a low compression ratio; its optimised attack time constant
allows it to start operating without any subjectively unpleasant transient effects.
Peak Limiter
The peak limiter primary function is to avoid massive clipping of the amplifier, which can have some
very audible artefacts and in some cases may be damaging to the loudspeakers. Modulation of the
amplifier’s supply voltage rails can create very low frequencies or high-frequency, high level harmonics.
Since these occur after the NX242 in the signal path, they are not filtered by the TDcontroller circuitry.
The threshold of the peak limiter is set by the user to match the amplifier’s clipping point.
The second function of the peak limiter is to avoid huge amounts of power being sent to a driver. Each
driver is protected against overheating and overexcursion, but there could be other failure modes that
cannot be predicted by simulation (especially mechanical damage to the cone). Each driver is specified
for a certain power handling and a factory set peak limiter threshold is tuned to avoid any abuse.
6.2 Cardioid LF and VLF
Cardioid LF and VLF is one of the key advances of the GEO D / GEO SUB system. This feature is only
achievable with a total control of the DSP chain. Although the basic concept as presented in audio text
books is relatively simple, producing a cardioid pattern from a loudspeaker without a major loss of
efficiency requires advanced DSP processing.
Other “loudspeaker management” DSP devices do not provide the algorithms that the NX242 uses to
optimise the cardioid operation of the GEO D10 and GEO SUB.
GEO D10 LF and GEO SUB dispersion are digitally set to a cardioid pattern by adjusting the front and
rear loudspeakers phase and amplitude relationship. Average rear to front attenuation is more than 12
dB.
6.3 GEO D NX242 Setups description
6.3.1 GEO D10 Passive Mode (Stereo Setups)
Hardware configuration
• Input can be selected in the MENU 3.2 (L, R or L+R);
• Output 1 drives left GEO D side-firing LF 8 inch neodymium transducers;
• Output 2 drives left GEO D front-firing LF/MF 12 inch neodymium transducers and the HF 3-inch
voice coil, 1.4 inch exit compression driver;
• Output 3 drives right GEO D side-firing LF 8 inch neodymium transducers;
• Output 4 drives right GEO D front-firing LF/MF 12 inch neodymium transducers and the HF 3-
inch voice coil, 1.4 inch exit compression driver.
6.3.2 GEO D10 Active Mode (Mono Setups)
Hardware configuration
• Input can be selected in the MENU 3.2 (L, R or L+R)
• Output 1 drives GEO D side-firing LF 8 inch neodymium transducers;
• Output 2 drives GEO D front-firing LF/MF 12 inch neodymium transducer;
• Output 3 drives GEO D HF 3-inch voice coil, 1.4 inch exit compression driver;
• Output 4 is not used.