Nexo GEO D Bedienungsanleitung PDF herunterladen (Seite 68)

Page 68/97 NEXO NX242 DIGITAL CONTROLLER FOR GEO D AND GEO SUB

R+L

Voice Coil Temp.

ChassisTemp

Command

PHYSIO 1

Command

PEAK SIMULATION

PATCH

Disp.

Command

Voice Coil Temp.

ChassisTemp.

LF TEMPERATURE

INPUT VU-METER

A/D EQ

A/D

DACMUTEEQ

SHELVING

A/D EQ

Command

HF TEMPERATURE

VCA

FALLBACK

AMP VOLTAGE

Signal

AMP POWER

AMP GAIN

Command

displacement

DISPLACEMENT 1

DELAY 1

ATT/REL.

SENSE 1

R+L

INPUT VU-METER

INPUT R

INPUT L

OUTPUT

CHANNEL 4

NX242 Digital TDcontroller Partial BLOCK DIAGRAM

Analogue path

Digital Audio

Digital servo & protections

HEADROOM

6.1.3 Protection

VCAs and VCEQs

Each channel has its own simulation and protection process.

Each audio channel contains a combination of controlled gain stages

(let's call them VCAs as in analogue circuitry). These VCAs are

embedded into complex composite signal chains that adapt change their

basic operation into frequency selective attenuation, similar to an analog

voltage controlled dynamic equaliser (VCEQ).

Each VCEQ and VCA is controlled via synthesis of several signals from

the various detection sections. That synthesis is in fact the envelope of

those signals, with an optimised release and attack time for each VCEQ

and VCA (depending on its frequency range and the cabinet selected).

Displacement Control

The Sense input signal is sent to a shaping filter producing a signal

whose instantaneous amplitude is proportional to the voice coil

excursion. This signal, after rectification, is compared to a preset

threshold matching the maximum usable value, as determined from

laboratory measurements. Any part of the signal exceeding the threshold

is sent to the VCEQ control buffer while the VCEQ acts as an

instantaneous (very short attack time) limiter to prevent displacement

from exceeding the maximum permissible value.

Temperature Control

Each sense signal is fed into a shaping filter (one per transducer), each

one producing a signal proportional to the instantaneous current flowing

into the voice coil of the transducer. After rectification, this signal is

integrated with attack and release time constants equivalent to the

thermal time constants of the voice coil and chassis, producing a voltage,

which is representative of the instantaneous temperature of the voice

coil.

When this voltage reaches the threshold value corresponding to the

driver’s maximum safe operating temperature, the VCA becomes active

to reduce the NX242’s output signal level until the effective temperature

falls below the maximum usable value.

In order to avoid detrimental effects induced by very long release time

constants produced by the temperature detection signal (system output

being reduced for an extended period, “pumping” effects, etc.), the

detection signal is modulated by another voltage integrated with faster

time constants that match the subjective perception of sound level. This

allows the controller to reduce the effective operating duration of the

temperature limiter and make it sound more natural, while the efficiency

of protection is fully preserved and protection thresholds are kept as high

as possible.

Physiologic Dynamic Control

The Physiologic Dynamic Control is intended to avoid unwanted effects

produced by long attack time constants. By anticipating the operation of

the temperature limiter, it prevents a high level audio signal appearing

suddenly, then being kept up for long enough to trigger the temperature

limiter. Without this, a rough and delayed gain variation would result that

would be quite noticeable and unnatural.

1 2 ... 63 64 65 66 67 68 69 70 71 72 73 ... 93 94

Kommentare zu diesen Handbüchern

Keine Kommentare

Nexo GEO D Bedienungsanleitung Seite 68

Kommentare zu diesen Handbüchern