D&b Audiotechnik D12 Hardware Manual - page 10
3.4.
D12 power amplifiers
The two power amplifiers fitted to the D12 can deliver 2 x 750 W
continuous sine wave power into an 8 ohms load, increasing to 2 x 1200
W continuous sine wave power into a 4 ohms load. These maximum
output ratings measured with sine wave are valid for minutes only until
the unit will switch into thermal protect.
IMPORTANT!
The D12 is specifically designed to produce high power
into low impedance loads, typically those between 4 and
16 ohms. Please check in the relevant loudspeaker
manual for the recommended maximum number of
cabinets that may be driven by each channel. Due to
differences in impedance response against frequency this
may vary depending on the specific loudspeaker type.
Connecting and driving more loudspeakers will not damage the
amplifier but will limit the quality and dynamic range of reproduced
sound as the load dips below 4 ohms. Driving low impedance loads at
high levels can also trigger the amplifier protection circuits for thermal
or output current overload.
A D12 will normally be operated with speech or music program -
complex signals where the average power requirement is below peak
power. The D12 will continue to operate indefinitely when the Crest
Factor is higher than 2.4, provided the device is installed to enable the
heat generated to be adequately dissipated.
NOTE:
Please also refer to section 6.2.1Power consumption and power loss on
page 24, and section 6.2.2. Operating conditions on page 25.
3.5. SenseDrive
The accuracy of a loudspeaker’s signal reproduction, both level and
transient response, is influenced by dynamic damping factor - the ratio
of the load to source impedance.
Whilst amplifier source impedance remains constant the impedance of
the cables and connectors will largely depend upon the length and type
of cable used - longer cables produce greater signal losses depending
on the loudspeaker impedance. The impedance of a loudspeaker will
vary markedly with frequency and especially those at low frequencies.
With long cable runs this impedance variation will significantly affect the
system response.
With d&b subwoofer systems using pin 3/4 and pin 5 of the EP5
connector d&b SenseDrive compensates for the electrical properties of
the loudspeaker cable. A “sense” wire connects the signal from the LF
driver back to the amplifier where it is compared and corrected to
compensate for the cable losses. Signal reproduction is enhanced by
delivering the correct signal to the loudspeaker terminals irrespective of
the cable losses.
The D12 SenseDrive circuit is gain limited and whilst this imposes a
ceiling on damping factor improvement, it guarantees stable operation
with no cable length restriction using speaker multicores such as d&b
MC5 or MC8.
IMPORTANT!
Not connecting SenseDrive for C-Series subwoofers (e.g. NL4
connectors) does not change the present performance of the system.
D12 Amplifier, Hardware manual
(2.0E)
Page 10 of 32