d&b D12 Hardware - Manual (Page 9)

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 6.2.1. Power consumption and power loss
on page 20and section 6.2.2. Operating conditions on page 21.
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 applicable d&b systems (EP5 and NL8 connectors only) 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.
Note: A detailed description of the D12 SenseDrive function is given in the
technical information TI 340 (d&b code D5340.E.).
Not connecting SenseDrive for C-Series subwoofers (e.g. NL4
connectors) does not change the present performance of the system.
D12 Amplifier, Hardware manual (4.9 EN) Page 9 of 28