D&b Audiotechnik D12 Hardware Manual - page 24
6.2. Operation
6.2.1. Power consumption and power loss
The power required from the mains supply and the waste heat
produced by the amplifiers power loss vary depending on the load
impedance and the signal levels and characteristics (e.g. speech, music).
In practice, the theoretical peak power consumption of a system will only
be sustained for a short period of time. Basing mains current and air
conditioning plant requirements on the peak power consumption of the
sound system would result in a generously over-specified installation.
The key factor in power consumption calculations is the crest factor (CF)
of the music or speech signal - the ratio of peak to sustainable RMS
voltage of the signal.
A crest factor of 2.4 represents 1/3 of the maximum sine output power
and it can be seen as the worst case signal that can be accessed in real
world conditions. A proper power distribution should be able to handle
the current ratings given in the table below (Tab. 7) referring to CF 2.4.
Using the D12 temporarily with well known signals of higher crest factor,
the power distribution can be downsized within the range given in the
table.
The table gives power figures for various types of signal waveforms.
They were measured on a D12 driving a 4 ohm load (both channels) to
the clipping point of both channels using a sine wave burst signal of 24
dBu with a variable duty cycle. The mains power supply used for the
measurements supplied an ideal sine wave with 230 V/50 - 60 Hz at an
internal resistance of 0.5 ohms (0.12/0.1 ohms for 115/100 V)
equivalent to a mains lead of 20 m (65.6 ft) with a cross section of 1.5
mm
2
(6 mm
2
/ 8 mm
2
for 115/100 V).
Signal
waveform
CF
Duty
P
out
[W]
P
in
[W]
P
loss
[W]
I
in(230V)
[A]
I
in(115V)
[A]
I
in(100V)
[A]
Highly
compressed
music*
2.4
1 : 3.3
800
1230
430
9.2
18.4
20.2
Music with low
dynamic range
3.5
1 : 7
400
640
240
5.3
10.6
11.2
Music with wide
dynamic range
5.0
1 : 14
200
360
160
3.2
6.4
7.0
Tab. 7: D12 Power balance
Key:
CF: Crest factor, Duty: Duty cycle, P
out
[W]: Max. average output power (sum of both channels), P
in
[W]: Input power (effective power)
P
loss
: Power loss (thermal power), I
in (xxxV)
[A]: Resulting current,
* Maximum practicle operation
D12 Amplifier, Hardware manual
(2.0E)
Page 24 of 32