Operation Manual

11. Operation and performance
D SERIES Lake Operation Manual rev 3.0.1
31
11.6.3. Manual configuration
11.6.3.1. Functional description
Manual conguration can be used in special cases where proper functioning requires setting of custom
measurement frequencies, custom measurement levels, custom warning thresholds, or combinations of the three.
Manual conguration addresses the following issues:
Speakers with non stable impedance – For the LoadPilot feature to function the load itself needs to have a
stable impedance at the frequency of the tone. Resonances in the speaker or other non linear phenomenons can
make the impedance at a certain frequency unstable. Stability needs to be veried by examining the impedance
response to make sure it is relatively at at the tone frequencies and by verifying LoadPilot readings when playing
signal through the speaker at the most extreme expected level. The frequency of the pilot tones can be changed
within certain ranges and a tone can be disabled. If a frequency where the speaker is stable can not be found one
tone can be disabled and LoadPilot relies solely on the remaining tone.
High noise levels – To obtain accurate impedance measurements, it is necessary to drive a current sufciently
above the noise oor. However, it is important to keep the level low in order to prevent audible artifacts from cone
travel. At very high impedances, the drive current may be insufcient. In the automatic mode, level is set around 60
mV which produces usable results for impedance up to 660 ohms.
Inductance in loudspeaker cables – Loudspeaker cable inductance at higher frequencies is very high relative to
passive resistance, and the inductance increases linearly with length. Consequently, monitoring at the 24 kHz pilot
tone frequency can be problematic with very long cables. The automatic mode will estimate cable impedance for
24 kHz and allow it to be used as long as it is less than 33% of total impedance presented by the load and as long
as the total impedance is below about 440 ohms.
DC blocking capacitors in loudspeakers – Some loudspeakers incorporate a capacitor designed to block
damaging voltages at very low frequencies. This may inhibit accurate measurements when using the 10 Hz pilot
tone. In automatic mode, LoadPilot will disable the 10 Hz tone if total impedance is above about 440 ohms.
Constant voltage loudspeakers – Loudspeakers driven via transformers in 70V/100V solutions are more likely
to exhibit wide variations in measured impedance as music and/or pilot tones are reproduced by the system. Also,
most constant voltage systems operate more than two loudspeakers in parallel. Therefore, in addition to manual
conguration of LoadPilot, additional step may be required. These include:
• Insertion of a series capacitor in each loudspeaker to block the 10 Hz LF tone – This will defeat measuring the
loudspeakers with the LF tone, but will allow the LF tone to propagate through the entire cable run.
• Insertion of EOL (end–of–line) resistors – This enables LoadPilot to detect cable faults in a spur of the system.
• Insertion of EOL (end–of–line) inductor – This is not mandatory, but it will avoid the loss of level at mid and high
frequencies due to the EOL resistor.
NOTE: Manual conguration of LoadPilot is implemented in CAFÉ versions 1.1.0. and later. For detailed
information on manual conguration of LoadPilot, please refer to the integrated guide in the software
program and to the CAFÉ Coach videos posted on the Lab.gruppen web site and on the Lab.gruppen
channel on YouTube.