Operation Manual

11. Operation and performance
31
D SERIES Lake Operation Manual rev 3.0.4
11. Operation and performance
30
D SERIES Lake Operation Manual rev 3.0.3
11.6. LoadPilot Load Monitoring
11.6.1. Introduction
LoadPilot is a feature in D Series ampliers that can continually monitor the integrity of loudspeakers and cables
connected to the outputs to ensure that they are functioning properly and free from major anomalies or faults.
By implementing LoadPilot, systems incorporating D Series ampliers can be certied in compliance with voice
evacuation standards such as EN54–16 and NFPA72.
LoadPilot functions by automatically superimposing low–level pilot tones on the input signal (if any present) to the
amplier. One tone is below the range of human hearing (approximately 10–20 Hz) and the other above (24 kHz),
so the activity of LoadPilot is inaudible regardless of whether the system is currently reproducing program content.
High–resolution current sensing on the outputs can calculate the impedance of the load at the frequency of the
tones. Hence a stable measurement of the impedance of the load can be obtained and potential anomalies or
faults can be detected that would indicate impaired loudspeaker function or total inoperability due to failure of the
loudspeaker or faults in connected wiring. The superimposition of pilot tones and analysis is interleaved across the
amplier’s output channels with a maximum total cycle time of around 20 seconds.
LoadPilot is implemented and congured in the CAFÉ software. Monitoring status and fault indication are displayed
on the front panel and both in CAFÉ and Lake Controller.
LoadPilot may be congured with the automatic calibration or through a manual advanced mode, depending on
monitoring requirements and characteristics of the connected loudspeaker loads.
11.6.2. Automatic calibration
11.6.2.1. Functional description
Automatic calibration is suitable for the following applications and requirements for error detection:
• If one or two low–impedance loudspeakers are connected; if two in parallel is default, it will warn if one is
missing.
• If there are one or two “spurs” with 70V loudspeakers connected; if two in parallel is default, it will warn if one
is missing.
• If there is a short circuit in the load.
• If there is an open circuit (all loudspeakers missing).
• For passive 2– and 3–way loudspeakers, if one or two LF drivers are connected and working; if two in parallel
is default, it will warn if one is missing.
• For some passive 2–way designs, if one HF driver is disconnected. (However, with some loudspeakers the
HF impedance is dominated by a passive component i.e. crossover lter and the anomaly will not be detected.)
NOTE: LoadPilot is enabled only when the amplier is On. It does not function while the amplier is in
Standby.
11. Operation and performance
D SERIES Lake Operation Manual rev 3.0.3
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.