Loudspeaker Line Monitoring - DC
From Zenitel Wiki
DC End-of-Line (EOL) monitoring uses a 10 kΩ resistor fitted at the end of a loudspeaker line.
The 10 kΩ resistor is utilised by the Amplifier Frame, which applies a small DC monitoring current across the loudspeaker line circuit, then measures the resistance. This in turn, allows the Amplifier Frame to continuously monitor the integrity of the circuit.
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| EOL Topology Example |
Interpreting Resistance Value to no of EOL10K's Fitted
- On a healthy loudspeaker line, the line resistance can be used to determine the number of connected EOL10K End-Of-Line devices according to the following table:
| Number of EOL10K's Fitted | Line Resistance (ohms) |
| 1 | 10K |
| 2 | 5K |
| 3 | 3K3 |
| 4 | 2K5 |
| 5 | 2K |
| 6 | 1K67 |
| 7 | 1K43 |
| 8 | 1K25 |
| 9 | 1K11 |
| 10 | 1K |
- A higher resistance than expected will indicate a cable break or missing EOL10Ks. If the cable layout and EOL10Ks locations are known, then this measurement can help track down faults.
- A very low resistance in the range 0 to 10 ohms usually indicates a cable short *.
- A low resistance in the range 10 to 200 ohms usually indicates that one or more loudspeakers do not have DC blocking capacitors fitted.
- Large numbers of missing DC blocking capacitors will give a very low reading and will look like a line short although this can be confirmed if the line has an acceptable impedance measurement.
- Earth Resistance is the DC resistance between either of the line conductors and earth.
- This will reveal whether any line-earth short-circuit faults exist or whether any water is present in the cable or connections
- For a healthy loudspeaker line, the earth resistance should be infinite. In practice this is usually only achievable with internal cable runs and loudspeakers. External loudspeakers and cabling tend to suffer water ingress
Key Points
- Simple and reliable.
- Cost effective.
- Commissioned in the ADT (Amplifier Dynamic Tool) of the SCT (System Configuration Tool).
- Allows Up to 10 End of Line spurred circuits per Amplifier.
- Unaffected by cable capacitance and presence of audio.
- Does not use signalling down cable screen.
- Compliant to EN54-16.
- Resistor is 10K 3 watt 1% with high temperature stability.
- We recommend Zenitel sourced EOL10K's are used to mitigate spurious faults.
"DC Blocking" Capacitor Information
All loudspeakers connected to the system must be fitted with "DC Blocking" capacitors. Loudspeakers are available with suitable capacitors pre-installed from a variety of suppliers. Alternatively, blocking capacitors may be retro-fitted. The following range of kits are available your Zenitel Stockist:-
| Maximum Loudspeaker Power Rating (Power Tapping - W) | Zenitel Part Name | Zenitel Part Number | Capacitance Value (uF) |
| 2 | LBC2W-10PACK | 1200530002 | 0.33 |
| 6 | LBC6W-10PACK | 1200530006 | 1 |
| 14 | LBC14W-10PACK | 1200530014 | 2.2 |
| 30 | LBC30W-10PACK | 1200530030 | 4.7 |
| 63 | LBC63W-10PACK | 1200530063 | 10 |
If alternative capacitors are to be fitted, they must be non-polarised and rated to at least 250Vdc and 160Vac. Polyester sealed case types are recommended.
The capacitance values listed above will provide negligible attenuation of (-3db) at 100Hz. If improved low-frequency performance is required, the "DC Blocking" capacitors may be increased in value. Doubling the value will halve the "-3dB" frequency.
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| "DC Blocking" Capacitor Placement |