UNITY DAU Installation & Maintenance Manual
It is desirable to have an impedance meter available (this measures the AC load that the UNITY DAU
sees). The measurement on the impedance meter should not be lower than 330 Ohms at 1KHz.
To work out the load from the impedance meter reading use the following equation:
P=10,000/Z
Where P is the power the amplifier sees, and Z is the reading in Ohms on the impedance meter.
Note! Once the speaker lines are tested, record the results and the location of the end
of line devices in the User Log book supplied.
The lines should now be checked for the DC resistance between cores, this should read 9K Ohms if the
wires from the DAU to the end of lines are complete.
The speaker lines should also be tested between each core and earth, this should be in excess of 100K
Ohms, if not check the cabling, record the results in the user logbook
Speaker cables must be earthed to the safety earth connection point (see earlier in this manual);
preferred types are screened soft skin cables such as FP200 although MICC can be used.
Cable Length Chart
The following table shows the maximum cable run to achieve a drop of no more than 1dB as required by
BS5839 pt 8, the table also takes into account high frequency losses which prevent systems performing
to the requirements of BSEN60849. This means the system needs to achieve a common intelligibility
scale value equivalent to 0.5 STI (speech transmission index), this requires a bandwidth of 200Hz to
7KHz
Maximum Cable Length
Cable Type &
Gauge
10W Load
20W Load
30W Load
1mm Soft Skin
1500M
750M
380M
1.5mm Soft Skin
2000M
1000M
500M
2.5mm Soft Skin
4000M
2000M
1000M
1mm
MICC
300M 200M 100M
1.5mm
MICC 500M 250M 150M
2.5mm
MICC 700M 300M 200M
Note
MICC has shorter runs for the same cross section area due to the higher load capacitance of the
cable and the effect this has on high frequency signals.
Document DCC UND 7001-01 Rev 1 June 2005
Page 11 of 17
