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Issue 2
BDM 208 and BDM 216
The BDM 208 and 216 dynamic microphones are designed for use with our MITRE, ADEPT and VIGIL
amplifiers.
To Operate
1.
Select zones needed. An LED will illuminate indicating selected zone.
2.
Press ‘Speak’ and make the announcement. If a pre-announcement chime is being used, the
‘Speak Now’ delay function must be selected. The LED will illuminate after 2.5 seconds
indicating that the system is ready for the message.
3.
During the announcement the speech volume indicator will fluctuate. Try to keep the indication
constant without the yellow segment illuminating. Maintaining a constant level will aid intelligibility.
Additional Features
Several important functions are incorporated into the microphones and maybe selected as required. DIL
switches are accessed with a screwdriver through the base - refer to Figure 2.
1.
Speak Now Indicator
The ‘Speak Now’ LED will operate in two different modes.
A)
Illuminates instantly when P.T.T. is pressed.
B)
Illumination delayed by 2.5 seconds to allow time for the chime to operate and finish. The delay circuit
is built into the microphone. This avoids having to feed a return back from the amplifier.
2.
Output Level Option
The balanced audio output can be selected to either microphone (2.5mV) or line level (250mV), switchable by
careful use of a small screwdriver or similar tool. Twin screened cable runs, up to 100 metres, generally
operate well at microphone levels. However, if cable runs in excess of 100 metres are encountered or amplifier
inputs are required to be wired in parallel, it is advisable to select the line level output and use amplifiers with
line inputs. Using this higher level ensures that any unwanted interference signals induced on the cable are of a
low level compared to the speech signal. If the amplifier only has balanced microphone inputs, it is possible to
convert them to line level using three resistors forming an attenuator as shown in Figure 1 below.
3.
Zone Select Cancel
This facility is selectable between cancel and no cancellation modes.
A)
When ‘Speak’ key is released, all zone selections will be cancelled. When a fresh announcement is to
be made, zones must be re-selected.
B)
When ‘Speak’ key is released, the zones will remain selected. This is particularly useful when repeat
messages to the same zones are made.
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Line
level
input
level
Mic
output
