GE865 Hardware User Guide
1vv0300799 Rev.9 – 27-07-2009
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 52 of 70
11.8.2 Frequency Behaviour
The frequency behaviour represents the effectiveness of the reproduction of the applied
signals. Because performance is related to a square driving waveform (whose
amplitude varies from 0V to V
pp
), if you modify the waveform (
e.g. from square to sinus
)
the frequency response will change.
11.8.3 Power Supply Influence
Applying a signal whose amplitude is different from that suggested by the
manufacturer, the performance change following the rule “if resonance frequency f
o
increases, amplitude decreases”.
Because resonance frequency depends on acoustic design, by lowering the amplitude
of the driving signal the response bandwidth tends to become narrow, and vice versa.
Summarizing:
V
pp
↑
Æ
f
o
↓
V
pp
↓
Æ
f
o
↑
The risk is that the f
o
could easily fall outside of new bandwidth; consequently the SPL
could be much lower than the expected.
11.8.4 Working Current Influence
In the component data sheet you will find the value of MAX CURRENT: this represents
the maximum average current that can flow at nominal voltage without current
limitation. In other words it is not the peak current, which could be twice or three times
higher. If driving circuitry does not support these peak values, the SPL will never reach
the declared level or the oscillations will stop.
WARNING:
It is very important to respect the sense of the applied voltage: never apply to the
"-" pin
a voltage more positive than the
"+" pin
: if this happens, the diaphragm vibrates in the
opposite direction with a high probability to be expelled from its physical position. This
damages the device permanently.
