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Controlling Sound Level- Electronic Method
For piezoelectric type audible alarms, the larger the voltage signal applied to the piezoelectric
transducer, the louder the sound level. This property can be used to electronically control the
sound level of these devices.
For audible alarm model MSR320R,
the sound level will vary from 65 dB
at 2 ft. at 3 Vdc up to 80 dB at 2 ft. at
20 Vdc. By varying the voltage from
3 to 20 Vdc, the sound level can be
varied by 15 dB. A 10 dB drop in
sound level will make the alarm sound
half as loud.
There are several ways of electronically controlling the voltage including:
1. Using a manual or digital potentiometer.
2. Using a selector circuit and different values of resistors.
3. Using PWM voltage signals from microcontrollers.
In all cases, care must be taken to make sure that the circuitry and voltage signals used do not
interfere with the internal circuitry of the audible alarm. This method of controlling the sound
level will probably not work well in the following cases:
1. The sound level of electro-magnetic type alarms do not vary much over the voltage range of
these devices, so most electro-magnetic type alarms are not suitable for this method.
2. When you only have a narrow operating voltage range to work with. For example, if you are
using the MSR320R at 5 Vdc, the sound level change from 5 Vdc to 3 Vdc is not very much.
3. When the voltage range of the audible alarm is narrow. For example, panel mount model
SC307NR only has a voltage range of 3 to 7 Vdc. Over this range, the sound level will vary
by only 6 dB. This sound level change is significant, but may not be enough to make a
difference in the application.
