The difference between the self drive and external drive buzzersDepend on the driving signal, the buzzer divide into self drive and external drive. However inner circuit/ no circuit, DC/ AC, and active/ passive are all mean the same.The design of the self drive buzzer is to set the circuit inside the buzzer and just offer the direct current to work.
The inner circuit has the designed frequency and voltage for the buzzer to generate sound, therefore the frequency of the self drive buzzer is fixed. However the frequency is still different from each buzzer, normally is 2300Hz, the acceptable range is +/-300Hz.However, the external drive buzzer needs to be drove by the signal of 1/2 square wave V 0-p (magnetic type), or square wave V p-p (piezo buzzer)It is convenient to use a self drive buzzer, but the disadvantages are the higher cost, the higher defective rate and the unchangeable frequency.
5/19/08
Buzzer drive circuits
For a self- drive buzzer ( DC/ circuit- built), either pizeo or magnetic just apply the rated current and voltage.
For the external-drive buzzer, it depends on,
1. We should give magnetic buzzer 1/2 square wave, and provide it at least 3 times the amount of the rated consumptive current.
2. Otherwise, we give square wave to the peizo buzzer instead of 1/2 square wave, because the half wave might cause the buzzer does not work.Therefore, voltage control is an important factor for a peizo buzzer which is driven by the voltage.
For the external-drive buzzer, it depends on,
1. We should give magnetic buzzer 1/2 square wave, and provide it at least 3 times the amount of the rated consumptive current.
2. Otherwise, we give square wave to the peizo buzzer instead of 1/2 square wave, because the half wave might cause the buzzer does not work.Therefore, voltage control is an important factor for a peizo buzzer which is driven by the voltage.
5/6/08
About microphone sensitivity
There are three reason might cause the problems,
1. Lower sensitivity of microphoneThe sensitivity of the condenser microphone is from -36 dB to -48 dB (0dB= 1V/Pa). If we use -44 dB microphones, the sound will be lower.
2. Defective design of amplifierThe impedance for the amplifier will affect the sensitivity and the frequency response.Normally, the higher the impedance is, the better the sensitivity will be. However if the impedance is too high to get enough voltage/current, the high frequency response may get worse.The lower the impedance is, the lower the SPL will be. The too much current will cause the insufficient voltage.Input higher voltage will increase the sensitivity. Depend on the design of the amplifier and the frequency, the sensitivity might increases around 0.3 dB to 0.6 dB by 1 V.3. Defective design of mechanismThe over-length or curved sound receiving holes leads to lower or unnatural sound.
1. Lower sensitivity of microphoneThe sensitivity of the condenser microphone is from -36 dB to -48 dB (0dB= 1V/Pa). If we use -44 dB microphones, the sound will be lower.
2. Defective design of amplifierThe impedance for the amplifier will affect the sensitivity and the frequency response.Normally, the higher the impedance is, the better the sensitivity will be. However if the impedance is too high to get enough voltage/current, the high frequency response may get worse.The lower the impedance is, the lower the SPL will be. The too much current will cause the insufficient voltage.Input higher voltage will increase the sensitivity. Depend on the design of the amplifier and the frequency, the sensitivity might increases around 0.3 dB to 0.6 dB by 1 V.3. Defective design of mechanismThe over-length or curved sound receiving holes leads to lower or unnatural sound.
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