The buzzer has noise

When the sound which the buzzer generates is not a clear beep sound, we call it noise or broken sound. There are two possible ways to cause the noise.Improperly used If the voltage we input is too high, the diaphragm will easily touch other components, which causes the noise. When we set the wrong frequency instead of the rated frequency is easy to have noise. For example, if the rated frequency is 2730Hz, but the user input 2400Hz, the noise appears easily, especially within the range 10% ahead of the rated frequency.Disqualified A diaphragm of the buzzer is just set on the braces not firmly attached. Therefore the external force will move the diaphragm and result in the noise. When we assemble the buzzer, or in the process of user’s production line, if there are some iron chippings invade into the buzzer, the noise will also be caused.

A & B Components

Waterproof Speaker

Generally speaking, a paper diaphragm speaker is easily to have the problem of molding or distortion in a humid environment, and is certainly damaged in the water. On the other hand, the mylar diaphragm speaker is normally waterproof that it can work with drip, fog, or even slightly in the water if we use the rubber ring to fix the diaphragm instead of paper ring.Another important thing is that all the diaphragms of the speakers are very thin, and the pressure of water might distort even break the diaphragm if it is too deep.In conclusion, the mechanism design is also very important, especially the joint should be completely sealed in order to reach waterproof function.

Self Drive (DC) and External Drive (AC) Buzzer

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.

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.

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.

Watt and sound output of speaker

Base on the premise that all the conditions are the same, if the drive circuit provides enough voltage, the speaker can generate higher sound pressure level. However, with the same voltage, but we use another speaker which applies higher rated power, it will be difficult to drive and output lower sound pressure level.For example, a circuit can only provide the power of 8 ohm 1 W, in order to generate higher sound pressure level we collocate a 2W speaker, the SPL will be lower instead of higher. It is because with the increasing of the power, the diaphragm should be thickened. The coil also needs to be replaced by thicker wires. However, the thicker wires results in lower impedance so we have to wind a bit longer more, and that makes the coil heavier than before. Oppositely, if we use another speaker which loads lower power or with lower impedance, it is likely to make a little bit higher SPL, however the noise or burning down will possibly happen in this condition.

Magnetic Buzzer and Piezo Buzzer

There are two types of buzzers, piezo and magnetic type.A piezo buzzer generates sound because of the piezoelectric effect from the piezoelectric ceramic which drives the metallic diaphragm to vibrate.

A magnetic buzzer is based on the electromagnetic principle, the metal diaphragm is pulled when input the power, and spring back without power.The piezo buzzer is driven by square waves, and the magnetic buzzer needs 1/2 square waves to drive.

We suggest inputting higher voltage for a piezo buzzer, normally over 9V to have enough SPL. On the other hand, a magnetic buzzer can be driven to generate 85 dB by only 1.5V, but the consumption of the current will be much higher than Piezo one.To compare the two types of buzzers, the magnetic type can have lower frequency response with the same dimension.Though being limited by the dimension, the SPL of a magnetic buzzer can only reach to 90 dB. The piezo buzzer can achieve the SPL of 120 dB in some spec., some larger size can also easily reach to 100 dB.