To distinguish a magnetic buzzer and a piezo buzzer by their appea

Both of the magnetic and piezo buzzer are black cylinder with two pins by appearance. There are a few methods can help you to determine the buzzer you have.

1. Testing the buzzer by a magnet or another same buzzer, if attracting, which means the buzzer you have is magnetic buzzer. On the contrary, piezo buzzer has copper plate inside, attraction does not happen.

2. Measuring the outer diameter of the buzzer, the common outer diameters of magnetic buzzer are 6.7mm, 9.0mm, 9.6mm, 12.0mm, 14.0mm, 16.0mm, and 25.0mm. Besides these diameters, others are all piezo buzzers.

3. Looking inside the buzzer sound hole, if you can find a yellow inner copper plate in a large size buzzer, it must be a piezo buzzer. However if you find a white iron color plate, then you cannot say it is a magnetic buzzer, because some piezo buzzers are also made with alloy plates.


Microphone array

With the constant enlargement of the internet bandwidth, the internet video conference has become possible. However, the wide bandwidth does not mean high quality of sound. The consumers usually need to wear the earphones to get the clear sound effects, and it is really inconvenient for them. Therefore, VISTA has already started to support the function of microphone array, which help to record sound more clearly, and can eliminate the noise and wind shear sound in the background. Naturally, besides the support of the operating system, the computer hardware also needs to be matched. Consequently, with the collocation of the microphone array and the DSP, the consumers can easily enjoy using the web phone such as SKYPE without wearing the headsets.

The theory of the microphone array is to set more than two pieces of microphones to record the sound separately, and than the DSP will pick the tonic we want. The simplest design is to pair a unidirectional microphone and an Omni directional one, which can limit the sound receiving range at the width of 120-140 degrees in front of the microphone, and then the SPL will be reduced over 20dB beyond this conical area. This is the reason why the ambient noises can be reduced widely and hardly to be heard.


How to choose a Buzzer (Transducer)

How to choose a buzzer

There are many different kinds of buzzer to choose, first we need to know a few parameters, such as voltage, current, drive method, dimension, mounting type, and the most important thing is how much SPL and frequency we want.

Operating voltage: Normally, the operating voltage for a magnetic buzzer is from 1.5V to 24V, for a piezo buzzer is from 3V to 220V. However, in order to get enough SPL, we suggest giving at least 9V to drive a piezo buzzer.

Consumption current: According to the different voltage, the consumption current of a magnetic buzzer is from dozens to hundreds of mill amperes; oppositely, the piezo type saves much more electricity, only needs a few mill amperes, and consumes three times current when the buzzer start to work.

Driving method: Both magnetic and piezo buzzer have self drive type to choose. Because of the internal set drive circuit, the self drive buzzer can emit sound as long as connecting with the direct current. Due to the different work principle, the magnetic buzzer need to be driven by 1/2 square waves, and the piezo buzzer need square waves to get better sound output.

Dimension: The dimension of the buzzer affects its SPL and the frequency, the dimension of the magnetic buzzer is from 7 mm to 25 mm; the piezo buzzer is from 12 mm to 50 mm, or even bigger.Connecting way: Dip type, Wire type, SMD type, and screwed type for big piezo buzzer are usually seen.SPL: Buzzer is usually tested the SPL at the distance of 10 cm, if distance double, the SPL will decay about 6 dB; oppositely, the SPL will increase 6 dB when the distance is shortened by one time. The SPL of the magnetic buzzer can reach to around 85 dB/ 10 cm; the piezo buzzer can be designed to emit very loud sound, for example, the common siren, are mostly made of piezo buzzer.


About microphone sensitivity

The sensitivity of the microphone is one of the most important factors, which affects the receiving result. The higher the sensitivity is, the higher the SPL can be received.Different from the production process of other products, the microphone is selected and sorted by its sensitivity after producing. We cannot get 1000pcs of what we need in sensitivity from just inputting 1000pcs of microphones’ material on the production line.
Therefore, in order to avoid discontinuing the production, we had better choose the spec. usually with the sensitivity of -40 to -44, which is popular and easily produced.About the volume, we can still improve it by modifying the circuit, such as the impedance, the voltage, and the amplification factor.We suggest that do not choose a special spec. with very high or low sensitivity at first, or the problem of lead time and lacking of material might happen.

A&B Components Co. Ltd.


Why the spekaer emit noise?

To analyze the usage, there are a few reasons explain why the speakers emit buzz sound or noise:1. Speaker is a passive component, and the drive circuit decides the sound. Therefore, giving the correct power and waveform to the speaker is the basic request.The too large power will lead to the too big amplitude of the diaphragm. The slight problem is distortion, but the serious problem is that the diaphragm might hit the mechanism or the magnet and cause the buzz sound. The basic waveform to drive the speaker is sine wave, if we give square wave or other waves, the efficiency of the speaker will reduce and easily get heated, the buzz sound may happen as a matter of course.2. The enclosure design of the product will also affect the quality of the sound. The well designed enclosure can improve the frequency response curve of the speaker.The area of sound apertures of the enclosure at least request over 1/8 area of the surface. We need to keep enough vibration space between the case and the diaphragm to avoid the diaphragm hitting the case when it works and emits the noise.


Soldering and assembling condenser microphone

Soldering manufactureThe diaphragm of the microphone is a very thin mylar membrane, it is easily being contracted and distorted with the high temperature. Therefore, we can only use hand-welded method to process, and the temperature of soldering iron cannot over 330°C, the welding work should be done within 2 seconds, the faster the better.

The best way is arranging the skilled welders to solder one wire/ pin first, and then finish the left one after the microphone cool down, this can avoid the high temperature causing distortion of the diaphragm, the worse sound receiving results or even breaking down.Otherwise, you can entrust the manufacture to us, our factory has special manufacturing tools to help the microphone cool down. Besides, we will test the sensitivity again after soldering in order to keep the qualification and the reliable quality.



Small speaker with high SPL?

In order to increase sound pressure level, we need to vibrate more air molecule by more power under unit time.For the two sizes speakers, the area of diaphragms of the 15mm speakers are around 176mm square (7.5*7.5*3.14),and the 20mm size speakers are around 314mm square(10*10*3.14). The 20mm speakers are only bigger by5 mm/ 25%, however, the diaphragm are bigger by 78%. Therefore when we input the same power, the 20mmspeakers can vibrate more air at the same time, and it result in higher sound pressure level.Generally, the speaker in bigger size can provide lower frequency response which is better for human’saudition. On the other side, we can also provide the smaller speakers more power to make higher soundpressure level, but it is limited by,1. Acceptability of the diaphragms2. Thermolysis of the speakers3. After increasing the power, frequency response will change too(because thicker diaphragm, heavier coil..etc)Therefore, what we can do is reform the material and the structure of the speakers to increase sound pressure level,but if it is possible to choose the bigger size, the problem of the lower sound pressure level will be improved immediately.