2008年10月29日 星期三

Piezo Element 有關壓電陶瓷蜂鳴片

Piezo Element
The good points to choose piezo element is that the cost is lower than others and you can design the sound chamber to reach a special sound. However, during assemblage, the experienced skill of soldering wires is strictly demanded, otherwise large defective products such as small sound, soundless, deviated frequency or electric leakage might happen. Defects are resulted from:

Piezo element and chamber both have their resonance points. How to match the two resonance points to get loud SPL and wide frequency range, the mechanical design has become a test. Material, thickness, size and depth of the sound hole and the capacity of chamber are the factors which will affect the chamber’s resonance.

The bad fix method
There are two methods for fixing the piezo elements:

Nodal mounting method
This method is to fix the nodal diameter of buzzer element to the supporting ring of the plate; better SPL can be obtained. Finding the pivot and resonance frequency of element, then the piezo element will have max vibration and SPL.

Circumference Fixing Method
This method is to fix the outside circumference of the buzzer element to the supporting right of the plate. Wide frequency range can be obtained, and easier to design. For these two methods, flexible adhesive such as silicon should be used between the buzzer element and the support ring.

Defective soldering
During the soldering, the size and position of the solder point should be the same. The temperature and pressure should be well controlled to avoid badly soldering, which will cause short circuit or insufficient isolated impedance. Besides, the iron need to be separated for the two solder points, because the ceramic wafer contain a large amount of lead, using the same iron will cause the fail of RoHS test.

選用壓電陶瓷蜂鳴片的好處是, 低成本,可自行設計音腔來達成特殊的聲音要求,但在組裝,焊線時的技術要求較嚴,若無相關經驗或技術,可能會有大量的不良品產生,小聲,無聲,頻率偏差,漏電都有可能會發生.這些不良大都起因於:



蜂鳴片及音腔都有各自的諧振點,如何將二個諧振點配在一起,取得最大的音壓,或是較寬的頻寬,這就考驗機構設計的能力,會影響音腔諧振的因素有: 材質, 肉厚, 音孔大小,音孔深度,音腔容積..等.


2008年8月6日 星期三

The influence of operation voltage on SPL of a buzzer

The SPL of a buzzer does not have a geometric ratio relation with the voltage directly, especially close to the rated frequency.
According to the graph below, at 2000Hz, we have 3V with 74dB, 6V with 80dB, and 12V with 90dB results; however, at 2048Hz, we have 3V with 84dB, 6V with 87dB, and 12V with 90dB.
Because the bandwidth of the buzzer will widen when the voltage raises, therefore we should pay more attention to the output frequency, even 100Hz difference might cause a big difference in 10dB!

2008年6月1日 星期日

Buzzer and Speaker 蜂鳴器與喇叭的比較

喇叭與蜂鳴器都是發出聲響的零件,若只是想發出一些警告音,提醒音,這二者其實都是可以使用的:Buzzer and speaker are the acoustic components that can generate sound, if you just need sound to warn or remind, both of them are fine.

蜂鳴器分為電磁式及壓電式二大類,在耗電流,尺寸,頻率,驅動方式上有些不同,但基本上都是將某一個頻點的音壓拉到最高,以期用最小的尺寸,就可以發出很高的音壓,若不在諧振點的音壓就會很小,甚至會相差20dB以上,且蜂鳴器的聲音,由於是用方波發出來的,人耳聽起來就比較刺耳一些,We divide buzzer into piezo and magnetic buzzer. There are some differences in power consumption, dimension, frequency and drive method between piezo and magnetic buzzer, however, both of them basically pull the SPL to the highest at a certain frequent point in order to generate as high SPL as possible in the small size. The SPL will be very low if it is not at the resonance point, even 20dB difference. By the way, the sound of buzzer is drove by square waves; therefore it is harsh to the human ears.

小喇叭是以弦波推動,相較於蜂鳴器人耳聽起來會舒服許多,但因為頻寬較寬,可用的頻率也較低,故在同尺寸時,音壓一定會小於蜂鳴器,且需要音箱的輔助來增進低頻的響應,不然整體的聲音會很小.Micro speaker is drove by the sine waves, to compare with buzzer, the sound is much more comfortable for us. However, the bandwidth is wider, and the frequency is lower, therefore, the micro speaker’s SPL must be lower than the buzzer with the same size, and also need enclosure to help the low frequency, otherwise the sound will be very small.

2008年2月13日 星期三

The difference between the speaker and the receiver 喇叭與受話器的不同

The basic structure of the speaker and the receiver is almost the same; the diaphragm generates the sound by the reaction upon the sound coil and magnet.
The main diversities are as below:

The different usage Depend on the size of the speaker; the distance between the speaker and the user’s ears is normally from several dozens of centimeters to several meters. However we always nestle up a receiver against our ears.

The different material of the diaphragm and the sound coil In order to bear the higher power, the diaphragm of the speaker is usually thicker than the receiver, the thinnest one is 18u. The larger of the dimension and the power is the heavier the diaphragm will be. The receiver takes the lower power, but requests for better low frequency curve; therefore we usually use the diaphragm with the thickness from 6u-12u. Besides the diaphragm, the receiver often works with a piece of paper or cloth to adjust the frequency response, which can help to meet all kinds of standards or to match up the resonant box of the mechanism.

The different electronic characteristic  We often see the speaker with impedance of 4-8ohm, the too high impedance leads to the higher power to drive the speaker, normally is from 0.2W to several dozens of watt. Depend on the circuit design, the impedance of the receiver is from 16, 32 to 150ohm. The general power is only from 0.01W to 0.1W.




2008年1月2日 星期三

Test condition makes the impact on the sensitivity of microphone 測試條件對麥克風靈敏度的影響

Generally speaking, the sensitivity of the microphone will increase when we raise the impedance at 2.2K of RL, the results as the graph 1 & 2.
The sensitivity also rises if we give higher voltage to the microphone, graph 3 & 4.

RL 2K =>3K ohm

RL 2.2K => 1.0Kohm

Voltage 2V=>4.5V

Voltage 2V=> 1.2V

Equipment : B&K 2012 + B&K 4227
Microphone : 6.0mm x 2.7mm -42+/-3 dB