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.
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.