There are three fundamental design considerations when using a piezo – optimization of the mounting method, sound level enhancement using a front Helmholtz resonator, and the electrical contact method. Each of these are addressed below to ensure optimal sound performance from a circular piezo element.
Depending on the application, piezos are typically either edge mounted or nodal mounted - or somewhere in between!
The mounting method can significantly change the frequency response of the piezo. Ole Wolff can tell you the optimal mounting method and placement depending on the frequency content of the desired output signal and the physical restrictions of the enclosure.
A front resonator can significantly amplify a piezo’s sound level.These resonators are typically high Q and are designed to enhance the highest requency of interest. The important design parameters of a resonator are the volume and the port dimensions.
Ole Wolff uses finite element methods software (COMSOL, Figure 1) to optimize the resonator design. As with all sound sources, it is critical to isolate the front and rear sides of the piezo to prevent sound cancellation.
With nodal mounting it is also necessary to isolate the inner and outer regions (inside and outside the nodal diameter). This is easily accomplished with the resonator and an enclosed back cavity created by the PCB
Electrical contact is typically provided by lead wires either soldered to the PCB or fitted with a connector.This method ensures the least obstruction to the piezo’s motion. Other connection methods include coil or bent springs soldered to the PCB. This simplifies the assembly process but requires careful consideration of the spring position and the contact force. For edge mounted piezos Ole Wolff recommends the spring contacts be placed as close as possible to the outer edge. For nodal mounting it is recommended to locate the contacts near the nodal diameter.