The percentage of open space to closed space for a grille covering the output of a speaker should be set between 60-65%. Hole diameter will be dependent on the size of the speaker though a typical size of 3mm is recommended. The grille should be designed so as to not have a parallel plane to the speaker face.

Any speaker assembly has the potential to achieve an IP rating if an IP rated mesh is incorporated on the grille. Many speaker diaphragm and surround materials will of themselves achieve an IP rating though water drainage should be considered.

A designer has the option of many chamber types which will offer unique speaker performance. The design can be very complex and involved and only a basic approach will be provided here. The most common and straight forward design types are sealed and aperiodic. For a sealed chamber design, thrice the volume of the speaker should be included into the chamber. Thiele Small parameters can be provided for all speakers at customer request if a more advanced design methodology is desired.

Two mounting environments need to be considered, the speaker to the overall assembly and the chamber to the speaker.

A. Two methodologies can be used to mount the speaker to eliminate vibration either a gasket stack-up or a glue joint. This guide will only discuss the gasket design as this is the preferred methodology for customer application and provides enhanced reliability for a manufacturing environment not designed to produce speaker assemblies.

• A typical gasket stack-up for the front face of the speaker uses a compressible gasket with a double-sided adhesive and pull tab mounted to the speaker front face. A typical gasket stack-up for the rear face of the speaker uses a compressible gasket mounted either to the speaker magnet or outer rear perimeter.
• Speaker selection can be made to include screw bosses for mounting to create the needed compression.

B. The same two design concepts applied to the speaker can be applied to mounting the acoustic chamber. The main intent when mounting the chamber is create an air-tight seal along the mounting joint.

A Piezoelectric Element, or Disk (often called a ’Bender’) is the most basic type of electronic component used to produce sound.

1. Low power consumption.
2. Inexpensive.
3. Used in many electronic products such as consumer, fire, & safety and medical applications.
4. Typically are round using metallic disk with a layer of ceramic that is ’sandwiched’ by an electrode.

When voltage is applied, the disk vibrates at a given frequency and produces sound. More voltage means a louder disk. The sound can be:

1. A steady ’Buzz’ or a ’Beep’.
2. A series of several notes, often called ’Sing-Tones’.

For a piezoelectric to make sound, it needs to sit atop a housing called a ’Chamber’. If placed on a flat surface, it will not be able to properly flex to produce sound. The chamber (a ’Helmholtz Resonator’) is typically designed to match the resonant frequency of the piezoelectric disk.

1. Metallic Disk
2. Ceramic Disk
3. Chamber

The best example of a piezoelectric application is a smoke detector.

Bi-Morph

A ’Bi-Morph’ Piezoelectric disk has the electrode and ceramic layer on both sides of the metal disk. When pulsed, a ’Push-Pull’ effect is created making the piezoelectric slightly louder.

A piezoelectric disk can also be used as a low-cost switch. When ’stressed’, a piezoelectric disk creates a small amount of voltage that can trigger a microprocessor or microcontroller.

Most Piezoelectric Transducers are IP capable on the front diaphragm, some even up to IP68. IP67 means the transducer can be submerged into a body of water up to a meter deep for 30 minutes and still operate. IP68 guarantees protection in water up to 3 meters deep also for 30 minutes and still operate. Both IP ratings are dust proof.

Electromagnetic Transducers are used when a design has tight width constraints or low frquency requirements. They consist of eight components that are quite small and are made with highly automated coil winding and assembly equipment.

1. Upper Housing
2. Magnetic Plate
3. Diaphragm
4. Permanent Magnet
5. Coil
6. Yolk Plate
7. Lower Housing
8. Terminals