Mechanism of sound

Basic knowledge of Piezoelectric Sound Components
- Structure of piezoelectric diaphragm -
Piezoelectric sound components necessary have piezoelectric diaphragms.
This is a simple structure which a piezoelectric ceramic is adhered to a metal plate of brass or nickel-alloy.

Structure of piezoelectric diaphragm

- Mechanism of producing sound for piezo diaphragms -
When a voltage is applied across the piezoelectric ceramics, it stretches in its plane. When a voltage is applied to piezoelectric diaphragm, as the metal plate does not stretch, it bends as shown in Fig (a). When the polarity of the applied voltage is reversed, the piezoelectric ceramics shrinks and the metal plate bends toward the opposite side as shown in Fig (b).
When the direction of applied voltage changes alternately, the state of Fig (a) and Fig (b) is repeated as shown in Fig. (c), producing sound waves in the air.

Mechanism of producing sound for piezo diaphragms

- Function of a case -
You can get higher sound by using the resonance effect when a product is case type.

Function of a case

1. The peak of sound pressure level of diaphragm
The peak of sound pressure level of diaphragm

 2. The peak of sound pressure level of amplified in a case
The peak of sound pressure level of amplified in a case

 3. 10 to 20 dB higher sound pressure level by resonance effect
10 to 20 dB higher sound pressure level by resonance effect

 By designing fosc and fcav close each other, you will get 10 to 20 dB higher sound pressure level compared to non-cased diaphragm.

Supplementation
fo
(Resonance Frequency)
Frequency in which a diaphragm resonate most efficiently.
fcav
(Sound Frequency)
Frequency that sounds resonates through the case.
Fcav changes by dimensions of the case and the sound emitting hole.

- External drive circuit and Self drive circuit -
External drive circuit
Lately external drive circuit is favored with wide spread availability of microcomputer.
  • Input signals from outside with IC etc.
  • Drive in synchronization with the signals → Sound production
    (Sound frequency is a frequency of an outside signal source)
External drive circuit

Self drive circuit
  • Compose an oscillating circuit with a transistor and resistors.
  • Applying DC voltage makes the circuit oscillate → Sound production.
    (Sound frequency is a resonant frequency of diaphragm.)
  • Built-in transistor and resistors → PKB series
10 to 20 dB higher sound pressure level by resonance effect

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