Piezoelectric ceramics are polycrystalline materials formed by high-temperature sintering and solid-state reaction of oxides, and exhibit unique piezoelectric properties after polarization at high DC voltage. This material can achieve bidirectional conversion of mechanical energy and electrical energy. The piezoelectric effect includes two aspects: positive piezoelectric effect - applying physical pressure to generate charges inside the material, converting mechanical energy into electrical energy; Reverse piezoelectric effect - applying an electric field to deform materials and convert electrical energy into mechanical energy. These characteristics make piezoelectric ceramics particularly suitable for use as sound emitting components.
The piezoelectric effect can generate charges when physical pressure is applied, or convert applied electrical energy into mechanical energy. (Image source: BeStar Technologies, Inc.)
In headphones, piezoelectric ceramic drivers use alternating voltage to vibrate the attached metal substrate layer to generate sound. This method has high energy conversion efficiency and extremely fast response speed. The hardness of piezoelectric ceramics is extremely high, second only to diamond. When used as a diaphragm material, this characteristic enables it to restore delicate and smooth string tones, bringing excellent listening endurance.
Breakthrough advantages of dynamic driver+piezoelectric ceramic earphones
The innovative application of piezoelectric ceramic units in headphones effectively compensates for the shortcomings of traditional dynamic coil drivers in high-frequency response. BeStar Technologies has developed a series of multilayer piezoelectric ceramics specifically designed for high-frequency compensation units in headphones. The characteristics of this series are small size, simple structure, and low driving voltage.
Compared with traditional dynamic coil drivers, piezoelectric ceramic units have significant advantages in high-frequency performance. Although typical TWS earphones typically claim a frequency range of 20 Hz to 20 kHz, dynamic coil drivers typically experience significant attenuation around 10 kHz. In contrast, piezoelectric ceramic units can only maintain a 15dB attenuation at 30kHz and a 30dB attenuation at 40kHz. This performance exceeds that of balanced armature drives. In addition, compared with balanced armature drivers, the combination of dynamic coils and piezoelectric ceramic drivers does not require complex frequency division networks, thus reducing audio signal loss during the conversion process and making sound transitions more natural. This method also helps to reduce size and save costs.
Practical products such as HONOR Earbuds 3 Pro have demonstrated the feasibility of this combination scheme through a coaxial dual drive design that combines dynamic coil units with ceramic high-frequency units.