Ferroelectric loudspeaker
A ferroelectric loudspeaker is a type of loudspeaker that uses a sound transducer made of a ferroelectric material or other piezoelectric ceramics as the main functional carrier .
They are therefore also called ceramic loudspeakers or, somewhat more appropriately, piezo loudspeakers or piezophones .
functionality
By applying an audio-frequency electrical voltage to electrodes on the ferroelectric, it begins to deform in the rhythm of the frequency. This movement is transmitted to a membrane , which then emits sound waves directly or via a horn .
Ferroelectric loudspeakers are largely a capacitive load for the amplifier , which puts an extraordinary strain on the amplifier . The load capacity of ferroelectric loudspeakers is not given in watts , as is the case with other loudspeakers , but in volts .
Workspace
- Frequency : The resonance frequency resulting from the mass and elasticity of the ferroelectric and its harmonics lead to a less linear frequency response and due to nonlinearities, undesirable harmonics occur. The stiffness determines the lower limit frequency to about 1 kHz. Ferroelectric loudspeakers often have a built-in 6 dB high-pass filter, but they can also be operated without a crossover if the permissible voltage is not exceeded: low frequencies below the transmission range only lead to low thermal and mechanical loads.
- Voltage : Above a maximum permissible voltage, breakdowns of the ferroelectric occur, which lead to destruction. With common products, the load capacity is typically around 25 volts ( effective value ).
- Polarity : One of the polarities of the control voltage leads to tensile forces in the ferroelectric, which destroy it when a limit force is exceeded. The opposite polarity, which causes compressive forces, can usually be about a factor of 10 higher. You can take advantage of this by push-pull control of two converters. However, this control is complex and therefore hardly to be found in practice, because ferroelectric loudspeakers are used more in low-cost systems.
- Temperature : Dielectric losses lead to temperature increases. Above a certain limit, structural damage occurs in the component. Depending on the material, the ferroelectric completely loses its ferroelectric properties between 80 ° C and 150 ° C.
Areas of application
Typical ferroelectric loudspeakers have resonance frequencies in the range of 1… 5 kHz, for ultrasonic applications also up to 100 kHz. This type of loudspeaker can therefore only be used for the mid / high range (0.5 ... 100 kHz).
However, the view that such converters are unsuitable for hi-fi applications is now outdated. If a resistor of 50 ... 100 Ohm is connected in parallel to the loudspeaker, the areas susceptible to interference can be masked out using the filter circuits of a normal loudspeaker crossover; above that spectrum, piezo speakers sound just as clean as high-quality dynamic tweeters.
Piezo sirens or piezo phones (replacement for buzzer ) are often used as acoustic signaling devices, e.g. B. on computer motherboards . These work in the vicinity of their natural resonance and some have feedback electrodes and a built-in driver transistor controlled by them. A storage choke is often used to generate a higher voltage .
Ultrasonic distance sensors or parking aids also use this transducer design, the same transducer also being used as a microphone.
The small size and the low price lead to applications in inexpensive telephones and cell phones .
Individual evidence
- ↑ B. Timmermanns, in Hobby Hifi 1/2013, p. 40f.
literature
- Wolfgang-Josef Tenbusch: Basics of the loudspeakers. 1st edition, Michael E. Brieden Verlag, Oberhausen, 1989, ISBN 3-9801851-0-9
- Helmut Röder, Heinz Ruckriegel, Heinz Häberle: Electronics. Volume 3: Communication Electronics. 5th edition. Verlag Europa-Lehrmittel, Wuppertal 1980, ISBN 3-8085-3225-4 .