Bending wave converter
The bending wave converter is a newer type of loudspeaker . The idea behind the classic loudspeaker is based on a coherent, rigidly uniform membrane movement. Flexural wave converters, on the other hand, stimulate the membrane to produce internal vibrations, from which the sound radiation only results as an average value that is complex to calculate. The effective sound radiation is a net effect of the spatially and temporally weighted, differently moving parts of the membrane.
The slang term " flat speaker " ( English flat panel loudspeaker ) refers more to the design than on the operating principle.
Principles
In the flexural wave converter according to Joseph W. Manger, an externally firmly clamped, flexible circular disc is driven by a central voice coil. Vibration patterns develop on the membrane at high frequencies. This is because the transit time of the deformations from the excitation center to the edge is visibly greater than the period of the excitation signal ( partial oscillations ). If the membrane edge is closed with the wave resistance at all frequencies, the flexural wave runs out without reflection. Another condition for effective sound radiation is strong damping of the outgoing wave on the membrane. The previous implementations, however, show reflections and a frequency-dependent variable attenuation, so that in addition to a rather low efficiency, the sound pressure frequency response is comparatively irregular. Because attenuation and phase velocity depend on the current shape of the membrane, the functional principle is susceptible to harmonic distortion and intermodulation .
In the Walsh system, flexural waves propagate on an elongated cone. This principle is a rigid membrane for low frequencies, z. B. made of titanium . It is possible to radiate the deeper part of the spectrum like a conventional loudspeaker by moving the cone as a whole in the direction of its axis.
The Manger disc as well as the Walsh cone aim at a regular oscillation pattern on the membrane. With the assumption of the exactly known vibration pattern, the calculation of the sound field is carried out and an optimization is sought in terms of the design.
The Distributed Mode Loudspeaker is also a bending wave converter. However, its constructive basis is not a regular vibration pattern. Rather, a diaphragm movement that is so changeable in detail is assumed that statistical treatment makes sense. The highest possible density of partial oscillations in the frequency range is achieved by a highly reflective clamping of the membrane, by low damping and multiple excitation at different locations by so-called exciters (surface exciters or surface transducers). The targeted construction uses the computer-technical solution of the relevant partial differential equations and has therefore only been practicable since the 2000s.
Depending on the design, efficiencies can be achieved that are comparable to those of conventional loudspeakers. The diffuse sound field inherent in these loudspeakers is a particular advantage in difficult acoustic environments.
With a bending wave converter, in principle any surface can be used as a membrane, provided that the material properties match the intended acoustic behavior and / or the signal is correspondingly equalized.
Applications
The application extends from loud public address systems to home devices, "talking" shop window glazing and sound-active displays of mobile phones. Depending on the construction effort, the principle enables an objectively excellent reproduction in all criteria.
Web links
- itwissen Lexicon itwissen Flexural Wave Converter
- Calculation of the bending wave converter: Diploma thesis Holger Hiebel
- Abendblatt.de: How does a flat speaker actually work?
References and comments
- ↑ There are hardly any citable explanations available for the design. Anything published online or in paper form is always linked to self-promotion by the production company. A change in this circumstance is not to be expected because the design has a negligibly small market share. In terms of engineering, the Manger-Schall converter (own name) does not seem to have any potential.
- ↑ German Physiks - High End Technology Loudspeaker Manufactur - DDD Driver - The DDD Driver. Retrieved May 6, 2018 .
- ^ Understanding the balanced-mode radiator - Electronic Products. Retrieved November 11, 2017 .