Juro Ohga

Method to update the coefficients of the secondary path filter under active noise control

In active noise control systems using a filtered-x algorithm, the secondary path must be identified before the coefficients of the noise control filter are updated. The secondary path, however, has an impulse response that is continually changing in practical systems. This change degrades noise reduction and the stability of the system. Therefore, the coefficients of the secondary path filter must be adjusted to actual impulse response samples at specific intervals. This paper proposes a method to update the coefficients under active noise control without feeding extra noise to the secondary source. Instead, this method uses estimation errors. The coefficients of the noise control filter generally have the different estimation errors whenever the coefficients are updated. To use the estimation error, this method implements the additional filter modeled on the overall path from a detection sensor to an error sensor, through the primary path, the control filter and the secondary path. Two different coefficient sets of the noise control filter derive two equations on this overall path. A solution of these concurrent equations naturally yields the impulse response samples of the secondary path. This paper uses a system identification technique to solve the concurrent equations. This technique is practical in that calculation errors are distributed equally over all coefficients of the secondary path filter. Finally, computer simulations explained in this paper confirm that the concurrent equation method can refresh the coefficients under active noise control.

Wideband piezoelectric rectangular loudspeakers using a tuck shaped PVDF bimorph

Piezoelectric loudspeakers are characterized by their very simple structure, however, their sound radiation performance in the low frequency region is poor because their diaphragms are too stiff for large amplitude vibration. In this paper the authors propose an innovative method for improvement of the low frequency radiation performance of piezoelectric direct-radiator loudspeakers. This method involves using a flat-boxy loudspeaker unit with a pleated tuck-shape flexible diaphragm formed of a laminated sheet of PVDF (polyvinylidenfluoride) piezoelectric film. In this paper an explanation of the proposed loudspeaker unit construction is followed by theoretical analysis. Then a few experimental results are shown. Finally a practical multi-way loudspeaker system with satisfactorily wide frequency range for music is constructed by combination of a few loudspeaker units.

Sound system with wideband piezoelectric rectangular loudspeakers using a tuck shaped PVDF bimorph

A flat rectangular loudspeaker is realised using a zigzag-tuck shaped diaphragm. This paper reports the practical performance of full-range loudspeaker systems formed using a few units of these flat rectangular loudspeakers.

Rectangular loudspeaker by tuck shape PVDF bimorph

A bimorph sheet of PVDF (polyvinylidenfluoride) film is applied to a flat rectangular loudspeaker as a folded zigzag-tuck shape diaphragm whose size is, for example, 240 mm/spl times/114 mm. This loudspeaker is characterized by moderate size with a wide frequency range, light weight and no magnetic flux radiation. This paper shows measuring results of acoustical and electrical characteristics by using a few samples, and the output level is examined by theoretical calculations.

New direct-radiator loudspeaker driven by piezoelectric ultrasonic motors

Completely new direct-radiator loudspeaker constructions as alternative of the conventional electrodynamic loudspeakers by using piezoelectric ultrasonic motors are introduced. The authors examined two sorts of constructions. One is actuated by continuous revolution of piezoelectric ultrasonic motors. The other is driven by linear ultrasonic actuators. They are useful for radiation of rather low frequency signal because it shows almost flat phase frequency characteristics in low frequency region.

Bendable Electro-Acoustic Transducer Fabricated Utilizing Frequency Dispersion of Elastic Modulus

To realize the speaker diaphragm that can be united with a flexible display without deteriorating lightweight properties and flexibility, a novel bendable electro-acoustic transducer (BEAT) based on 0–3-type piezoelectric composites has been developed. To overcome the trade-off between flexibility and the transmission efficiency of vibration energy, a viscoelastic polymer that has local maximum points in the loss factor as well as large frequency dispersion in the storage modulus near room temperature was employed as the matrix of the piezoelectric composite layer. Against the comparatively slow (10 Hz or less) deformation from the outside, the viscoelastic matrix is viscous enough to prevent cracking and delamination. On the other hand, in the audible range (20 Hz to 20 kHz), the matrix is elastic enough to transmit piezoelectric vibration energy, maintaining a moderately large loss factor as well as a high sound velocity. For the first time, we successfully demonstrated a rollable speaker that can continue to generate a high-quality sound while being rolled and unrolled repeatedly onto a cylinder with a curvature radius of 4 mm.