Hirokazu Negishi

A new loudspeaker for low frequency radiation by linear motion type piezoelectric ultrasonic actuators

The authors had proposed new direct-radiator loudspeaker constructions with a conventional paper cone radiator driven by ultrasonic motors (USM), as a substitution for voice-coil motor. However, those models needed a revolution to linear motion conversion mechanism, and avoiding zero region non-linearity, like class A amplifier. These complications came from the conventional USM, since it is a rotational and having zero region non-linearity inherently. Here, the authors would propose a new mechanism by using new ultrasonic linear actuators, called longitudinal-bending multilayered transducers with independent electrodes (LBMTIE). The beauty of LBMTIE is linear and to control vertical motion and horizontal motion independently, hence zero region non-linearity avoided. Therefore, it is possible to substitute the voice-coil motor directly, which avoids the complicated mechanisms mentioned above. In this LBMTIE driven loudspeaker, vertical movement voltage be fixed and horizontal voltage is driven by audio si...

Loudspeaker for low frequency signal driven by four piezoelectric ultrasonic motors

The authors are developing a completely new direct-radiator loudspeaker as an alternative of the conventional electrodynamic loudspeaker. It is driven by continuous revolution of piezoelectric ultrasonic motors, It is useful for radiation of very low frequency signal because it shows almost flat phase frequency characteristics in low frequency region.. A preliminary model, named DMDS (dual-motor, de-spin) model, included co-axial two ultrasonic motors. Stator of one motor is fixed to the base and it of the other is connected to the cone radiator. Velocity modulation for any motor induces driving force for the cone radiator. Output sound at low frequency range (for example, 30 - 120 Hz) by this model was excellent because it has no significant resonance in this frequency region. However, its output sound was occasionally poor. At this Congress, a highly improved model named QMDS (quad-motor, de-spin) model is presented. It uses two co-axial DMDS mechanisms. The experimental model has a cone radiator of 46 ...

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.

Two driving constructions of loudspeakers for low‐frequency range by piezoelectric ultrasonic motors.

The loudspeaker driven by piezoelectric ultrasonic motors is characterized by a precise very‐low‐frequency reproduction due to its high‐driving mechanical impedance. It has a lot of merits comparing to the conventional electrodynamic loudspeakers. One of the reason will be that this loudspeaker is a power flow modulator, not a transducer. In this presentation, two sorts of ultrasonic motors are compared as driver elements of the loudspeakers. One is an ordinary revolution‐type motor and the other is a reciprocal linear motion type actuator. The authors constructed and improved practical low‐frequency‐range loudspeakers by using continuous revolution of ultrasonic motors. Its final model uses combination of two motors with same axis, which drive two cone radiators moving oppositely. This model shows a satisfactorily large output sound pressure and stable reproduction. However, its complicated elements for connection of the motors and the cone radiators cause a mechanical weakness. The authors, therefore, p...

Loudspeaker using continuous revolution of a piezoelectric ultrasonic motor

Volume displacement of a direct radiator loudspeaker diaphragm is inversely proportional to the square of its signal frequency. The lowest frequency of a flat response is restricted by the diaphragmfs fundamental resonance frequency. Therefore, a loudspeaker diaphragm for radiation of a low‐frequency signal shall have large amplitude and low resonant frequency. The authors propose the application of a piezoelectric ultrasonic motor for this purpose. It produces a completely controlled large output force because its output mechanical impedance is much greater than any conventional transducer or motor. An ultrasonic motor whose stator is connected to a direct‐radiator loudspeaker cone diaphragm by a rod and whose rotor is loaded by a heavy metal ring rotates with a constant velocity. Modulation of the velocity by the audio signal causes driving force to the diaphragm because a heavy ring with large inertia tends to rotate with constant velocity. This paper reports construction of a practical experimental mo...

A multidimensional overview for ultrasonic motor driven loudspeaker development

Twelve years of history for the development activity of the ultrasonic motor driven loudspeaker show a multidimensional aspect. Three main axes are geography, frequency, and mechanical impedance. Geography came first since initial conception was in the UK, yet the prototyping was in Japan. The origin was an idea for a stepping motor driven digital loudspeaker that was to address improving abnormalities coming from the fundamental resonant frequency, the so‐called ‘‘F0.’’ Consultation revealed the idea was weak but unexpectedly ‘‘ultrasonic motor’’ was recommended. This led the prototyping to be in Japan, where the invention and development of the motor took place. The second is frequency. For audible sound reproduction, inaudible ultrasonic frequency is employed. Although combination of these two regions in frequency is not new for sound reproduction, a couple between the bottom end of the audible sound reproduction and the ultrasonic motor is completely new for this arena. The third is mechanical impedan...