Takehiro Sugimoto

A lightweight push-pull acoustic transducer composed of a pair of dielectric elastomer films

A lightweight push-pull acoustic transducer using dielectric elastomer films was proposed for use in advanced audio systems in homes. The push-pull structure consists of two dielectric elastomer films developed to serve as an electroactive polymer. The transducer utilizes the change in the surface area of the dielectric elastomer film, induced by an electric-field-induced change in the thickness, for sound generation. The resonance frequency of the transducer was derived from modeling the push-pull configuration to estimate the lower limit of the frequency range. Measurement results presented an advantage of push-pull driving in the suppression of harmonic distortion.

Semicylindrical acoustic transducer from a dielectric elastomer film with compliant electrodes

A semicylindrical acoustic transducer was constructed using a dielectric elastomer film with compliant electrodes that is an electroactive polymer composed of a polyurethane elastomer base and polyethylene dioxythiophene/polystyrene sulfonate electrodes. The use of this dielectric elastomer is advantageous because polyurethane is a common material that keeps its shape without any rigid frame. Because the dielectric elastomer films are essentially incompressible, electric-field-induced thickness changes are usually translated into much larger changes of the film area and side length. Here it is proposed that this change in side length can be utilized for sound generation when the film is bent into a semicylindrical shape. Accordingly, a semicylindrical acoustic transducer was fabricated using a film of thickness of 300 μm and its acoustic characteristics were investigated. The transducer can be operated at low applied voltages by reducing the film thickness, as long as the film is thick enough to generate sufficient force to overcome sound radiation impedance. The second harmonic distortion of the transducer was also investigated as a function of the ratio of the direct current bias voltage to the alternating current audio signal amplitude.

A Narrow-Angle Directional Microphone With Suppressed Rear Sensitivity

A novel microphone that enables rear sensitivity to be significantly suppressed has been developed to improve open-air recording quality. Its assembly comprises a line microphone capsule and a second-order pressure gradient directional microphone. In conventional line microphones, residual rear sensitivity causes an influx of unexpected noise, especially at lower frequencies. Our microphone successfully suppresses rear sensitivity by more than 10 dB compared to conventional line microphones in the frequency range below 1 kHz in which major outdoor noise often occurs. Furthermore, it needs no complicated signal processing circuit and can be driven by a normal 48 V phantom power supply. Finally, our microphone was tested in on-the-spot broadcasts. Its rear sensitivity suppression proved to be effective for practical use, and its sound quality was found to be sufficient for use in TV programs. This paper describes the fundamental principle of the microphones rear sensitivity suppression, the measurement results of its acoustic characteristics and field-test results obtained with it in on-the-spot broadcasts.

22.2 ch Audio Encoding/Decoding Hardware System Based on MPEG-4 AAC

A 22.2 multichannel (22.2 ch) sound system has been adopted as an audio system for 8K Super Hi-Vision (8K). The 22.2 ch sound system is an advanced sound system composed of 24 channels three-dimensionally located in a space to envelop listeners in an immersive sound field. NHK has been working on standardizing and developing an 8K broadcasting system via a broadcasting satellite in time for test broadcasting in 2016. For an audio coding scheme, NHK developed a world-first 22.2 ch audio encoding/decoding hardware system (22.2 ch audio codec) capable of real time encoding/decoding. The fabricated 22.2 ch audio codec is based on MPEG-4 AAC and was assembled into the 8K codec together with the 8K video codec and the multiplexer. The audio quality of the fabricated 22.2 ch audio codec was assessed in an objective evaluation, and the evaluation results revealed the operational bit rates of the fabricated codec. An 8K satellite broadcasting experiment was carried out as a final verification test of the 8K broadcasting system, and 22.2 ch audio codec was found to be valid.

Production method for simulcast in 22.2 multichannel sound broadcasting

The 8K with 22.2 multichannel (22.2 ch) sound broadcasting is planned to be launched since December 2018 in Japan. NHK is going to simulcast 2-channel stereo and 5.1 surround together with the 22.2 ch sound for backward compatibility with existing home reproduction equipment, e.g., AV receiver and soundbar. However, individual production for each audio format is impractical because it needs many engineers and a lot of production equipment compared with a production in single format. Hence, an efficient production method for simulcast which does not demand additional production resources is required. The first proposal is a tone compensation for downmixing from the 22.2 ch sound to the other audio formats. The energy spectrum of the downmixed signal is compensated to harmonize with that of the 22.2 ch sound. The second proposal is a loudness chase to have the loudness level of the downmixed signal follow that of the 22.2 ch sound. The loudness level of the downmixed signal usually differs from that of the 22.2 ch sound, so that the loudness chase successively adjusts the loudness level without unnatural level change and matches them by the end of the program. The 8K with 22.2 multichannel (22.2 ch) sound broadcasting is planned to be launched since December 2018 in Japan. NHK is going to simulcast 2-channel stereo and 5.1 surround together with the 22.2 ch sound for backward compatibility with existing home reproduction equipment, e.g., AV receiver and soundbar. However, individual production for each audio format is impractical because it needs many engineers and a lot of production equipment compared with a production in single format. Hence, an efficient production method for simulcast which does not demand additional production resources is required. The first proposal is a tone compensation for downmixing from the 22.2 ch sound to the other audio formats. The energy spectrum of the downmixed signal is compensated to harmonize with that of the 22.2 ch sound. The second proposal is a loudness chase to have the loudness level of the downmixed signal follow that of the 22.2 ch sound. The loudness level of the downmixed signal usually differs from that of the...

Development of a small size narrow directivity microphone

We developed a new microphone that has very sharp directivity even in the low‐frequency band. In an ordinary environment of sound pick‐up, the energy of background noise is distributed mainly in frequencies lower than 1000 Hz. In such frequencies, a typical cardioid microphone has the directivity pattern close to that of omni‐cardiod. Consequently, it is difficult to pick up the objective sounds clearly from background noises. To suppress the noises with very small level, the directivity pattern should be also sharpened in the low‐frequency band. In this report, we describe a new method to sharpen directivity for the low‐frequency band. The method requires three microphone capsules. One capsule is the main microphone with a very short acoustic pipe. The others compose a second‐order gradient microphone to cancel the signal that comes from behind the main microphone. A special feature of this microphone is to control a dip frequency of behind sensitivity without changing the frequency response of the front...

Anechoic measurements of particle‐velocity probes compared to pressure gradient and pressure microphones

Microflown probes are true figure‐of‐eight‐pattern velocity microphones having extended response down to below the lowest audible frequencies, low noise, and high output. Unlike pressure‐gradient microphones, velocity probes do not measure acoustic pressure at two points to derive a pressure gradient. When particle velocity is present, acoustical particle velocity sensors measure the temperature difference of the two closely spaced and heated platinum wire resistors, and quantify particle velocity from the temperature measurement. Microflown probes do not require a membrane and the associated mechanical vibration system. A number of anechoic measurements of velocity probes are compared to measurements of pressure‐gradient and pressure microphones made under identical acoustical conditions at varying distances from a point source having a wide frequency response. Detailed measurements show specific response changes affected by the distance to the source, and focus on the importance of transducer calibration with respect to distance. Examples are given from field work using microflown probes to record acoustic response of rooms to test signals. The probe’s cosine directional selectivity can be used to change the ratio between early reflections and the diffuse sound since only the 1/3 of the power in the diffuse sound field is measured with the particle velocity probe.