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Last Updated: 20070405, mei

P18 - Microphones and Loudspeakers - 2

Monday, May 7, 14:00 — 17:00

Chair: Martin Opitz, AKG Acoustics GmbH - Vienna, Austria

P18-1 Applications of the Acoustic CenterJohn Vanderkooy, BW Group, Ltd. - Steyning, UK and University of Waterloo, Waterloo, Ontario, Canada
This paper focuses on uses for the acoustic center concept, which in this paper represents a particular point for a transducer that acts as the origin of its low-frequency radiation or reception. The concept, although new to loudspeakers, has long been employed for microphones when accurate acoustic pressure calibration is required. A theoretical justification of the concept is presented and several calculation methods are discussed. We first apply the concept to subwoofers, for which the acoustic center is essentially a cabinet dimension away from the center of the cabinet. This has an influence on its radiation pattern in a normal room with reflecting walls. A second application that we consider is the effective position of a microphone, which is necessary if it is to be used for accurate calibration of acoustic pressure. A final application that we consider is the effective position of the ears on the head at lower frequencies. Calculations show that the acoustic centers of the ears are well away from the head, and the effective ear separation is larger than expected. This has implications for the human localization mechanism. Measurements on a Kemar mannequin show that the separation is even larger than expected from the calculations, and most of this can be understood, but the measurements at the lowest frequencies are somewhat uncertain.
Convention Paper 7102 (Purchase now)

P18-2 Development of a Finite Element Headphone ModelDominik Biba, Martin Opitz, AKG Acoustics GmbH - Vienna, Austria
For the development of high-end headphones, numerical simulation of the acoustic behavior is an efficient tool. While lumped-element models are valid for frequencies up to a few kilohertz, finite-element models are valid for higher frequencies too. A headphone model using finite elements and boundary elements was built in three phases. In parallel to building the numerical model a real-world sample was built and measured. The validity of the model was verified by comparison of both the radiated sound field and the membrane modal behavior. Agreement between measured and computed amplitude frequency responses was achieved.
Convention Paper 7103 (Purchase now)

P18-3 Development of Camera Mountable 5.0 Surround Microphone and Method of 3-ch to 5-ch Signal Recomposing SystemMinoru Kobayashi, Sanken Microphone Co., Ltd. - Tokyo, Japan; Setsu Komiyama, Satoshi Kikkawa, Takako Kawashima, NHK Japan Broadcasting Corporation - Tokyo, Japan; Takeshi Ishii, Sanken Microphone Co., Ltd. - Tokyo, Japan
This paper describes the development of small 5.0 surround microphone and 3-channel to 5-channel signal re-composing system. The principal reason we started this study was broadcasters’ recent demand for a small, light-weight camera-mounted 5.0 surround microphone for documentaries, dramas, and sports shooting outdoors. We have produced a 5.0 surround microphone; but if we want to use it as a camera-mounted microphone, there is a limitation we could not ignore. The limitation is the number of audio tracks. The commonly available HD cameras in the market have only 4 audio tracks. In order to overcome the limitation, we developed a 3-channel to 5-channel signal re-composing system.
Convention Paper 7104 (Purchase now)

P18-4 Noise-Robust Recognition System Making Use of Body-Conducted Speech MicrophoneShunsuke Ishimitsu, University of Hyogo - Himeji, Hyogo, Japan; Masashi Nakayama, Toyohashi University of Technology - Toyohashi, Aichi, Japan; Toshikazu Yoshimi, Pioneer Corp. - Kawagoe, Saitama, Japan; Hirofumi Yanagawa, Chiba Institute of Technology - Chiba, Japan
In recent years, speech recognition systems have been introduced in a wide variety of environments such, as vehicle instrumentation. Speech recognition plays an important role in ships’ chief engineer systems. In such a system, speech recognition supports engine room controls, and lower than 0-dB signal-to-noise ratio (SNR) operability is required. In such a low SNR environment, a noise signal can be misjudged as speech, dramatically decreasing the recognition rate. Hence, speech recognition systems operating in low SNR environments have not received much attention. Therefore, this paper focuses on a recognition system that uses body-conducted signals. Such signals are seldom affected by background noise, and thus a high recognition rate can be expected in low SNR environments such as an engine room. Since noise is not introduced within body-conducted signals that are conducted in solids, even within sites such as engine rooms, which are low SNR environments, construction of a system with a high recognition rate can be expected. However, within the construction of such systems, in order to create models specialized for body-conducted speech, learning data consisting of sentences that must be read in numerous times is required. Therefore, in the present paper we applied a method in which the specific nature of body-conducted speech is reflected within an existing speech recognition system with only small numbers of vocalizations. Simultaneously, the measure by pretreatment was also worked on.
Convention Paper 7105 (Purchase now)

P18-5 Revisiting Proximity Effect Using Broadband SignalsLaurent Millot, Université Paris - Paris, France, ENS Louis-Lumiere, Noisy Le Grand, France; Mohammed Elliq, Manuel Lopes, ENS Louis-Lumiere - Noisy Le Grand, France; Gérard Pelé, Dominique Lambert, Université Paris - Paris, France, ENS Louis-Lumiere, Noisy Le Grand, France
Experiments mainly studying the proximity effect are presented. Pink noise and music were used as stimuli and a combo guitar amplifier as source to test several microphones: omnidirectionnal and directional. We plotted in-axis levels and spectral balances as functions of x, the distance to the source. Proximity effect was found for omnidirectionnal microphones. In-axis level curves show that 1/x law seems poorly valid. Spectral balance evolutions depend on microphones and, moreover, on stimuli: bigger decreases of low frequencies with pink noise; larger increases of other frequencies with music. For a naked loudspeaker, we found similar in-axis level curves under and above the cut-off frequency and propose an explanation. Listening to equalized music recordings demonstrates will help to demonstrate proximity effect for tested microphones.
Convention Paper 7106 (Purchase now)

P18-6 Anechoic Measurements of Particle-Velocity Probes Compared to Pressure Gradient and Pressure MicrophonesWieslaw Woszczyk, McGill University - Montreal, Quebec, Canada; Masakazu Iwaki, Takehiro Sugimoto, Kazuho Ono, NHK Science & Technical Research Laboratories - Setagaya-ku, Tokyo, Japan; Hans-Elias de Bree, Microflown Technologies - Zevenaar, The Netherlands
A number of anechoic measurements of Microflown™ particle 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 range. 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.
Convention Paper 7107 (Purchase now)