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High-frequency directivity simulations vs. measurements comparison for the final design approach in the 1,000-16,000 Hz frequency range.
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Head-related transfer-functions (HRTF) are a central part of spatializing audio. However measuring the near-field HRTF at close source distances presents unique challenges. In particular the existing sound sources designed to be appropriate for near-field HRTF measurements on human subjects exhibit a notable issue of being unable to generate a suff...
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... Therefore, a 12-sided omnidirectional speaker, reduced to 1/10 size, was used to conduct an ISO 354 [33] experiment in the scaled reverberation chamber. The scaled omnidirectional speaker that was used was built by us, and methods for producing scaled omnidirectional speakers are detailed in B. Chojnacki's research results [34,35]. Furthermore, based on a study conducted by Baruch et al. [36], humidity was maintained at 10% because humidity absorption is high at high frequencies. ...
Acoustic standards for classrooms around the world are still being studied, but the placement of sound-absorbing materials to meet these standards is still unclear. The present study examined an appropriate location for applying sound-absorbing materials inside an elementary classroom to ensure speech intelligibility while meeting the RT criterion using three scientific experimental methods, namely, computer modeling, a 1/10-scale model, and field acoustic measurement. A sound-absorbing material was applied to the rear wall or ceiling, and the ceiling was further divided into front, center, and rear sections. The acoustic performance was predicted using a 3D computer model of a standardized classroom based on the location of the sound-absorbing material. Subsequently, a 1/10-scale model following the law of similarity was used to compare the acoustic performances based on the location of the sound-absorbing material. Finally, field measurements were performed in an actual classroom to verify the acoustic performance based on the location of the sound-absorbing material. The findings revealed that the sound-absorbing material was most effective when applied to the rear wall, followed by application at the center, front, and rear of the ceiling.
... Similarly to isobaric speakers, they are connected cone to cone but excited by signals in a coherent phase. A detailed explanation of the proposed concept and its preliminary verification was described in the referenced papers [30,31]. In the given research, the direct comparison between the coupled speakers and most common omnidirectional sound sources was conducted, employing also the cubic sound source and omn idirectional sound source from Bruel & Kjaer. ...
... Similarly to isobaric speakers, they are connected cone to cone but exc by signals in a coherent phase. A detailed explanation of the proposed concept and preliminary verification was described in the referenced papers [30,31]. In the given search, the direct comparison between the coupled speakers and most common omn rectional sound sources was conducted, employing also the cubic sound source and o idirectional sound source from Bruel & Kjaer. ...
Omnidirectional sources used in room acoustics usually take the form of multi-speaker sources. Few alternatives for the most commonly used dodecahedral sound source have been derived recently. The project aimed to measure room acoustic parameters using three different sound sources: a dodecahedron, a cube, and a new source of two coupled loudspeakers. The measurements were made by rotating the sources every 15 degrees. The differences in the EDT, T30, D50, and C80 parameters in the function of the rotation angle of the sources were analyzed. Statistical analysis was carried out to examine the sensitivity of the measured parameters’ JND (just a noticeable difference) on the source’s rotation angle. This presentation will show the results and analysis of measurements showing the influence of the used source on obtained parameters and the validation of coupled speakers’ use. A comprehensive discussion of the results obtained with different sources (coupled, dodecahedral, cubic) will be provided. The results confirmed using the coupled speakers as an alternative for omnidirectional sound source in the range of 250–2000 Hz.
... The further need for scale modeling sources development was noticed [8]. The current project is based on the previous research [9], where the basic FEM simulations were performed together with fundamental experiments, which allowed to formulate the design principles for optimal omnidirectional sound source construction. The recent development of novel sound sources for scale modeling is presented together with their frequency and directivity characteristics. ...
... The most commonly used method for evaluating sound source directivity is described in ISO 354 standard [13]; however, it is usually used for diffuse field measurements. A detailed explanation and judgment on directivity rating parameter selection were presented in previous papers [9,12]. We used the modified standard deviation presented in [14]: ...
... As proved in previous research, to achieve omnidirectional sound propagation from the source, it is essential to cover a possibly large surface of the enclosure with speakers [9,15]. Following this principle, square transducers like piezoelectric speakers Sonitron SPS29 and cubic enclosure are possibly optimal for omnidirectional sound source creation. ...
Acoustic measurements such as scale modeling measurements require a particular type of miniature omnidirectional sound source. The most important aspects of those devices are small sizes (usually below 100 mm in diameter) and different frequency ranges compared to traditional, omnidirectional sound sources used in room acoustics. The required frequency range differs regarding the used scale factor in different models, which leads to the troubles in frequent source changes and the need for a unique source design for every model. The project will present the recent achievement in miniature omnidirectional sound sources development. The optimal sound sources for the given measurement functions were developed based on the previous numerical simulations and experiments such as FEM sound directivity simulations or transducers' parameters tolerance testing. The sound sources presented are used for applications such as acoustic sound insulation scale measurements (frequency range 800 63 000 Hz), scaled reverberation chamber measurements (300 80 000 Hz), or acoustic reduction models measurements (400 70 000 Hz). The paper will cover a detailed technical explanation of the laboratory environment's source construction aspects and validation measurements.
... However, it cannot produce sufficient sound output levels at low frequencies (below 300 Hz) while maintaining an omnidirectional pattern. To address this problem, Chojnacki et al. [260] proposed a new design to overcome the limitations of this low-frequency range at higher frequencies. Gari et al. [261] analyzed and rendered multi-channel RIR (Room Impulse Response) by parameterizing the sound field as a series of plane waves for the Spatial Decomposition Method (SDM). ...
Unlike previous studies on the Metaverse based on Second Life, the current Metaverse is based on the social value of Generation Z that online and offline selves are not different. With the technological development of deep learning-based high-precision recognition models and natural generation models, Metaverse is being strengthened with various factors, from mobile-based always-on access to connectivity with reality using virtual currency. The integration of enhanced social activities and neural-net methods requires a new definition of Metaverse suitable for the present, different from the previous Metaverse. This paper divides the concepts and essential techniques necessary for realizing the Metaverse into three components (i.e., hardware, software, and contents) and three approaches (i.e., user interaction, implementation, and application) rather than marketing or hardware approach to conduct a comprehensive analysis. Furthermore, we describe essential methods based on three components and techniques to Metaverse’s representative Ready Player One, Roblox, and Facebook research in the domain of films, games, and studies. Finally, we summarize the limitations and directions for implementing the immersive Metaverse as social influences, constraints, and open challenges.
... Therefore, we aim at designing a sound source which is small enough in size but can provide sufficient lowfrequency power, for accurately measuring near-field HRTFs. [4], (c) spherical dodecahedron [5], (d) improved spherical dodecahedron [6]. ...
In near-field HRTF measurements, where the sound source that is used for emanating the excitation signal is placed in the proximal range (<1 m) of the subject’s or the KEMAR’s head, care must be taken when deciding what kind of sound source to use. The ideal sound source should be infinitesimally small and omnidirectional, i.e. it should be a point source. When a large sound source is used, sound reflection and diffraction at its surface can introduce inaccuracies
in the measured near-field HRTFs. However, an ideal point source is physically unachievable. Besides, the acoustical behavior of a small sound source would be degraded. In this paper, we introduce the development of a special sound source that resembles the behavior of an ideal point source with particular design considerations of its low-frequency feature. The frequency response and directivity pattern of this sound source are tested under free-field conditions. Based on the analysis of the test results, the suitability of the sound source for usage in near-field HRTF measurements is discussed.
