Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Browsing Phd Degree / Doktora by Subject "Acoustical engineering"

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    Doctoral Thesis
    A Model for Early-Reflection Acoustic Design of Rooms for Speech
    (01. Izmir Institute of Technology, 2023) Sözer, Mahmut; İlal, Mustafa Emre
    The room acoustics treatments in conventional rectangular classrooms, if applied, usually appear as a sound-absorbing suspended ceiling in the entire ceiling. This approach to achieving a recommended reverberation time value underrates the importance of early reflections, particularly for speech intelligibility in the back rows. The research proposes a room acoustics design methodology named early-reflection-oriented room acoustics design (ERORAD) for rooms for speech based on a model where early reflections are prioritised and quantified by the G50 parameter. On-site measurements were conducted in the 'IYTE Yeni Amfi' room. A 3D computer model of the sample room was created to simulate and test various acoustic conditions. Binaural listening tests were conducted using the auralised audio material of the relevant scenarios mixed with background noise signals at varying levels representing the active classroom background noise. The study showed that an early-reflection-oriented room acoustics design (ERORAD) methodology increases relative sound levels of direct speech and its early reflections. This improves speech intelligibility at distant audience locations better than conventional approaches by categorising the room surfaces as functional surfaces (ERS) for early reflection of speech sound and as appropriate surfaces for absorption (SfA) for the absorption of the late reflections to control reverberation time. The findings suggested that G50 can be a primary parameter to determine the optimal trade-off point between speech sound energy and reverberation time to achieve required speech intelligibility in the audience positions away from the speaker at relatively high levels of active classroom background noise.
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    Doctoral Thesis
    A Study on Number Theoretic Construction and Prediction of Two Dimensional Acoustic Diffusers for Architectural Applications
    (Izmir Institute of Technology, 2011) Döşemeciler, Ayşe; Doğan, Fehmi
    Defined as the scattering of sound independent from angle, optimum diffusion is very important for the perception of musical sound. For this purpose, Schroeder used mathematical number sequences to propose ʼreflection phase grating diffusersʼ, of two main types: Single plane or one-dimensional (1D) diffusers that scatter sound into a hemi-disc, and two dimensional (2D) diffusers that scatter into a hemisphere to disperse strong specular reflections without removing sound energy from the space, which is the main advantage of these devices. Currently, two methods are used to design 2D diffusers:Product Array and Folding Array Methods. Both are based on number theory and used methodologically in the field of acoustics, producing results that offer limited diffusion characteristics and design solutions for a variety of architectural spaces ranging from concert halls to recording studios where Schroeder diffusers are widely used. This dissertation proposes Distinct Sums Property Method originally devised for watermarking digital images, to construct adoptable 2D diffusers through number theoretical construction and prediction. At first, quadratic residue sequence based on prime number 7 is selected according to its autocorrelation properties as the Fourier transform of good autocorrelation properties gives an even scattered energy distribution. Then Distinct Sums Property Method is applied to construct 2D arrays from this sequence from which well depths and widths are calculated. Third, the aimed scattering and diffusion properties of the modeled 2D diffuser are predicted by Boundary Element Method which gives approximate results in accordance with the measurements based on Audio Engineering Society Standards. Fourth, polar responses (i.e. the scattering diagrams for specific angles) in each octave band frequency are obtained. Finally, predicted diffusion coefficients for uniform scattering are calculated and compared to the reference flat surfaceʼs coefficients and previous studieʼs results.