Room acoustical applications of the FDTD method

OData support
Supervisor:
Nagy Attila Balázs
Department of Networked Systems and Services

Besides ordinary measurements, different simulation processes for examining room acoustic problems, which are getting more and more accurate due to the improvement of IT technology, are coming to the front. Ray tracing-based methods used in room acoustics design tasks only use a simplified model (bound by planes) to represent the space being measured, being unable to show diffusion or diffraction effects or ones caused by structured surfaces. However, the Finite Difference Time Domain method (FDTD) is able to model the mentioned phenomena.

FDTD is a mesh-based algorithm which can simulate the propagation of sound waves travelling in isotropic media or being reflected from medium boundaries, complete with the known wave phenomena, based on a mesh node model of the acoustic space with a high enough resolution. The work presented here used a two-dimension FDTD algorithm implemented in a MatLab environment, allowing the examination of various acoustic problems.

Such a room acoustic problem is the phenomenon of Seat Dip Attenuation (SDA), in the course of which sound waves travelling above the seat rows of a concert hall become subject to frequency-dependent attenuation, causing the listeners sitting further back in the auditorium to perceive a volume lower than expected based on the distance at lower frequencies. The underlying cause of this phenomenon is the periodic placement of seat rows. A two-dimension FDTD simulation of the cross section of the auditorium allows the investigation of the phenomenon and its ruling parameters.

To improve the acoustics of various rooms with primarily music- or speech-oriented designs, acoustic diffusers are often used, which cause diffuse reflections due to their structured shapes, which in turn largely influence the acoustic perception of the room. To be able to show that different diffuser setups operate with different efficiencies, a simulated arrangement has been created in which the operation of the diffusers can be demonstrated and their efficiency quantified.

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