Working Group
1.73
Room Acoustics
Simulation of the Acoustic
Properties of Rooms with Computer Programs
General information about room acoustics are
found on the page "room acoustics"
Two methods are applied to the calculation of
sound fields in large rooms:
1. the ray tracing method in which the way of individual rays or beams (conical or
pyramidal) is followed on its way from a source via a large number of wall reflections to
the receiver
2. the mirror image method in which the
resulting sound field is calculated by the superposition of the sound of an individual
mirror sound source behind each reflecting surface (also of higher order).
Most programs today use both methods. The mirror image method for the investigation
of early sound reflections from the walls. The ray tracing for the later arriving sound
and the reverberation which mostly is approximated by statistical methods towards the end
of the tracing procedure. Thus a compromise is possible for getting a sufficiently precise
result in a manageable calculation time on a personal computer. By means of room
simulation programs the most important room acoustic properties of any room can be
calculated in the planning stage which leads to a visible reduction of development
costs.
The most important room acoustic parameter of a room is its impulse response
resulting from a selection of a fixed sound source and receiver position. It will be
calculated by energy add up of single sound particles built by multiple reflections, even
though there are no phase relationships and no edge or diffraction effects considered in
most available programs for the time being. The impulse response will be evaluated by
different mathematical methods and from it the acoustical parameters will be calculated.
The input parameters for such room
simulation programs are besides the three dimensional room geometry mainly the absorption
and diffusivity factors of the room limiting surfaces and the furniture in the room. There
are measurements of the absorption factors available for the most practically used sound
absorbing materials and constructions that were measured in a diffuse soundfield of a
reverberation room.
Such measurement results for the
diffusivity factor are unfortunately not available on a large scale. The quantity of this
parameter is generally just estimated. Because of this fact discrepancies can appear
between simulated and measured results of room acoustic properties.
Example of a
room simulation problem: Optimize the position of loudspeakers in the lecture hall
of the PTB.
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