Combining Image and Equivalent Sources for Room Acoustic Simulations

Room acoustic simulation tools based on geometrical acoustics fail to predict accurately the behavior of rooms at low frequencies. This inaccuracy can lead to poor acoustic conditions especially in rooms of moderate volume, such as classrooms and meeting rooms. The present paper tackles this problem by introducing a simulation technique for room acoustics based on the Image Source Method and the Equivalent Source Method. These methods are implemented in the time domain to achieve efficient calculations with reliable results for low to medium frequencies. Given a source emitting a pulse signal in a room, image sources up to different orders are defined to determine early reflections. With the direct sound field from the original source and the contributions of the image sources, the remaining part of the sound field is solved by the Equivalent Source Method to account for late reflections and diffraction effects. The results of the test simulations carried out show that this combined Image-Equivalent Source Method is a suitable option for room acoustics.