Sound fields can be represented using spherical and cylindrical harmonics using higher order Ambisonics (HOA). The representation can be made more accurate by increasing the order N of the harmonics used. It has been shown by Solvang that, assuming plane wave emitting loudspeakers, for a listener placed such that kr > N there will be a spectral impairment of the sound image when more than 2N + 1 loudspeakers are used, where k is the wave number. However, in practical situations the loudspeakers are placed at a finite distance from the centre of the array, and the assumption that they emit plane waves often no longer holds. This may cause a spectral colouration that differs from far field loudspeaker placement. Further colouration may occur due to boundary reflections, depending on the room as well as the placement of reproduced sound source. This paper gives an account of the effect of near field loudspeakers in free field as well as in a simulated room. The influence of reflections on the image quality is analysed objectively. A comparison of simulated enclosed HOA systems with sound field measurements in the reproduced area is made.
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