8 Spherical speaker array system

A spherical speaker array system is an equipment with many loudspeakers in a circularl order. A motor is installed at the bottom of the system to rotate the sphere automatically. The minimum rotation angle is 0.1.

the diameter 3.55 m
the distance from center to each loudspeaker 1.5 m
the number of loudspeakers horizontal plane 36
vertical plane(except bottom) 35
the angle interval between a diacent loudspeakers 10 deg.
Spherical speaker array system
Spherical speaker array system

 Significance of the spherical speaker array system

    People can localize a position of a sound source by analysing the input sounds to two ears. This ability is known to relate with HRTFs (Head Related Transfer Functions), which represent transfer characteristics from the source to eardrum in a free field. (free field : a space without reflected sounds) HRTFs depend on the position of sound source. Therefore the measurement of a set of HRTFs requires many sources from all directions around a listener. This is the main purpose of our spherical speaker array system to achieve that efficiently.

 Creation of a desired sound image

    With synthesized HRTF, one can make such a situation that listener feels as he is in a real sound field while in fact he wears headphones only. Such virtual sound source is referred to as a sound image by comparing to a visual image. To make a desired sound image, it is important to examine how to deal with HRTFs. This equipment enables us to help with this problem in addition to the HRTF measurement.

Desired sound image is obtained when HRTF from the position of desired sound image to a listener and HRTF which is showed to listener is equivalent.
Example of sound image