This invention is directed to a method of ice seeding a biological samples, such as cells, harvested tissues, and cellular biological constructs such as culture tissue equivalents. The bolt includes a necking part at an upper end thereof. The conveyor may be readily moved between the positions with a moderate application of force. The socket has a top part and a cuff, which are formed in the manner of a sleeve and can be pushed into each other and locked. These HRTF are useful in stereo enhancement and multi-channel virtual surround simulation. The control system includes a zero crossing detector and variable ramp generator for generating control signals to a switching rectifier to generate a regulated DC signal.