tuners, batteries
38m x 1,3m x 2.3m

a 38 meter long tunnel is divided into 25 equal sections of 1.5 meters. each section is equipped with a chromatic tuner which plays back a reference tone. they are tuned in barely noticable 1 hertz steps so as to cover a half tone in equal temperament.
in contrast to the visual appearance of a line with distinct increments, the acoustic result is a cluster of frequencies at any position in the tunnel.