AXYS Tunnel Case Study : St Helena Tunnel, Byron Bay
Traditionally, hundreds of daisy-chained 100V constant voltage speaker boxes would line a tunnel all set to the same time-zero. The STI from such a system would be miserably low. STI stands for Speech Intelligibility Index. A score of 1 is perfect and a score of 0 perfectly dreadful. A score of 0.5 is the sort of benchmark you’d find specified for an emergency message system in a tunnel. Scoring 0.5 with a conga line of 100V speakers is just not going to happen.
Duran Audio gave this some thought and introduced the AXYS ABF-260 tunnel horn. The product is based on a 100W single compression driver with a two-inch voice coil, but the trick is in the horn. The ABF-260 is installed onto the ceiling of the tunnel, pointing down the length of the tunnel and between each lane of traffic. The official dimensions of the horn is 1391mm(L) x 892mm(W) x 345mm(H) but the ceiling of the tunnel actually serves as part of the waveguide. The bright idea means you decrease lateral (side-to-side) reflections quite considerably by using the ceiling as part of the baffle.