British Columbia Legislature
In 1997 we were first retained by the HANSARD department at the BC Legislature to evaluate the 24 year old loudspeaker system in the BC Legislature as part of a plan for refitting the system. The original loudspeaker was a custom fabrication using forty-eight 5" full range loudspeakers mounted on a 45" diameter aluminum sphere to provide the desired coverage pattern. Using the TEF analyser, we were able to measure the direct sound coverage of this unusual loudspeaker throughout the government and opposition seating, and to map the large interference variations that were limiting the gain before feedback of the reinforcement system, and reducing intelligibility in about 1/3 of the seats. The measured loudspeaker coverage did not agree with the original 1973 predictions of a spherical segment radiation pattern. The actual coverage was similar to a curved array column speaker, producing a coverage pattern exactly opposite that expected and required. The 2 - 4kHz region had over 10dB of level variation throughout the floor seats. Further complications include a lively acoustical environment and microphone pickup distances between 24 - 36".
We modelled the original Legislature with a computer simulation of the original 48 speaker sphere. This gave us a baseline for comparison between our actual measurements and the predicted performance of the old system. The computer model results were very similar to the measured response. We then modelled the room with a new array of three horn loaded full range speaker systems. By using a single horn loaded system to cover the press gallery, and a full range horn loudspeaker for each of the government and opposition seating areas, we were able to smooth the coverage uniformity in the seating areas, and steer the destructive interference out of the listening areas. The new system is noticeaby more articulate, delivering good speech intelligibility throughout the entire floor seating, and for the first time ever to the press gallery. The 2- 4kHz region has less than 2dB of level variation throughout the floor seating and press gallery.
The new speaker system had to fit in a spherical housing very close to the original spherical speaker dimensions, which meant having to find the most compact full range horn loaded speakers available. The installation work and spherical grille fabrication was carried out by Jim Gardner and the in-house technical staff of the BC Government's HANSARD - (Official Reports of the Debates) service.
In January 2009 we were engaged to look at modifying the speaker coverage to fit a revised and expanded seating layout. We were able to adjust the speaker aiming in the computer and adjust the signal processing to expand the uniform coverage area without any significant capital expenditure by the HANSARD department.
Mc Squared System Design Group, Inc
323 - 901 West 3rd Street, North Vancouver, BC. V7P 3P9 Ph 604-986-8181