Lucasfilm Ltd THX sound system born from THX 1138 Lucas first film. The first THX cinema crossover monitor was named after THX 1138 in this order.
Take the letters and few numbers from THX 1138 (THX 31) swap numbers around.
Then take LUH 3147 and take numbers (47) swap them around then add the numbers in sequence with the letters gives you THX 3417 crossover monitor.