We purchased our advance tickets via Classictic.com. We have been using this on-line company both in Paris and Venice extensively and can highly recommend it. The carre d'or (the best category) tickets were more than affordable, 44 euro per person. The official start of the show is 7 PM, the Classictic.com advises to arrive early, at 6:15 PM. We would take it even a notch early, especially if the intention is to get best seats available in your section/category. The lines are quite long, one has to move through almost the entire Palais de Justice to reach the La Chapelle.
The interior is fabulous, and so are the acoustics; the musician were doing a very good job. We would sincerely recommend the venue to our fellow TripAdvisor travelers and suggest it as a great and enlightening addition to your Paris plans. Especially for the money spent. Especially in Paris.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.