This is very interesting.
There are few Baha'i Houses of worship in the world, and only one on this continent. One of the rules in all of them is that only the human voice is to be heard in the sanctuary. The building, by the way, is 9-sided, a huge open space, maybe 4 stories high inside?, with windows all around, covered by a concrete filigree pattern so the light comes in dappled, I guess. There's a choir that sings from way up high. It's quite beautiful and moving. If you're ever in the Chicago area, go up Sheridan Road to Wilmette, about 40 minutes north of the Loop, and the House of Worship is there, right by the lake. It's open all the time, as a sanctuary for anyone who wants to go there. I'm not sure when the singing happens, though. Might be Sunday afternoons.