What about entrance reducers?

[Harrison]

I have entrance reducers on all our hives. I have been going through the hives, pulling out the reducers one by one, waiting a few minutes, then going back to make recordings. I don't know if this is enough delay to allow the bees to settle into their "normal" state of sound.
On a positive note, this does get each hive ready for a dose of oxalic acid vaporization.