I had a visitor to my apiary this morning who had a good idea. I demonstrated my "ear to the hive" technique to listen to the cluster, I spared him my rendition of "AH, AH, AH, AH, stayin' alive".
He couldn't hear them when he pressed his own ear to it, but then he pressed his cell phone against the hive and recorded the sound; When he played it back on high volume he could hear it clearly.
I haven't seen this idea suggested before, and thought it might be useful to other beekeepers with some hearing loss.