I'm enjoying the CW acoustic speaker discussion on the Topband list but here's an entirely different idea: I was a US Coast Guard radioman back in the 70s when almost all maritime traffic was conducted in Morse. We were issued government headphones that had a metal diaphragm held in place with a magnet.
A colleague used a pair of metal cutters to cut out a small rectangular area from the diaphragm and riveted a reed from a harmonica in its place, then reassembled everything. Adjusting the receiver BFO to match the reed's frequency resulted in that reed acting as an incredibly sharp and narrow bandwidth filter.
Pretty soon we were all bringing harmonicas to the station and removing our favorite musical frequency reed to do the modification! This really helped clear the pile ups on the HF maritime frequencies during the every-six-hour weather OBS from the ships. (Ham pile ups are nothing compared to what we encountered!)
Today's headphones no longer have metal discs so some other method would have to be employed to implement this idea.
Station name: US Coast Guard Communication Station Honolulu, callsign NMO.
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72 / 73 / 3579,
Jeff KH6O