Kenwood SP23 Extension Speaker
To compliment the Kenwood range of transceivers, matching external speakers are available as are power supply units to make a complete line-up.
I use a Kenwood SP-23 external speaker, while not being perfectly matched (in size) to the TS-850, but instead to the slightly smaller TS-450 & TS-570 transceivers, it still gives clear audio due to the front facing speaker, unlike the radio which has the speaker on the top panel as do most other radios.
Some of the higher specification external speakers contain filters to allow the operator to tailor the sound to their liking and make weak signals easier to hear.
Some contain circuits for noise reduction which can also help in picking out really weak signals from man made and atmospheric noise.