Based on the question specifying SSB Phone operations, then additional considerations should be made. For folks that only need an external speaker for squelched FM Phone operations, then Digital Noise Reduction (DNR) isn't needed and speaker choices are simplified. Since DNR works at the audio frequency level, it can be added external to the radio unlike most other types of signal filtering technology.

By the way, I've seen DNR defined as Dynamic Noise Reduction, Digital Noise Reduction, and DSP Noise Reduction depending on the source.

If your radio has built-in DNR processing, then a simple, inexpensive speaker like the MFJ-281 ($18.95 @ Gigaparts) or a $10 swapfest external CB radio speaker works very well in my opinion. You don't need deep bass or high fidelity reproduction as most SSB phone audio will be in the 300 Hz to 2300 Hz regime.

If you radio lacks DNR processing, then I'd recommend looking at something like a West Mountain CLRSPKR or a sweet deal like the one KM4BWW Brian picked up at the Orlando Hamcation in 2019. It was a small mobile speaker with a DNR circuit built-in, something that used should have gone for $50 or more but Brian got it for less than half that (it was so good of a deal, the dealer offered to buy it back once he realized what he let go of!)

You can also try the hybrid approach by buying a stand-alone DNR processor like the Audio DSP Noise Reducer DNR Digital Filter and then adding a simple, inexpensive speaker. This may be cheaper than the integrated options just mentioned as you may be able to pull this off for under $100.

If money is no object, the OEM matching speaker for your base rig is always another option. You'll be paying for the name and the aesthetics and it may not have the performance of other third party speaker options, but it'll look nice in your shack.

73,

N4SFS