I was debating whether to cross post this, but I want to start on the DB forum because, well, that's mostly what I play.
Pre-pandemic, I went to jams and open mics regularly to play with other folks, and sometimes it's a lot of miles to travel and you only end up playing one or two songs. So I started looking for a decent fretless acoustic bass guitar. My first wish is to find one that is as loud as I can get so that I could potentially not bring an amp along. My secondary wish is a bass that has a sound that is, at least, suggestive of an upright.
The best instrument I've tried so far is the Breedlove Solo Jumbo CE fretless bass. It could be louder, but it has a pickup if necessary, and at $800, great bang for the buck.
Any thoughts?
I own a Thunderchief CB10. I will second what @GretschWretch has said, you have to judge from the perspective of the audience. From the perspective of the player, IMHO it's very unsatisfying to play ABG with an ensemble. If the instrument is set up with high action, you can make a contribution with instrumentation such as acoustic guitar, cajon, melodica, and couple of vocalists. But you will have to put a lot of energy into the ABG and you will not have any sensation of power like you get with amp. The tone will be very middy sounding.
Some of the Breedlove basses have a port on top of the instrument so the player can hear a bit better. This may degrade how well the instrument projects to the audience though. I would definitely consider one of the top of the line Breedloves though as the seem to be very nice instruments.
Spector makes a well reviewed ABG called the Timbre, which seems obviously patterned after the Tacoma. Videos of the Spector sound very similar to the Tacoma as well. IMHO the Tacoma is one of the louder ABGs, tone is fairly even across the strings, but the fundamental is pretty weak unless you use an amp.
Edit: Unfortunately I don't think they make a fretless 
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Rather than trying to force an ABG to work acoustically, I think it's far more realistic to use one with an amp. About the smallest amp I would recommend is the Roland Cube Street EX. (Bass) Users of this amp suggest it work even better if you run a battery powered HPF and compressor in front of it.
I would not personally bother with the regular Cube Street or Micro Cube Bass RX. I have tried both and they were barely louder than my Tacoma, and I had to really control my dynamic range to avoid causing them to fart out. The Cube Street EX is not what I would call loud, but it does make 10 times the power of regular Cube Street and Micro Cube Bass RX.
If you don't need/want battery power, most small bass combo amps will probably out perform the Cube Street EX. Or use whatever relatively small amp you already own, or whatever happens to be at the jam session.
If you use an amp all the time, the acoustic volume of the ABG is not as important. In fact, an ABG that it designed to produce more acoustic volume will generally tend to feed back sooner when run through an amp.
My Tacoma actually sounds absolutely fabulous through an amp, but I would say it's only usable at low to perhaps medium volume because it is sensitive to feedback. As you increase the volume the tone begins to change and become uneven, and eventually the bass will begin to feedback. My Tacoma has one of the Fishman preamps so it has a notch filter, phase/polarity switch, and a variable frequency mid that can be used to compensate quite a bit, but at some point you loose control.
Some other fairly cheap ABGs that produce very little acoustic volume are known for sounding fabulous through and amp and being able to cope better with high stage volume.
A sound hole plug can help with high volume as it keeps the sound from entering the body of the instrument and rumbling around. There used to be 3rd party sources who made plugs for the Tacoma but I never bought one. If you buy an ABG with a round sound hole, it's probably more likely that you will be able to find a plug.
