A generation apart: Sonus faber Duetto is the newer design, against a 2019 model. Newer is not automatically better, but the older one is more likely to be discounted or near run-out.
| Area | Better | Why |
|---|
| Bass | B | Buchardt A500 digs deeper - 25Hz against 37Hz. |
| Built-in power | A | Sonus faber Duetto has the bigger amplifier (700W vs 450W RMS). |
| Connections | A | Sonus faber Duetto adds Bluetooth, streaming, HDMI and digital inputs. |
| Size | depends | Similar cabinet size - neither is easier to fit. |
| Cabinet | depends | Ported vs Sealed. Sealed is tighter and happier near a wall; ported digs lower but wants space behind it. |
| Expandability | A | Sonus faber Duetto: a sub output. |
| Price | evenly matched | Much the same money ($3,999 vs $3,850 a pair). |
A Sonus faber Duetto B Buchardt A500
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both speakers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Sonus faber Duetto has the edge on paper, though the margin is not large. The rows marked "depends" may matter more to you than the score does. If a subwoofer is in your plans, the bass gap largely stops mattering - you would be crossing over above 37Hz anyway, so judge these on the other rows instead.
And remember what a spec sheet cannot show: how each looks in your room and whether the finish suits it, what dealer support and warranty are like where you live, and how they actually sound to you. If you can hear them first - ideally with your own music - that will tell you more than any number above.