They are more similar than alike, as Michael Børresen was the chief designer of Raidho for ten years or so. With his Borresen line of speakers, the major differentiators are:
A more advanced tweeter - is thinner, but with more versatile membrane which is faster, more resolving and can be turned up to concert levels without frying the tweeter. Raidho tweeters have historically been more fragile and I would worry about playing music above 95dB peaks.
Cabinet designs - Borresen is fine tuning cabinets to continue to optimize around smaller driver arrays, so they are narrower, but deeper and more tapered to reduce resonance. They require much more room behind them, however, given the speed and force of the air they push out. Newer Raidho cabinets designed by Bruno Meldgaard are starting to implement larger drivers in wider, less deep cabinets, which can play lower and closer to walls.
Both lines have improved their drivers. At first, Borresen speakers far surpassed the Raidho’s drivers, but the later Raidho TD series with titanium in the drivers are really quite good, too.
If you want a very neutral, fast and resolving speaker that has a higher fidelity sound, and you have the ample space in the room to let them breathe, Borresen is the way to go. Borresen, I have found, are overall harder to drive and require very good electronics that can control them. Raidho are more room-friendly and easier to get emotionally engaged with a wider variety of electronics, but they are just a bit sweeter and softer on top.
