Tom,
You have been given very good input here. Almarg's points about impedance was definitely spot on (as usual in his posts): both as a key speaker attribute when considering to match with SET, and in showing your current speakers aren't the best fit with SET. The main points were around impedance variability over the frequency range. I also want to point that impedance magnitude is very important for SET matching as SET amps are constant current sources.
Most other amps are constant voltage sources, so as you halve the speaker impedance they deliver twice as much power, or half as much power as you double impedance. You've probably amps specs saying 200W into 8ohm and 400W into 4ohm. Here's the simplified math behind that:
Power (P) equals voltage (V) times current (I). P=V*I.
Also V=Z*I, where Z is impedance.
You can replace in the first one: P=V^2/Z. If an amp is constant voltage, power is inversely proportional to speaker impedance. Double Z, halved P.
On the other and SET are constant current, so in P=V*I you can replace into P=Z*I^2. As you double speaker impedance the amp delivers twice the power.
Look into speaker designs by SET amp manufacturers. For example Coincident Technology. Their speakers are 95dB-ish sensitive and 10 ohm, low variation impedance. Just looking at the 95dB sensitivity might lead you to believe they aren't good match for a 300B 8W, but the designer had that amp in mind when designing. BTW, note these aren't horns. While horns are indeed a good match for SETs, not only horns are suitable for SETs.
Also, another consideration often brought up by Ralph from Atmasphere: SETs produce extremely low distortion provided you run them at say 25% of their rated power, and low distortion up to 50% of their rated power. Distortion grows fast as you approach rated power. So while it's true SETs produce more distortion, that is true at their rated power, and a well designed system that incorporates SET should take into consideration running them as easily as possible. Hence it's also true SETs produce very low distortion, with the added benefit of producing more pleasing harmonics when they do.
Bottom line: it's all about execution. No blanket statement can be made. SETs could be better or worse. Your existing speakers aren't a good match for SET. But you also mentioned they are too small for your room. Maybe you want to go SET knowing you will replace your speakers with SET friendly later. Or replace your speakers first and then find an amp to match.
Sorry for the length!
You have been given very good input here. Almarg's points about impedance was definitely spot on (as usual in his posts): both as a key speaker attribute when considering to match with SET, and in showing your current speakers aren't the best fit with SET. The main points were around impedance variability over the frequency range. I also want to point that impedance magnitude is very important for SET matching as SET amps are constant current sources.
Most other amps are constant voltage sources, so as you halve the speaker impedance they deliver twice as much power, or half as much power as you double impedance. You've probably amps specs saying 200W into 8ohm and 400W into 4ohm. Here's the simplified math behind that:
Power (P) equals voltage (V) times current (I). P=V*I.
Also V=Z*I, where Z is impedance.
You can replace in the first one: P=V^2/Z. If an amp is constant voltage, power is inversely proportional to speaker impedance. Double Z, halved P.
On the other and SET are constant current, so in P=V*I you can replace into P=Z*I^2. As you double speaker impedance the amp delivers twice the power.
Look into speaker designs by SET amp manufacturers. For example Coincident Technology. Their speakers are 95dB-ish sensitive and 10 ohm, low variation impedance. Just looking at the 95dB sensitivity might lead you to believe they aren't good match for a 300B 8W, but the designer had that amp in mind when designing. BTW, note these aren't horns. While horns are indeed a good match for SETs, not only horns are suitable for SETs.
Also, another consideration often brought up by Ralph from Atmasphere: SETs produce extremely low distortion provided you run them at say 25% of their rated power, and low distortion up to 50% of their rated power. Distortion grows fast as you approach rated power. So while it's true SETs produce more distortion, that is true at their rated power, and a well designed system that incorporates SET should take into consideration running them as easily as possible. Hence it's also true SETs produce very low distortion, with the added benefit of producing more pleasing harmonics when they do.
Bottom line: it's all about execution. No blanket statement can be made. SETs could be better or worse. Your existing speakers aren't a good match for SET. But you also mentioned they are too small for your room. Maybe you want to go SET knowing you will replace your speakers with SET friendly later. Or replace your speakers first and then find an amp to match.
Sorry for the length!