^^ That is correct.
The ideal for amp and loudspeaker interface has been the idea of the voltage paradigm or voltage rules, wherein the speaker is 'voltage driven' and the amp behaves as a 'voltage source' which means it can make constant voltage regardless of load.
But SETs and a good number of other amps (including ours) do not work on those rules. Fortunately there are a good number of loudspeaker manufacturers that prefer the sound of tubes, and so make speakers that do not require that the amp be a perfect voltage source- far from it, in some cases.
The idea behind the voltage rules is plug and play flat frequency response with no adjustment needed to the amp or speaker. However no speaker is entirely flat and it turns out that the human ear/brain system has tipping points where tonality created by distortion is favored over actual frequency response errors. So the benefit of having perfectly flat response is reduced in the face of the fact that to get it, many amps have to employ loop negative feedback. Such use is known to add harmonic and IM distortions of its own, so many designers choose to use no feedback at all. This means that you have to be a bit more careful about speaker choice, but the result is more musical and more neutral.
This has been going on in high end audio for decades. So the result is that you simply have to be careful to match the amp and speakers together. Its my opinion that you go with the amp first and the speaker second, because the first problem to solve is whether you prefer tubes or transistors. People that prefer tubes usually don't like it when things are bright, so if you already got the speaker first you may wind up flushing a lot of money down the loo without satisfaction.
The ideal for amp and loudspeaker interface has been the idea of the voltage paradigm or voltage rules, wherein the speaker is 'voltage driven' and the amp behaves as a 'voltage source' which means it can make constant voltage regardless of load.
But SETs and a good number of other amps (including ours) do not work on those rules. Fortunately there are a good number of loudspeaker manufacturers that prefer the sound of tubes, and so make speakers that do not require that the amp be a perfect voltage source- far from it, in some cases.
The idea behind the voltage rules is plug and play flat frequency response with no adjustment needed to the amp or speaker. However no speaker is entirely flat and it turns out that the human ear/brain system has tipping points where tonality created by distortion is favored over actual frequency response errors. So the benefit of having perfectly flat response is reduced in the face of the fact that to get it, many amps have to employ loop negative feedback. Such use is known to add harmonic and IM distortions of its own, so many designers choose to use no feedback at all. This means that you have to be a bit more careful about speaker choice, but the result is more musical and more neutral.
This has been going on in high end audio for decades. So the result is that you simply have to be careful to match the amp and speakers together. Its my opinion that you go with the amp first and the speaker second, because the first problem to solve is whether you prefer tubes or transistors. People that prefer tubes usually don't like it when things are bright, so if you already got the speaker first you may wind up flushing a lot of money down the loo without satisfaction.