What am I missing?
Grannyring got it in one- well done!
Apparently that this applies specifically to SETs and not to other kinds of amps. For example, despite being zero feedback (like SETs), our amps make a fraction of the distortion at full output (about 0.5% if set up correctly) so you have a much greater *percentage of usable output power*.
I like to use that idea of ’percentage of usable output power’ as its a number that can vary widely from amp to amp. Generally speaking, tubes have greater usable output power than solid state amps seem to have but SETs are the exception.
This is all about distortion, which all amps make so the ’percentage of usable output power’ has to do with the **kinds** of distortion that are particularly objectionable to the human ear. These are the higher ordered harmonics (5th and above, particularly the 7th), IM distortion, and in the case of class D, inharmonic distortion (caused by intermodulations with the scanning frequency; similar to aliasing in digital audio).
Because the ear converts all forms of distortion into tonality (including aliasing), the distortions above all manifest as some form of brightness and hardness. By contrast the lower ordered harmonics are perceived as ’warmth’ and ’bloom’.
Its quite worthy of note that these objectionable distortions always occur in very small amounts as opposed to the lower ordered harmonics- the issue is that the ear is far less sensitive to the lower orders. In this regard I propose a ’weighting’ scheme so that trace amounts of higher ordered harmonics can be seen for what they really are- which is to say: audible!
In SETs, the first onset of higher ordered harmonics is heard as ’dynamics’ by the ear as musical energy often occurs on transients where greater power is required (in a way fundamentally different from solid state, which tends to make the the higher ordered harmonics all the time). What happens is the higher ordered harmonics (to which very importantly the ear uses to calculate sound pressure) are thus only showing up initially on the leading edges of transients and no where else, so then it is perceived as ’dynamics’. The problem is, once you are aware of this fact its easier to hear that what is really happening is the amp is making distortion. So the simple act of reading this paragraph may have ruined it for some people. To avoid this you simply need more power or more efficiency. More power in an SET means it won’t sound as good and therein lies the dilemma!
Of course all forms of distortion are to be avoided, but avoiding the the objectionable forms is far more important overall for a pleasant listening experience. This, in a nutshell, is why tubes are still around nearly 60 years after being declared ’obsolete’.
One thing that has really become evident in the last 15 years or so is that if the loudspeaker is a higher impedance that avoiding the more objectionable distortions is easier to do **regardless** of the amplifier technology. I think speaker manufacturers are slowly figuring this out as there are more 16 ohms speakers now than there were 15 years ago. Put another way, if you are tying to make a lower powered tube amp sound like music, a four ohm load is absolute anathema!
Its my opinion and also my experience that four ohms has no place in high end audio (IOW if high quality audio production is in fact the goal). The cables are more critical and all amps sound harsher and less detailed on four ohms as opposed to eight or sixteen all other things being equal. Its not only audible, you can see it in the specs of any amplifier made.
