How could 100 Watt class a has more head room than a 300 Watt amp Class AB


Put aside which brand or make.
I put two amps into a test, both highend amp came from the same manufacturer.
Both double down the power with half of the impedance load, and THD is about the same.
Regardless of the size and cost difference, from a pure science perspective.
300 watt in theory should provide more headroom and sound ease when it reaches 100db, but the reverse is the true, the class A 100 watt seems to provide more headroom.
I have tried to use another set of speakers which is much easier to drive and it reaches the same conclusion.
Can someone explain why?
Quality or quantity of watt, how do we determined?
samnetw
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Mastersound PF 100 Monos. 110 class A SET. 
Quite an experience. Take a control over the speakers unseen for me before.  The only amplification I can confirm that kef reference are musical. 
Simply amazing 
Gentlemen,

Unless you are using a sound level meter to determine the actual sound pressure level what you are probably experiencing is the following phenomena which is that we think something is playing louder when it starts to distort and don't think it is too loud when it is not distorted.

Under circumstances of no instrumentation to aid your perception the 100 watt amp sounds louder because it is distorting sooner, the 300 watt amp sounds less loud because it can play louder with out distortion.

Your brain and ears are deceiving you..


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To compare meaningfully output power of two amplifiers (all external factors being equal) it is useful to know several parameters.
--the manufacturer's definition of the power output metric. It should be
   "continuous power", meaning the amplifer's delivery  is not time limited  and it does not overheat in the ambient temperature 
--what is the distortion 20hz-20khz
--what is the signal/noise ratio
--what peak output power can be reached at 2-4-8 ohm, for how long, at what frequency and with what distortion
The peak parameters are useful to know, as musical peaks may need 5-7 times value of the continuous output power.