I found the video per the link below pretty much by accident when searching for something rather different. I have to be honest, I found this to be utterly gobsmacking, I had always suspected that amps needed a little more power than simple maths based on required dB(A) and speaker efficiency would suggest, but nothing like this. The video of the amp's display is a little blurry, but's lets just say that I has mentally parked the decimal point in the display a factor of 10 backwards until it dawned on me what was really going on.I would say it is well worth 10 minutes of your time to watch.https://www.youtube.com/watch?v=bRMR9JZ1m0s&app=desktopSo what exactly are the amplifiers measuring? As mentioned in the video it is the peak / tranient power that is captured, so not a continuous average. The amps are CH Precision A1's. This from the CH Precision manual:Power monitoring. Each power amplifier board is equipped with a DSP that monitors the instantaneous output voltage and current of each M1 channel. Both values are sampled at around 100 kHz, ensuring peak values are properly detected. This circuitry has several purposes: give the user a feedback of the peak power fed to the loudspeakers, and detect malfunctions such as short-circuits or amplifier damage.As many will know, Harbeth's are not the most efficient speakers you can buy, in fact rather the opposite, the 40.1's are rated at a lowly 85dB/w/1m.This is another video showing the CH Precision power meters. It is not clear what speakers are used here, but the peak levels are clearly lower than are seen on the Harbeth's. (but still hit the odd spectacular peak)https://www.youtube.com/watch?v=UP8i8F62OlMI have to say that when I first viewed the Harbeth clip I was staggered by what I was seeing, this was not what I expected at all. Thinking about it though, it does make sense of some of my past experiences. For example, I first listened to the KEF Blades with a Devialet Expert D240. This appeared to drive the Blades with ease, which is what you might expect. Later, I heard the Blades with a D170. It was terrible. This was not some subtle step back in performance, but a case of the amp not really working with the speaker, dynamics vanished, the bass was a mess. Not good to listen to at all. I remember being puzzled by this at the time. The Blades are rated with a sensitivity of 91dB/w/1m. So for normal listening levels surely you only need 10 or 20 Watts or something? Why should the drop from 240 to 170 make any difference? Based on simple maths re dB(A) levels and power, it did not make sense. However, looking at those figures that the CH Precision amps are displaying, it would seam possible that the D240 was coping with the Blades, but the D170 struggling, with audible consequences.It also reminds me a Devialet event at Oxford Audio, when Devialet's Chief designer Mathieu Pernot stated that his perfect amplifier design would have "infinite power". This seamed slightly absurd to me at the time and I was talking to him about this later in the day. I was making a real world point about the rated power capability of typical speakers. In response Mathieu pointed out that there is no agreed method or protocol for measuring manufacturer quoted speaker power ratings, no agreed standard if you like, so manufacturers tend to give figures that are more like "recommended amplifier power ratings. He then went on to explain that a speaker "rated" for say 50w to 400w, could easily take instantaneous peaks of power way over the 400w "maximum" with ease. OK, try putting that kind of wattage through continuously and heat will generate, voice coils will melt or seize, but very high transient peak power levels are not an issue. For me, knowing (based on maths) that a typical speaker could run at well over 100dB(a) with less than 20W, Mathieu's explanation seamed a little theoretical. Now I have seen the above video, it makes perfect sense. I have always though that higher power amplifiers provide a certain sense of "ease" to the presentation, but I could not really rationalise the science behind what was just a subjective view. Now I have seen the above video, many things make a lot more sense. For those interested, this is a link to the track used in the Harbeth video:https://www.youtube.com/watch?v=XhuJxdaU87IPlaying this at home, I would have to say that it does include some rather extreme bass content, which combined with the Harbeth's low efficiency does perhaps go some way towards explaining the rather high power figures on that CI amp. I can also see that my habit of using one or two electronic tracks when auditioning kit might have some merit, I can't see any other music genres providing quite the speaker / amplifier challenge of something like the Pan Sonic track linked above. (plus, I quite like electronic music) Although even with miserable YouTube 128kbs streaming, it does sound pretty awesome with my little Devialet providing the thundering bass power.