Watts! How many do we need?

There's nothing like a well designed class A amplifier to bring out the best  performance in your speakers.  I once owned an original Bedini 25/25 that was a nice match with my 15 ohm Rogers LS3/5A's.  It was also supposed be a great match for the original QUAD ELS 57.  The Bedini 10/10 was also a good choice for the ELS 57.  One of the best sounding and most powerful class A amplifiers that I have ever heard is the Classe Audio DR3VHC. It was one of Classe Audio's first products when David Reich was running the company. 

My advice, take it or leave it:  is to note what the speaker manufacturer recommends as a minimum power recommendation into the 8 Ohm load of the speaker, then note what the minimum (not nominal) impedance is, then double down the recommended power for each halving of impedance e.g. 10 Watts into 8 Ohms, 20 Watts into 4 Ohms, 40 Watts into 2 Ohms, etc.. When faced with a non-standard impedance, drop down to the lower standard amplifier rating, for example for 3 Ohm minimum speaker load go to the 2 Ohm standard amplifier ratings unless the amplifier manufacturer offers non-standard ratings (such as the Benchmark amps). Using that as a minimum power need. While room size and desired output levels will actually determine how much power one will need, as a general rule of thumb for most people, in most rooms will most probably be better suited by doubling the manufactures minimum power recommendations into that minimum impedance as noted above for satisfactory results. The important thing is actual power into that lowest impedance. I don't recommend relying on so called "stable into X load " claims, as that only means the amp won't go into osciallation when presented with that impedance. it is not a guarantee of power output or distortions levels into that load. Don't be swayed by manufacturers, dealers, etc., annecdotal suggestions; let them put it writting. Using the above considerations can go a long way towards preventing speaker damage, and offering satsifying sound.

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If you want to know accurately and in realtime how much power your amp is  consuming then look into purchasing Emporia Smart Plug with energy monitor (on Amazon).

The Emporia Smart Plug allows you to monitor the energy use realtime and control most appliances from anywhere with the Emporia App on your mobile

 It takes very accurate reading every second (resolution of 0.1W) and you can see all the peaks and troughs on a graph and even download the data in a spreadsheet!

@rshank64 
 

I have noticed that with my McIntosh MC7200 amp (non autoformer) and ADS 1590/2 speakers, 2 watts on the meters will almost burst my eardrums. No technical observance here, just noticed this bit of info when listening to all kinds of music in my room. 

watts are watts, a watt will do the same work regardless of how its derived.

amp topology, power supply type, amount of components in the circuit, speaker efficiencies, etc. will make differences. as long as your not clipping the amp, putting the amp into harm i.e. oscillating, etc. should all be similar as far as power requirements for a given speaker. Probably much lower then most would like to admit.

Bragging rights, power wars, room size and volume, etc. seem to be more an issue. don't get me started on "oh its hi current" well of course, because its low voltage. Power=Current x Voltage after all.