Is powerfull Amps only for low sensitivity speakes?

Ideally the more power available the better, the higher sensitivity rating the better but there are good reasons not all speakers are 100db+ and there are plenty of 3-4 watt power amplifiers that are worth listening to. Ultimately the more power you have in reserve not being used (duty cycle) the more headroom you have for dynamics and this also relates directly to the power supply. Think of an 18 wheeler going 50mph vs a moped going the same speed. One is giving it everything (which translates into distortion in audio) while the other is barely breaking a sweat. When you have 200 watts available but your speaker is putting out 3 watts- which is a decent listening level- that extra 197 watts is just sitting there like a heavy duty reserve power storage not being used so when a loud cannon blast comes along the level will increase dramatically as it would in real life. That's my best explanation. Ultimately some very refined and superb speakers will only have an 86db rating due to drivers used and crossover design but that's by no means any way to determine the quality of the speaker. Amplifier watts are used far too often to determine quality when in reality the old rule applies- pick it up. Is it heavy? That means it has a proper power supply and although that's only a start, it's a good sign.

Thank you all for your contributions.
Dear Pokee thank you also for the example.
regards

We'll start with i design amps - and have done some in hgih end commercially.

Your question is a little bit vague, os let me re-pose it two ways:

1. Is the primary benefit of powerful amps the ability to drive inefficient or power hungry (big room, big capability) speakers?  Yes.

2. Is there any *disadvantage* to powerful amps with efficient or small speakers?  No.

There is nothing about a powerful amp that is inherently a compromise of sound for power except for one thing: the cost of a big transformer, many transistors, and heat-sinks necessary for big power.  So in that sense there *is*  a trade off; yet in those many-$1000 power amps, no such trade off has been made.

I have built my primary design in two formats:  low power class-A (almost) and high power class A/AB, using nearly the same parts. They sound very similar, until one runs out of power and either clips or compresses. But that usually happens after my ears or the speakers are in distress.

Let's look at the flip side: modest power on large full-range speakers.  I currently drive huge, 89 dB efficiency speakers (Mahlers if you care, very fussy) with the 60 wpc version with no problem. Most would select a higher power amp.  I see no need, even though 3-4 are lying there idling, free for my use

So, within reason, select simply the best sounding amp.  Also remember that there is more to "power" than rater power into an 8-ohm resistive load. Most speakers are FAR from an 8-ohm resistive load, and it may take some serious muscle to control them.  That means low output impedance and ability to drive high current into a load that might drop to 2-ohms., or in many cases (read this carefully: negative impedance for  a brief moment when the voice coil is traveling backwards). Electro magnets work both ways :-)  And speakers are electro-magnets at their core.

Funny, on my moprning run, before reading your note, i was thinking about the best price/performance way to build a great, low cost (ok, maybe < $1000, so not that low), low power amp.

Happy listening.

G

My speakers are 94db and I have twin magtechs (2 X 900 watts).  They sing, they breath and sometimes, they even cry.