Very important for proper hi-fi system performance and dynamic range.
This combination of technical parameters determines the actual sound pressure level you can attain without distortion and also tells us a lot about the dynamic capabilities of the system. As usual, science provides the answers.
For example, let’s say you have a low-powered amplifier, say something up to around 30 Watts per channel. To achieve realistic dynamics and sound pressure levels, you’ll need sensitive speakers, over 90dB/Watt sensitivity, preferably a lot more, to be able to play loudly, with realistic dynamics. If that amplifier is matched up with speakers with relatively normal sensitivity, the result will be a system that sounds strained and lacking in dynamics at anything but very low levels. It can work, but only just, and in the right context, ie mellow music, small room, no desire for realistic sound pressures.
Conversely, let’s say you have a very powerful amplifier, something like 300 – 500 Watts per channel or more. This gives you a lot more room to move and means you can use speakers down to relatively insensitive 83 to 85dB/Watt. This gives you more choice and allows crushingly high sound pressure of course with speakers of 88 – 90dB/Watt sensitivity or more. It also gives you great dynamic range and headroom which means your amplifier is almost always coasting. Coasting tends to sound good, straining, not so much.
Is one approach better than the other? Not really, both have merit. I use a powerful amplifier (200 Watts/channel) to drive speakers of ‘normal’ 90dB/Watt sensitivity. This allows for a good mix of everything, micro dynamics, punch and bass control and high sound pressure levels if needed.
I’ve also heard amazing sounds from super low-powered valve amplifiers, say 7 Watts/channel, and super-sensitive horn speakers at around 100dB/Watt, which can yield similar or even greater dynamics in some cases, and often better micro-resolution, because sensitive speakers tend to give you that. Then again, sensitive speakers are often more coloured, so swings and roundabouts.
What you don’t want is a low-powered amp driving speakers of average or low-ish sensitivity. This is always an unfavourable marriage.
