Critically important for proper hi-fi 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 system’s dynamic capabilities. As usual, science provides the answers.

Low Power

For example, let’s say you have a low-powered amplifier up to around 30 Watts per channel. To achieve realistic dynamics and sound pressure levels, you’ll need sensitive speakers rated at over 90dB/Watt sensitivity, preferably a lot more, to be able to play loudly and with realistic dynamics.

If that 30 Watt amplifier is matched up with speakers with relatively normal sensitivity, the result will be a system that sounds strained and lacking in bass control and dynamics at anything other than very low levels. This combination can work, but only just, and in the right context, with mellow music, a small room, and no desire for realistic sound pressures.

High Power

Conversely, let’s say you have a very powerful amplifier, something like 200 – 500 Watts per channel. This gives you a lot more headroom and means you can use speakers down to relatively insensitive 83 to 85dB/Watt, which are often some of the better sounding options. ATC and B&W designs spring to mind.

This gives you more choice and allows crushingly high sound pressures and dynamics with regular speakers of 88 – 90dB/Watt sensitivity or more. It also gives you dynamic range and headroom, allowing your amplifier to almost always coast rather than strain at the limits. Coasting tends to sound good; straining, not so much.

Is one approach better than the other? Not really. Both have merit. I currently (2025) use a high current class A amplifier (around 70 Watts/channel) to drive speakers of ‘normal’ 89dB/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 of around 5 – 10 Watts/channel and sensitive horn speakers of 98 – 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 also often more coloured, so swings and roundabouts.

What you don’t want is a low-powered amp driving speakers of average to low sensitivity. This is always an unfavourable marriage.