Two numbers on the spec sheet decide whether your amplifier and speakers will get along: sensitivity and impedance. Get them right and a modest amp can sound effortless; get them wrong and an expensive one can strain and distort. This is the one piece of 'system matching' worth understanding before you buy — and it's simpler than the forums make it sound.
Sensitivity — how loud, per watt
Sensitivity, quoted in decibels (e.g. 87 dB), tells you how loud a speaker plays from one watt measured a metre away. It sounds abstract, but the scale is steep: because decibels are logarithmic, every +3 dB roughly doubles the loudness you get from the same power.
- An 84 dB speaker is fairly power-hungry — it wants a strong amplifier to reach lively volumes.
- An 88–90 dB speaker is comfortable with modest amplification.
- A 93 dB+ speaker is very efficient — the kind that sings on low-power tube amps.
Impedance — the electrical load
Impedance, in ohms (Ω), is how hard the speaker is to drive electrically. Most are nominally 8 Ω (easy) or 4 Ω (more demanding). The nominal figure only tells part of the story: impedance varies with frequency, and a speaker that dips to a low minimum impedance (say 3 Ω) at some frequencies asks more of the amp's current delivery than its '6 Ω nominal' label suggests.
That's why TrueScale lists both nominal and minimum impedance when the maker publishes them — the minimum is the number that stresses a weak amplifier.
Reading them together
Sensitivity and impedance combine into one practical question: how much clean power does this speaker need, and can my amp deliver it into that load?
- Easy load: high sensitivity + 8 Ω + a high minimum → happy with almost any amp.
- Demanding load: low sensitivity + 4 Ω + a low minimum → wants a robust amp that doubles its power into 4 Ω.
A quality amplifier that comfortably delivers its rated power into your speaker's load, landing in the upper half of the speaker's recommended power range, is the goal.
The myth: 'more watts damages speakers'
It's usually the opposite. Most blown drivers come from an underpowered amp pushed into clipping — when a small amp runs out of clean power, it sends distorted, spiky signal that cooks tweeters. A larger, clean amplifier played at sensible volume is safer than a tiny one pushed to its limit. Don't fear headroom.
Active speakers skip all of this
If matching sounds like a chore, remember that active speakers have the amplifier built in and tuned by the maker to the exact drivers — so sensitivity and impedance stop being your problem. That's a big part of their appeal for a first system; see Choosing your first hi-fi speakers.
The bottom line
Higher sensitivity = easier to drive. Higher, steadier impedance = easier on the amp. Check both — and the minimum impedance — before pairing passive speakers with an amp, aim for clean headroom over the bare minimum, and don't fear a bigger amp. Every TrueScale page lists these figures for passive models; find your match by spec in HiFi Search.