# Sensitivity and impedance: what amplifier you need

The two numbers that decide whether your amplifier can drive a speaker.

Source: https://truescaleaudio.com/en/guides/speaker-sensitivity-and-impedance

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](/guides/how-to-read-a-speaker-spec-sheet), 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](/guides/choosing-your-first-hifi-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](/hifi-search).