Amplifiers for 4 Ohm Speakers: Which Ones Publish a Real Rating

A 4 ohm speaker draws twice the current of an 8 ohm speaker at the same voltage, and current is the thing an amplifier’s power supply and output stage run out of first. That is the whole reason the impedance matters. It is also why the honest measure of an amplifier for a 4 ohm load is not its 8 ohm wattage but whether the maker publishes a 4 ohm figure at all, and under what condition.

What a 4 ohm speaker asks for

An amplifier is, to a first approximation, a voltage source. Halve the load impedance and the current doubles, so the power — voltage times current — doubles too, if the supply can deliver it. A perfect amplifier rated 45 W into 8 ohms would give 90 W into 4. No real amplifier in our brackets does that, and the ratio between the two published figures is a fair measure of how much current the supply has in reserve. A ratio near 2 means a stiff supply; a ratio near 1.3 means the amplifier is running out of current before it runs out of voltage, which is how amplifiers get hot, clip, or drop into protection with a hard load.

Which speakers are 4 ohms? In our registry, the KEF Q7 Meta publishes 4 ohms nominal with a 3.2 ohm minimum. The ELAC Debut 3.0 DF63 and DF53 are published as 6 ohms on ELAC’s product pages and 4 ohms in ELAC’s owner’s manual, which our under-$2,000 floorstanding page documents. Polk publishes no nominal figure at all for the Monitor XT range, only “compatible with 4- and 8-ohm outputs”. And a nominal 8 ohm speaker can dip well below that at some frequencies, which our impedance guidecovers — the reason a published minimum, which only KEF gives, matters more than the nominal.

The four kinds of 4 ohm rating, best to worst

1. Continuous, full band, both channels driven, with a distortion figure. The same condition as the 8 ohm rating. This is a real specification and it is rare at our prices.
2. Continuous at 1 kHz only, with a looser distortion figure. A real measurement at an easier condition. Comparable to the 8 ohm figure only if you notice the condition changed.
3. Dynamic power only. A short-burst IHF measurement, typically 20 milliseconds. It tells you the supply can deliver current briefly. It is not a continuous rating and should not be read as one.
4. A number with no condition, or no number. A 4 ohm wattage with no distortion figure and no bandwidth, or an 8 ohm figure and silence about 4. Either way you are guessing.

The four amplifiers ranked on this page are one of each, in that order, and the ranking is the disclosure, not the wattage. Our power-rating guide explains each measurement condition in more depth.

Full-band 4 ohm rating: the Marantz PM6007

Marantz publishes 45 W into 8 ohms and 60 W into 4 ohms, both across 20 Hz to 20 kHz with both channels driven, the 8 ohm figure at 0.08% THD. It is the only amplifier we cover whose 4 ohm rating is taken under the same bandwidth and drive condition as its 8 ohm rating. It also publishes a damping factor of 100 across 40 Hz to 20 kHz and a phono stage with 83 dB signal-to-noise. It ranks first here on disclosure alone. Its cons are that 45 W is the joint-lowest 8 ohm figure on the under-$1,000 page, and that the 4 ohm figure carries no distortion condition of its own.

1 kHz 4 ohm rating: the Denon PMA-600NE

Denon publishes 45 W into 8 ohms across the band at 0.07% THD, and 70 W into 4 ohms at 1 kHz and 0.7% THD. Both are real continuous measurements; the second is taken at a single frequency and ten times the distortion, which is the easier test. Read the two numbers side by side and the 4 ohm figure looks generous; read the conditions and it is a different measurement. Denon does not publish a damping factor. It ranks second because a 1 kHz continuous figure is still a figure, and because Denon prints the condition next to it rather than hiding it.

Dynamic power only: the Yamaha A-S501

Yamaha publishes 85 W into 8 ohms across the band at 0.019% THD — the best continuous 8 ohm figure and distortion figure of the four — and, for 4 ohms, only “High Dynamic Power/Channel (8/6/4/2 Ω): 130 / 150 / 185 / 220 W”. That is an IHF burst measurement, not a continuous rating, and the 185 W figure circulating in search results as the A-S501’s 4 ohm output is that number misread. The dynamic series does say something useful: the supply delivers rising current into falling impedance all the way to 2 ohms, briefly. What it does not say is what the amplifier delivers into 4 ohms for more than a few milliseconds. It ranks third: excellent 8 ohm disclosure, no continuous 4 ohm figure. The same is true of the Yamaha A-S301, which publishes 100 / 120 / 140 / 150 W dynamic and no continuous 4 ohm rating. Our review covers the rest of the amplifier.

A number with no condition: the WiiM Amp

WiiM publishes 60 W per channel into 8 ohms and 120 W into 4 ohms — a perfect 2.0 ratio — with no distortion figure, no bandwidth and no statement of how many channels were driven attached to either number. A Class D amplifier with a switching supply can genuinely double into 4 ohms, so the ratio is plausible. But a figure with no condition cannot be compared with the three above, and our Class D guide explains why the missing distortion figure matters more for this topology than for the others. It ranks fourth on disclosure while offering the highest published 4 ohm number on the page, which is the point of ranking on disclosure. The Cambridge AXA35 publishes 35 W into 8 ohms and nothing for 4, and the Fosi Audio V3 publishes only a 4 ohm figure (300 W per channel, no distortion condition) and no 8 ohm figure at all; neither is ranked.

AV receivers and 4 ohm speakers

None of the AV receivers we cover publishes a 4 ohm power rating; every figure is an 8 ohm, two-channels-driven number, and several manuals carry an impedance selector that lowers the rail voltage for low-impedance loads rather than adding current. If the plan is a 4 ohm pair on a receiver, the honest position is that the maker has told you nothing, and a receiver with front pre-outs feeding a stereo amplifier with a real 4 ohm rating is the route that has a number attached.

What we would do

For a 4 ohm speaker with a published minimum — the KEF — buy the amplifier with the full-band 4 ohm rating and accept its modest 8 ohm number; the ratio, not the wattage, is what the speaker cares about. For a speaker whose maker gives two impedances — the ELACs — plan for the lower one. For a speaker whose maker gives none — the Polks — treat it as 4 ohms until proven otherwise, because that is the direction in which being wrong is harmless. Our matching guide takes the sensitivity side of the same decision, and the series-parallel page covers the one case where the load is your own doing.