All-Channels-Driven Power All-Channels-Driven (ACD) Power Rating

What 'all channels driven' means

An all-channels-driven (ACD) rating is the continuous per-channel power an amplifier can deliver while every channel is being driven into its rated load at the same time, for the full rated bandwidth and distortion. The US FTC Amplifier Rule defines the multichannel test condition as 'all associated channels fully driven to rated per channel power,' with left-front and right-front constituting the minimum associated channels for stereo systems. A '1-channel-driven' or '2-channels-driven' figure, by contrast, is measured with the other channels idle, and so does not reflect what the amplifier sustains when every output is loaded simultaneously.

16 CFR 432.3 fixes the geometry of an FTC-compliant rated power output. Power must be 'continuously applied at full rated power for not less than five (5) minutes' into '8 ohms impedance'; 'any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N)'; and the device must first be preconditioned by 'operating all channels at one-eighth of rated power output for one hour using a sinusoidal wave at a frequency of 1,000 Hz' in still air at 25 °C, on a 120 V / 60 Hz supply with less than 2% total harmonic content.

Section 432.2 then governs how that result must be presented. Whenever any direct or indirect representation is made of an amplifier's power output, power band, or distortion, the manufacturer's rated power output must be disclosed 'clearly, conspicuously, and more prominently than any other representations or disclosures', must be 'clearly and conspicuously labeled "FTC Power Output Rating"', and 'shall not be made by a footnote, asterisk, or similar notation'. That requirement is what produces the canonical FTC-shape spec line: a watts-per-channel figure with bandwidth, load, distortion, and channels-driven all stated together (e.g., 'XXX W per channel, 20 Hz–20 kHz, 8 Ω, 0.08% THD, both channels driven').

CTA-2006 (formerly CEA-2006) is the Consumer Technology Association's amplifier-power standard widely used in consumer audio. The current revision specifies that 'the output signal from the amplifier must contain no more than 1% total harmonic distortion plus noise', that 'test loads (resistors) be within 5% of their target impedance' (commonly a 4 Ω load), that 'test duration for power output must be at least 15 seconds', and that an A-weighted signal-to-noise ratio be reported alongside the continuous-power figure.

Why per-channel and ACD numbers diverge

Almost every consumer AVR uses a single power supply — one transformer, one filter-capacitor bank, one heatsink budget — to feed every output channel. Continuously delivering 100 W into 8 Ω requires the supply to deliver roughly 100 W of real load power per channel; with seven channels driven that is about 700 W of load power before output-stage and supply losses, well beyond what a typical AVR chassis is sized to dissipate. That is why a single-channel-driven figure can sit hundreds of watts above the same AVR's all-channels-driven figure even though the rated output stage hasn't changed.

The wall outlet itself sets a hard ceiling. A standard US receptacle supplies 120 V at 15 A — about 1,800 W of input power before the breaker trips — and class-AB amplifier efficiency at full rated power is typically only 50–60%. So even ignoring losses, an AVR cannot deliver more than roughly 900–1,100 W of total continuous output across all channels from a normal outlet. A '7×140 W' nameplate would imply 980 W of load power on its own, before any losses — physically impossible to sustain ACD on a 15 A circuit. Gene DellaSala (Audioholics) makes this argument explicitly: 'almost no multi-channel amplifier rated beyond 150 watts per channel can meet the ACD specification for continuous power delivery on real-world AC power lines.'

Sustained-sinewave ACD is also more demanding than any real program. Music and film soundtracks have crest factors typically in the 10–20 dB range, meaning average power is one-tenth to one-hundredth of peak power; only the peaks momentarily approach rated output, and they almost never line up across all channels at once. Audioholics frames ACD as an engineering torture test rather than a use-case spec: 'program material—whether movies or music—never taxes all channels continuously at full power.'

Reading AVR power specs honestly

Audioholics bench data shows the divergence concretely. The Marantz MM8077 (a higher-end external 7-channel amp) measured 'seven channels driven continuously into 8-ohm loads ... 108.9 watts at 0.1% distortion' against a 2-channel rating in the 140 W class. The entry-level Denon AVR-X1200W measured only about 47 W per channel at 0.1% THD with seven channels continuously driven into 8 Ω. The Denon AVR-X3700H rates 105 W per channel at 0.08% THD with two channels driven, and in field reports drops to roughly 70 W per channel with five channels simultaneously driven. As a working rule, Sound United guarantees its mid- and upper-range Denon/Marantz models 'to have at least 70% of the quoted 2 channel power output still available when 5 channels are driven', while smaller AVRs and any spec quoted with only 1 channel driven can drop below 50% under ACD.

The most useful single-number AVR comparison line is one measured under the FTC's full conditions: 20 Hz to 20 kHz bandwidth, 8 Ω load, ≤1.0% THD+N (manufacturers typically publish at 0.05–0.1%), both channels driven for five minutes after preconditioning. Every other AVR rated the same way is on the same scale. Single-channel-driven, 1 kHz-only, peak, dynamic, and 'maximum' figures each use a more permissive subset of the FTC test geometry and inflate the headline number relative to what the amplifier can actually sustain into a real load.

Dedicated external multichannel amplifiers escape the AVR ACD-spec problem by sizing the power supply, transformer, and heatsinks to actually meet an ACD rating. Anthem's MCA 525 Gen 2 publishes '225 watts per channel into 8 ohms (20–20,000 Hz) at 0.015% THD with all channels driven, 400 watts per channel into 4 ohms, and 600 watts per channel into 2 ohms' — an FTC-shape spec with all five channels driven. That is what 'all channels driven' looks like when a manufacturer is willing to engineer to it; AVR makers generally are not.

Common power-spec mistakes

Marketing power figures labelled 'peak', 'max', 'dynamic', 'music power', or 'PMPO' are not measured under the FTC continuous test geometry and cannot be cross-compared with FTC rated power. Under the 2024 amendments, any such non-FTC power figure on a US product disclosure must be 'clearly and conspicuously labeled "This rating was not tested under the FTC standard"', without footnotes or asterisks, and must be 'less conspicuously and prominently made than any rated power output disclosure required in § 432.2' — meaning the FTC continuous figure must dominate the spec sheet whenever both are shown.

Per-channel-driven and ACD numbers do not track each other. An AVR rated '170 W × 9 (1 channel driven, 0.08% THD, 1 kHz)' may deliver less ACD power than a competing AVR rated '125 W × 7 (2 channels driven, 20 Hz–20 kHz, 0.05% THD)' because the second spec was measured under a tougher load condition closer to ACD. Because amplifier dissipation budget — not the per-channel rating — determines ACD output, two AVRs with identical headline numbers can perform very differently with all channels driven, and a smaller honest spec can outperform a larger optimistic one.

On June 12, 2024 the FTC published final amendments to 16 CFR Part 432, effective August 12, 2024. The amendments expanded the rule's scope from amplifiers and AV receivers to all home-entertainment audio products, including powered speakers, soundbars, and subwoofers; formalised prior staff guidance on associated channels so that multichannel ratings must drive at least the front-left and front-right channels used for stereo programming simultaneously (now codified in 432.3); and required non-FTC power claims to use the exact phrase 'This rating was not tested under the FTC standard' rather than the originally proposed 'This rating does not meet the FTC standard'. The amendments did not change the underlying test bandwidth (20 Hz–20 kHz), distortion ceiling (1.0% THD+N), or 8 Ω load reference.

Two cautions follow from how these specs are produced. First, a watts-per-channel figure quoted without test conditions — load, channels driven, bandwidth, distortion — is not comparable to anything; the FTC label exists precisely to force those four variables into the open. Second, neither the FTC nor CTA-2006 publishes a single conversion factor between a 2-channel-driven figure and a 5- or 7-channel ACD figure; the safest reading is to compare model-to-model on the same line of the spec sheet, prefer the most demanding condition the manufacturer is willing to publish, and treat absence of an ACD figure as itself a data point.