We are a professional audio company integrating R&D, production and sales. We have been focusing on the production of mixers, active power amplifiers, microphones, and related electronic components and equipment for many years.
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A 500 W Class D amplifier module and a similar-power Class AB module dropped into the same 12-inch powered speaker behave very differently before anyone even starts talking about sound. The Class D board runs warm after two hours of programme material; the Class AB board is hot to the touch, and the battery pack behind it drains noticeably faster. The question of Class D sound quality usually arrives later, once the module is measured properly — and by that point, most of the old complaints have already shrunk into a much shorter list. That shorter list is the subject of this article. It is written for engineers and purchasing teams choosing amplifier modules for powered speakers, line arrays, subwoofers and portable systems — the people who need to separate the parts of "Class D sound" that are genuine design trade-offs from the parts that were simply inherited from the early 2000s. The Short Answer on Class D Sound Quality A well-designed Class D module is transparent enough that, inside a modern powered speaker, it is difficult to distinguish from a good Class AB module of the same power. It is also measurably better at the things an amplifier is judged on in real deployments: thermal stability, output consistency under load, and long-duration performance at high volume. The differences that remain are not caused by the letter D. They come from four design decisions: The switching frequency and the output filter built around it. The power supply topology, specifically whether the module uses power factor correction and an LLC resonant stage. The signal chain in front of the amplifier, including DSP, EQ and limiting. Thermal design and board layout. The practical consequence is that comparing "Class D versus Class AB" at catalogue level tells you almost nothing. Compare the power supply, the filter and the DSP, and the sound quality question largely answers itself. Why Class D Earned a Bad Reputation for Sound The criticism was justified once, and it is worth knowing exactly why, because the same failure modes still appear in inexpensive modules today. Output filter roll-off. Early modules switched at roughly 50–150 kHz, which forced the output filter to begin cutting well below 20 kHz. The result was a rolled-off top end that listeners described as dull or closed-in. Dead-time distortion. The blanking interval that prevents shoot-through in the output stage introduces a nonlinear error. Without compensation, that error lands in the treble, exactly where the ear is most sensitive to it. Poor supply rejection in open-loop designs. With no feedback loop, ripple on the supply rail appears directly at the output, and rail sag under load turns into audible compression. EMI from careless switching layout. Noise coupled into the preamp stage and input cabling, producing hiss and buzz that had nothing to do with the audio path itself. Every one of these problems has a known engineering answer: higher switching frequencies, dead-time compensation, closed-loop modulation and disciplined EMI layout. What matters for a buyer is not whether Class D can sound good — it clearly can — but whether the specific module in front of you has had those answers applied. The Four Things That Actually Decide Class D Sound Quality Switching Frequency and the Output Filter The switching frequency sets how much room the output filter has to work in. Professional Class D modules commonly switch somewhere between 300 kHz and 1 MHz. The higher the switching frequency, the higher the filter corner can sit, which keeps phase and amplitude behaviour clean up to and beyond 20 kHz. The cost is greater switching loss and a more demanding EMI design. For an OEM project, the practical checks are straightforward: What switching frequency does the module specify? Where does the output filter corner sit relative to 20 kHz? Can the supplier provide a measured 20 Hz–20 kHz response curve rather than a printed "±3 dB" claim? Power Supply Topology: PFC, LLC and Why They Appear in Datasheets A Class D output stage draws current in switching pulses, so the amplifier is bounded by the quality of the rail feeding it. Two supply features are worth knowing by name. Power factor correction (PFC) keeps the module stable across a wide mains voltage range, which matters for products exported to markets where the grid is not tightly regulated. LLC resonance is a soft-switching topology. It lowers switching loss and EMI, produces cleaner output ripple, and holds efficiency well under heavy load. In practice, the same Class D stage fed by a basic flyback supply and by an LLC resonant supply will not behave like the same amplifier — the difference shows up first in bass control and in how composed the system stays during loud passages. EON520: LP400W+HP100W PFC+LLC Resonance Wide Voltage Class D Power Amplifier Module● High Efficiency Switching Power Supply with PFC+LLC Resonance: 800W ● Self-adaptive Wide Voltage Input: 100V-240V ● Mid and Low-Frequency Power Amplifier: CLASS D 40...View Product → Modules that combine both approaches — a PFC plus LLC resonant design rated LP 400 W / HP 100 W with wide-voltage input, for example — exist specifically to hold output quality steady when the mains supply moves. DSP and the Signal Chain in Front of the Amplifier By the time a powered speaker reaches the listener, the sound is the product of the DSP and the amplifier together, not the amplifier alone. That is why DSP modules built on the ADAU1701 chip are so common in active speakers: crossover, EQ, limiting and preset switching all live in a single device. Three DSP behaviours translate directly into perceived Class D sound quality: Limiting. A properly set limiter keeps the amplifier out of hard clipping, which reduces bass distortion at high volume compared with a module relying on the amplifier's own protection. Protection logic. Speaker and thermal protection that ramps output down instead of cutting it abruptly avoids the audible dropouts that make a product feel unreliable. Presets matched to the cabinet. Preset EQ modes are only useful when they were tuned for the specific driver and enclosure, not copied from a reference design. DSP1903: 4 Customized Preset EQ Modes 2.1CH Linear Array Speaker ADAU1701 Based DSP Functi● Designed based on ADAU1701 sound audio system. Use sigma studio DSP software to configure signal processing parameters. ● Selectable four customized preset modes whi...View Product → A multi-channel DSP front end offering several customised preset EQ modes is a typical example: the amplifier stage stays identical, but the tonal behaviour of the finished speaker changes completely. Thermal Design and Board Layout Class D generates far less heat than Class AB, but it still generates heat. A module that enters thermal rollback after twenty minutes will sound soft and compressed no matter how good its bench measurements look. What to verify: Heatsink area and airflow path matched to the real enclosure. Protection thresholds set with enough margin that normal programme material never triggers them. Burn-in data from long-duration full-load testing, not just a short bench run. This is also the part of the evaluation that cannot be done from a datasheet. A supplier running its own SMT lines, assembly lines and an audio testing room can produce burn-in logs and impedance-load test results; a trading company usually cannot. The manufacturing setup behind the module is worth an on-site visit before committing to a production run. Class D, Class AB and Class H Side by Side The choice is rarely about which class sounds best in isolation. It is about which one fits the product's thermal envelope, battery budget, weight target and price point. Efficiency ranges are widely cited in audio engineering literature and amplifier design application notes; actual figures vary with topology, load impedance and output level. Amplifier class Typical full-power efficiency Distortion behaviour in modern designs Heat and physical size Typical module applications Class A 20–30% Very low crossover distortion, warm tonality Very high heat, large heatsinks Small audiophile amplifiers Class AB 50–70% Low and well understood, easy to tune Moderate to high heat Home audio, smaller powered speakers Class H 65–80% Clean at high output thanks to rail tracking Moderate heat, linear transformer required High-power subwoofers, installed sound Class D 80–95% Transparent when filtering, supply and feedback are done well Low heat, compact footprint Portable, battery, line array and subwoofer modules Typical Full-Power Efficiency by Amplifier Class Class A25% Class AB60% Class H75% Class D90% Indicative ranges; real numbers depend on topology, load and output level. The efficiency gap is not a marketing figure — it is the reason a battery-powered speaker can run for a full evening, and the reason a line array cabinet can carry more channels in a smaller box. If you want a deeper walkthrough of how these trade-offs play out in real products, this comparison of Class D and Class AB efficiency and sound quality covers the same ground from a design perspective. Specifications Worth Writing Into a Purchase Agreement Module catalogue pages tend to list power, impedance and a handful of features. If sound quality is a contractual requirement, ask for these instead: THD+N at rated power and at 1 W. The 1 W figure is the one that exposes idle noise floor and crossover behaviour. Frequency response measured at the speaker terminals, not at the line input, because the output filter and the load interact. Output impedance or damping factor across 20 Hz–20 kHz. This is what separates a module with tight bass from one that sounds loose. Power supply topology and switching frequency. PFC present or not, LLC resonant or hard-switched. Protection thresholds and recovery behaviour. Ask for actual trigger points, not simply confirmation that protection exists. Thermal test data at full load over at least one hour. Suppliers who design and build their own modules can usually answer these questions with test data. Suppliers who resell cannot, and that difference shows up in the field long after the sample has been approved. Where Class D Modules Make the Most Sense Class D stopped being a compromise in every application where efficiency and size matter more than absolute thermal headroom, and that list keeps growing. Portable and battery-powered speakers. Efficiency is the entire design constraint. A Class AB module would need a substantially larger battery pack for the same play time. Active line array systems. Multi-channel modules with LLC resonant supplies fit the 2.1 and 2.2 channel configurations these systems use, and low heat output lets designers pack more channels into a smaller cabinet. Powered subwoofers. BTL Class D output stages deliver high power into low-impedance loads without the heatsink mass a linear design would require. A dedicated subwoofer module rated LP 1500 W into 8 ohms illustrates what that looks like in production hardware. Column speakers and installed sound. Low heat means the amplifier can be sealed inside the enclosure with no additional ventilation. EON521+1500:LP 1500W/8ohm Pro Audio BTL Subwoofer Power Amplifier Module●LLC Resonant High Efficiency and High Reliability Switching Power Supply: 1800W ●BTL Power Amplifier: CLASS D 1500W-8 Ohm ●U-shaped Aluminum Radiator, Stable Power Ou...View Product → Signal and Power Path Inside a Class D Powered Speaker Module PFC + LLC Power Supply DSP Front End ADAU1701 Class D Stage + Output Filter A Practical Evaluation Checklist for a Production Project Before freezing a Class D module into a production bill of materials, run it through the same sequence every time: Confirm rated power at the actual load impedance of your speaker, not the impedance used in the headline specification. Measure frequency response at the speaker terminals with the real load connected. Run a one-hour full-power burn-in and log heatsink temperature alongside any protection activity. Play programme material with heavy low-frequency content at high level and listen specifically for compression and limiter pumping. Check idle noise with the input shorted; this is where inexpensive modules are exposed. Verify behaviour at the low end of the mains voltage range if the product ships to markets with unstable supply. Confirm that preset EQ modes and protection thresholds can be customised for your cabinet. Customisation is a normal part of the module business, not an exception, and a supplier who will not adjust a preset is unlikely to support the product after launch. Frequently Asked Questions Q1. Is Class D amplifier sound quality actually worse than Class AB? No. A well-designed Class D amplifier module is transparent enough to be hard to distinguish from a comparable Class AB module. Perceived quality depends far more on switching frequency, output filter design, supply topology and DSP tuning than on the amplifier class itself. Q2. What switching frequency should a Class D amplifier module have? Professional modules commonly switch between 300 kHz and 1 MHz. Higher frequencies push the output filter corner further above the audio band and improve treble behaviour, at the cost of higher switching loss and stricter EMI layout requirements. Q3. Does a Class D module need a DSP to sound good? Not strictly, but in a powered speaker the DSP shapes the final result through crossover, EQ and limiting. A properly configured limiter alone prevents hard clipping and noticeably reduces bass distortion at high volume. Q4. Why does a Class D amplifier lose bass control at high volume? Usually it is the power supply, not the amplifier stage. Rail sag under heavy load reduces output headroom and effective damping. An LLC resonant supply with adequate bulk capacitance holds the rail far more stably than a basic hard-switched supply. Q5. Can Class D amplifier modules drive both 4-ohm and 8-ohm speakers? Many can, but rated power differs between the two. Always confirm power ratings at the impedance your cabinet actually presents, and check that protection thresholds were set for that load rather than copied from another model. Q6. How should sound quality be tested before mass production? Measure THD+N at 1 W and at rated power, take frequency response at the speaker terminals with the real load, run at least one hour of full-power burn-in, and listen for limiter pumping on bass-heavy material. .article-section table{display: table!important;width:100%;border-collapse:collapse;margin-bottom:16px;} .article-section thead{display: table-header-group!important;} .article-section tbody{display: table-row-group!important;} .article-section tr{display: table-row!important;} .article-section th{display: table-cell!important;} .article-section td{display: table-cell!important;} .article-section caption{caption-side:bottom;font-size:16px;margin-bottom:12px;font-style:italic;color:#808080;} .article-section th{font-weight:bold;border:1px solid #cccccc;padding:8px;} .article-section td{border:1px solid #cccccc;padding:8px;} .article-section ol{margin-bottom:12px;list-style-type:decimal;list-style-position:inside;padding-left:0;} .article-section ul{margin-bottom:12px;list-style-type:disc;list-style-position:inside;} .article-section li{list-style:inherit;font-size:16px;margin-bottom:6px;} .article-section h2{font-size:22px;font-weight:bold;text-align:left;margin-bottom:12px!important;} .article-section h3{font-size:16px;font-weight:bold;text-align:left;margin-bottom:12px;} .article-section p{font-size:16px!important;margin-bottom:12px;} .chart-box{width:440px;margin:0 auto 20px;} .diagram-box{width:440px;margin:0 auto 20px;} .diagram-box svg{width:100%;height:auto;display:block;} .chart-title{font-size:14px;font-weight:bold;text-align:center;margin-bottom:12px;color:#1f4e79;} .bar-row{display:flex;align-items:center;margin-bottom:8px;} .bar-name{flex:0 0 78px;font-size:13px;color:#444444;} .bar-track{flex:1 1 auto;height:16px;background:#eef2f7;border-radius:2px;overflow:hidden;} .bar-fill{display:block;height:16px;border-radius:2px;} .bf-a{background:#c8d6e4;} .bf-ab{background:#9dbcd8;} .bf-h{background:#6f9ec8;} .bf-d{background:#2f6fb5;} .bar-pct{flex:0 0 42px;text-align:right;font-size:13px;color:#444444;} .chart-note{font-size:12px;color:#808080;font-style:italic;text-align:center;margin-bottom:0;} .faq-grid{display:grid;grid-template-columns:1fr 1fr;gap:14px;} .faq-item{background:#f3f7fb;border-left:4px solid #2f6fb5;border-radius:4px;padding:12px 14px;} .faq-q{font-size:15px;font-weight:bold;color:#1f4e79;margin-bottom:6px;} .faq-a{font-size:14px;color:#333333;line-height:1.5;} @media (max-width:640px){ .chart-box{width:100%;} .diagram-box{width:100%;} .faq-grid{grid-template-columns:1fr;} } .product-card{display:block;margin:20px 0;border:1px solid #e5e7eb;border-radius:10px;overflow:hidden;font-style:normal;background:#fff} .pc-inner{display:flex;text-decoration:none;color:inherit;align-items:center;min-height:120px} .pc-img{width:160px;min-width:160px;aspect-ratio:4/3;height:auto;min-height:120px;object-fit:cover;flex-shrink:0;display:block;align-self:stretch} .pc-body{padding:12px 16px;flex:1;min-width:0;display:flex;flex-direction:column;align-self:stretch;justify-content:center} .pc-title{display:block;font-size:15px;font-weight:600;color:#111;margin:0 0 6px;line-height:1.4} .pc-desc{display:-webkit-box;font-size:13px;color:#6b7280;margin:0 0 8px;line-height:1.5;overflow:hidden;-webkit-line-clamp:2;line-clamp:2;-webkit-box-orient:vertical} .pc-cta{display:block;font-size:13px;font-weight:600;color:#11700F;margin-top:auto} .pc-inner:hover .pc-title{text-decoration:underline} .article-section a:not(.pc-inner),article a:not(.pc-inner){color:#11700F}.pc-cta{color:#11700F!important}
Short answer: the amplifier class used for subwoofers is Class D in nearly every powered design built today between roughly 200 W and 3 kW. Class AB still makes sense below about 150 W and in some hi-fi and automotive subwoofers, while Class H holds a place in high-power professional subwoofer channels. The class is a heat, size and cost decision before it is a sound-quality label. Sourcing a powered subwoofer, a plate amplifier or an OEM amplifier module usually starts with a power target and a cabinet drawing. The class decision then shows up in the heatsink, the power supply, the chassis depth and the bill of materials — and only later in the marketing copy. The sections below explain why Class D took over the low-frequency channel, where the linear classes still win, and which measurements actually tell you whether a subwoofer amplifier module will survive production. Why Class D Became the Default Amplifier Class for Subwoofers A 1,000 W subwoofer channel is unremarkable today, so the useful question is what the amplifier does with the power it never delivers to the driver. At about 60% efficiency — realistic for a Class AB stage driven hard — roughly 670 W of every 1,000 W leaves as heat. A Class D stage running at 90% leaves about 110 W. That ratio decides heatsink mass, fan noise, chassis depth, and whether the rear of the cabinet has to be vented at all. The frequency band suits the topology as well. A subwoofer crossed over at 80–120 Hz never asks the amplifier to reproduce switching residue in the audible midrange, and modern modulator designs close a feedback loop around the output filter, so the low-frequency distortion penalty that early Class D modules carried is now largely a historical problem. Typical full-power efficiency by amplifier class 25% 50% 75% 100% Class A ~25% Class AB ~60% Class H ~75% Class D ~90% Typical ranges quoted in amplifier design literature and manufacturers' datasheets; real values depend on load impedance and drive level. This is why a Class D subwoofer power amplifier module rated 650 W into 8Ω can sit on a rear plate without forced cooling, while a comparable linear design needs a heatsink several times larger and a heavier transformer behind it. EON180S+2092: LP 650W/8Ohm Pro Audio BTL Subwoofer Power Amplifier ModuleWe have a strong R & D team that can develop and produce products according to drawings or samples provided by customers.View Product → Class AB, Class D and Class H Compared for Subwoofer Duty The table compares the four classes that genuinely reach subwoofer products. Efficiency ranges are typical figures quoted in amplifier design literature and manufacturers' datasheets; real values move with load impedance, rail voltage and how hard the amplifier is driven. Typical efficiency by amplifier class and the heat each one produces for 1,000 W of subwoofer output. Heat figures are derived from the efficiency ranges shown. Class Typical efficiency Heat per 1,000 W out Where it still appears Main trade-off Class A 20–30% 2,300–4,000 W Niche hi-fi and studio subwoofers Very low distortion, very large heatsink Class AB 50–70% 430–1,000 W Sub-150 W systems, automotive, some studio subs Simple and EMI-quiet, but heavy and warm Class H 70–80% 250–430 W High-power professional subwoofer channels Cooler than AB, still needs a large transformer Class D 80–95% 50–250 W Default for powered subs, line array subs, portable Highest efficiency, layout and EMI care needed Heat generated per 1,000 W of output (watts) 750 W 1,500 W 2,250 W 3,000 W Class A ~3,000 W Class AB ~670 W Class H ~330 W Class D ~110 W Derived from the efficiency ranges above: heat = (100 / efficiency − 1) × output power. The Specs That Decide the Class in a Real Project Class is only the first filter. These are the numbers that separate a workable module from a datasheet that falls apart in production. Power at the real load. A module rated 650 W into 8Ω and one rated 650 W into 4Ω are different products. Ask for continuous power at the impedance the driver actually presents, not a peak figure. Damping factor at low frequency. Output impedance at 50 Hz controls how tightly a subwoofer cone starts and stops. It matters more below 100 Hz than any number measured above 1 kHz. THD+N below 100 Hz. Request the curve, not a single value at 1 kHz. The subwoofer band is where a class claim is genuinely tested. Thermal behaviour at continuous output. Heat is the reason Class D won. A module that meets its rating for a few seconds is not the same product as one rated for continuous use. Protection that matches real faults. Over-current, over-temperature, DC offset and short-circuit behaviour at the output should be defined, not implied by the word "protected". Idle and standby consumption. Retail channels in Europe and North America increasingly ask for standby figures, and they are cheapest to design in from the start. Inside a Powered Subwoofer Amplifier Module A subwoofer amplifier module is usually two or three boards stacked on standoffs: a power stage on an aluminium base, an output PCB carrying the devices, and a control or DSP board on top. That stack explains most of the thermal and layout constraints an integrator will face. DSP and control IC Amplifier output PCB Aluminium heatsink and power stage Layer stack of a typical powered subwoofer amplifier: heatsink base, output PCB on standoffs, and a control or DSP board on top. Where the heatsink sits, how much air the chassis allows and how far the DSP board is from the switching stage all change with the class. A linear Class AB stage usually needs vertical fins and an aluminium rear panel; a Class D module can often use the rear plate itself as the heatsink. Integrators who need a specific board outline, connector set or rail voltage can frequently adapt a standard module instead of starting from a blank PCB — that is what a customization service is for. How DSP and the Power Supply Shape the Class Result The amplifier class decides how much heat the output stage makes; the DSP and the power supply decide how well that output can be used. A limiter, crossover and EQ implemented in DSP let the power stage run closer to its ceiling without clipping the driver, which is why so many subwoofer modules pair a Class D stage with an ADAU1701-based DSP board and preset EQ modes. The supply matters just as much. A resonant LLC stage with power factor correction keeps efficiency high and holds the rails steady when heavy bass demands current in short bursts — the behaviour behind LLC resonant supplies in subwoofer systems that OEM buyers now treat as standard. DSP2405SUB Powered Subwoofer Amplifier with LLC Supply and BluetoothFor high-power subwoofer builds, this 1200W Class D amplifier pairs LLC resonant supply with DSP, Bluetooth TWS, and 1000W 8-ohm sub output.View Product → Where Class AB and Class H Still Earn Their Place Class D is not universal, and pretending otherwise leads to over-engineered products. Below roughly 150 W, a small Class AB design is often cheaper to build, needs no output filter and produces no switching EMI — which matters in compact enclosures with sensitive wireless circuitry nearby. Class H sits between the two. It keeps a linear output stage but steps the supply rails with the signal, so it wastes far less heat than Class AB at high power while avoiding switching noise altogether. In professional subwoofer channels where the platform is already linear, a Class H module such as an 800 W linear-transformer design remains a sensible choice. AMP800H Class H Subwoofer Amplifier Module with Linear TransformerFor linear subwoofer systems needing lower heat without switching noise, this 800W-transformer Class H module delivers 600W into 4-ohm loads.View Product → Frequently Asked Questions What amplifier class is best for a subwoofer? Class D above roughly 200 W — it runs cooler, weighs less and costs less per watt than Class AB at the same output. Below about 150 W, a small Class AB build can still be the cheaper option. Is Class D good for subwoofers, or does it sound worse? In the subwoofer band, a correctly designed Class D module is not audibly worse. What decides the result is damping factor at low frequency, THD+N below 100 Hz and how the supply behaves under load. Why do subwoofer amplifiers use Class D instead of Class AB? Heat. A 1,000 W channel at 60% efficiency wastes about 670 W as heat, while a 90% Class D stage wastes roughly 110 W. That gap sets heatsink size, chassis depth and fan requirements. What is the difference between Class D and Class H subwoofer amplifiers? Class D switches the output devices on and off; Class H keeps a linear output stage but steps the supply rails with the signal. Class H runs cooler than Class AB but still needs a larger transformer. How much power does a subwoofer amplifier module need? Match continuous power to the driver's RMS rating at its real impedance — 8Ω or 4Ω, not the peak figure on the carton. For a 15-inch to 18-inch professional sub, 600–1,500 W RMS is a common range. Do Class D subwoofer amplifiers need a special power supply? Not special, but well matched. Most designs pair the Class D stage with a switching supply using PFC and LLC resonance, which keeps efficiency high and output steady when heavy bass pulls the rails down. Choosing the amplifier class of a subwoofer comes down to three numbers: how much continuous power the design needs, how much heat the enclosure can shed, and how much the bill of materials allows. Class D answers all three for most modern subwoofers, while Class AB and Class H stay relevant at the low-power and professional ends of the market, where their specific strengths still pay for themselves. .article-section{color:#24292f;line-height:1.65;} .article-section h2{font-size:22px;font-weight:bold;text-align:left;margin-bottom:12px!important;} .article-section h3{font-size:16px;font-weight:bold;text-align:left;margin-bottom:12px;} .article-section p{font-size:16px!important;margin-bottom:12px;} .article-section ul{margin-bottom:12px;list-style-type:disc;list-style-position:inside;} .article-section ol{margin-bottom:12px;list-style-type:decimal;list-style-position:inside;padding-left:0;} .article-section li{list-style:inherit;font-size:16px;margin-bottom:6px;} .article-section table{display: table!important;border-collapse:collapse;width:100%;margin-bottom:16px;} .article-section thead{display: table-header-group!important;} .article-section tbody{display: table-row-group!important;} .article-section tr{display: table-row!important;} .article-section th{display: table-cell!important;} .article-section td{display: table-cell!important;} .article-section caption{caption-side:bottom;font-size:16px;margin-bottom:12px;font-style:italic;color:#808080;} .article-section th{font-weight:bold;border:1px solid #cccccc;padding:8px;} .article-section td{border:1px solid #cccccc;padding:8px;} .article-section .answer-box{background:#f2f7fd;border-left:4px solid #2f6fb3;border-radius:4px;padding:14px 16px;margin-bottom:16px;} .article-section .chart-wrap{width:440px;margin:0 auto 10px;} .article-section .chart-wrap svg{display:block;width:440px;height:auto;} .article-section .chart-note{font-size:13px;line-height:1.5;color:#6b7280;text-align:center;margin-bottom:18px;} .article-section .faq-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:12px;margin-bottom:12px;} .article-section .faq-item{background:#f4faf6;border:1px solid #dcebe2;border-top:3px solid #2f8f63;border-radius:6px;padding:12px 14px;} .article-section .faq-item:nth-child(even){background:#fdf8f2;border-color:#f0e2cd;border-top-color:#d08a34;} .article-section .faq-item h3{color:#1d6b47;margin-bottom:8px;} .article-section .faq-item:nth-child(even) h3{color:#9a5a18;} @media (max-width:640px){ .article-section .chart-wrap{width:100%;} .article-section .chart-wrap svg{width:100%;height:auto;} .article-section .faq-grid{grid-template-columns:1fr;} } .product-card{display:block;margin:20px 0;border:1px solid #e5e7eb;border-radius:10px;overflow:hidden;font-style:normal;background:#fff;box-shadow:0 0 5px rgba(31,41,55,.08)} .pc-inner{display:flex;text-decoration:none;color:inherit;align-items:center;min-height:148px} .product-card .pc-img{width:auto!important;min-width:0!important;max-width:min(36%,240px)!important;height:auto!important;min-height:0!important;max-height:148px!important;aspect-ratio:auto!important;object-fit:contain!important;flex:0 0 auto;display:block;align-self:center} .pc-body{padding:12px 16px;flex:1;min-width:0;display:flex;flex-direction:column;align-self:stretch;justify-content:center} .pc-title{display:block;font-size:15px;font-weight:600;color:#111;margin:0 0 6px;line-height:1.4} .pc-desc{display:-webkit-box;font-size:13px;color:#6b7280;margin:0 0 8px;line-height:1.5;overflow:hidden;-webkit-line-clamp:2;line-clamp:2;-webkit-box-orient:vertical} .pc-cta{display:block;font-size:13px;font-weight:600;color:#11700F;margin-top:auto} .pc-inner:hover .pc-title{text-decoration:underline} .article-section a:not(.pc-inner),article a:not(.pc-inner){color:#11700F}.pc-cta{color:#11700F!important}
Putting a 500-watt subwoofer into a cabinet forces one specification decision before anything else: which amplifier class will drive the output stage. That single choice determines heat sink mass, power supply weight, enclosure volume, and how much headroom remains before distortion becomes audible. The practical conclusion for system builders: Class D dominates new professional audio module designs because it converts 85-95 percent of supply power into signal. Class AB remains the analog reference for transparent sound and predictable servicing. Class G and Class H deliver a middle path for high-power linear stages that need less heat. Class A and Class B matter mainly as concepts today, but their conduction-angle behavior explains every class that followed. What Defines an Amplifier Class? Every amplifier class is defined by the conduction angle of its output devices - the portion of each input cycle during which the transistors pass current. A device that conducts for 360 degrees stays on continuously; a device that conducts for 180 degrees handles only half of the waveform. The conduction angle sets a theoretical efficiency ceiling, because a conducting device that is not contributing signal still dissipates power. It also predicts the distortion signature of the stage. The classes below cover everything an audio system designer will encounter. Class C appears for reference only: operating below 180 degrees raises efficiency above 70 percent, but flattens the output so badly that it is restricted to radio-frequency transmitters rather than audio. Efficiency values are practical ranges cited in established electronics references and module datasheets; exact numbers depend on supply voltage, load, and operating level. Amplifier class conduction angle and practical efficiency in audio designs. Class Conduction angle Typical efficiency (audio) Main trade-off Class A 360 degrees 20-30 percent Lowest distortion, highest heat Class B 180 degrees 55-65 percent Crossover distortion without bias Class AB 180 to 360 degrees 50-65 percent Balance of linearity and heat Class C Under 180 degrees Above 70 percent (RF) Not usable for audio quality Class D PWM switching 85-95 percent Filter and EMC design needed Class G Switched supply rails 65-80 percent Multi-rail supply complexity Class H Modulated supply rail 65-80 percent Tracking supply cost Class A up to ~30% Class B ~60% Class AB 50-65% Class D 85-95% Class G ~72% Class H 65-75% 0% 25% 50% 75% 100% Class D delivers roughly three times the efficiency of the linear classes, which changes heat sink and power supply choices completely. Class A: Linearity at a High Operating Cost Class A output stages conduct for the full 360 degrees. A single device, or a pair running in single-ended mode, stays in its active region even when no input signal is present. That makes Class A the most linear topology of the analog families: there is no handoff between devices, so crossover distortion is absent by definition. The price is enormous idle dissipation. Practical single-ended Class A efficiency sits between 20 and 30 percent, so a 100-watt amplifier discards 200 to 300 watts as heat. Heat sinks grow, transformers grow, and running costs become permanent. In professional audio modules, full Class A output stages exist only at preamp level; within power amplifiers, Class A survives as the small-signal bias region of a Class AB input stage. Class B: The Push-Pull Origin Class B splits the waveform into two halves: one transistor pushes the positive half-cycle and the other pulls the negative half-cycle, so each device conducts for exactly 180 degrees. Theoretical efficiency rises to 78.5 percent, but the transition at the zero crossing introduces crossover distortion when neither device is fully in control. No serious audio output stage runs in pure Class B because the discontinuity is audible at low signal levels. Designers add a small bias current so both devices stay slightly on at the zero crossing, and that adjustment is what defines Class AB. Class AB: The Analog Workhorse Class AB adds controlled quiescent bias to the push-pull structure. Both output devices conduct a little at the zero crossing, eliminating the crossover notch, then step back toward cutoff as the signal grows. Efficiency settles between 50 and 65 percent in practical audio designs. A 600-watt Class AB module still throws off 200 to 300 watts when driven hard, so heat sinks with deep fins and sometimes forced air remain part of the design. Engineers choose Class AB when tonal behavior is the priority and enclosure size is permissive. The relationship between bias current, distortion, and thermal load is so delicate that manufacturers calibrate it over years of production refinement. That is also why engineers spend as much time on the output stage as on the drivers, because the amplifier module's contribution to sound quality is easier to hear than to measure. Class D: Switching for Efficiency Class D abandons the conduction-angle model completely. The output transistors alternate between full saturation and full cutoff at a carrier frequency well above the audio band, usually 400 kHz to 1 MHz, and the audio signal rides on the duty cycle of the resulting pulse-width-modulated waveform. An LC filter reconstructs the audio band at the output. Because a saturated switch drops almost no voltage and a cutoff switch passes almost no current, theoretical efficiency approaches 100 percent; real modules deliver 85 to 95 percent. The consequences for loudspeaker design are immediate. A 500-watt Class D stage keeps heat sinks small enough for a die-cast chassis, while an equivalent Class AB stage needs a heavy extruded profile and a larger transformer. Modern post-filter feedback corrects the distortion mechanisms of early switching designs, and well-implemented Class D modules pass blind listening comparisons against good analog amplifiers. The real engineering effort sits in the output filter, the EMI behavior, and the dead-time management of the switching stage. Suppliers who specialize in this area typically pair the switching core with a resonant or power-factor-corrected front end instead of treating the filter as an afterthought. EON522SUB Active Subwoofer Amplifier Module with LLC Resonant SupplyThis 500W Class D subwoofer module pairs an LLC resonant 800W supply with overload, short-circuit, and thermal protection, making it a practical fit for high-efficiency bass applications discussed in the surrounding text.View Product → Class G and Class H: Smarter Supply Rails Class G and Class H keep the linear output stage of an AB amplifier but feed it with a supply rail that adapts to the signal. Class G maintains two or more fixed rails, switching to the higher one only when signal peaks require it. Class H modulates the rail voltage continuously, tracking the signal envelope with a few volts of headroom. Output devices remain linear in both cases, so the distortion profile resembles Class AB, but the average voltage across the devices is lower. That reduces waste heat and pushes efficiency into the 65-80 percent range. The cost moves into the power supply: multi-rail transformers with switch-over logic for Class G, or fast tracking regulators for Class H. These classes suit subwoofer and line-array modules, where music with a high crest factor means the higher rail is active only for short peaks. The H-class approach is a common choice for bi-amplified enclosures with a linear transformer supply, which is why module suppliers list this combination as a standard configuration. Comparing Amplifier Classes in Real Modules The class decision is never made in isolation; it interacts with the power supply, the enclosure, and the duty cycle of the music program. The chart below shows why Class D is so attractive in portable and compact systems. 0% 25% 50% 75% 100% 0% 25% 50% 75% 100% Class D Class AB Efficiency versus output level for Class AB and Class D modules. Class D holds high efficiency far deeper into the operating range. Class D maintains high efficiency over most of its output range, while Class AB efficiency collapses at low listening levels. A 50-watt average output from a 500-watt Class AB module may sit at about 25-30 percent efficiency; the same condition keeps a Class D module above 75 percent. Over a touring season, that difference shows up in electricity cost, rack heat, and how often thermal protection triggers. Class recommendation matrix for common powered loudspeaker applications. Application Preferred class Reason Battery-powered portable speaker D Efficiency extends runtime and shrinks heat sink Mid-power PA monitor AB Predictable analog tone and simple supply Multi-channel line array D Low heat and compact PFC/LLC front end Subwoofer with heavy bass program D or H D for power density, H for linear feel Fixed installation AB, H, or D Depends on service familiarity and rail cost Understanding what an active power amplifier module contains helps buyers apply this matrix correctly. The class letter describes only the power stage; the supply design, feedback topology, and protection circuits determine real-world reliability. A subwoofer module, for example, combines a high-voltage rail with output limiting to survive continuous bass program, so the class choice and the protective features must be evaluated as one system. EON180S+2092 BTL Subwoofer Amplifier Module for Professional AudioFeaturing a 650W Class D BTL output and 800W switching supply, this subwoofer module includes protective circuits suited for continuous bass duty, aligning with the amplifier-class considerations described above.View Product → Anatomy of a Power Amplifier Module The cross-section of a modern module shows how the class interacts with everything around it. The input stage accepts balanced or DSP-processed signals, the driver stage shapes the switching or linear control, the output stage follows the chosen class, and the power supply sets the efficiency ceiling. The isometric diagram below shows the typical arrangement of these blocks in a self-contained module. Input / DSP Output filter Heatsink Power stage Typical block arrangement of a professional power amplifier module: input/DSP processing, switching or linear power stage, output filter, and heat sink. Frequently Asked Questions about Amplifier Classes Which amplifier class is best for professional audio? Class D offers the best balance of efficiency, weight, and heat for most pro audio modules. Class AB remains the analog-first choice, and Class H fits high-power linear stages. What is the difference between Class AB and Class D amplifiers? Class AB runs output transistors in the linear region, producing low distortion but wasting 30-50 percent of power as heat. Class D switches the transistors fully on and off, reaching 85-95 percent efficiency with an output filter. Are Class D amplifiers good for live sound? Yes. Modern Class D modules with LLC or PFC power supplies are widely used in line arrays and subwoofers; they handle high crest-factor program, stay cool, and reduce cabinet weight. Which amplifier class is the most efficient? Class D is the most efficient class used in audio, delivering 85-95 percent of input power to the load. Class C reaches even higher efficiency but is not usable for audio. Do Class D amplifiers sound as good as Class AB amplifiers? A well-implemented Class D module can sound very close to a well-implemented Class AB module. Output filter design, feedback loop, and power supply quality matter more than the class letter. What does amplifier class mean for speaker design? The class sets the conduction angle and efficiency of the output stage. 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