Why does the stereo sound so quiet?

“Who Stole the Watts?”

We should say at once that this is the simplest and the most widespread and popular configuration of car audio system – four speakers (a pair of front and a pair of rear), connected directly to the head multimedia device, in common parlance it is still called “head unit”. Without additional external amplifiers and various other components, which are so loved by fans of advanced car audio!

So if you think that the more expensive the model and more authoritative the manufacturer of car multimedia device is, the higher power of its sound is, accordingly, you’re wrong!

Regardless of price and brand, size (1 or 2 DIN), the diagonal of the display and the availability of various functions and options and the 15-year-old “cassette player” and a modern touchscreen “android” have the same output power sound path – 4 channels of 45-55 watts. This combination of numbers appears on the packaging, in the passports and instructions of boomboxes as from the market flagships, as from the brands of the second and third echelon and frankly Chinese-bottom.

In principle, at first glance, 4×45 or 4×50 is not bad at all. Even a lot! Almost 200 watts of sound! But remember some home audio system from the Soviet era – an amplifier like “Kumira” or “Briga” in tandem with the notorious S90 speakers – only two channels of 35-50 watts, and at full volume it shook three floors of Khrushchev building at least! On the other hand, four channels of 50 watts won’t shake anything, except maybe for the rear view mirror on the windshield. Sometimes you want to play something driving and desperate, but it doesn’t work… The sound, let’s be frank, is weak even at maximum – it’s absolutely unclear where all these impressive 200 watts are… In addition, even without reaching the volume limit, there is a noticeable ear distortion, caused partly by the boombox amplifier overload and partly by the rattling of the weak speakers. So why does this happen and “who stole the watts”?

How many watts are actually in the “4×50”?

As an amplifier in 99% of the head units (even the simplest, even the most sophisticated android) is a specialized powerful chip, which contains four independent amplifiers with a common input (the very four channels) and separate outputs for the four speakers. The chip generates a lot of heat during operation, so it is installed on the radiator located on the back wall of the multimedia device case.

We would not like to delve into rather boring formulas for calculating the RMS value of the sinusoidal voltage at the amplifier output, as well as into the features of bridge circuits of amplifiers, explaining the principle of the output power formation. It is clear to electronic engineers, but the information torn out of context without a thorough preliminary introduction will be incomprehensible and uninteresting to those who are far from electronics.

Therefore, straight away conclusion in the dry residue: maximum values of output sound power (not peak, advertising, but honest, long-term!) of amplifier fed from 12 volt voltage, cannot exceed 16-18 watts per channel without appearance of unacceptable sound distortions!

Yes, it is possible to squeeze out 20-23 watts with a croak and crackle, but we are not going to consider it.

So, practically all “car radios” (or “head units” or “car multimedia centers” – whatever you like) actually have four channels of about 16-17 watts of quality sound. Total – 64 watts. And not 200 watt… Not that it’s not enough, but it is more than three times less than we expected…

To answer the begging question “why do some car amplifiers produce hundreds of watts from the same 12 volts?”: everything is simple – inside their cases there is a powerful converter which transforms 12 volts into high voltage power supply and often it is bipolar.

Where is the deception?

But why on the boxes, front panels and even in the manuals of all head units, do they write not “4×16”, but much nicer “4x50W”? Ok, if it were the Chinese from Aliexpress, who lie without fear of the devil, but why the biggest world companies from the first ten manufacturers of car-audio allow themselves that? Alas, this is the established practice… The deception here, as always, is very conditional, which is not a legal deception. The union of engineering and marketing has formed a deceptive tradition, which eventually became the norm.

The fact is that in the circuitry of the majority of modern amplifier chips, designed for use in automotive 12-volt audio equipment, the so-called “technology of volt-addition” is used. The essence of volt-switching is generally simple and understandable even to those who have not graduated from the radio department.

As we’ve already said, 16-18 watts per channel is practically the maximum achievable at 12 volts. However, in the circuit of the head unit audio circuit, there is a capacitor, also charged to 12 volts, which the amplifier chip connects if necessary in series with the supply voltage. It connects it at power peaks, when the input of the amplifier is a high level signal and it needs to be amplified proportionally and without distortion. Accordingly, for a short time the supply voltage increases, and the output power rises. And considering the fact that the certification measurements (in order to provide beautiful figures in the advertising and manual) are also carried out at the maximum voltage of car on-board network (up to 14,4 volt and even higher), formally the manufacturer has a reason to announce the output of head unit as “4х45W” and even “4х55W” relatively honestly and without fear of legal claims…

So there is no cheating? Yes, there is!

Well, since the issue is solved with that very “volt additive”, then the high power of the head unit in total 200 watts is still real, right? Actually – also no…

The thing is that for effective work on the principle of such “doubling” of supply voltage, the capacitor of “voltaboost” should be of great capacity and be able to charge very quickly. In fact, it is small, and only enough to handle a short peak pulse. To put it simply, when you switch on a dynamic music track the amplifier will work the first drum beat, giving out 45 watt for a short while from each speaker, but all the next ones won’t… The volume knob is turned all the way up, the signal from the source (radio, disk, flash drive etc.) is high, but the amplifier can’t handle it and overloads, grunting and wheezing. So, in fact, the role of “volt-additive” technology in 12-volt amplifiers of traditional and most popular circuitry is only a “legal cover” for manufacturers of car audio equipment…

By the way, there is some purely technical sense in the real (rather than advertising) power, which is produced by car stereos. In fact, even 60-70 honest total watts from four channels in continuous mode is a decent power, which is accompanied by the emission of the incidental heat on the chip, and the cases of boomboxes have very limited opportunities for arrangement of the effective heat sink in them. A radiator with the dimensions like on the photo below is a typical radiator of most “two-hundred-watt” head units and its area is just about enough to take heat away from the real 4×16-18 Watts… If the real 4×45-55 Watts would be in the head unit, this weak piece of aluminum wouldn’t be able to handle it!

Is 4×16 watts the limit? After that, only an external amplifier?

It turns out that it is impossible to amplify the audio system of the simplest configuration by buying more expensive, more branded, more functionally advanced head unit… This is partly true: whatever “head unit” is, its power limit is the declared 4×45-55 watts, which in fact is 4×16-18 watts. It makes sense to set more qualitative and powerful acoustics instead of regular cheap stuff, only using the “head” as a source of a weak signal, and the amplification is carried out by the external amplifier.

But, again, not everyone is ready to build car audio system with external amplifier. A lot of car owners dream of “making it louder” with little effort: simply installing more powerful speakers and connecting it to a more powerful “head” without creating and laying additional wiring, without installing an amplifier and the like. And there is a way out – head units with built-in amplifiers of the so-called “class D”, a relatively new class of amplifiers. These amplifiers are able to output a REAL 45 watts per channel – that is almost 200 WATTS of REAL, let’s repeat, power!

Frankly speaking, marketing gimmickry tactics didn’t disappear and advertising numbers on boxes and in instructions of such devices promise even 100 watts per channel and 4×100 in total… However, I don’t care about these tricks – we don’t need 400 watts, but 4×45 without fools – these are characteristics of an external entry-level amplifier even without any amplifier: the base boombox works!

How do D-Class stereos work?

A few years ago, audio equipment with output stages operating in the so-called “D-Class” began to appear on the market. This letter does not stand for “digital”, as you might think, although such amplifiers are often, but mistakenly, called “digital”. They are not digital – ordinary analog, just signal amplification in them occurs according to an entirely different principle than in traditional audio equipment, both in cars and at home.

The basic idea of class D is the use of pulse width modulation. Whereas in conventional amplifiers music is processed “as is,” with the amplitude of the input signal increasing without any change, in Class D the input signal first modulates the carrier frequency (very high, hundreds of kilohertz), and the resulting “mix” is then amplified. The signal with which the amplifier stages work has always the same amplitude regardless of the volume, and the “music is encoded” in the pulse duration. Pardon the slight slip into electronics – in simpler terms, a Class D amplifier is interesting because it provides the highest, tending to 100% efficiency. For the average user, this means that the amplifiers are dramatically reduced in size to an unbelievable degree, emitting a minimum of heat, which is dissipated by tiny, literally symbolic radiators. Accordingly, the space freed up in the case can be occupied by electronic modules that increase the supply voltage, which will raise the output power honestly, without cheating!

Modern head units with class D output stages really increase the sound power of the simplest audio system configuration – without any additional external amplifiers. The only nuance when installing such head units is the need to pull a separate power plus wire to them. For the section of the weak wire in the standard and universal car ISO-connector for connecting head units, as well as the fuse in this circuit is designed just for those very 4×16, rather than an honest 4×45…

How to find a D-Class head unit on sale?

Despite the obvious and obvious advantages of head units with D-class amplifiers, they have not yet displaced the traditional ones due to the inertia of manufacturers, who prefer to promote the approach to the reining in of audio systems through the installation of external amplifiers, which provides a larger “average check”. At the same time, they make powerful external D-class amplifiers more active than headphones with such amplifiers on board. Nevertheless, in the range of many brands of car-audio (if we speak about solid brands, from the first ten) there are necessarily one or two models of head units with D-class amplifier. The presence of such amplifier may not be reflected in the description on the website or packaging, but its power output – as a rule, all such models are announced as “4×100 W”. Visually they often have no radiator on the back wall, there are usually no other differences. Some manufacturers make “hybrid” variants: they offer 4×45 D-amplifier (claimed as 4×100!) as a separate tiny unit, but not as a separate remote one, but as an “attached” one, fixed on the back of the radio by the analogy with the way mini office computers nettop are fixed on the back of the computer monitors.


The author apologizes to the prying readers who find the oft-used word “boombox” piercing to their eyes and ears. Alas, this woefully outdated and has long been a slang term used for two reasons: the undiminished recognition of it in the masses, and the lack of a fully adequate modern equivalent. The widespread “head unit” is an ugly combination of letters, which has no clear connection with the meaning put into it in the audio context; not much better and long and boring analogue is “car multimedia center”…


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