Why are soundbars so much better than TV speakers, and dedicated speakers better than soundbars? It's about volume (and not the one on your remote)

If you've read our coverage of the best soundbars at all, you'll know that we recommend them as a huge upgrade over the speakers that are built into most TVs. Even the best cheap soundbars will be a massive improvement over the speakers in not only budget TVs, but lots of mid-range TVs too.

Of course, if you go reading about soundbars in home theater communities online, you'll find that people consider them to be the work of the devil, and that anything except a system with dedicated separate speakers is a fool's errand.

There are reasons for all of this, of course – there very much is a sound quality hierarchy, from the built-in speakers, through to soundbars, up to home theater speakers. And that's due to physics.

The built-in speakers on TVs have to be small, especially in today's world where TV makers want to brag about how thin the sets are. And to avoid them taking up space on the front of the unit, they're often downwards firing, so they're not projecting directly towards you.

Speaker drivers make sound by vibrating and moving air, and being able to make a more powerful sound, and in particular being able to make mid-range and bassy sounds, requires moving further and displacing more air.

The easiest way to do that is by having a larger speaker, which is why bass-providing subwoofers are the biggest kind of driver (whereas tweeters, which produce treble sounds, are very small). It can also be achieved by having the speaker membrane move more deeply forward and back (known as 'high excursion'). Both of these require more space for the speaker to sit in, though.

And remember, you need space both in front of and behind the speaker drivers, as well as the driver itself being a large 3D object. And the bigger a speaker is, the stronger the structure around it needs to be to absorb the vibrations it creates in reaction to the generated sound – you don't want to 'hear' these sounds, but the energy has to go somewhere. Again, physics.

So the speakers in TVs are not very big, and are able to move a very limited volume of air, meaning that they're limited in their dynamic range, and they will get more distorted as you turn them up.

So how can we add more space for bigger speakers in a unit that's still pretty slender and will fit with a TV? Soundbars have been the answer – they can face directly towards you, include larger speaker drivers and a deeper frame to accommodate them, have a heavy structure to absorb unwanted vibrations better, and many come with a separate subwoofer so that there's no trade-off with having a big hefty bass driver. Good bass is supposed to be directionless, so it can just go somewhere else; easy.

Some of the best TVs for sound have something a lot like a soundbar built into their structure, and they don't worry about being taller and thicker as a result. Same principle, they're just cutting out having a separate unit.

The best Dolby Atmos soundbars will also take the opportunity to include speakers at different angles, and use sound processing to create a positional feeling to elements in the audio, using a combination of having dedicated width or height speakers, and 'psychoacoustic' tricks, where tinkering with the timing of a sound element, for example, can change how we perceive hearing it. The idea is to make the sound feel like it's coming from more directions than just a small bar in front of you.

Soundbars are still small in size, of course, and some get around the limited physical volume by using multiple identical speakers, for example, which is another way to move more air at once in a particular part of the frequency range. They also often use oval 'racetrack' drivers instead of circular ones, again as a compromise between being able to move more air but not to be too tall.

For example, a soundbar might only be able to house a driver that's two inches tall, but by using a racetrack driver that's three inches wide, rather than a circular one, then you've got 50% more surface area. (Not all of this is useful surface area, but you get the idea.)

But we're still talking drivers that are three inches in size, and not even three inches and circular. Capable, but not the hardcore stuff.

Switch up to real home theater speakers, that can be as tall, wide and deep as they want, and you'll be looking at drivers that are between four and seven inches within the main speakers, while subwoofers will be between eight and 15 inches typically.

And again, you might have multiple of these drivers per speaker. Floorstanding speakers might have two or three large woofers with one smaller tweeter, while it's common for subwoofers to have two 12-inch drivers in one box.

This means that they're capable of a wider range of sound, and are going to be a lot louder without straining detail. The sound also tends to become more natural and dispersed from larger speakers, so it'll feel more like sound is coming from the right area in the room, not directly from a small point.

Speakers like this will be heavy too (very heavy in some cases) – not just because the drivers, powered by hefty magnets, become large and weighty themselves, but also because absorbing all the unwanted reaction vibrations from a larger and more powerful set of speakers requires a heavier and stronger body for the speakers to sit in. There might be a metal skeleton, multiple layers of wood, and a load of resin all sitting inside a simple-looking wood finish.

It all comes down to area. The size of the speakers, the volume of the air moved. Clever processing and other tricks are used, very successfully in some of the best TVs, to create a bigger and clearer sound, but you just can't fight physics.

Soundbars have bigger and better-quality drivers than TVs do, and dedicated home theater speakers step it up again.

But obviously, there's a huge convenience factor to all of this. Some people will choose a high-end soundbar with rear speakers because they don't want the cables and connectivity wrangling that a separate system entails. On the flip side, some of the best stereo speakers are active speakers with built-in amplification and an HDMI eARC input, meaning they can work with a TV as easily as a soundbar does, but with bigger sound.

Which route you go will come down to whatever works best for your environment, but if you find yourself wondering why they can't just make TV sound as good as soundbars, or why hardcore home theater fans look down on soundbars, now you know: physics.

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