In general, this is easy to explain: it seems that the capabilities and sound of the system mainly depend on it. Unfortunately, this is not so: you certainly need to pay attention to acoustics. We’ll talk about it today.
The simplest acoustics are designed for the so-called sound "background" in the car. Indeed, if you listen to the news on the radio, why the extra waste? Quite possibly, even the simplest broadband speakers will be enough. Their frequency range does not give either deep bass or truly high frequencies, but for those not too demanding on music, all this will not cause obvious disgust. By the way, in most machines such speakers can be installed already at the factory.
If you move up the price range, then the next speaker is coaxial. The design of such speakers is actually … a few! The playback range is divided into areas - each "subordinate" to its own dynamics. Special filters (crossovers) are used as “separators” of the electric signal, and then each speaker has its own dynamics. For more serious models, the crossover can be in a separate case, but on models it’s easier sometimes they even cost a capacitor (the simplest filter) on the speaker case. Properly selected filter components play a significant role in the sound of acoustics in general. The advantage of a coaxial speaker over a broadband speaker is its wider coverage of the reproduced frequency band. The main residence of coaxial acoustics is all the same regular places, but the most expensive representatives of this “breed” can be found in serious projects - with the manufacture of podiums and other tricks.
The next variation on the theme of acoustics is the component one, the most common among car enthusiasts who are not indifferent to the sound. The playback range - just like the “coaxials" - is divided into several parts. Here all the same crossovers, but the speakers are not made in a single design, but individually - by components that no longer “interfere” with each other (for example, tweeters do not stand in the way of low-frequency wave propagation). But this solution has a minus: “coaxial” plays “from one point”, and component acoustics - as it is installed. Hence the conclusion: the speakers should be as close as possible to each other and this is especially true for mid- and tweeters in a three-way system. A significant role in the formation of the sound stage is taken by the tweeter. Due to its small size, its position is not difficult to vary, and if it is successful, it will seem that all the acoustics are located at the top. You know, listening to music "from under your feet" is not very cool …
To reproduce lower frequencies (deep bass), you will need speakers with a large diffuser area. This dependence is somewhat reminiscent of the well-known: in some cases, the car engine power is proportional to the displacement. Thus, for reproducing bass, installing forward 16-17-cm speakers will be preferable to “younger brothers”. True, for sounding in the region of the lowest audible frequencies and they will not be enough, not to mention the options of "13 and 10 cm." The way out is to install a subwoofer (it will perfectly complement the playback area of the very bottom), but this will increase the cost of the system by an order of magnitude!
Almost any speaker working in the field of mid and low frequencies also implies a specific acoustic design, roughly speaking - a box. The situation is somewhat similar to springs and shock absorbers in a car: the role of the latter in this case is assumed by the volume of the box. For example, speakers with a size of 6x9 inches do a good job with bass - the desire to "stick" them into the front door is quite reasonable. But here you are facing the very nuisance with the volume that they play. "Ovals" are usually inserted into the rear shelf, and this is work "on the volume of the trunk." In this case, it can be considered infinitely large (this is already hundreds of liters), but the door is much smaller (almost 10 times) - this is a box. So, if you don’t have the necessary bass, there’s nothing much to be surprised about. Speakers of standard size “10, 13, 16 cm”, etc. most are designed specifically for the volume equivalent to the door or even smaller. But along with general trends, there are exceptions. Volume recommendations can often be found either on the box or calculated by Thiel-Small parameters (but more on that another time).
Car sound is now in fashion. And for a truly stunning result, you may need an amount in excess of the cost of the car. Therefore, the surest way is to listen to what you are about to acquire. And don't be afraid to experiment.