Let’s start from the beginning: what exactly are professional study monitors and what are they for?
It’s a type of monitor designed specifically for critical listening during the various phases of production and musical creation. Essentially, the job of a studio monitor is to allow you to listen to a source of sound in its purest and most transparent form.
There are two different geek groups of person in this sector: those who listen and those who produce. Those who buy a monitor to listen to music, usually choose those that artificially accentuate certain frequencies, so that the music is more attractive to heard (usually, they are low frequencies with bass-boost).
Instead, producers need professional speakers to return the image of a sound as faithfully and honestly as possible. This means that the frequency response must be flat, without any device that amplifies one or more frequencies.
The purchase of studio monitors is, therefore, essential for those who want to mix their pieces autonomously.
Passive - Active
Passive monitors are those that need an external amplifier to operate. On the other hand, active monitors have an integrated amplifier and do not need any amplifier.
No model is better than the other, but active monitors are certainly more effective, and you will not have to worry about matching your speakers, assuming the manufacturer has built the best possible amplifier for the technical characteristics of the speakers.
In general, the model name of the speaker is determined by the size of the woofer, which is measured in inches. The JBL LSR30 5 has a 5 "woofer, while the JBL LSR30 8 has an 8" woofer, and so on.
The sizes of the woofer are particularly important in the response to low frequencies. In simpler terms: a larger woofer plays looser bass. And if you produce electronic music, you know how important it is to have an image of the most faithful low frequencies possible. Another way to do this is to add a subwoofer to 5"or 6" monitors, which is designed to reproduce those frequencies in the best way (WARNING! If yours is a home-studio, think twice: a subwoofer can cause you a lot of problems with the neighbors).
The power of a monitor is measured in watts. The higher there are, the more volume you will hear. There is no need to exaggerate in size, because, in any case, there are near field monitors (which should be placed close to the listener.
The range of frequencies audible to the human ear goes from about 20Hz to 20Khz. Monitors specify which frequency range they reach and can be something like 35Hz-35Khz. A frequency starting at 35Hz means that the monitor will not reproduce frequencies below that threshold.