Factors to consider while buying Speakers:
Active Or Passive Speakers - Speakers, especially bookshelf speakers are engineered in two formats - Active & Passive. Active speakers do not need external amplification and are relatively easy to set up and connect. They can be plugged into a power socket and are ready to use. Passive speakers need external amplification and don’t have to plug into a power outlet, which may open up more placement options for them in your space.
Wired Or Wireless - Depending on your preference and needs, you may choose to go for a wireless portable speaker that you can carry with you or move from one room to another. While in the other case, if you are someone building a listening room or setup, you may prefer to go for wired Bookshelf speakers as they can be placed in a particular position for optimal listening pleasure.
Connectivity - This defines how you connect your source device to your speakers. Many wired speakers come with connector options like XLR and RCA stereo, and wireless speakers offer connectivity via Bluetooth and Wi-Fi protocols. This is something you need to consider depending on your requirement and source setup.
Frequency Response - Every Speaker advertises its frequency response, which is the effective range they can reproduce of bass, mids, and treble. Some Speakers have a frequency response beyond what humans can hear (5 to 35,000 Hz for example). What you should look for in a pair of Speakers is accuracy and keep in mind its frequency response curve.