One of the most commonly integrated pieces of technology present in nearly all spheres of life from our cars to our smartphones, speakers are ever-present. Regardless of their design, their job is to produce audio output for us to be able to hear. A fluctuating electric signal runs through the coil which temporarily becomes magnetised and is repelled or pulled by the permanent magnet inside which in turn makes the cone it is connected to pulsate and thus pump sound into the air. How loud speakers are is measured in decibels (dB). Today we get such high-quality speakers that hearing music on them is a treat as it should be! From headphones to portable speakers the quality available is near unreal. Though one needs to be careful as in the long run too much loud sound can damage one's hearing, so music should be heard at a comfortable volume level with the highs balanced and not too sharp.
Tiny versions are built into laptops and smartphones but these are usually not very loud and miss the lower end, the bass that is such an important component of music. They can work for movies on the laptop and for calls that are on speaker-phone when using a smartphone, which is more the intended usage.
Today a very common use of speakers is Bluetooth speakers that are portable and run off a battery, connected to our smartphones for the input and a relative range depending on what chip is powering the Bluetooth in the speaker and your phone. These are usually complete devices with the speaker producing the high and low frequencies from one source. They tend to have an AUX input as well which tethers a short cable so one is a little restricted as to how far they can step about, one could buy a longer cable separately. These same kinds of speakers at times also come with weather proofing so a bit of rain might not affect their running and definitely add to one's time outdoors. The smaller ones pack a little less bass, but with the plus of not taking up too much space when you are carting it.
Speakers in headphones or earphones have such a large catalogue as well, brands are competing continuously to provide better audio daily! Also a vie for more comfort and less ear fatigue given that the speaker is so close to one's ear.
An older version has the speakers separate from the bass-bot and connects to a music playing device through AUX and Bluetooth at times. At a time these were known as computer speakers. Multimedia home systems have a 5.1 surround sound set up which means you have 5 speakers spread out to create an immersive environment when you are watching a movie, the directional abilities add to where the sound is coming from making you a part of what is going on on the TV! At events like concerts, large speakers are used that are enough to produce sound ample for a few hundred people. These are powered through a more complex system of amps and connected to a mixer so the sound can be controlled and sculpted for the space they are being used in.
Car audio has a whole other level of crazy sound available to people, speakers from so many brands specifically built for that space. Essentially 2 good speakers could set you up well enough to enjoy your music but that is a cultural sphere where people build insane sound systems that keep getting louder and louder. Another basic usage of speakers is PA (Public Address) systems which are set up in hospitals and airports in case of and emergency or if any other important announcement needs to be made.
All these various uses have so many different brands producing specific speakers for the devices at many different price ranges and for varied environments, some of the most known brands are Harmon Kardon, Bang & Olufsen, JBL, Bose, Sennheiser, Klipsch, Yamaha, Sony and Bowers & Wilkins to name a few top producers of the speaker!