Do you need an amplifier for subwoofer speakers?

You will need an amp or a head unit powerful enough to drive the sub. Typically subs are best pushed through an amp.

it depends or how many watts your stereo is putting out for example: lets say it gives out 50 watts per channel(Speaker) and each speaker is 100 watts rms your losing 200 watts rms (multiplied by 4 speakers) that could make your system less powerful so you would use an amplifier to get all 100 watts per channel in your case 4. P.S.- those speakers are call 2-way speakers cause it has a mid-range driver(speaker) and a tweeter their just considered 2-way speakers

there are 2 kinds of speakers,one type is for mids and highs and some lower tones,these are for your doors and rear deck of your ride.and can run off your stereos internal amplifier for now and can also run off an external amp set up to power speakers for mids and highs,the key is buying the right stereo/HEAD UNIT this is the brain of the system, with all the proper inputs for running 2 amplifiers one for door and rear deck speakers its called a 4 channel amplifier.then there are sub woofer speakers that are only for the bottom end of the sound spectrum.these are best powered by a class d or mono amplifier,this is built for powering sub woofers,its a single channel Amplifier.and the best way to power them.first you need the right head unit to run external amplifiers and i pod or i phone if needed.its the brain as i said earlier.then you need the class d amp a sub woofer en closer and sub woofer.and a wiring kit for the amplifier to run the sub woofer.now to run your speakers for now there is an internal amplifier in your new head unit to run these speakers for mids and highs so now you have a working stereo and a powered sub woofer if you read the instructions that come with each piece of equipment and wire it right.then later on when you have extra cash you can buy a 4 channel external amplifier to run your door and rear deck speakers with a lot more power so buy good brand name equipment ,all of the pieces.starting with the door and rear deck speakers.then you remove the speaker wiring from the internal amp and attach it to the external amplifier itself and you add 2 more RCA cables like you will get with wiring kit for the sub woofer amplifier there's only one in that package,so for your door and rear deck speakers to run off an external amplifier you need 2 more RCA cables for this purpose.they plug into the rear of the head unit and into the 4 channel amplifier,and you have to learn what the remote turn on wire for the amplifier is its marked on the rear of the new head unit and has to be attached to each external amplifier,this is how its powered up and down with a turn of the key. then the power and ground and were they go.so im sure there's plenty of sht here to wrap your head around.and there's also a wiring Adapter that connects to your new head units wiring harness and plugs into your factory wiring harness under the dash were you unplugged your factory head unit from.go to wall mart to the car audio area and tell them the yr make and model of your ride and they will sell you the right plug in for your car.they call it plug and play.no need to be cutting any wiring under the dash this is a no no.well that is my typing lesson for today lol,good luck this is how its done and there's many how to videos on youtube.com/car audio or go to the electronix warehouse.com/education and you will get the basics from there to.