Ignore the above, an active sub is a good addition and an easy way of beefing up the sound
Sorry for getting lots of people are happy with noise.
With the standard head unit and front speakers, adding a sub just introduces low tones, will not complement the sound stage.
The weak link is the head unit; until this is changed there is no way of improving the sound. Adding a sub just gives a BOOM BOOM washing out the poor mid-tone’s already produced by the head unit. People then try to compensate by turning up the treble.
This then leads to a BOOM BOOM, TISS TISS, not a good sound.
Adding lower base to an ICE install needs to be balanced and matched to the intended choice in music. Following some very simple rules can dramatically improve the overall quality of sound, you don’t need to spend silly money on this (doing so will transform things, but that a different story).
Purchasing off the internet or places like Halfords is a poor choice. Go to any reputable ICE dealer that has demo cars or demo room and find out what it really is all about. A balanced sound system is enjoyable; throwing things together will always just produce noise.
Surprisingly if done right you can have base too loud to listen to in the car, but when trimmed down you can have a system that plays very loud emphasizing each sound on a track.
Even on a budget (bit more than £100) you can put together ICE that will bring out sounds in your music you never realised was there. The sound of a drum brush being topped then dragged over a base drum, each reverb of a snare drum, full resonance from a cymbal.
Acoustically a car can be setup better than the average living room or bedroom, get the sound point at ear level to converge over the handbrake and you now have a soundstage people will envy.
Most of the time I’m hitting my head against the wall, but for those who have actually taken the time to sit and listen to a balanced ICE system, know exactly what I am on about. You don’t have to go to the extremes I did in competition but the same basic rules apply.
Before you do anything spend £30 on some sound proofing and dampen your front speakers. 100% guaranty you will hear a difference. Now with luck, you’re on the right road to improving the sounds in your car. Just adding a sub is not the way forward for anyone, you cannot make a silk purse out of a pig’s ear.
