What to upgrade first, how DIN sizes and fascia kits work, what wiring you need, what fitting costs, and the mistakes that cause flat batteries and dead steering-wheel controls. Last checked: 16 August 2026.
Quick answer: what to upgrade first
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Upgrade in this order: front door speakers first (the biggest change per pound), then the head unit if you want Apple CarPlay, Android Auto or DAB+, then an amplifier, then a subwoofer, and finally sound deadening. Most cars leave the factory with the cheapest speakers the accountants could sign off, which is why a five year old hatchback sounds muddy at motorway speed even with a good phone plugged in.
Car speakers: coaxial vs component
Coaxial speakers put the tweeter in the middle of the main cone: one unit, one hole, straight into the factory door opening. Component sets split the tweeter out so it can sit on the A-pillar level with your ears, which images far better but needs a crossover and usually an amplifier.
Match RMS power to what the head unit or amp actually delivers and ignore the peak power figure on the box. Sizes are usually 6.5in in doors, 6x9in in parcel shelves and 4in or 5.25in in dash pods. Check depth as well as diameter, because a deep magnet can foul the window glass when it drops.
Head units: DIN sizes explained
Single DIN is roughly 180mm x 50mm, double DIN is 180mm x 100mm. Floating-screen units give a big display in a single DIN slot, and vehicle-specific units keep the factory look on curved dashboards. Measure the aperture with a tape before ordering.
Almost every fit needs three extra parts: a fascia adaptor so the unit sits flush, an ISO harness so you are not cutting the factory loom, and a steering-wheel control interface if the car has buttons on the wheel. A DAB aerial is the fourth item people forget. Cars where the radio also shows climate, parking sensors or trip data need a vehicle-specific interface to keep those functions alive.
Subwoofers, amplifiers and wiring
An active powered sub has the amp built in and often fits under a seat, keeping the boot. A passive sub in a box needs a separate amp and gives more real output.
Wiring is where jobs go wrong. Power comes from the battery on correctly sized cable with a fuse within about 30cm of the battery terminal, through a proper grommet in the bulkhead. Earth to a clean paint-free chassis point near the amp, and run signal cables down the opposite side of the car from the power cable or you will hear alternator whine that rises with revs.
What car audio fitting costs in the UK
As a rough 2026 guide, expect around £40-£80 to fit a straightforward head unit, £50-£100 for a pair of front door speakers, and £120-£250 for an amplifier and subwoofer install depending on the cable run and how much trim comes out. Fascia kits, interfaces and wiring kits are extra.
DIY is realistic on older cars with an ISO connector, provided you use trim tools rather than a screwdriver. Disconnect the battery negative first and know what you are unplugging on cars with airbag modules behind the dash.
Common car audio mistakes
Buying on peak power instead of RMS; forgetting the fascia kit, harness or steering-wheel adaptor; cutting the factory loom instead of using an ISO adaptor; speakers too deep for the door; an unfused power cable at the battery, which is a fire risk; running RCA leads alongside power cable and then blaming the amp for the whine; not declaring the modification to the insurer; and skipping sound deadening, then wondering why an expensive speaker still rattles the door card.
Frequently asked questions
What is the best car audio upgrade for the money?
Front door speakers. On most standard cars the factory paper-cone speakers are the weakest link, and a decent set of coaxials plus the correct adaptor rings transforms clarity for far less than a new head unit.
What is the difference between single DIN and double DIN?
It is the size of the hole in the dashboard. Single DIN is roughly 180mm x 50mm, double DIN is 180mm x 100mm. Measure the aperture before ordering and check whether the car needs a vehicle-specific fascia adaptor.
Will a new stereo break my steering wheel controls?
Not if you buy the right adaptor. Most cars need a CAN bus interface or a steering-wheel control lead matched to the vehicle; without it the buttons stop working and on some cars the ignition-live feed is wrong too.
Do I need an amplifier for new speakers?
No, most modern head units drive replacement coaxials fine at around 18-22W RMS per channel. An amp is worth it for component speakers, higher clean volume, or a passive subwoofer.
Does aftermarket car audio affect my insurance?
It can. Modifications should be declared, including a new head unit, amplifier or subwoofer. Most insurers accept audio upgrades; not telling them is what causes claims trouble.
Can I fit a car stereo myself?
On many cars yes, with trim tools, an ISO harness and a fascia kit. Cars with amplified factory systems, fibre-optic audio, or a stereo that also controls climate are best left to an installer.