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Installing An Active Sub

Mod Description
Fitting an active sub is very easy, a handful o connections and you are done
Mod Details
PremiumNo Difficulty Mod ID829 Creditevilution For450 Fortwo451 Fortwo452 Roadster454 Forfour Link Copy to Clipboard

Wiring An Active Sub

Active subs have the amplifier built in so you have less connections to worry about. Here is a very typical layout. You will have ground, switched live, permanent live and an audio input. The audio inputs may be either or both high or low level. High level inputs connect to your speaker outputs, low level inputs connect to similar low level outputs on the rear of most aftermarket stereos. The standard smart stereos do not have low level outputs.

You may also have a wired remote connection.

OK, One At A Time

Ground, also called earth. Symbolised by GND.

Connect this terminal to a ground point in the car. There are several around the car. They will be a stud with other wires connected to them. Remove the nut, fit the ground cable to it and replace and tighten the nut. Attach the other end to the GND connection on the sub. It is a good idea to cut this cable down so you don’t have excessive cable. Having too much cable can increase the amount of interference that the sub picks up.

The next connection is REM, also called remote. It is a switched live cable (usually blue) that turns the amp on. Do NOT connect this straight to the battery or it will flatten it when the car is off.

The switched live connection can be picked up from the cigarette lighter socket or the switched live auxiliary connections on the side of the SAM unit. Ideally you should use a SAM fuse holder but as it only uses a very low amperage I usually crimp a spade connector on the cable and push it in.

Permanent Live, also shown as +12V.

Your active sub should come with the correct wiring kit. The permanent live cable will probably be yellow but could also be red. Chances are it will have a ring terminal on the end of it. If for some reason it doesn’t you will have to crimp a ring terminal in place. Attach the sub end of the wire first.

Expose the battery and locate the positive terminal.

Remove the nut, put your live cable over the stud and refit the nut tightly.

High Level In, also known as high power input.

The standard smart stereos will require you to use the high level inputs as they do not come as standard with low level outputs. In this instance you have CH1- & CH1+ on the left and CH2- & CH2+ on the right. Some active subs will be labelled L- & L+ and R- & R+.

Remove the stereo and find the speaker wires, determine the left + & – and the right + and – wires. Splice into the existing wires with the wires going to the sub.

Low Level In are RCA connections that match similar connections on the back of most aftermarket stereos.

Your aftermarket stereo may have a left and right audio output (colour coded white and red). Or, on my stereo, it had a dedicate subwoofer output. Again white and red but only outputs lower frequencies.

With stereos that have a dedicated bass output, you have better equaliser controls in the settings.

Never cheap out on the RCA leads. They are the biggest cause of static and electrical noise if you buy cheap. You want something long enough (2M is usually fine) and something shielded. Something like these.

If your active sub has a wired remote control it usually just plugs straight into the sub.

They generally use a LAN or telephone style RJ45 connector. Plug it in and run the remote to somewhere suitable. I used some 3M VHB double sided tape to fix mine under the handbrake.

Be aware that these remotes are usually brightly illuminated so don’t put it where it’ll affect night driving.

Types Of Active Sub

Here is a list of under-seat (compact) subs.

Running Wires

The wiring that comes with all aftermarket subs is always far too long. They give you enough slack for normal length cars. It’s easier to hide the excess cable than it is to shorten the cable. I usually just stuff it all into the battery tray. Yeah it’s a mess but…

…with the foam foot rest block in place, it’s all covered.

The footwell carpet is easy to lift to help run the wires.

Most models of smart have a separate front and rear carpet. You can see the join bside the seats.

You can remove the seat if you want to but I find it faster to just push the wires under the carpet in front of the seat, push the seat all the way forwards, stuff your hand in the join of the carpet and pull the cables through.

Keep as much of the excess cable in the battery area. That can’t be helped with the remote wire though. With that I just coiled it up and left it under the seat.

Best Place To Put Them?

Under or behind the seat is the most popular as they don’t take up much room. However, some are too big and can either be placed in the passenger footwell or, in the instance below, in the boot (trunk). Velcro (hook) tape is usually strong enough to hold them in place.