When replacing the factory head unit with an
aftermarket one, consider wiring-in the new unit in so that the original plug
remains intact. This can be easily done if instead of cutting off the old plug,
you make connections to the wires upstream of the original plug. The advantage?
When you sell your car you can easily remove the new head unit and then simply
plug-in the old one – returning to standard is then just a 5 minute job.
Remember, you seldom get extra for your car even when it’s fitted with a better
than standard sound system. (Of course, to be able to do this, you’d better keep
the old head unit!)
However, there’s one area where instead of making
the connections to the original head unit’s wiring, it’s best to put in some new
wiring. And that area is the power supply. Most factory head units have very
small gauge power supply and ground wiring, and if you’re not to suffer a
voltage drop when using the internal amp of a high powered head unit, you’d
better run new wires to supply it with the needed juice.
If you do lots of long-distance driving and you’re
installing a UHF CB radio (which, even with mobile phones, can be a real life
saver), consider wiring it so that it’s always fed power. That is, it’s not on
an ignition-switched circuit. The downside is that you’ll have to manually turn
it off when exiting the car, but the upside is that it can be used in an
emergency even when the ignition key isn’t available.
People love ignoring the in-built four-channel amp
in a good head unit, instead fitting an external four channel amp to run the
front and rear speakers. (We’re leaving the sub out at this stage.) That’s of
course fine, but in many cases one of the pairs of speakers can be run by the
internal amp with no loss in quality. For example, if you’ve got a sedan, the
rear speakers can be optimised to use the boot volume and so can develop good
bass. Because bass needs power, it makes sense to run those speakers off a
dedicated amp. But the front speakers – usually stuck in the doors or the dash –
are never going to sound fantastic - there’s simply not sufficient space behind
them. In that case you may use the head unit to drive them direct. The saving is
that you can get away with a two channel amp, or if using a four channel amp,
bridge two of the channels to drive the sub.
The above approach works even better if you make
the fronts operate just as mid/treble units. The easiest way to do this is to
install crossover capacitors to stop the deepest bass reaching the small
speakers. In a 4-ohm system, a non-polarised 400uF capacitor wired in series
with the speaker feed will roll-off frequencies below 100Hz. You’ll need two
(one for each front channel) and they’ll cost you about AUD$15 each from an
electronics store like Jaycar. That’s a total of thirty bucks – but still cheap
performance.
When mounting navigation screens, take your time
and think through the various locations. Portable stick-ons on the windscreen
can easily obstruct driver vision, increasing front-angle blind spots. They can
also badly reflect in the windscreen at night, making for a nightmare
distraction. (And, talking about night use, make sure you know where the dimmer
control is!) Permanently mounted nav screens should be located so that they also
don’t reflect in the windscreen, are shaded from direct sun (most displays
remain visible but the sunlight makes them harder to read) and can be seen by a
passenger as well the driver. In most cases, the centre lower part of the dash
works best.
The GPS antenna for an in-built nav system must be
mounted so that it has as wide a viewing angle of the sky as possible. In a
modern sedan with a very shallow angled rear window, placing the antenna in the
middle of the rear deck works well. But what about in a hatchback? If the parcel
tray is never to be removed, again putting it directly under the middle of the
rear glass is fine. But in some cases, you’ll need to look at sticking it to the
underside of rear glass or the windscreen, or mounting it in the middle of the
dash. Get it wrong and the number of satellites accessed will plummet,
deleteriously affecting accuracy.
Sorting out OE car speaker wiring is fairly easy.
Firstly you'll need just a normal 1.5V battery with a couple of wires connected
to it. What you do is apply the voltage from this battery across the terminals
that you suspect of being connected to a speaker (having measured them first and
found no 12V feeds on them!). When you have found a pair of speaker leads, that
speaker will make a scratchy pop as you connect and then disconnect the battery.
Furthermore, when the positive lead of the battery is connected to the positive
lead of the speaker, the speaker cone will move forward. (If you can't see the
speaker, a sheet of paper over the grille will usually indicate the direction of
cone movement.)
Getting the speaker polarity right (as described
above) is important. You won’t blow up a speaker if it is connected backwards -
and in fact, if you have all the speakers connected backwards, there will be no
problem at all. But if you have some connected one way and others connected the
other way, there will be a lack of bass and the imaging will be odd. The lack of
bass is because as one speaker cone is pushing forwards, the other will be
pulling backwards. In other words, one will cancel the other. An easy way to
quickly see if this is the case is to use the balance/fader control to move to
all the extremes. If the systems has more bass when only one speaker (or one
pair of speakers) is selected, something is wrong in the connections of the
positives and negatives (normally called phasing). Reverse the connections, one
speaker at a time, until it all sounds right.
The speakers built into navigation systems and CB
radios are normally very small. They sound tinny - and worse, when you turn up
the volume, they distort. And the last things you want distorted are radio coms
and navigation voice instructions! However, nearly all decent quality CBs and
nav systems have jacks for external speakers. The easiest and cheapest way of
sourcing one of these is to use a boxed speaker from a built-in car phone
system. New these are now rare new but millions were sold – the boxed speakers
pop up secondhand everywhere. These speakers are universal – that is, they can
be plugged into phone systems, nav systems and CB radios. Mounting is usually
easiest up under the dash, using double-sided tape.
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