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Installing amplifier/better speakers/under-seat sub
An audio system upgrade to approximate FIAT's Interscope
Published by alexGS
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Installing amplifier/better speakers/under-seat sub

The aim of this upgrade is to approximate FIAT's Interscope system (which I have never seen or heard) by adding (to the standard head unit) improved speakers, an amplifier for the speakers, and an under-seat subwoofer.

I finally reached the stage of hitting the power button this evening - and it all works - wiring up this sound system and sound-deadening one door seems to have taken most of the day I would have thought only a little simple wiring was needed - an hour's work? - but it seems to take a bit longer than that. Maybe eight hours!

Here are the details for my sound system install, in case they are of interest to anyone attempting something similar. To keep things fairly clear, I'm going to describe each part in a separate message.


Amplifiers should have a direct supply from the battery; there was someone who used the cigarette lighter wire as a power supply with success, but it's best not to, especially if you have two amplifiers. The car's own wiring to that socket is really not very generous and neither is the fuse rating.

On the other hand, there's no need to go over the top for the power supply cable and fuseholder - 8-gauge cable and a 60A glass fuse may seem like a good idea, but they are only really necessary if you have 300W+ of amplifier power (RMS, not peak!), and in the 500, the standard battery and alternator are lightly-rated, so it's probably not the best car for 'dB-drag racing'.

I wanted a standard underbonnet appearance, so I used a sealed fuseholder with regular blade fuse - maximum rating for this type is 40A. The fuseholder has 12-gauge wires attached. I extended one wire to an eye terminal, which is fastened onto a spare stud on the battery positive terminal. For the power cable into the car, I used 10-gauge. Again, this is appropriate for currents up to 40A (4% voltage drop at this maximum current). Expected loading for a 60W RMS/2 channel amp plus 50W RMS/1 channel amp is 14.1A, at which there will be approximately a 1.4% voltage drop. I shall fit a 30A fuse.

I found an unused grommet in an ideal place, under/behind brake pipes on the bulkhead, next to the brake servo. I removed the grommet, cut a hole in it, then used a Philips screwdriver to make a hole through the bulkhead soundproofing (inside the car) - the brown outer layer is surprisingly soft and crumbly, so it is easy to perforate. The cable comes out in a fairly clear area behind the dashboard (left/passenger's side).

The corrugated loom tube provides extra protection against abrasion and runs right through the grommet and inside the car. Helps with the 'standard' appearance; also has red heatshrink applied at intervals to identify as a power cable, which seems to be the done thing these days at FIAT, except they use red insulation tape

  1. Fuse holder circled in yellow, cap secured by nut that holds ECU onto bracket
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  2. Cap again circled in yellow, fuse holder shown removed and 40A fuse installed, also note battery terminal with added wire
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  3. Holder clipped into place and battery terminal cover fitted
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  4. Grommet and corrugated loom tube through bulkhead - brake servo on right of pic
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  5. Cable emerges above brake linkages - needs to be kept clear
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The next part explains the installation of the speakers.
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Old 18-09-2012   #1
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Re: Installing amplifier/better speakers/under-seat sub

Well, maybe a guide isn't supposed to have separate messages, but here is a second message anyway.


Speakers in the 500 are the 'component' type, which means there is a woofer (low frequency) in the door, and a tweeter (high frequency) in the windscreen pillar trim.


The standard woofers are a cardboard cone about 6" diameter, in a customised mounting rivetted to the door. They deliver surprisingly good sound considering the low cost of manufacture.

I wanted to replace the white polystyrene sheet with something more substantial, to soundproof the door. Therefore, I had to drill out the three rivets (10mm drill bit) and that's what started this whole speaker upgrade project.
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The back of the speaker is even more pitiful (tiny magnet!) and it is very surprising that it produces the quality of sound that it does. Someone paid attention to the sealing of the speaker, which is nice, except that the rest of the door is sealed only by that thin polystyrene sheet, and the grille isn't sealed properly onto the front of the speaker because of a cut-out for the plug.
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This is what a good-quality speaker looks like. It has a cast-alloy basket (frame), rather than the usual stamped steel or FIAT's plastic. It has a much larger and stronger magnet, which means the voice coil (coil of wire that moves the speaker cone) can move more strongly. The cone is made from a Kevlar reinforced fibre, for rigidity (less distortion), and the surround is made from rubber (rather than foam) for durability.
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Unfortunately, I ended up returning these good-quality speakers for a refund, due to numerous faults The tweeters did not function properly - not shown here, they were a special ribbon design normally used in high-end home audio systems. They produced less than 1/10th of the sound level of the originals. Also, one crossover was faulty and sent a very weak signal to the woofer.

The speakers I bought next were half the price. They are made by Sony and have the usual stamped steel basket, the usual rubber surround, but an unusual foam material for the cone. They are claimed to be 6.75" speakers, but they fit in a 6" hole. I decided there was much less chance that cheap speakers would be faulty...

I decided to use an MDF spacer ring to mount each speaker, rather than fixing the speaker straight onto the door. There are two reasons to use a spacer:
  1. The thickness of the ring adds a little rigidity to the mounting (less flex of the sheet metal)
  2. The front of the speaker might seal against the speaker grille (with the help of some foam tape) which helps to enclose the back of the speaker and improve the sound

Here, I am applying foam tape to the back of the spacer in order to eliminate any vibration against the sheet metal.
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To mount the spacer onto the door, I suggest self-drilling screws as shown below, as a useful time-saver. Alternatively you will need a drill bit followed by fairly long self-tapping screws - and it would be best to drill a clearance hole in the MDF first, otherwise the screw will thread into the MDF and tend to push the spacer away from the door. The screws I use have a fine thread that doesn't thread into the MDF properly, which is good. When it bites into the steel, it draws the spacer tight against the door.
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The standard speaker wires are thin - perhaps too thin for amplified speakers. Also, the same wire is connected (somewhere in the dashboard) to the tweeter, which is a problem if you need to fit a crossover. Most aftermarket component speakers come with a crossover box - a filter that splits the signal into low frequency for the woofer and high frequency for the tweeter. Obviously for this to work, you need a separate wire to each speaker.

I decided to run replacement speaker wires. Again, it would be easy to go over the top and fit very bulky speaker wires. Instead, I used the twisted pairs supplied as standard on the Alfa Romeo 166. I happen to have a wiring loom left over after I installed a DSP amplifier from another 166, so I have several metres of speaker cable (the 166 is a big car), and the wires are much thicker/have more copper strands than the wires supplied in the 500. The only slight snag with this approach is the confusing range of colours - but more on that later.

It is easy to thread the wire through the rubber concertina into the door - a simple direct design compared to the type used on more expensive cars, which usually have an S-shaped conduit so that the wire doesn't have to bend as much. I expect there will be problems one day with broken wires here, due to the simple design, but in the meantime it is easy to get the wire through.

I've used a lever-action crimp tool to apply spade terminals that match the speaker. Compared to a normal spade terminal, these are 'small' and 'very small'!
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I prised off the windscreen pillar trim and found these tweeters installed behind the snap-in grilles. High-frequency sounds are very directional, and these tweeters are angled away from the windscreen by the design of the mounting.

These standard tweeters perform very well. I suggest not bothering to upgrade them. If you decide to, then read on.
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Some aftermarket tweeters, especially the cheap ones, produce piercing high sounds from a piezo-effect device or a small hard dome. The better designs tend to be a larger dome design (like a headphone speaker) and produce more sound towards the mid-range, leaving less of a frequency difference between the woofer and the tweeter.

More expensive speakers tend to have larger tweeters. For example the Infinity Kappa speakers have tweeters the size of a round air vent. These are a challenge to install in standard locations.

The speakers I bought were the most expensive in the shop, though it was a shop filled with cheap brands. Unlike for all the others on offer, the ones I got have a tweeter larger than FIAT's design, so I have used a multi-tool to enlarge the hole in the pillar trim. At first, I made it large enough for the tweeter only, but it proved difficult to secure in the middle. So I made it large enough for the flush-mount bezel (supplied with the speakers), which the tweeter screws into. I thought it was easy to trace the circular shape in the moulding - but due to the angle, it wasn't actually a circle and I made a huge mess of it - see the later picture of the front... ::
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Because I wanted to use the standard grille and it wouldn't quite fit on properly, I ended up gluing the bezel onto the back of the trim. The polypropylene trim melts at a relatively low temperature - the nozzle of the hot glue gun melts it, so you have a plastic welder in your hands!
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I wanted the wires at the bottom, which meant the tweeter was upside down - the real problem, though, was that the FIAT grille would not fit over Sony's bulbous design.
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The next step is to butcher the tweeter until it is as flat-faced as possible. The first time I did this, I managed to put a big dent in the cone, and then when trying to use a heat gun to remove the dent, I thought I had damaged the voice coil/seized the tweeter (quite easy to do). Therefore I had to stop and hook up some wiring/crossovers for a test. Turned out the heat-tortured tweeter with a dent in it sounded a little louder than the one without the dent, so all's well that ends well!

I did manage to get the dent out using Blu-tack (press on gently, pull off quickly).

After removing the Sony grille, cutting out the centre trim supports, and sanding the surround flush, the tweeter will fit behind the FIAT grille. Earlier I tried to remove the tweeter from its casing - several loud crack sounds but no joy.
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Doesn't this sort of thing waste a lot of time...

Especially when you connect up the replacement speakers on one side and the original speakers on the other side, and it turns out that the replacement tweeter is a little quieter and less clear (probably because the mounting is not angled towards the listener...)

I made a few more tests with tweeters removed and was very surprised that the replacement tweeter with a significantly larger cone area actually produces less useful sound than the small (and cheap) tweeter fitted by FIAT. Therefore, I'd suggest not bothering to 'downgrade' them. FIAT do fit different tweeters on the Interscope version, which casts that shadow of doubt over the originals - so at the end of the day, your decision

The next part (to be continued at a later date) explains the speaker wiring and amplifier wiring.
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Last edited by alexGS; 18-09-2012 at 15:50.
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Old 21-09-2012   #2
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Re: Installing amplifier/better speakers/under-seat sub

Awesome guide, I've just ordered an under-seat sub for my 500 Sport so this is pretty useful for me. I had a front-speaker sub setup in my last car. Don't think I'll be replacing the front speakers in the 500, instead I will switch on my head unit's Hi-Pass filter and fade 100% to the front.

I ran amped front speakers at 50 watts RMS in my last car, but I patched into the manufacturer wiring rather than running new speakers. Patching into ISO adapters if you have an aftermarket head or using a T-Harness with the stock head unit can be very useful for this.
Previously: '81 Ford Fiesta 1.3GL, '03 Fiat Punto Active, '08 Ford Fiesta Zetec;
New Car:'08 Fiat 500 1.4 Sport; Also in Garage: '99 Mazda MX5 1.6s

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Old 20-06-2020   #3
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Re: Installing amplifier/better speakers/under-seat sub

Can you tell me the best place to connect the earthing wire
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