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A Budget Sound Upgrade

Doing it on the cheap...

by Julian Edgar

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If you're after a budget sound upgrade, one good approach is to buy an OE head unit and speakers second hand from a more expensive (or more recent) car. But why are we suggesting that you buy a lousy system of the sort that gets put into standard cars? Well, for an older second car -especially if you're not all that into sound systems anyway - an ex-OE system is a good starting point. Cheap, too.

But what do you buy - and how do you make sense of all those wires?

The Head Unit

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Bought for this story was a single CD AM/FM head unit. Manufactured by Eurovox, it's installed in lower line Mercedes Benz vehicles in Australia. Which explains the 'Mercedes Benz' and star on the faceplate. It was destined for my 1988 Nissan Maxima Turbo and it had three attractions for me:

  • CD capability - lots of old and secondhand head units are radio cassette only. Since I haven't played a cassette in decades (except in my interview-recording Sony portable tape player), I don't need a tape player in my car.
  • A rotary volume control. I hate pushbuttons for volume up/down - since volume is an analog variable, why operate digital pushbuttons to change it?
  • An Original Equipment appearance. I didn't particularly want an aftermarket flashing, multi-coloured display with weird squares lighting and dimming at random but showing nothing.

Not so good - but along with the AUD$100 asking price - was a lack of line-level outputs (only direct speaker feeds were provided) and a similar lack of explanation of what the 13 wires connected to the provided loom actually did. At least the security code was available - an absolute necessity on any late-model secondhand gear.

Bench Testing

The first step was to get it home and do a web search. 'Eurovox 4880MB' found only one entry on Google - and that was no help in sorting out the wiring. Dropping the 'MB' (for Mercedes Benz, I assume) also revealed nothing, and a search of Eurovox sites found a complete dearth of technical support. But my lack of success shouldn't be off-putting: a web search is the first thing to undertake if buying a head unit of unknown specs.

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The next step was to closely examine the provided wiring harness. The harness was a short one with two plugs. One end plugged into the head unit and the other was obviously designed to connect to the Mercedes Benz body wiring loom. That loom would have the connections for the four speakers (ie 8 wires), constant power, ignition switched power, earth and probably an electric aerial connection.

But how to work out which was which? The eight speaker wires were likely to be grouped into pairs, and a quick examination indeed showed four pairs of colour: two yellow, two green, two orange and two white. One of each pair was marked with a trace, showing the positive. Hmmm, looking good - that's the speaker wires out of the way.

The power and earth wires are critical to get right - you don't want to get them reversed! The earth wire is most often black or green, and - yes - here was a thick wire that was black and hadn't been assigned a job. Paired with the black wire was a thick pink, and also in there was a red. Given that the pink was paired with the black it seemed most likely that these were the constant 12V and earth wires, while the red was most likely the ignition-switched 12V. (On some units there are fuses in the 12V and ignition-switched 12V leads - a dead giveaway.) That left over another yellow (separate from the 13-pin plug) and given that it had a bullet connector on the end, that one was most likely for the electric aerial. Hmm, and the remaining grey and orange wires? - no idea! (Reading the handbook later indicated that one of these was probably an input for a telephone mute control - ie the radio mutes when a call is received. And the other is probably an instrument panel lighting input, allowing the display, to auto-dim.)

I gingerly applied power to the black and yellow wires, and to my relief watched the red 'security' LED come up flashing. (If you have a variable voltage power supply, start off low and bring the voltage up slowly.) Then when I connected the red wire (ignition-switched 12V) the security code request came up. I plugged that in and the radio appeared to work. Of course, there was no sound at this stage - no speakers were connected.

Connecting a single speaker to each pair of 'like' colour speaker wires and then twiddling the fader and balance controls soon allowed me to sort out which speaker wire pair was which. Make sure that you label the wires as soon as you know their function!

So my $100 radio CD was working. Now to get it into the car....

The Old One Out

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The first step was to remove the (previous) factory system and do a reverse sorting out of which wires were which. The sound system in the Maxima was the original 1988 system, comprising an AM/FM radio and attached equaliser/amplifier. Because the FM band is different in Australia to Japan, this grey market import had previously had a frequency adaptor fitted. It was controlled by a pushbutton hanging from a stuck-on piece of tape. Removing the factory radio required firstly, undoing screws holding an escutcheon in place, and then undoing more recessed screws that held the radio brackets in place. After that the whole unit could be pulled out forwards.

The Wiring

Before the plugs are disconnected it pays to take a long, hard look at them. The plugs included connections for:

  • the separate up/down electric aerial pushbuttons (to be retained with the new head unit)
  • earth
  • ignition-switched power
  • the four speakers
  • and in this case, the cable connections between the two units.

Using the same rules of thumb that were used to work out the power and earth supplies on the new head unit, I guessed which plug was one that had the power feeds. Then, using a multimeter (set to volts) and probing the plug terminals, I found the constant 12V, ignition-switched 12V and earth connections.

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Sorting out the speaker wires is always 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.)

With all the connections sorted it's then just a case of soldering all the right wires together. Note that if the power and earth supplies for the radio are pretty small in diameter, there may be an unacceptable voltage drop when you put in a higher-powered head unit. The way around it is to run heavier gauge wires, eg straight to the battery.

The New One In

How you mechanically fix the new head unit in place will vary with each installation. In this case I used a mixture of glue (yep, glue) and two aluminium brackets that I made to suit. The head unit came supplied with one of those slide-in cradles that allows the unit to be removed by the insertion of two long-pronged tools. But I don't like the cradle system and so decided to install the unit permanently in place.

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The head unit sat up against one of the original brackets holding the assembly in place and with a large area in contact, I used contact adhesive to bond the two surfaces. This was never going to be enough to completely hold the radio, but it prevents lateral and twisting movement. The two aluminium brackets were also used. One locates on the rubber-encased bolt protruding from the back of the unit and the other supports the weight of the head unit, pushing the two top glued surfaces together. The brackets were folded-up from scrap sheet aluminium, using a bench vice.


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This is what the job looks like finished. At this stage I have only placed a digital inlet air temp gauge in the new panel - other controls and indicators will follow. The new head unit is very rigidly held in place and the simple controls (including the volume control placed closer to the driver rather than on the other side) allows easy operation. I understand that in some cars this head unit also came with a wired remote and a CD changer - some things to look out for on the secondhand market.

The installation process cost me nothing at all - I already had the glue, aluminium, electrical tape and solder. So this very major upgrade - CD capability and the right FM band, not to mention better sound - cost me AUD$100 in total. And just how is that sound? Well, those four old speakers needed an upgrade, too - and here's how we did that.

The Speakers

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The first step was to listen to the speakers that we already had. In the case of the Maxima, use of the fader and balance controls soon demonstrated that the front right door speaker had a terrible 'pop' in it, the front left speaker was very faint, while the two rear speakers sounded OK - but there was a real lack of treble all-round. A visual inspection (off with the door trims) showed the reason for the popping - the rubber roll suspension was completely missing. And the other (faint) front speaker? Most of the cone was gone!

At the back the reason for the lack of treble could also be quickly seen - when the car (a grey import) was complianced, new rear seat belts were fitted. They went where originally the tweeters sat in the two-way rear speakers, so out had come the tweeters, with the rear grilles chopped in half with a saw. Hmmmm.

Obviously the front speakers would need to be completely replaced, and the rear speakers had to be neatened in appearance in addition to being improved in sound.


As with the head-unit, there are some real advantages in going second hand Original Equipment. The first is that the speakers are cheap - really cheap. At a wrecker AUD$30-40 can get you a pair of 6-inch speakers from a late model car, while if you're prepared to go smaller in size, you'll probably be able to pick up two pairs for that price. The second major advantage is that factory speakers tend to be very efficient. That is, they are relatively loud with the input of little power. Because amplifier power costs big bucks, the manufacturer saves by specifying efficient speakers and keeping the amp power down. For the same reason, these speakers also suit our needs!

The downside is that you're not going to find any cheap, high-power speakers of huge aftermarket-style performance.

Measuring one of the Maxima's original front door speaker showed that a 6-incher just wouldn't fit. That's a pity, because one of the cheapest commonly available speakers around (from the front doors of Commodores) is a 6-inch design. (Expect to pay about $35 for a pair of these, complete with rear water shields.)

What was needed in this particular application was a 5-inch speaker, no more than 2 inches deep. (Be careful about measuring the available depth: door speakers normally have a very small clearance to the window and its winding mechanism.) For the Maxima the new rear speakers could be either quite large - or alternatively, no more than 4-5 inches in diameter. The difference depended on whether I wanted to go to the trouble of cutting rear deck metalwork and making a new shelf. In this budget, quick and simple upgrade, I was leaning towards the smaller speakers - but it depended on what I could find.

The first wrecker had no speakers out of cars, and refused to let me look around the yard for myself. That was no good to me, so I went to another wrecker that had probably 20 pairs of speakers already removed.


Traditionally, when picking speakers that you aren't going to be able to listen to before buying, you select the heaviest speakers - those with the biggest magnets, widest voice coil diameter, longest-travel suspension and highest power handling. And these rules still apply, but not quite to the same extent as when buying new. In this application, it's better to:

1. Sort the selection down to the sizes that suit your application

2. Move the cones up and down manually (spread your fingers and apply pressure across the face of the cone) to make sure that there's no binding

3. Inspect for water damage, perishing rubber suspensions, etc

4. See if they're car company branded

5. Then pick on magnet weight, power rating, etc

Don't get too hung up on the marked wattages. Unlike really cheap aftermarket speakers, factory stuff tends to have at least semi-realistic power ratings. A rating of 10 watts, for example, might send the car sound nuts into hysterical laughter but for normal in-car listening (as opposed to blasting), 10 watts of power handling by an efficient speaker is quite loud.

Some speakers will have a roll surround (front suspension) that's reversed. Rather than the curve of the suspension projecting outwards, it curves inwards. This allows the speaker to be mounted either with the face of the flange against the panel (or grille) or the back of the flange against the panel. Curiously, these speakers look less attractive and so may be cheaper... Dual cones (where there is a much smaller secondary cone nestling around the voice coil dust cap) stretch the high frequency (treble) response, and so if given the option, select dual cone rather than single cone designs. Also keep in mind whether you need grilles and any other mounting hardware in your particular application. Always buy 4-ohm speakers.

I bought two pairs of speakers - the cost was $45 for all four speakers.

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The first pair was from an SB Barina and had a diameter of 5 inches. They were mounted in a weird plastic arrangement but easily came out of these mouldings when rotated. These speakers use the reverse suspension mentioned above, are dual cone and have quite a small magnet. The other pair was from an SV21 Camry. These look much higher in quality, although at only 3.5 inches they're probably from the dashboard. They have a built-in dust-protecting grille, and are also dual cone.


The last thing that you want to do is spend time doing a custom install - only to find that the speakers are worse than the ones you are replacing! The first step should therefore be a bench test. You can use the car sound head unit, but I chose to use my domestic amplifier (which has a power meter). At low power levels there is no problem with using 4-ohm car sound speakers with a domestic amplifier.

Tested bare on the bench the speakers will sound terrible, but there shouldn't be any pops or buzzes. Furthermore, you should be able to get a feel for the power handling - usually as in, how low is it?

I compared the cheap and nasty looking Barina speakers with the better looking (but smaller) Camry speakers - and found that the Barina speakers were better! That was partly because the Barina speakers are larger - the bigger the cone area, the smaller the cone movement for a given audio output.

Then it occurred to me that I should test the speakers from the Maxima in the same comparative way. The front door speakers were stuffed, but what about the rears? Removal of a speaker showed it to be a 4-inch single cone design (it was originally matched with a tweeter, remember). And on the bench, I thought it sounded about midway between the two speakers I had bought.

Decisions, decisions....

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Not mentioned so far is that I'd also bought two brand new (gasp!) dome tweeters. These were also ex-Original Equipment, being a special purchase made by Jaycar Electronics (see "Tweet Tweet"). At only AUD$8 each (including their crossover capacitors) these are excellent value. (You can also pick up such tweeters at later model wreckers, although you'd be pushing to get them cheaper.)

The tweeters were going to be mounted on the front doors, which meant that the main mid-range speaker didn't need to be a dual-cone type. Hmmmm. So what I decided to do was to use the old rear speakers in the front doors, together with the new tweeters. The back deck could then get the Barina speakers. And the surplus Camry speakers? Put into storage for now.

Front Speaker Installation

The front speakers in the Maxima are located behind grilles in the door trim. Unlike some more recent cars, the grille is just a grille - rather than being acoustically coupled to the speaker. That meant that nothing fancy was needed in the speaker mounting, other than to make sure that the speaker didn't project too far outwards from its mounting surface.

The new speakers (the ones previously used in the rear deck with the missing tweeters) were smaller in diameter than the originals. However, an adaptor ring was easily cut from some thin surplus aluminium sheet with an electric jigsaw.

That was easy, but a bit harder was the tweeter installation. Firstly the crossover capacitor needed to be unsoldered (allowing it to be remotely mounted and providing more clearance) and then the sticky gasket on the front surface had to be peeled off. The tweeter could then be mounted in the door trim. However, to provide rear clearance, a little panel work was first undertaken with a hammer and dolly.

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When mounting the tweeter the following steps were undertaken:

1. The centre of its location was marked on the outside of the trim

2. A small diameter hole was drilled through at the mark

3. A holesaw was then used from the rear, with the cut going only through the backing masonite, and not through the velour.

4. A knife was then used to cut through the velour, forming four flaps that could be then folded back through the hole

5. The tweeter was pushed into place from the front

Taking this approach means that no bare backing can peer through the hole - the edge of the trim remains neat and the result looks good.

The tweeter was wired to the main door speaker, with the crossover (preventing bass frequencies getting to the tweeter) provided by the capacitor that came with the tweeter.

To make sure that the aluminium adaptor plate sealed neatly against the metalwork (and to prevent any rattles) some silicone sealant was applied to the back of the plate before it was screwed into place.

Rear Speaker Installation

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The rear speakers were even easier. An adaptor was cut from 10mm MDF and painted black with a spray can before the speaker was attached with nuts and bolts. Black grille clothe was then stretched over the front of the assembly, being tacked into place on the back. The use of a baffle larger than the speaker allowed the easy covering-up of the holes created by the previous speakers, providing a visual lift as well as preventing air from the back of the cone cancelling-out sound waves from the front. Note that any cloth that is see-through when held up to the light can be used as grille cloth.

The baffles were secured in place with self-tapping MDF screws inserted from below. If the shelf is uneven, a foam rubber gasket may be needed to stop air leakage around the edges of the baffle.


Including the CD tuner head unit, the total cost for this sound system upgrade was AUD$161 - and that price resulted in a surplus pair of speakers! For the money I now have CD capability and proper FM reception (remember, the car previously had a Japanese FM frequency range), new rear speakers and vastly improved front speakers that include dome tweeters.

The system won't win any awards for sound quality at a competition, but it's an absolutely massive improvement, and all for very little money.

Speaker Phasing

For best results, the speakers need to be connected so that they all push forward simultaneously - rather than one 'pushing' and one 'pulling'. The 1.5V battery trick can be used to work out which of the speaker terminals is positive, but sometimes it's easiest to do the phasing by a simple listening test.

Set the fader so that you can hear only the front or rear speakers, then swap the wiring polarity at one speaker. With one particular polarity, the amount of bass that's present should increase. Wire the speakers so that there is max bass. When you have done one pair, do the other - then check that the front/rear phasing is correct.

One easy trick to see if you have got it right is to check that the bass doesn't suddenly get better when you have the fader and balance controls in any of their extreme combinations - that listening to either a pair or even a single speaker doesn't improve the bass response.

Speaker phasing can make an immense difference to how the system sounds.

Huh? What's this?
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As you can see, as the concluding step I whacked in the boot a dirty great big sub with its own dedicated amplifier. So how does that square with the cheap-as-chips approach of the rest of the system. Answer? - not very!

The subwoofer was built for an article in Silicon Chip magazine (it was featured in the May 2003 issue - It uses two Jaycar 10-inch drivers in an enclosure formed from two pre-built Jaycar boxes. The ports are unique to the design but use Jaycar flared ends and hardware store plastic pipe. Actually, overall it's a very cheap and easy design for its excellent performance - but in this case still extravagant, given the cheapskate approach that has been taken with the rest of the system. The amp was bought in order that the sub could be adequately tested.

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Since the two other cars in my household come with very good factory sound systems (complete with in-built subs), the sub and its amp had been sitting around doing nothing. But when I found that the combination fitted into the Maxima perfectly, well....

The amplifier is fed via the rear speakers, using a speaker-level to line-level adaptor. The rear seat is normally left in its upright position, rather than folded as in this photo.

As you would expect, the presence of the sub boosts the quality enormously. The fuller bottom end also means - perhaps oddly - that the treble provided by the two new tweeters also sounds cleaner. In fact, with the sub and its amp fitted, the major limitation becomes not the frequency response of the system, but its loudness. That's not surprising when you remember the cost of the door and rear deck speakers, and that the head unit uses no additional amplifier.

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