Tim's Z Custom Gallery  •  Upgrading rear 4-in speakers

Which type of speakers do you have?
Some audio specialists will suggest not to bother with rear speakers, but I think they are essential in an open-topped roadster. Very early Z3s didn't have any rear speakers, then around 1997/98 BMW started fitting 3-inch speakers behind the seats. From around April 1999 build, the rear speakers were increased to 4-inch.

If your speakers look like the ones above, you have 3-inch speakers and you should checkout the article on upgrading these on MZ3.net at http://www.mz3.net/articles/219.html.

Removing the 4-inch speakers

The speakers on my M roadster were buzzing on base tones, so I decided to replace them with higher-quality units. 4-inch speakers are a lot easier to replace than 3-inch units, and you start by gently levering off the grill cover with a narrow screwdriver, taking care not to scratch the plastic.

This reveals four fixing screws which you remove before pulling out the speaker.

The green/black cable is wired to the positive terminal of the speaker, the green is negative.

Chosing replacement speakers

The rear speakers are coaxials driven directly from the head unit. Based on audio articles on mz3.net and reviews on Car Audio Direct, I decided to go for Boston Acoustic or MB Quart, and as the Boston Acoustic FX4s were cheaper (49.99 incl VAT and delivery) I went for them.

The stock speaker is on the left, the new Boston Pro FX4 is on the right. The Boston Pro looks like a direct replacement with identical screw holes.

I suppose you can't judge quality on looks alone, but no stock unit should look as shabby as this, especially in a 36,000 M-powered BMW!

As other people have written, once you remove the stock units, there's no way you could consider sticking them back in again!

Unfortunately, that's what I had to do as the Boston Pro FX4s are too deep. Nevertheless I fitted one of the speakers, turned on the CD radio, put all the fade to the rear, then played with the balance so I could determine the difference between the FX4 and stock speakers. Err.. no comparison.

Car Audio Direct were happy to take the FX4s back and after checking dimensions on the MB Quart web site, I ordered MB Quart DK110 instead (64.99). These come with their own grill which I didn't use, but the grill and neat dimensions makes these speakers an ideal upgrade for 3-in units.

The DK110s were OK on depth but the screw holes didn't match as the speakers are slightly narrower. Measuring diagonally, the holes on the stock speakers are 115mm apart, whilst on the DK110s they are about 105mm.

I realised I could just about fit them if I drilled new holes, so marked the positions with some typist's correction fluid.

The way the terminals are connected make it wide at one point but I worked out that fitting them slightly rotated would ensure nothing was touching.

This shot is after I have drilled new holes and fitted the self-tapping clips.

The new holes didn't slow things down much and the first speaker was quickly connected. As before I tried a comparison against the stock speaker, and if anything, felt the overall effect was better than the Boston Pro FX4s.

Tim Cullis, November 2002

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