Those familiar with the BMW Z3 and M variants, will need no explanation of why one would want to go to all this trouble to upgrade the stock Harman Kardon stereo system.  In a few short words; it’s terrible.  I’m beyond my big booming stereo days, but this system is simply inadequate to anyone who wishes to listen to anything beyond AM talk radio.  But, if you are like me, you don’t want a gaudy aftermarket head unit staring back at you, especially in such a rare car.  A modern day classic like the M Coupe deserves something a bit more discreet.  This almost always means more work, and this build was no exception.

I’ll let the photos do most of the talking, as it’s pretty easy to see what I did.  In order to install a subwoofer of any power, you’ll have to makes some modifications to the stock enclosure.  It simply doesn’t have the depth to accept anything with a moderate sized magnet.  For me, I chose a Hybrid Audio Imagine 6.5″ sub.  It’s the same diameter as the stock sub, but significantly beefier.  It’s also designed to operate in relatively small ported enclosures, while requiring very little power.  I’ll be using a JL XD 500/3 to power it, more on that in another post.

Template of what little flat area I had to work with after sanding down the plastic nubs utilized by the stock speaker.  Then cut a piece of 3/4″ MDF as the base, held in place with T-nuts/allen bolts/washers.


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MDF Ring cut and positioned to allow for as much clearance as possible.  This took quite a bit of sanding and shaping.


Fleece stretched across the MDF, then soaked in epoxy resin.  Cut away the excess, lots of sanding, filler, more sanding.  Lots of fiberglass and resin were applied to the inside.  I wasn’t going for a showroom finish, just presentable (to who I don’t know, as this is all hidden once installed.)

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One corner of the OEM enclosure had a soft spot, which could present issues further down the road.  So I formed a patch out of fiberglass, then adhered it to the corner.  The white coating is a plastic primer.

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Mount adhered and bolted to OEM plastic enclosure, then coated with plastic primer.  Finally coated with rubberized undercoat to help tame any rattles.

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More to come once I have the subwoofer installed.


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