Z3 Stereo upgrades, and the $2 Subwoofer fix


I love my car, but the achilles heel has been the stereo system. I got the HK factory system with my '99, and it sounds good, until you lower the top - there's just not enough volume. Over the life of the Z3, BMW has made some improvements to the stereo system. The first system just used a pair of speakers in the front foot wells, then they progressed to having small filler speakers behind the seats, and then finally BMW installed a subwoofer between the driver and passenger, in the place where there used to be a lockable storage bin.



At this point, you'd think this would make for a decent system, but it still isn't quite there. It distorts at higher volumes. Tied to that, the factory subwoofer apparently doesn't hold up well. Some have reported (and I have experienced) rattling coming from the subwoofer, which gets worse when you crank the volume, enough to force you to listen at a lower volume than you otherwise would.


If you read the Z3 message board or the articles on MZ3.net You'll find that most people remove as much of the stock stereo system as possible, and often they remove it entirely. For a time, I considered that path, but you'll find that I'm cheap :-). I started with the easier things, such as replacing the stock head unit with a Blaupunkt Toronto CD player and a pair of front speakers from Crutchfield.com. The Blaupunkt installation was a snap, as Crutchfield supplied a wiring harness adapter. On the other hand, the speakers I ordered did not fit into the standard foot well space available, even though they matched 5 1/4" size of the factory speakers. The screw holes in the speakers were too close together to properly fit. I was doing this just before the 1999 Homecoming event, so I didn't have too much time to worry about it. Instead, I had read that Boston Acoustics RX-57 speakers were a good fit, so I promptly purchased a pair, and mounted them in the parking lot of the store I bought them at.

The improvement in the stereo was substantial, but not quite enough. At higher volumes, I was experiencing the dreaded subwoofer rattle. After some inspection, I found this to be related to the horn that comes out from the subwoofer area. Basically, the subwoofer I have is ported, and there is an L-shaped oval tube (often called a horn), and it directs the sound from the subwoofer area to the bottom of the grille area shown above.

To get a better look inside, you have to remove the grille. In my model year, this is achieved by carefully prying out the bottom of the grille, and lifting up, where the top of the grille acts as a hinge. Once removed, you can get a look at some of the guts behind the grille.

If you wish to learn more about the guts of the stereo, you can check out this article on MZ3.net that Robert Leidy put together when he dissected his subwoofer. It suffices to say that the horn fits into the oval that you see, and it opens out at the bottom. As you can see, the corners of the horn have caused the indentations that you see in the carpeting at the bottom of the inside of the grille area.

I decided to experiment a little with using the horn. With it removed, I did not experience any buzzing in the stereo, but the bass response was substantially muted. It became obvious that the horn is necessary for proper audio response of the subwoofer. I spent a little bit of time with the grille off and the horn installed, and I began to notice that the horn would not stay in place. Subwoofers, in general give off puffs of air on deeper bass notes, and these puffs of air (which I like to call poots :-) were actually causing the horn to dislodge itself from where it connects in to the subwoofer area. Later on, I reinstalled the grille, and the buzzing returned. Clearly, the horn was only buzzing when it was confined behind the grille.

I decided to see if there was some way to cushion the horn so that it wouldn't rattle around when it was behind the grille. Rather than pad the whole area behind the grille, I decided to pad just bits of the horn itself. I chose some 3/8" self-adhering home window insulation from Home Despot, and placed it on areas where I saw potential for contact between the horn and the rest of the compartment. I chose foam insulation rather than foam rubber, because it's spongier, and appears to me that it would last longer. Here's where I attached the insulation.

As you can probably see, the insulation is not staying glued to the horn around the rounded corners, but you get the general idea. After taking these pix, I trimmed off the portions around the sides so it wouldn't peel off completely.

The result? Well, I'm very impressed at how much of a difference it made! I do NOT hear any buzzing, even at higher volumes. The subwoofer is still underpowered (remember, I haven't replaced the Amplifier yet), but given the elimination of the subwoofer buzz, the quality ain't terrible.

You may have noticed in the top pic that there's a crease in the insulation. That comes from the center of the grille, so you can see that there's some cushioning between the grille and the horn. Also, in the top pic, you'll see that I placed two pieces of insulation at the 'corner' of the horn. Those two pieces seem to keep the horn in place instead of having it pop out when the subwoofer is pooting.

Not bad for a $2 cost. If you're not really into spending hundreds of dollars to replace the sub, this is worth considering! I still haven't replace the amplifier yet, but I may yet do that!

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