4 Inch Rear Speakers

In the continuing quest for better sound in a Z3, I decided to replace the stock rear 3″ speakers in my 99 2.3 with 4″ speakers, or possibly 4×6″. Model year 2000 and newer have 4″ speakers, so I knew that in theory at least, I should be able to fit a decent set of 4″ co-ax’s back there. The stock 3″ speakers are pitiful single paper cone drivers, “designed” for “filtered” midrange sound from the factory amp. I found their sound lacking, even annoying. They did not add anything to my audio experience. I am cheap, …..let’s say cost conscience,…… so I am always looking for more bang for the buck and aftermarket speakers have always provided more satisfying sound over stock OEM drivers. The first step was to see what kind of volume and interferences I had to work with. I popped out the little hatch, shown in first photo, but even with a flashlight it was difficult to get a clear view. The 3″ speakers are held in place by a threaded collar, essentially a giant knurled nut. If you take a large screwdriver and tap the knurls through the little hatch counter clockwise with a rubber mallet to start, it then unscrews easily. The speaker pulls out to reveal a circular hole with a chord (flat spot), that is supposed to prevent the speaker from spinning. This allowed a better view and some discouraging news as well.

There’s a bunch of stuff in there…the seat belt retractor, the structural steel for the roll hoop and the re-enforcing cross member that goes across the vehicle. The steel is a problem because it is so close to the plastic trim housing. This limits where the speaker can be placed, because either the driver basket or magnet will hit something. Depth is about 2 ½”, but variable because the housing slopes. In addition, the 3″ speaker opening is located far to the outside, because the tiny magnet does not interfere with anything. It is actually easier to install a new speaker if you have NO rear speakers; ie. you can cut a new hole farther inboard without worrying about the existing hole showing beyond the coverage of the speaker trim/grill.

Luckily, 4″ speakers are strange creatures, many appear to have grills with trim that increases the coverage area. This was critical in this case; if the trim were any smaller, it would not have been possible to mount the speakers and avoid interference, and still cover the existing opening. The last photo shows the grill coverage outline (courtesy of dirt sticking to Armorall……will stop using that stuff!). I looked at installing a 4×6 speaker, but quickly found that only Blaupunkt 4×6 seemed to come with grills! The other manufacturers assume you are replacing an OEM installation and do not include them. I was not impressed with the Blau 4×6 specs, so I decided to go 4″.. Based on listening and a car audio store recommendation, the speakers I installed were Pioneer TS-A1086. They had nice plain black grills, and once I dremeled off the Pioneer name and made a P-touch label that spelled “BMW” to put in its place, it really looked stock. They have a cut out requirement of 4 1/16″, and a magnet diameter of 2 3/4″ . The trim and grill actually covers a diameter of about 6″.. I also looked into installing Infinity 452i speakers which are a “plus one” 4 inch size; ie the cone is 30% larger for the same cutout. It has a magnet that is ½” larger in diameter and ½” deeper, so it would be trickier to fit, but has a rubber surround, silk tweeter, and higher power handling capability. It would be easier to install the 452i, if there had not been any rear speakers. And since they were out of stock at the time, I went with the Pioneers. My cutout (from the outside edge of the hole, closest to the measuring point) ended up being 3/8″ vertical down from the upper trim piece end that starts the groove (leaves about 1/8″ left in bottom trim piece TO the groove) and 1 5/8″ horizontal from the center trim piece. This allowed the magnet to clear (actually JUSTS touches the carpet over the cross member), the speaker trim to cover the old opening, and still contain the plastic cut within the lower trim piece. I was afraid that cutting into the upper trim piece would cause the assembly to be too flimsy and buzz or rattle. There are also some interference issues, if you feel up under and into that area. The upper and lower trim pieces snap together, and I wanted to try to avoid breaking that connection for aesthetic and structural reasons. The plastic is thick, about 1/8 to 3/16″ and is ribbed on the backside for more support. I used a Dremel tool with a cutting blade that resembles a tiny circular saw. It cut through the plastic like butter, but it is CRITICAL that you tape the surrounding area, as it is VERY easy for the saw to jump and instantly mar the surface for good. It is easier to work the saw with the seats removed but I actually only removed the driver side; once I had my measurements I did the passenger side with the seat moved all the way forward, but then I also have a flexible extension that really helps…YMMV.

The pictures are pretty self- explanatory. There was a very noticeable increase in clarity and volume with the new speakers, even hooked up to the stock amp. I ended up running dedicated, unfiltered speaker wires directly from my Toronto head unit under the center console to get full range (for a 4″, anyway) sound, which sounded MUCH better than the stock amp connection. Even firing into the back of the seats, they are so close to you that they provide significant “top down” midrange and high sound. I find the stereo sound similar to that of wearing headphones; it is as if you are “in” the sound, not “in front” of it. Some people don’t care for that…I like it. Another idea to try instead of the Infinity co-ax’s, would be to use a 4″ component set and locate the tweeters up and outboard in the upper trim unit for better separation and directionality. I found the Pioneers to be a significant upgrade to the sound system for very few dollars. Now if I can just find a way to put in a powered subwoofer and lose no legroom or storage space……..