BMW E36 HK Audio System
Speaker Upgrade DIY

Spurred by a need to replace a failed midrange driver, I decided to
replace all of the speakers in my E36.

Introduction

This article explains how I replaced the speakers in my 1998 HK-equipped E36 using aftermarket drivers.

Before we get started, some background is necessary. The HK system uses an external, trunk-mounted amplifier that contains passive crossovers. This means that the speaker outputs of the amp are not full range signals so you can't just plug those into a component set with its own crossover and expect to get something listenable. If you intend to keep the amplifier and simply replace the speakers (definitely the simplest solution), that limits the number of options for replacement drivers. See "Choosing Drivers" below for more.

There have been a couple revisions of the audio system over the production run of the E36. Early systems came with a complement of round drivers mounted to the rear deck in a large square enclosure, while later models like my 1998 came with a smaller oval enclosure consisting of a 6x9 driver woofer and 2" component tweeter. You can easily determine if you have 6x9 drivers by sticking your head in the trunk and looking up at the rear deck. A black plastic oval enclosure indicates you have 6x9s. If that's the case, you can follow this DIY verbatim to replace the drivers.

If your vehicle is equipped with the older square boxes, you will have to buy some aftermarket mounting adapters as buying the BMW adapters pictured as provided in later vehicles is not an economically viable solution unless you can lift them from a parts car or a junkyard. I recommend using the adapters sold by BSW with one caveat: they do not provide a mounting location for a component tweeter. If you need to use these adapters, that means you have a few options:

Eliminate the tweeters and accept that you'll only hear from around 500Hz and below out of the rear deck. Some would suggest that is not only perfectly acceptable, but desirable. Of course I might disagree, but I won't debate the relative merits of that solution here.
Find a 6x9 component set that mounts its tweeter in the center of the woofer like a coaxial, but routes its signal wires down to a separate set of terminals or binding posts so you can splice those with the outputs from the HK amp. The MB Quart reference series component set (RCE 269) did exactly this. I'm not sure that the set is available anymore, or if an equivalent set from MB Quart or another manufacturer is available. Let your fingers do the walking.
Rig up a tweeter on the rear deck, or possibly on a bracket fabricated to fit over the BSW adapters. Be creative.

Choosing Drivers

Front Tweeters: Most 3/4" and 1" units should work. The Polk dB1000 1" soft dome unit is shown and is an almost perfect press fit. It also sounds great, as its presentation is more up-front than the OE unit but not glaring or annoying like some aftermarket units. "Smooth" would be a good word to describe the soft dome unit's performance.
Front Midranges: You have two choices if you want to retain the HK amp and the 3-way component system: buy the OE units from BMW for $160 (pair) or get the custom replacements available from BSW for $100 (pair).
Front Woofers: 5.25" will fit without modifications, but the bolt pattern is not a perfect match. Additionally, the driver should be as shallow as possible since depth in the kick panel is limited unless you remove the sound deadening material (not recommended). Pictured is the Polk 5510 from one of their 2-way component sets.
Rear Tweeters: CDT units are pictured and fit the BMW adapter nicely. Make sure the driver you choose has a surface-mounting option and the diameter of the mounting flange is 2" or more. For this reason a 1" tweeter will probably fit better than a 3/4" unit.
Rear Woofers: The CDT 6x9 units are pictured and are a perfect solution for this system as they are designed for infinite baffle operation.

No matter what drivers you choose, if you intend to retain the HK amp, keep in mind that running any driver without the crossover designed for it may result in poor sound quality or, in a worst case scenario, damage to the driver. This is especially critical with tweeters and Polk units in particular. I've blown my share of Polk tweeters in the home to know better.

Prerequisites

Replacement of the speakers in the E36 requires the following:

Speakers of choice as outlined above.
BMW or BSW 6x9 adapters as required.
8mm socket to remove selected bolts on the kick panel.
Right angle philips screwdriver or socket with ratchet. You'll need this to remove the screws holding the speaker assembly to the rear deck.
Some extra door panel fasteners. Get the ones with the small foam washer for maximum leak protection. These are used in later model cars but are compatible with the E36.
A tube of construction adhesive or a couple sets of two-part epoxy compatible with plastic and fiberboard applications.
A handful of crimp or solder-on terminals that fit spade connectors on speakers.
A handful of mid-line splice connectors to aid removal of the drivers in the future.
Roughly 5 hours. If you break the door panel, you'll need to glue it up and set it aside for 12-24 hours, so be prepared

Front Speaker Replacement

Remove the door panel. By now there are a ton of DIYs out there on this procedure so I won't belabor how to do that here. The only thing I'll pass on is that I consider a door panel removal tool essential to this job. Also, whenever you remove the door panel on an E36 you risk breaking off the mounting tab at the top of the panel. In fact, there's a good chance it has already separated from the door panel, so be prepared for it. FYI, every time I have pulled my door panels off I've had to reglue them. I haven't found the perfect glue for this application yet and I'm not sure there is one. When you remove the door panel, inspect the mounting tab and glue it up if necessary. Note that if you have to glue it, you'll need to set it aside until the glue dries, which may mean 12-24 hours. Oh, and while I can't advocate driving without the door panels, particularly if you have side airbags, I was able to do it.
Remove the midrange from the grill assembly. Remove the midrange and grill assembly from the door panel by unscrewing the locking ring from the back of the door panel. Once it's removed you'll see that there are two locking tabs that must be depressed with a screwdriver to release the driver from the grill assembly. You'll reuse the grill assembly, so do yourself a favor and protect the grill side with some blue painters' tape. It would be a shame to scrape that up and have to buy another one at $80 a pop.
Install the new midrange in the grill assembly. The BSW units were a snap fit, but I found them a bit loose in the grill assembly. To prevent vibration I used a hot-melt glue gun to secure the driver to the grill assembly. I found it a bit difficult to get the glue in the right place because the gun was too big to fit into the recess between the driver and the grill, but tilting the grill assembly at just the right angle allowed the glue to fall right into place. Hot melt glue cools and solidifies fairly quickly (which is good or bad depending on how you look at it...if you don't know what I mean, you will), and I found I didn't need much to secure the driver.
Remove the tweeter from the grill assembly. The tweeter assembly may be removed from the door panel in the same manner as the midrange. When it came to release the driver from the grill it was a bit more involved as I found my tweeters secured to the grill with a bit of glue. I broke that free with a screwdriver and then popped the tweeter out of the grill.
Install the new tweeter in the grill assembly. Before the Polk db1000 tweeters would fit nicely into the grill assemblies I had to grind down the locking tabs on the grill. I used one of the abrasive stones on my Dremel. Literally five seconds per tab is all it took and the tweeters press fit right in like a glove. One note of caution, though -- when I mean press fit, I mean press fit. It's not like I couldn't remove the drivers if absolutely necessary, but it was pretty obvious the drivers wanted to stay put. Make sure you're ready to install them for good and push them home. As you will note in my pictures, I did not push them all the way into grill, and that was intentional so I could use a screwdriver to pry them out of the grills at some later point if necessary. I applied a few small beads of hot melt glue to secure the driver because I had the gun there ready to go, but it wasn't strictly necessary.
Prepare the car's wiring to accept the aftermarket midrange and tweeter. The bad news is you'll need to cut off the factory connectors. The good news is Polk provides pigtails off of their driver and BSW provides some wires with pre-crimped, polarized spade connectors that are a perfect fit for their drivers. All I did was cut the pigtails to an appropriate length (about 18") and splice them in with the stock wiring using some mid-line splice spade connectors to facilitate later removal of the door panel. All wiring was bell spliced and covered in heat shrink because I can't stand butt splice connectors, but use what you want in your car.
Remove the kick panel. Removal of the kick panels requires removal of the footwell ceiling panel. Both panels require removal of two screws and the wiring associated with the footwell lighting. All in all pretty easy. Then, to remove the driver's side panel, unfasten the hood release and set it aside. Finally, remove the kick panels themselves by pulling them aft before pulling them away from the car.
Remove the woofer and install the new unit. Removal of the woofers requires an 8mm socket or screwdriver. Once the drivers have been pulled out of the cavity in the kick panel you may note that one of the terminals is smaller than the other. Depending on the vehicle and the chosen speakers, you may need to cut off the factory spade connector(s) and affix your own. Basic stuff, really. When done installing the new drivers, keep the kick panels off the car until you've completed system testing.

Front Speaker Replacement Highlights

The most annoying part of this job is removing the door panel. And that long, curved black piece you see at the top of the door is why. That's supposed to be attached to the door panel, but it broke free because BMW interior subcontractors apparently don't know how to build a door panel.	This is the interior of the door panel. The round white clips around the perimeter fasten the panel to the door frame. The panel is then fixed to the door with three T20 torx screws. One fits through the black hole to the rear of the airbag deployment fabric, while the other two fasten through holes in the door handle.	My technician recommended I replace any damaged door panel fasteners with the newer versions that include a foam washer. This helps seal the door and prevent moisture infiltration. I ordered a dozen and replaced them as needed.
The original wiring is sheathed from the factory and terminated in what is obviously a proprietary connector. BMW generally uses brown to mean "ground" or in this case, "negative" so you can use that as a guide if your wiring doesn't look like this.	While I would normally try to save all of the OE wiring and connectors it's just not possible in this case. I make it a practice to bell-splice, solder, and heat shrink all electrical connections in vehicles so there is never a chance they will come apart.	A screwdriver can be used to press the retaining tabs in enough to pop the driver out of the grill. The midrange driver that failed (not pictured) had a broken surround. All things considered, these look pretty good for nine year old drivers.
BSW sells these drop-in replacement midrange drivers for a $100 a pair. If you intend to keep the factory amplifier, they are the lease expensive alternative to the OE parts. If you are planning to replace the factory amp, then my advice is to just buy a new component setup.	A simple hot melt glue gun is a required tool for this work. Just remember to conduct work on a non-flammable surface. I used this dust pan I had within arms reach.	The BSW midrange just snaps into the grill but is a bit loose. I secured it with a bit of hot melt glue. The benefit to hot melt glue is that while it holds the driver securely, it's easy to remove if necessary.
The black / brown gunk you see in the original tweeter assembly on the right is a bit of glue that must be removed to free the tweeters. The tweeter is actually mounted to a circuit board, and that board is held in the grill assembly much in the same way the mounting flange of the midrange is held in place. Use a screwdriver to release the locking tabs.	The best fit of the Polk db1000 tweeters required the removal of the very tip of the retaining tab. I accomplished this in a couple seconds of grinding using my Dremel and a stone abrasive bit. Oh, and for the anal retentive readers...no, I didn't do the grinding here on my desk. That is a dusty procedure best suited to the outdoors.	I already had some 5.25" Polk woofers hanging around from a previous project so I bought a set of db1000 tweeters. They come with pigtails and a very simple high-pass filter that operates at 4500 Hz. This is reportedly higher than the factory amp crossover, so really all I gain by using the Polk crossover is overdrive protection. You can also see tape wrapped around the grill to protect it from scratches.
Remounting the new driver assemblies is a piece of cake. I reused the factory spade connectors but removed a bunch of excess wire I didn't want in the door, hence the extra splice. Oh, and that electrical tape covers another bell-spliced, soldered, and heat shrinked connection. This isn't a hack. Also pictured is the Polk crossover, such as it is, attached to the door panel with high strength velcro.	The dead pedal and kick panel are one piece. In the center of the panel you can see the clip that is only released when you pull the panel aft. To the right is the rear of the 90 degree twist lock, which is recessed behind the hood release handle.	The rear of the passenger side kick panel shows that it fastens to the car the same way as the driver's side part does. Remember to pull it aft before you try to pull it away from the car or you'll break that mounting tab..
Nothing much to see here except the original driver's side woofer and factory soundproofing, which is quite effective.	And this is the original midbass driver installed on the passenger side. Note that if you intend to do the surgery required to fit larger woofers here, take a close look at how close the top of the drivers is to the footwell ceiling panel. Unless you modify that panel, the driver may hit the panel.	Here you can see that the soundproofing also serves as a baffle for the driver. It also no doubt protects the driver from moisture so be careful cutting that out. If you do that, be sure to glass in a suitable replacement.
Sometimes it's hard to find drivers that will fit without modifications, so I figured I would show the relative sizes of the Polk 5510 and the OE unit. As you can tell, the bolt pattern of the Polk unit is slightly bigger than the OE unit.	Here you can see that the Polk 5510 is a bit deeper than the OE unit, but it does fit (barely). Of course, you could probably get deeper units to fit if you cut out the sound insulation / baffling, but I didn't want to do that.	The most obvious difference between the Polk and OE unit when viewed from the front is obvious. The OE unit surround is inverted, no doubt to eliminate clearance issues during excursion. Fortunately, the Polk units don't seem to rub the kick panel grill. Be aware that a larger driver with a greater excursion limit may rub.

Rear Speaker Replacement

Remove the speaker grills from the rear deck cover. The trick to this is wedging your fingers under the center of each side of the grill and carefully pulling upward. The grill will bend upward in the center and consequently pull in the front and rear tabs that fasten the grill to the deck cover.
Disconnect the wiring from the top of the enclosure. The woofer and tweeter connect with the amplifier via a connector on the top of the enclosure. Remove this connector by just tugging upward. Be sure to grab the connector body, however, and not the wires, or you may rip the wires out of the connector. If you intend to reuse the BMW enclosure, you'll need those connectors undamaged.
Remove the three screws holding the speaker enclosure to the rear deck. Removal of the grills will expose three screws used secure the speaker enclosure to the rear deck. Some of these screws are too close to the rear window to use even a stubby screwdriver, so I used a philips socket and a ratchet to make quick work of them. Once the screws are removed, the enclosure will be held to the rear deck with a metal clip and a small protrusion in the enclosure that acts as a hinge. To remove the enclosures, go around to the trunk, tug the inner side of the enclosure downward to release the clip, and then pull the assembly toward the center of the car to release it.
Remove the enclosure and drivers. The 6x9 enclosure is of a clamshell design and is easily dismantled by removing the four machine screws that hold the upper and lower halves together with the woofer sandwiched between them. The upper half incorporates a tweeter mount that is sealed from the rear to prevent the tweeter from being affected by the pressure waves from the woofer during normal operation. I purchased the BSW adapters to replace the BMW enclosure, but I quickly realized that the BSW adapters lacked any provision for mounting a component tweeter. This motivated me to salvage the BMW enclosures. In fact, the only the lower half of the BMW enclosure was discarded because it would not fit over the CDT woofer and it's large magnet.
Modify the enclosure to accommodate the new woofers. After a brief period of trial and error, I realized that the CDT tweeters would fit the BMW enclosure tweeter pod perfectly and I only needed to made a few modifications to the enclosure to accommodate the CDT woofers. The most obvious modification included grinding down the four plastic standoffs on the upper half of the enclosure. This served to close the gap between the enclosure and the woofer. I used a palm sander for the first one as an experiment, but found a grinder with a stone abrasive wheel made quick work of the remainder. I found that leaving approximately 7 mm of the standoff produced the best bit. To perfect the fit and eliminate the chance for vibration, I installed some thin adhesive-backed foam and trimmed it to fit.
Install the speakers in the modified enclosure. I installed the tweeter first and used the surface mount installation hardware to produce what looks almost like a factory installation. A bit of hot melt glue solidified the installation. I then bell spliced the tweeter wiring in with the existing enclosure wiring in order to retain use of the special press-fit enclosure wiring connector and reinstalled the protective cover on the tweeter pod. Next I mated the CDT woofer with the upper half of the BMW enclosure using some 8/32 x 1 1/4" machine screws, nylon locking nuts, and some washers. I used some special concave neoprene washers on the driver side of the connection only because I had them handy from an earlier project and I figured they would further help reduce vibration. All of the materials were purchased at the local home center.
Reinstall the enclosures in the car. With both enclosures finished, I reinstalled them in the car, reconnected the wiring and turned on the stereo to test them. The first thing I noticed was the increased bass because a portion of the shelf was rattling on bass peaks. I quickly determined that it was caused by the rear deck cover hitting the metal shelf so I stacked up a few three inch long pieces of the same adhesive backed foam I used earlier and wedged it between the shelf and the cover. No more rattling, and no heavy (and expensive) Dynamat needed!

Rear Speaker Replacement Highlights

The CDT 6x9 infinite baffle subwoofer is a perfect match to the BMW provided you use the right adapter. This is designed for use in unsealed enclosures (so called infinite baffles) such as the trunk of our BMW. In fact, any subwoofer you mount to the rear deck must be designed to operate in an infinite baffle of you'll easily exceed its excursion limits.	Although I'm a fan of Polk tweeters, I bought the CDT tweeter set to mate with the CDT woofer so in case I installed an aftermarket amp I could buy the CDT crossover designed specifically for these drivers.	The BSW 6x9 adapters (on top) are a good solution if you don't mind giving up the tweeters, as they provide no mounting provisions for them. Also shown is the BMW enclosure (bottom left) and the new CDT 6x9 driver.
The BMW enclosure is used to mount a 6x9 woofer and component tweeter to the rear deck. It is shown here dismantled. Clockwise from the top: The original HK woofer, the top half of the enclosure that contains the sealed tweeter mounting pod, the bottom half of the enclosure, and the protective felt insert. The insert and bottom half of the enclosure are discarded in this upgrade.	Here's a closeup of the original assembly. It effectively sandwiches the 6x9 driver between the upper and lower halves and connects using four machine screws. The L-shaped bracket and metal spring clip on top of the enclosure combine to temporarily hold the unit in place on the rear deck so you can insert the screws that permanently mount it. The female connector used to connect the signal wires is just to the left of the mounting screw.	A few philips screws provide access to the original tweeter. HK sealed the tweeter so it wouldn't be affected by the woofer pressure waves. The really odd thing about this enclosure is how they routed the wires from the signal connector (to right of the tweeter) to the woofer by just putting the wires in some foam and routing them through the junction between the woofer and enclosure (pretty much as depicted).
I had to shorten the standoffs so the CDT driver would mate properly with the top half of the enclosure. This is a decidedly permanent modification, so there is no going back after this. I started out with 150 grit sandpaper on a palm sander before giving up and using the grinder in the garage.	I also had to made some minor modifications to the CDT driver, including elongating the mounting holes and removing just a bit of the mating gasket so the standoffs would mate with the metal frame.	I used the CDT tweeter surface mounting option to install the tweeter in the enclosure. The ring around the back of the tweeter is a press fit and not particularly secure, so I used just enough hot glue to keep the unit secure, yet a small enough amount to facilitate later removal.
Every good connection starts with a bell splice, solder, and heat shrink. I found this heat shrink at my local home center's electrical aisle but any electrical supply house would have it too.	Here is a closeup of what a bell splice looks like. The wires are stripped about 1 inch back, cross with each other at the 1/2 inch point and wrapped in a spiral motion back on themselves. The result is a low-profile splice that is surprisingly strong, even without solder.	With the wiring soldered and the heat shrink applied, the tweeter is ready to be closed up. With a connection this secure, there is no chance that the connection will loosen up or short out.
To help seal the enclosure and reduce vibration I installed some thin adhesive-backed foam on the mating surface of the top half. I then used a very sharp construction knife to remove any unnecessary material.	The HK system will obviously never compete with a good aftermarket system but from the looks of these drivers I'm surprised the system performs as well as it does. These drivers promptly found their way into the circular file.	I bought some 8/32 screws and nylon locking nuts along with some washers to mate the CDT 6x9 with the enclosure. The concave neoprene washers were a leftover from another project and are most certainly not necessary.
Side shot of the new enclosure. Note how the foam nicely seals the driver with the enclosure.	This shows how nicely the CDT tweeter fits the enclosure.	While the temptation exists to torque down the mounting hardware, the nylon lock nuts make this unnecessary. To retain the best seal, it is best to evenly tighten the hardware.
Note how the neoprene washers nicely support the driver.	Left side enclosure reinstalled. Looks almost stock!	Right side enclosure ready for action. Hmmm...that CD changer sure would look better as an Ipod! Maybe next time...

Conclusion

Replacement of the speakers in the E36 is a relatively simple process. The most difficult aspect of the procedure is dealing with the door panels, and only because BMWs interior subcontractor doesn't know how to build door panels.

As far as sound quality is concerned, the resulting system is subjectively 50% better than before. The bottom is is certainly better defined, but the overly-aggressive subsonic filter in the HK amp really prevents the drivers from achieving their full potential. The most improvement comes in the high end, which seems to indicate that the OE HK tweeters were the weak link in that region. The high end is certainly smoother, at least in the front. On the other hand, I find the CDT tweeters to be almost offensively bright and "metallic" sounding at times (which surprised me given that they are a soft-dome design) but that is very likely because I am driving them with the crossover in the HK amplifier. Hardly an ideal configuration.

The weak link in the BMW HK audio system is clearly the amplifier, so if you can afford to invest the time and money I recommend replacement of the HK amp with an aftermarket unit so you can provide a full range signal to the crossovers that come with the component sets. Not only will the frequency response be what the driver manufacturers intended, a more powerful amplifier will be able to cleanly drive the speakers to levels you simply will not achieve using the HK amp.

The E36 is known to be an electrically "noisy" car, so if you do decide to replace the amp, be sure to get one that supports balanced differential inputs, or you may experience a lot of RFI / EMI. Zapco makes the perfect amplifier and line adapters for this car -- check out the DC Reference line and their Symbilink converters. If I ever get around to upgrading the amp in the car, that's what I plan to use.

BMW E36 HK Audio System Speaker Upgrade DIY

Spurred by a need to replace a failed midrange driver, I decided to replace all of the speakers in my E36.