July 31st, 1998
By: Robert Leidy

Certain parts of my new stereo system puzzle fell into place quickly. In my previous Z3 I had used Boston Pro series 6.4 component speakers. They worked so well with the odd acoustics inside the Z3 that they were the first piece of the puzzle to be locked into place. At the time I was shopping for stereo equipment Boston Acoustics was starting to place advertisements for their new 6.5 component speakers. They weren't available yet but plenty of stereo places were putting the 6.4 component speakers on sale to clear the shelves and get ready for the new 6.5 models. I have no idea what the new 6.5 speakers will sell for but the 6.4 speakers were normally in the $400 range, on sale you can find them in the sub $300 range.

The Boston Pro Series 6.4 speakers almost fit without modification. However the speakers did come in contact with the plastic kick panel that installs over the speaker. The solution proved to be simple, a protruding plastic ring was sanded down on the back side of the kickpanel. This provided the extra room necessary to properly install the 6.5 inch speakers.

The next piece of the puzzle involved a new device that I had no experience with. Alpine had a product they were calling Bass Shakers. Alpine was saying that these Bass Shakers could be installed under the seat and they would trick you into thinking you were hearing low bass sounds when what it was really doing was just creating the vibrations associated with low frequency bass sounds. It sounded pretty far fetched to me, but the local stereo shop set up a demo with one of these shaker things mounted to a wood box. The demonstration let you listen to a stereo and step on and off the wooden box to "feel" the difference. It was very strange to be tricked like that but sure enough, when I stepped on the box it really did seem like someone turned on a subwoofer somewhere. I still wasn't fully convinced of this products capabilities inside a Z3, so I posted my Z3 Bass Shaker question on the BMW roadster message board. It turned out several had not only felt the Bass Shakers before, a few had even felt them inside a Z3. Once I got the virtual thumbs up from a few individuals I started shopping prices on the internet.

After a little research I found out there are a few different Bass Shaker models available. A company by the name of Aura actually makes these devices and offers two different models, the Bass Shaker, and the Bass Shaker Pro. The pro model is physically bigger, heavier, and handles more power which results in more "shake". I believe that Aura also makes Bass Shaker Pros under the Alpine brand name. Down deep I think the Aura Bass Shaker Pro and the Alpine Bass Shaker are actually the same product, but the Alpine salesman was telling me his version was slightly larger when I was trying to get him to price match on the Aura Bass Shaker Pro. However I think I basically just paid extra for the Alpine name. On the internet I found the Aura Bass Shaker Pros for $180, but I ended up paying just over $200 for the Alpine brand.

To install the bass shakers, the seats needed to be removed. Initially the installer said I would need to take the Z3 back to BMW after the installation because removing the seats would set off the SRS light on the dash. However Larry Nissen (BMW Certified Tech) told me how to remove the seat without setting off the SRS light on the dash. The secret is to never put the key in the ignition. Every time the key gets put in the ignition it triggers a self test that will notice the seat is missing and turn on the light.

My attention then turned to the stock BMW subwoofer. Under the stock conditions the subwoofer seemed to do well up to a point but then it started buzzing and thumping. I removed and dissected the HK subwoofer to see how the thing worked and what could be done to improve it. It was too hot to be working out in the garage so once it was removed I took the subwoofer inside and using some old crossovers I had hooked it up to my home stereo system. (Note: one of the speakers gets wired backwards, reversing the positive and negative wires so the two speakers will work together by pushing in the same direction at the same time even though one is facing the opposite direction).

I was actually quite shocked at what happened, suddenly the bass got much cleaner at high volume, the muffled-buzzy sound was gone. What I learned is that the HK sub still has its limits, but if you give it a good clean power source it actually does pretty well. I could tell that this upgrade was going to get expensive so I decided to stick with the stock subwoofer. As long as I can get a good, clean, power source for the sub it was going to be fine for now (but maybe the subject of a future upgrade). Vibration was really my only concern with the stock BMW sub, especially if I was going to start sending it even more power. I had already found a fault with the rubber porting tube, so I knew I would have to secure it better. But I also suspected that I should invest $20 into some vibration dampening material in an attempt to cut down on the amount of buzzing and rattling the plastic components make as a result of the subwoofer.

I then started looking at those tiny speakers behind the seats, I just wasn't sure what to do here. It was obvious the current speakers were not worthy of being part of this new stereo system, but what could replace them. I had seen what a/d/s/ did in their show car in regard to rear speakers and liked that solution. But one quick check of the rapidly depleting budget made this decision a little easier. I decided to physically leave the stock speakers in place, but they would not be hooked up to anything. The budget played a big part in this decision, I decided to give up rear speaker sound fill in order to save some money right now. If the desire for rear speaker sound hits me in the future I will deal with it then. However if possible, I should attempt to plan my amplifier selection so I could add rear speakers at a later date if I choose to do so.

There were two pieces left to the puzzle, the CD player and the amp. I went back and forth on the CD player. On one hand I could spend $500 on the BMW CD changer, mount it in the trunk and stick with the stock head unit. This option has many advantages such as retaining the speed sensitive volume, and weather band features on the stock head unit. It also would maintain a totally stock look to the stereo system which is practically a stealth mode shield against car stereo thieves. On the other hand spending the same $500 could get you a much better in dash CD player installed which would probably sound better and offer tremendously better FM reception. The hangup on the in dash option that eventually led me to choose the overpriced changer route was purely cosmetic. It seems the trend on aftermarket stereos now is to add lots of flashy multi-colored light displays. But what I really liked is how that constant simple orange display lights up the dash at night. I didn't want to break up that look so I choose to purchase the BMW trunk mounted CD Changer. I'm not sure if I made the right decision here, but I figured I could sell the changer at a later date and install an in-dash CD without loosing too much money.

About a week after taking delivery of the CD Changer one additional fact came to light that might have led me to choose an in-dash player if I would have know about it ahead of time. The BMW CD Changer now has two different mounting location possibilities. I had only seen the side mounting location in the Z3 and assumed that is where the CD Changer would be mounted in the M roadster. However now there are some rumors that BMW is mailing me an M Mobility system that will fit in roughly the same area as the side mounting location making me either relocate the CD to a less desirable location (pictured) or remove the nice gray flannel cover around the CD changer. If the M Mobility kit ever shows up I'm probably going to wish I would have gone the in-dash route.

So now the only part of the puzzle left to put in place was the amplifier. A quick count of speakers tells me I need to power 6 separate channels

1. Boston Pro series 6.4 Component Speaker Set (Left - Front)
2. Boston Pro series 6.4 Component Speaker Set (Right - Front)
3. Alpine Bass Shaker (Left - Front)
4. Alpine Bass Shaker (Right - Front)
5. BMW Subwoofer (Left - Rear)
6. BMW Subwoofer (Right - Rear)

Picking the Amplifier