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Anyone here worked on BMWs?


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#1 of 4 george.Legeza

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Posted December 04 2003 - 06:20 PM

Okay, a few questions. First of all, my current car is a '97 BMW 740iL. Won't be doing any work on this car since I'll be trading it in on a '97 or '98 BMW 540i soon enough, but since the two cars use similiar speaker setups I've been investigating exactly what's possible. In doing this, I've noticed a few things.

The system is powered by a stock amp in the trunk, not by an amp in the headunit. Apparently this is true on the 540i as well. Next, the head unit isn't a standard size and can't be replaced since the OBC controls are in it. What is a standard size is the unit with the equalizer controls. It would seem that if I wanted to put a new head unit in I'd have to pull this out. Of course, this would leave me with not only useless radio controls still present in the cabin, but useless steering wheel controls as well. Besides becoming somewhat attached to having controls on the steering wheel, having the radio controls be present but non-functional would drive me crazy. I'm just a sucker for things looking stock (on the bright side, if I were to replace the equalizer with a head unit there's a piece of wood trim that slides down and blocks it anyway).

My solution to this is to work around the head unit, but I'm not sure how well this would work. What I want to do is replace the stock amp in the trunk with two new amps. One will power the front speakers the other will power a subwoofer. The rear speakers will be removed all-together since I really don't have any need for rear fill. Moreover, I'll be replacing the front speakers with a new set of components and adding a single (probably 10 or 12") subwoofer in the trunk. Finally, I've learned that there's a 10-disc MP3/CD changer that can be swapped with the standard 6-disc CD unit on the 540. It'll work with the stock head unit, although tracks have to be searched through one by one. It's a bit of a compromise, but I think I'll manage.

Okay, so that's my plan. With any luck, this means I'll be able to keep all of the stock functionality, but gain a significant upgrade in sound quality. The main hurdles that I foresee are getting my hands on a wiring diagram for the stock amp in the trunk (although I've already located the outs from the stock head unit, not sure if these will be in the same place on the 5, though) and taking the risk of having the stock head unit seriously degrade the overall sound quality.

Beyond this, does anyone who has worked on BMW sound systems in the past foresee any problems? Or anyone familiar with car audio in general? Since I'll be trading the vehicle in sometime in the next month I'm hoping to have enough planned ahead that I can start purchasing things immediatly. BMW really did a poor job with their stock sound systems, so I'm hoping to not have to deal with it again on my second one. Posted Image

#2 of 4 Jay H

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Posted December 05 2003 - 05:46 AM

I have a '97 E36 328i and the only thing I did was replace the head unit with one with a CD player in it, because I didn't want to shell out $700 for a CD-Changer.. At the time, there wasn't an interface for the I-bus audio that the BMW uses and the unit came with only a cassette deck. As the 3-series back then did NOT have any steering wheel controls, (And I didn't get the OBC) the only features I lost when I changed was the secondary antenna (The BMW has two antennas which most afterunit HUs wont be able to use and the NOAA weather band channels.) I don't think the head unit is that bad, as you describe it, it is made by Alpine, unlike the Panasonic one that is in my MR2 Spyder.

When I did replace it, I heard two different stories about the amp that is in the trunk. Crutchfield told me I needed a line level adaptor while a local install place told me I didn't. Not knowing what the amplifier is and after having a hell of a time getting that line level adaptor to fit in the dashboard, I took it out and haven't used it since. (This was about 3 years ago now, so far so good...)

But other than that, I haven't touched the speakers or anything so can't really help you.

From what I've heard on bimmer.org the Amp is the weak link in the system and not the head unit. The amp has something like 10% THD or something outrageous like that. I would see if this website has anything on it. I use this website alot for any E36 reference stuff, but it does have links to the '97 E39 5-series:

http://www.unofficia.../frame_e39.html

Jay
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#3 of 4 Sean^M

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Posted December 05 2003 - 05:59 AM

you couldn;t discern anything under 10% THD in a car anyway from an amplifier. THD is a very misleading spec for an amplifier.
McIntosh tube amps are rated at 10% THD as well, and people willingly shell out $35K for those.
Ignore THD ratings on amplifiers. The spec is meaningless to be honest, and depending on how it's measured, by FCC or EIA standards, the measurements can be very misleading, as nobody ever specifies how they measure their amplifiers unless it's to point out FCC specs, which are the more accurate means.

as for the BMW, Metra probably makes a replacement kit for those controls and an aftermarket radio. They do for otehr similar cars like the Ford Taurus which also incorporates ehater controls into the same panel as the radio.

#4 of 4 Andy Hardin

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Posted December 18 2003 - 09:38 AM

This might not be too helpful but I had an '89 525i that had a similiar setup sound setup to yours (internal amp and 8 speakers).

This was before I did all of the work myself but the shop I worked with recommened that I just remove all of the BMW stuff and rewire the entire vehicle for the new system (5 1/4 components in front and dual subs in back, it was pushed by two amps).

Rewiring eveything from scratch ended up being a better solution for me.