Re: E28 audio system recommendations and my webpage

["Aaron Bohnen" <bohnen@xxxxxxxxxxxxxxxx>]

Hi everyone,

Rick writes:

> Subject: <E28> Need Speaker recommendations
> 
> Good morning! I have searched my files for information on speaker
> upgrades to my '86 535i and I don't seem to find any. I would like to
> ask any long term owner of an E28 who has made changes to his factory
> speaker selection to give me the benefit of his experiences. 
> I have the tweeters in the door post assembly, smaller units in the
> front foorwells , and shelf speakers with angled tweeters in the back.
> They are stock BMW, and they say ITT I believe.

Yep, this is the "premium sound" package for an E28. There is also a 
trunk-mounted amp that accepts speaker-level inputs from the head unit.

> They seem to have a
> resistor (probably a cross-over) and another wire 'coil' built into
> them. I'm concerned about replacing these units with speakers that don't
> have these items included. What are these items on the speakers,

The unit you are referring to as a resistor is a bipolar electrolytic 
capacitor and forms a nominal 6 dB/octave high-pass filter for the 
tweeter. The wire coil you are seeing is an inductor which forms a nominal 
6db/octave low-pass filter for the midrange driver. You need a crossover 
for whatever speakers you wind up with in this location. That means if you 
swap these drivers out for other units you should substitute the other 
units' crossover.

Personally I don't mind the sound of these speakers. They benefit greatly 
from improved tweeter filter caps. I suggest Solen or other reasonably 
high-quality polypropylene or polystyrene caps in this application. Mylar 
or generic "film" caps will not give you as much benefit.

By the same token, replacing the filter cap in the front, door-mounted 
tweeters is also a very good idea. Replace these caps with a same-value (or 
very slightly higher), 50+ volts rated capacitor.

> and
> what recommendations does anyone have for a drop-in replacement? I have
> a Sony CD in-dash receiver, 4x12.5 with what appears to be the stock BMW
> amp in the trunk under the window shelf.

I'd suggest a decent aftermarket amp running on line-level signals from 
your head unit would greatly improve the sound quality in your car. If you 
were to use a 5-channel unit you would even get an extra channel for a 
subwoofer which could be mounted in your trunk.

> In the back, the stock shelf units hold two speakers each; a tweeter
> apparently, and a midrange. Should I attempt to replace the units in the
> boxes, or is there a recommendation to replace the entire unit with say
> a 6 by 9 unit?? Any recommendations?

The clearance below the shelf is pretty well nil - that's why the stock 
speakers are situated in those little boxes that raise them up above the 
parcel shelf. You will have a very difficult time fitting a 6x9 in there 
unless you are willing to do some cutting to the steel panel below the 
parcel shelf.

> Any help with this audio system would be a help. I just want clean sound
> and a bit more bass. I mostly listen to bop and jazz, but I like it
> loud... oh... and the big guy occasionally!

I'd say replace the tweeter caps as I've suggested, replace the stock amp 
with a good quality unit, run line-level instead of speaker-level leads to 
it, and (optionally) add a subwoofer. I think that is a pleasing 
arrangement in the E28's.

Alternatively, there is also a cavity behind the kickpanel beneath the 
front of the rear seat. It is accessible by removing the bottom rear seat 
cushion. You could make some use of this space by installing a pair of 6x9 
subwoofers for example. You'd have to be careful about how you go about 
mounting them (use grilles, etc.) in order to prevent them from being 
trashed by being kicked by rear-seat passengers. It's a hassle, but would 
get you away from a trunk-mounted subwoofer system.

> email me direct if you would please unless the information I seek is
> already public knowledge..

I sincerely hope this helps. Please feel free to contact me if I can help 
you further.

Thanks,

Aaron

p.s. - I have a section on the crossover capacitor replacement in my column 
in October's issue of "Ausblick", our local BMW club's newsletter. You can 
see it on my website here:

http://www.civil.ubc.ca/home/bohnen/

Just click on the "Other Things, mostly Just for Fun" link or scroll down 
to the Just for Fun section and click on "Adventures of a Do-It-Yourselfer"

I put this column up on my website simultaneously with the publication of 
our newsletter. The next installment is in January, called "Simple 
Service and Easy Upgrades" and deals with tools, manuals, oem parts, 
dealers, fuel, oil, transmission and diff fluids and drainplugs. The next 
installment after that, called "More Upgrades for your BMW" deals with 
brake pads and fluid, brake ducts, stabilizer bars, headlights, etc. If 
these things interest you, stay tuned!
___________________________________________________________
Aaron Bohnen                     email: bohnen@domain.elided
- -Ph.D. Student, Civil Engineering Department, U.B.C.
- -Technicraft Engineering Services

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