e86 M Coupe and e85 with premium - Sub add on (56k WARNING!)

great write up!

Thanks for sharing all your research and hard work.

I ended up liking the mid-bass connections the best for tapping. I tried the sub connections, but I found those inputs to be very "hot", resulting in an over-driven input level. At least with my sub, the speaker level input was not able to down convert the 16v sub level input correctly. There was too much gain at such a low level on the amp, which lead to very distorted bass etc. From my experience working in the biz, it is best to have your input at 85-95% capacity and have the amp work at 50-70% of it's capacity. I found the mid-bass connections are the best so far, but not as good as I would like, potentially still a bit to hot. Ultimately it's the problem with using speaker level connections verse line level connections. Also, I don't think it's clear what exact frequency range we are getting out of any of these connections. I have used this subwoofer before in another car, but with an Alpine HU with a 4v preamp subwoofer output. With this setup the sub sounded great at all frequencies and even responded very well in the 20-40hz range.

I may try the sub connections again, but this time with an outboard adjustable speaker level to line level adapter. I am hoping that if I can get this tuned in correctly, that I will find better low-end response, 20-40hz range that is.

My basic setup includes:

1. Tapping Mid-Bass Front Drivers
2. Gain setting is at about 55% on amp.
3. My sub has a fine tuning gain dial for in the car and this is at about 25%
4. Crossover set at about 65hz
5. Phase setting is at 180degrees (at least with mine, changing from 0 phase made a big difference)
6. I also lined the back trunk area, underneath factor carpet, with some moving blankets I had laying around, this helped a lot with eliminating any boomyness and random rattles.

With this configuration , after about 15hrs of tuning to different music types etc., I am pretty happy with the sound of the setup. I can listen at what I would consider 85-90% level on radio with no slapping on the driver and good clean tight bass. Overall, it was worth the time and fills in the missing link of good bottom end to the factory system.

Thanks for all the info that "peeti" and others posted!

When I originally tapped the front mid-bass, I had to set my gain to max. It was fine for jazzy tunes, but fell short on sounds that had more bass. When I started working on adding my rear-view camera (another Ron Stygar inspired project), that area was exposed again and I decided to try and rewire to the subs. It allowed me to set my gain to about 40-50% and had a bit more control of the bass. I'm curious about the 180deg phase on your setup...could the pos-neg wires be switched? I've got my crossover set to about 80Hz, but I haven't really played with it, yet. I might try something lower like yours. Cheers!

Seems to me the difference in our gain levels, must be related to the built in speaker-line converters in our amps. I couldn't even have my amp gain at 5% when hooked up to the sub wires, it was just completely over input gained.

Besides the gain issue, I am curious if there is any difference in signal frequency range coming out of the amp to the sub vs. mid-bass? I also wonder if the factory subs are truly subs, in the fact that they are getting a combined sub signal, rather than separate left/right? If they do get a separate combined "sub" signal, then i could tap only one sub, thus reducing overall gain to the amp. I might try this, just to see...

Check out the first link on post 42 above. It has info on the freq range of each speaker channel. SHouldn't make a difference as far as low-pass for a sub.

I finally had an opportunity to finish this project up over the weekend. I used the factory sub speaker level inputs and started out using a Scosche LOC80 line output converter and while it worked OK, the MTX REQ sounds significantly better. I am not using the bass enhancement feature or crossover on the REQ since my amplifier handles these tasks. I picked up a Rockford Fosgate Punch 45 amplifier (the 2005 25th Anniversary model) for sentimental reasons, bridged it pushes out about 260 watts RMS. I went with the JL 10W1v2-4 subwoofer for a few reasons- I was happy with this speaker in a JL StealthBox in my old car where it only had .45 cubic ft of airspace, and it has a relatively shallow mounting depth which was a key requirement for the box I desired to build. The airspace requirements are .625 cubic ft so my .50 cubic ft box stuffed with about .75 lbs of fiberfill should be close or a little over. I wanted to use fiberglass but with time constraints settled on MDF and it turned out better than I thought it would, both cosmetically and in the way it sounds. Because of the way I wanted the box to take up a small amount of space, including some weird angle areas that see little use, I ended up moving the hatch light to a spot above the battery cover and also had to slightly modify the battery cover slot for the lowest hook so that it could work with the box flush against the battery cover. I notched the box so that the hatch cover could continue to fold down and lock on the base.

I'll put together a write-up in the next few days but here are some pics of the end result (EDIT- My write-up is here- http://www.billswebspace.com/MZ4Subw...stallation.htm):





Thanks again for all of the people on this thread and others that did a lot of the pioneer/ first adopter work, now my stereo sounds like it should have.