Adding a subwoofer to the E89 Professional Stereo

Justjeff1972

Justjeff1972

Member
 Nebraska
Hello Z4 experts. In the interest of never leaving well enough alone, I have decided to do some stereo upgrades to my 2012 sDrive 35IS while she is laid up for the winter. My car has the Professional stereo which is OK. It just has no low end. The 8" speakers behind the seats don't seem to do anything and the 6.5's in the footwells are meh at best. I'm replacing the 6.5s with 6.75 kicker subs. Passenger side is done and still have to do the driver's side. I'm also making/attempting to make a custom enclosure for an 8" kicker L7T solo baric shallow mount sub that will fit in the ski-pass. I have a Kicker 400W Class D mono amplifier to power the sub. Looking for some advice on the connections.

First off... for high level inputs to a line output converter, I am looking at two options. First is to take the signal from the 8" subs behind the seat. Second would be to tap a signal off of the footwell speakers, which are already mono, as I understand it. With the DSP system, both should only receive base frequencies, as I understand it. If anyone has experience with pulling high level signals from the amplified systems, do you have any preference?

For the connections to the amp, I'm considering powering all three subwoofers from the Kicker amplifier in a series/parallel combination yielding 2 ohms. If I disconnect the factory subs from the amp, will that fault the system? If it will, I can use the signal from the amp to the factory subs as the input to the LOC, which will give a load and "hopefully" resolve that issue.

Alternately, I can leave the factory 8's alone and power the 6.75 speakers with the kicker sub. Advantage here would that those are 4 ohm each, in parallel, so I can do a parallel/parallel combination for a final load of 1 ohm. The amp is stable at this load.

I'm keeping the factory connectors so it should be easy to revert if things go South. The Kicker sub will be installed in a 3D printed, sealed enclosure. Min volume is 0.2 cuft but I think the finished size is closer to 0.45. If anyone has done this, or something similar, and has advice, I'd greatly appreciate it. I'll follow up with photos and lessons learned when I'm done (or when I give up...).

Thanks!
Jeff
 
A few people have done a sub enclosure in the boot..mixed reviews..some rave reviews..some say it doesn’t really pass through the bulkheads…

Your issue with tapping into any speaker feed is that it’s highly tailored to suit the specific cheap n nasty OE speakers and as part of the total system..best intercept point is between the head unit and the amp as that feed by default is flat..

Really the subs need their own DSP processed feed to deal with time alignment , phasing etc etc ..

Most of your proposed solutions, imho, are somewhat botches ..but..if you’re happy who cares..

I would have thought you’re far better getting some decent woofers for the footwells and having your mega sub and disconnecting the rear OE subs..

But as I said the OE dsp was set up to solve a problem you’re riding rough shod over..

Having done this now twice with a 676 and then a 677 based system it’s not what I’d do..
 
Wanted to circle back to this now that I’m more or less finished. I installed two kicker 6.75 woofers in the footwells to replace the 6.5 factory speakers. All the speakers were connected using adapters so none of the factory wiring had to be cut. I did have to design and print some adapters to mount the new speakers with the factory fasteners but not a big deal. It took a couple of prototypes but I finally got a design that worked. No issue with room for the larger drivers.

This improved the bottom end but not an earth shattering change. Next step was a true sub. I decided to use a Kicker 8” L7T. Primary deciding factor was required sealed volume. Box lower limit is 0.25 cu ft. I designed a box for the ski pass (that I would never otherwise use). Box volume ended up at about 0.4 cu ft using back of the napkin math.

I pulled the high level signal from the 8” factory woofers and sent the signal to a line output converter which fed a kicker CTA-400.1 class D amp at 1 ohm. The sub is a 2 ohm voice coil wired in parallel.

This made a significant difference and accomplished what I’d wanted… some base you can feel and frequency response that the factory speakers cannot achieve.

The box is 3D printed with a very open in-fill that I backfilled with epoxy resin for mass and rigidity. I tried printing it with a high level of in-fill but the large flat pieces kept warping and causing the parts to fail. The epoxy added and extra step but wasn’t too bad wir 5% gyros in-fill.

Anyway, just wanted to let the group know what I ended up going with. Hope everyone had a great holiday and a Happy New Year.
 

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Well done - that looks like a pretty tidy install & doesn't take up a ton of room in the boot.

Good job.

I would be tempted to add another beauty panel in the boot, covering over the wiring entirely & just leaving the faces of the boxes exposed, and spend another 15 minutes tweaking the edges of the carpet liner inside the cabin (top edge).
 
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matsmith749 said:
Well done - that looks like a pretty tidy install & doesn't take up a ton of room in the boot.

Good job.

I would be tempted to add another beauty panel in the boot, covering over the wiring entirely & just leaving the faces of the boxes exposed, and spend another 15 minutes tweaking the edges of the carpet liner inside the cabin (top edge).
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Thanks... What do you mean about the carpet inside the cabin? I didn't really mess with that. The carpet on the box isn't perfect but I didn't really touch the carpet liner in the cabin.
 
Your first picture shows the woofer (in between the seats) - looks like where you have replaced the door to the pass through compartment.

I've been told I can be a bit OCD (just a bit) - but the top edge looks a bit rough to my eye.

The install looks 90% amazing - not much needed to get it looking 100% imho.
 
Justjeff1972 said:
Wanted to circle back to this now that I’m more or less finished. I installed two kicker 6.75 woofers in the footwells to replace the 6.5 factory speakers. All the speakers were connected using adapters so none of the factory wiring had to be cut. I did have to design and print some adapters to mount the new speakers with the factory fasteners but not a big deal. It took a couple of prototypes but I finally got a design that worked. No issue with room for the larger drivers.

This improved the bottom end but not an earth shattering change. Next step was a true sub. I decided to use a Kicker 8” L7T. Primary deciding factor was required sealed volume. Box lower limit is 0.25 cu ft. I designed a box for the ski pass (that I would never otherwise use). Box volume ended up at about 0.4 cu ft using back of the napkin math.

I pulled the high level signal from the 8” factory woofers and sent the signal to a line output converter which fed a kicker CTA-400.1 class D amp at 1 ohm. The sub is a 2 ohm voice coil wired in parallel.

This made a significant difference and accomplished what I’d wanted… some base you can feel and frequency response that the factory speakers cannot achieve.

The box is 3D printed with a very open in-fill that I backfilled with epoxy resin for mass and rigidity. I tried printing it with a high level of in-fill but the large flat pieces kept warping and causing the parts to fail. The epoxy added and extra step but wasn’t too bad wir 5% gyros in-fill.

Anyway, just wanted to let the group know what I ended up going with. Hope everyone had a great holiday and a Happy New Year.
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Awesome build, I had the boggiest of the bog standard sound in mine (no tweeters or anything) and sent it to my local car audio specialist who fitted new mids, set of tweeters, DSP/AMP and a lovely sub. If you are into your music, audio upgrades are always worth every penny (or cent).
 

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James35i said:
Awesome build, I had the boggiest of the bog standard sound in mine (no tweeters or anything) and sent it to my local car audio specialist who fitted new mids, set of tweeters, DSP/AMP and a lovely sub. If you are into your music, audio upgrades are always worth every penny (or cent).
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How did that sub perfrom "free air"? Is that a 10"?
 
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