I then liberally covered all flat panels with Silentcoat.
- F9.jpg (169.2 KiB) Viewed 2451 times
For the speaker plate I was originally going to use 18mm ply, but had some concerns: cutting the 149mm diameter hole for the speaker accurately enough; the speaker would sit very far forward and may interfere with the grille; the speaker screws would be very close to the edge of the 149mm hole and may break through. I decided instead to use 4mm aluminium sheet, this was easy to shape and cut with good accuracy.
- F10.jpg (187.75 KiB) Viewed 2451 times
I smeared RTV silicone gasket around the edge of the plate and bolted it in place with 6mm bolts.
- F11.jpg (177.13 KiB) Viewed 2451 times
Once the silicon had set I loosely filled the speaker box with polyester sound wadding, connected up the speakers and then pop riveted them in place with 6.4mm x 15.5mm sealed end pop rivets. I finished off with a section of silentcoat and covered it with closed cell sound deadening foam.
- F11.jpg (177.13 KiB) Viewed 2451 times
- F12.jpg (195.16 KiB) Viewed 2451 times
I finished off with a pair of carver grills from my BMW dealer
- F13.jpg (206.06 KiB) Viewed 2451 times
The Amplifier:
I fitted two 6mm x 60mm long studs onto the rear bulkhead to hold the amp in place and fitted two 6mm rivnuts to secure the top of the amp. I built some spacers out of ply for two reasons: To keep the amp away from the carpet and allow some air to flow behind; It was risky fitting the amp so close to the stereo (it is inches away) as there could easily have been interference. In this case my plan was to sandwich a grounded steel plate between the head unity and the amp. Thankfully this wasn’t required. The amp was powered with two 10 sq.mm power cables and a 60A fuse adjacent to the battery positive terminal (75mm of cable unfused). I made a pair of 2.5 sq.mm twisted pair speaker wires which connect the amp speaker front output to a 3 way crossover under the heater unit for my front speakers.
- F18.jpg (179.61 KiB) Viewed 2451 times
I connected the front speakers line in to the Head unit front line out and the rear speaker line in to the head unit sub woofer out.
Setting it all up:
Having wired it all up I switched it on and put a test CD in and began tweaking. The rear speakers are 6dB/W less sensitive than the front speakers so I adjusted the input sensitivity to give more power to the rear. With default head unit settings the power was very good, the bass was not bad but needed some work, but the most annoying thing was there was too much directional sound from the rear which upset the soundstage. I went into the settings and noticed that the low pass filter was not set for the sub woofer, so I switched this on. But I still wasn’t happy with the bass, sure it was loud but it was not tight and with the work I had put into sealing the enclosure. I realised the woolly bas was coming from the front focal footwell speakers. Thankfully the headunit had a high pass option for the speakers. After a few experiments I settled on rear subs LP filter 125hz, front speaker HP filter 125hz. Bass now much tighter, just have to get the level of bass to my liking but the head unit allows fine tuning in 1dB steps.
- F14.jpg (111.86 KiB) Viewed 2451 times
Modes:
Hands Free
Bluetooth Streaming
USB
CD
DAB
FM (not used)
Aux (used for front radio which has FM, CD, Aux of its own)
The cost:
Amplifier: £80
Head Unit: £120
Speakers: £66
Materials estimate: £50
Carver Grills: £81
Why:
The biggest disappointment I had with my Z4 when I picked it up was the audio system. The lack of a mid range speaker in the front doors and the inclusion of a mid range speaker in the rear bulkhead didn’t create the soundstage to my taste. In addition I was keen for more power and bass than the standard head unit (6W RMS/Channel I believe) and more features (DAB, USB, Bluetooth, Handsfree etc.). I improved the soundstage immediately by fitting 3 way Focal 165 AS3 speakers and fading all the sound to the front. To improve the features and power I decided to replace the headunit with an aftermarket one with line out, handsfree, DAB and ability to play FLAC files. This would be combined with an aftermarket 4 channel power amp. My original intention was to fit the AM headunit in place of the existing BMW Business CD using facia adapters, and this was a driver for my choice of Pioneer DEH-X8700DAB, I liked the simple look and thought it would best suit the Z4. However when I installed in the dash with a facia adapter I just didn’t like the look. I tried a different design adapter and still didn’t like the look. So I decided to embark on this modification.
The setup in use:
There is a lot I like about the setup, I like the features and how the headunit functions, the power is more than adequate without noticeable distortion and the bass is nice and solid, to be honest if it were louder it wouldn’t be safe. There are a few things that are mild annoyances:
Traffic Announcements on the headunit appear only to work in FM radio mode, and I am unlikely to ever use that.
Controlling seek, volume etc in a unit behind me is far from ideal. If I had known I was going to fit the headunit here when I bought it I would have chosen an alternative model that could be controlled remotely from my phone. It isn’t a major issue because I mostly stream FLAC files from my phone anyway. In addition I have bought a remote control and intend to fit an IR receiver/transmitter so I can point the remote forward.
Things still to do:
Trim the wiring in the boot (highest priority)
Fit IR receiver/transmitter (medium priority)
Trim the gap at the bottom of the headunit (lowest priority)
Z4 3.0L 2005. Titan Silver. Audio Upgrade Second Stereo Pioneer X8700DAB, Sony Xplode 4 x 70W Amp, 6.5" Reckhorn Subs in rear cubby, Focal AS165-3 in fronts.
.. well done sir 
