B3 shelf speaker deletion / Duo-Sound Project

[Mellis46]

This may be another long post so here goes:

I have added a few bits and pieces to my 90 over the years but haven’t been able to find a sun blind parcel shelf. This had been winking at me on ebay.de along with the rollo to go with it on another listing since before Christmas...! A couple of weeks a ago I thought, sod it, a shelf without any hooks is better than no shelf, puts me on the road?

New, old stock, still in the original wrapper, and with no holes cut in it:





At the back of my mind was the fact that, since fitting the B4 door cards set, the 90 has effectively had 10 speakers, 2 in the dash, 2 mids and 2 tweeters in the doors, and the 2 standard 90 passive shelf speakers with tweeters. Having fitted a Delta headunit (which was only capable of driving the front two on its own) and in order to have all of the speakers working, I was running a 2 channel amplifier on the Delta’s rear pre-out at 2 Ohms to drive all of the rears. On the pass through port of that amplifier was a second identical 2-channel amp, bridged, running a JBL GT3 sub.

Two issues I had with that setup, Firstly the duo sound headphone connection could not be used, as its switch would only kill the shelf speakers, even if the fader on the headunit was used. Secondly the 90’s standard speakers although acceptable are nothing to write home about, and adding some more in the rear doors from an 80 had left the sound-stage very muddled and rear biased, despite the amp being tuned to match as best as I could.

The reasons for this project, are again twofold. Firstly to delete the rear shelf speakers, returning the car to a more standard spec of 6 speakers (plus sub). The new shelf would not have to be cut for speaker holes which seemed like sacrilege(and looked tricky TBH!). I would move the subwoofer amp onto the Deltas front pre-out channel thus, secondly, the ability to fade the fronts (and sub) down would be restored to leave the rear headphone connection viable. Yes, my intention was to preserve the Duo-Sound unit!

One of the more quirky pieces of the 90’s standard equipment, I wanted to keep it as to lose it would mean losing some spec which even the most lowly of b3 saloon models had, well in the UK at least. I am unsure if the B4 80 was ever available with Duo-Sound or an equivalent so it was worthy of study.

So, an experiment was required! Would the 90’s Duo-Sound loom work with my B4 doorcard speakers? I removed the loom from my old 2.2E to try it as at this stage I did not want to hack the current car up unnecessarily.

FAIL! The loom did not work. The B4 speakers, although having the central socket, did not have the required number of pins, missing the common ground present in the 90 loom but deleted in the B4, so the speakers did not cut out when the headphone position was selected. Crap, I thought. But then...

The 90 shelf speakers are similar to the B4 80 ones in that they both have the 3 –plug arrangement that confuses many a new owner. Could the internals be swapped I wondered, after all, Audi would not have “re-invented the wheel” by discovering a whole new way of building speakers? At some point after the proprietary gubbins there would be 2 wires into the voicecoil surely?

I decided to sacrifice an old Nokia 90 shelf speaker i had in the 2.2E, and a dud Haes door speaker I found in a box in the loft. The 90 speaker would not prise apart, but the bottom could be clipped away using a pair of cutters. The 80 speaker came apart by running a screwdriver aound the seal and then levering it off. What I found surprised me:



There was no gubbins in there at all?! Just bridging pins, and one more set in fact on the 90 shelf speaker than the B4 one. So: Game On! Time to bite the bullet and break open one from the car and get to work. I transplanted the 90’s pins into the 80 door speaker (another Haes unit):





Would it work back on the car? This time I used the connection at the rear shelf to test it, as effectively the Duo-Sound should think this franken-speaker was from a 90. It worked a charm, and cut out when the switch was flicked.

Time to whip the other door card off and make another franken-speaker. This one was a Nokia unit, which was appreciably harder to crack open than the Haes. It just seemed to have more glue on it. Regardless, once opened it was of identical construction, and it was possible to make another 90/80 hybrid by sacrificing another shelf speaker.

Next, deep breath back seats out, parcel shelf out, passenger side front seat out, centre console out, carpet lifted!! It was a case of relocating the shelf wiring down to the doors, extending them as required, retaining that crucial ground wire that loops everything together. I also ran that extra 5m phono-to-phono cable to take advantage of the Deltas front channel.

The door card loom took some fettling too, mine are the type with the box that covers the speaker, some B4s are like this, some aren’t I have found, anyway the upshot is they have a loom extension piece into the box so you can remove the doorcard without dismantling the speaker enclosure. I used the Duo sound loom I removed from my own car to make an extension by clipping it and soldering a female 4-pin plug onto it as per the Audi made one for the source wires:



And:


Once in I checked everything still worked. It did (thank feck) I rebuilt the car having cut my new sunblind equipped shelf with a hole for the Duo-Sound unit using my old shelf as a a guide:



As a side note the replacement shelf is softer fabric on a composite board, rather than rough fabric on a cardboard one. Looks nice fitted as when hoovered the pile moves making it look plusher. Wonder why this is?





Anyway, all fitted:



Retaining the Duo-Sound was just a bit of fun really. I can't remember ever having used it! I know Audi did matching Audi Design headphones when the cars were new, wonder who coughed up for those Other than the shelf, which I would have bought anyway, the project cost me £9.99 for another phono lead and I think the car is better for it. The rear bias has gone and the sound in the car, although only as good as a set of crap stock speakers will allow, is less muddied. It looks more factory as any car equipped with door speakers wouldn’t have them on the shelf and vice versa.

Now I just need to improvise / find a set of compatible hooks for the blind which I am going to set my mind to this week. Suggestions?!

[Kenquattro]

Excellent write up.

[Mellis46]

Thanks Ken. Was happy to finally get my hands on a sun blind parcel shelf and gave me a good excuse to iron out a few bits and bobs at the same time

[Ben]

I had to google to see what Duo sound does
So how rare are 035 vag 307 headphones and did anyone spec them as a £22.60 option back in 88?

[slacky]

Sorry , only just commented on your thread Mark ,as Ken said very good
report /research thanks for sharing