Audi TT Bose sound with an aftermarket head unit

The Audi has come from the factory with the basic Concert system with Bose speakers, based on the factory equipment list. At some later point, one of the previous owners has stripped the Concert head unit and CD changer and swapped them for something more powerful.

The car has signs of having been in tuning / showroom use at some point. It came with large tuning shop emblems partially left on one side. The trunk has screw marks from a torn out subwoofer installation. Even the spare wheel well has a modified lining for a subwoofer that was there at some point. Also, on removing the spare wheel lining, I found a bunch of screws and a LOT of stripped cable bits. Certainly marks of a (lazy) installation.

The car came to me with an entry model cd player installed, which did not work. Being uncertain as to the shape of the car's audio interfaces, speakers and everything, I invested lightly and purchased the cheapest 1 DIN player I found that had a hands free Bluetooth option. Finally it appeared the audio did not work just because the cables behind the harness were stripped, split and joined into a huge mess. For a reason beyond my understanding.

Interestingly, looking closer into the cabling, it seems the car has not one but two sets of cables for subwoofer installation. There is one power cable that runs from the battery through the firewall and under the carpet all the way under the rear seat. Then there's another that is split from the audio unit harness and runs above the carpet but underneath the center console. Plus two sets of audio cables. Plus another for control. More is better I guess.

Anyway, the new audio unit sounded rather thin and it appeared that the fader controls did not work at all. Googling up various forums it seems that the Bose speakers are originally set up in an unorthodox way with the speakers all in the front channel. The factory head unit uses other means of creating a balance in sound.

But the fun thing is, the rear speakers are really powerful. You just cannot get them to play back unless you play the head unit at a ridiculous level. They reminded me of an old bass element I had in a home theater system once that required a good deal of gain before it kicked in. Once started, it would play along nicely.

So what if you dropped the gain from the front speakers much much lower so the rear speakers would get sufficient power so as to be heard? The Pioneer head unit has a rudimentary EQ which allows for a good deal of range. Boosting the low end of the spectrum substantially and dropping everything else heavily is not a very pretty EQ curve. The image is created on the computer and is not actual but shows the idea.

Surprisingly, the results are pretty good. Perhaps not showroom quality but there is enough bass to do some justice to the speakers that are not that bad actually.