Glenn Richards wrote:

The stock system in my A4 has a sub, 8" mounted under the rear shelf.
This is powered from the same amp as the rear speakers.

Not quite sure why Audi have that arrangement, surely it would make
more sense to have the front speakers amplified as the sound is a lot
better from an offboard amp.

Depends how good the onboard amp is... Also it may be allowing them to
bi-amp the front speakers direct from the head unit using the internal 4ch
amp. Sounds very much like the system in the 75 which had an amp in the boot
and and sub under the rear shelf. Pike gits broke into my car through the
rear window though and I ended up with a sub full of glass fragments - took
some sorting...

Only thing to watch with this arrangement though is that the stock
head unit drives the "line" level at 9V RMS (standard line level is
2V RMS). This gives you 3 options:

Standard line level is 0.775V (0dbu, but you knew that...) - car stereos go
for higher "line" levels either to improve immunity to noise or by tapping
the speaker output before the current stage...


I've actually reduced the level of the rear speakers by around 3dB, as
in the normal driving position you can hear the tweeters in the rear
doors quite clearly, and it sounds a little strange. A 3dB gain
reduction on the rears eliminates this problem without making things
sound weird in the back of the car.

I've noticed this in Golfs, when I change the rear speakers in mine they'll
be coax so the tweeters will be down the bottom of the doors. I'm only
changing the rears out of guilt for anyone who travels in the back of my
car...


In the past I've actually had a surround processor hooked up to the
rear speakers to get a surround sound effect (similar in concept to
playing a stereo CD through a Pro-Logic decoder). Unfortunately this
sounds very strange to any rear seat passengers. What would be
interesting is to use the pressure sensors under the rear seat (used
to determine which airbag behaviour to use) to switch into normal
stereo mode in the rear if anyone was sitting in the back of the car,
otherwise switch the rear
speakers into surround mode.

Volvos have a surround mode button on the head unit - but then they have the
rear effects speakers in the rear shelf and the rear door speakers are
"front" for the purposes of surround.

One thing Audi did get right was the speakers. The front component
speakers in my A3 (1999 T-reg) were fantastic, although the rear co-ax
drivers weren't quite so good (3-door, I believe the 5-door had
components in the rear as well). Both the previous A4 (Y-reg 2001) and
the Quattro I have now (52-plate 2003) have particularly good speakers
fitted in the doors. While I'm sure it's possible to improve on
these, I doubt it would be worth the effort.

What I am considering doing though is replacing the factory speaker
cable with some 105-strand OFC stuff I've got a big roll of, as I'm
sure this will improve things. On my first car (1995 M-reg Fiesta) the
factory speaker cable was little more than bell wire, and upgrading
this made a huge difference.

I'm highpassing the main speakers anyway so the current draw to them is
reduced by a lot...

--
Just remember that you're standing on a planet that's evolving / And
revolving at 900 miles an hour / That's orbiting at 19 miles a second,
so it's reckoned, / A sun that is the source of all our power. / The
sun and you and me and all the stars that we can see, / Are moving at a
million miles a day / In an outer spiral arm, at 40,000 miles an hour,
/ Of the galaxy we call the Milky Way.