So annoying - please help

[Carlsworth]

Followed the guides and fitted a pioneer sub in shelf of 2009 a5 coupe with b&o system and dynamat all over 

It sounded poo - changed wires, 4 + 8 ohm setup etc etc 

 

Still sounded poo- 

So, bought a sub box fitted that and it sounds much better, but now what's happening is 

Whenever bass kicks in, the sound level drops a lot, maybe 40 % 

Seems to sound great when car is off, but when driving it's quiet and bass is real quiet 

 

Maybe I need to fit stand alone amp, but getting to a audio specialist is hard work - nearest one here is 45 mins away and need car for work

 

Any ideas?? 

Thanks muchly 😘