Upgrades to the audio system in a 2001 325i. The existing electronics are preserved (minimizing effort) while significant gains are made by replacing only the speakers. A methodical case-by-case study is done to pinpoint the weakest parts of the whole system. Photo illustrations and disassembly tips are provided.
The stock BMW e46 audio sounds OK at first, but when you have to turn it up, or listen for a long time, it becomes worse. It's harsh, and incomplete. This is the non-HK (standard) audio, with Alpine amp and non-branded speakers. But, I've looked at the Harman Kardon system and I don't see that it's much better - The speakers are basically the same untreated paper cones with foam surrounds, in both the stock and Harman Kardon versions. The sound is loud enough, but the bass is really distorted. The tweeters don't reach high enough in the audio spectrum, I'm guessing they top out around 15 KHz. The mids sound blaring at upper volumes. But, the sound does fill the car.
Indeed, the Alpine amp is rated at 200 W, while the Harman Kardon system is rated at 300 W. Not a significant difference in amps. And the drivers are all foam-paper, regardless of stock / HK.
The weakest part of this whole BMW car sound system is the transducers. The speakers are just plastic-framed paper & foam. As with many other types of electro/mechanical and electro/optical systems, the transducers must be a primary suspect when system fidelity suffers.
Non-standard (yet not bad) Electronics
The BMW e46 audio electronics are very non-standard. The CD player - amp interworking is complicated by the use of balanced / differential signals through the body wiring harness. The harness already has 6 separate channels between head unit and amplifier, already equalized. Signalling is done at relatively high levels. Any modifications require signal converters or complete overhaul. With all this complexity, and the fact that a 200 watt Alpine amp is being used, this is not a weak area that needs any changes.
There is a very early point of diminishing return with money spent on car speakers. The speakers are way off axis, sound bounces off hard glass, everything's out of phase, energy propagates through vibrating door panels, ambient noise comes from all sides, etc. This is not the place to try and squeeze out every last subtle nuance with high-end speakers like Focal, ScanSpeak Revelator, etc. I propose that the most significant gains are made at the low-dollar end of the spectrum.