So I bought a 2015 CPO ML250 last month which was loaded except for the Harmon Kardon stereo upgrade. I noticed the speakers were struggling with the low end/bass...kind of sounded muffled on certain songs like a hand or object was pressing on speakers. I replaced the speakers this past weekend with brand new JBL 6.5" speakers front and back and for some reason the speakers sound even worse. The car stereo shop I replaced them with then replaced the front speakers with Kicker speakers while keeping the JBL's in the rear. There is now hardly any bass and when you turn the volume up to mid-level, it becomes somewhat distorted. The installer showed me the factory speakers and they were paper and light-weight. The new speakers were definitely heavier and appeared to definitely be a better quality. So they had me bring the vehicle back to install a "power pack", aka amplifier, but after taking the head unit out, said it wasn't an option because they would have to cut the harness. They think the head unit has an equalization component that is somehow interfering with the signal processing, as well as the head unit not having adequate power. They are recommending I install an amp and sub to handle the bass and are pretty much guaranteeing there will be significant improvement. My question is, how could installing new, quality, name brand speakers not result in sound improvement over the factory speakers which to me were not ideal to begin with? I can't believe the sound got worse. Also, has anyone installed a four channel amp successfully to provide more power to the interior speakers? If so, what amp did you use and was there anything special about the install. I've got to get this corrected and have never had this issue in any of my previous seven vehicles (Audi, Cadillac, BMW, Benz, another Audi).

 

If you want to get into it....yes there is "equalization" linked to the OE speaker configuration"... to get deep into it - Match "mini" DSP/AMP + PP-AC 94A Cable

https://www.audiotec-fischer.de/en/m...lifiers/m-5dsp

https://www.audiotec-fischer.de/matc...e/adapterIndex

 

Thanks for your reply fabbrisd1...I'm still confused...so the amp and wiring harness are needed to fix my problem? Will I be able to keep the new speakers because I'm afraid the stereo shop probably discarded the OE speakers? I don't see anywhere to purchase these items in the links provided. Any additional info you can provide is greatly appreciated.