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Discussion Starter #1
Hi, I would like to know if any of you guys know a way to get a flat signal out of the OEM head unit. I have noticed that there seems to be a high pass filter of ~-6 db per octave @40 Hz in the factory head unit, which really bothers me since I listen to a lot of hip-hop with a lot of content below 40 Hz.

I know that using the AUX input bypasses that annoying EQ, but I can not use the AUX input while driving. It just isn't safe to change songs by looking down at your phone. This is why I want to find a way to be able to keep using my usb cable connection to my iPhone, which allows me to use the head unit and steering wheel controls to switch songs etc. and get a flat signal to play on my aftermarket audio system.

Also, does any of you guys know if the built-in EQ is constant according to the volume? Because I've been looking at digital sound processors that could DE-EQ the OEM eq curve, but only at a certain volume level. The issue with that is if you modify the volume at which the de-equalisation was set, you get an even less flat signal. With this kind of DSP, you have to use their remote control to control the volume, which I don't want. I want my car to look like it came out of the factory, but with an awesome flat audio system.
If the factory EQ curve is constant with volume, that means I will be able to keep using the headunit's volume control with the DSP, which would be really really awesome to have. I would have, for my needs, the perfect audio setup, since right now it is near perfect.

Only thing missing are those low-lows. It botters me everytime I hear them quieter than the other notes.

Looking forward to your answers.
 

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Discussion Starter #3
I didn't mention that I already have my speakers, subwoofer and amplifier installed. So I am not looking for a flat signal for the factory speakers.
 

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I've had the same issue with my 2016 6 (non Bose). I have a Fosgate 360.3 which auto-equalizes the OEM signal, I had a glimpse of the OEM signal when I did this and it definitely was not flat - there was some EQ in the mid-high range and the sub-40Hz cutoff seemed much more drastic than 6dB/oct. It was so much that the EQ in my 360.3 couldn't fix, and what it did "help" sounded "loose" bass. Maybe an artifact of a poor internal amplifier in the OEM system?
I'm not sure if the OEM curve changes according to volume level; I'd calibrated my 360.3 using a fairly high volume signal.

I tapped the dash tweeter wires for my signal. I'd thought about trying the door speakers but the front door speakers appear to be tapped off the same wires as the dash tweeters according to Mazda schematics. I am not sure if the rear door speakers are any different...have you tried?

So I'm taking a completely different approach of using a Raspberry Pi with external DAC - controlled via an app in the infotainment system. A SLOW work in progress but I was happy to SEE 7Hz playing in my test setup.

The 360.3 is a tremendously flexible unit, and once integrated you don't need to touch it. I do not believe it is capable of adjusting the curve you've set according to volume level though. I plan to keep using it with the Pi.
 
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