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TLDR:
3800 mod only changes front speaker settings. You need to also change the middle code block at address 727-01-01 to affect rear speakers. This post contains a list of all the code values you can use and what they do.
FULL POST:
What I have detailed below is applicable to my 2021 4 door Base. YMMV.
My "as built" values in ACM were:
727-01-01 382B 14F1 0098
727-01-02 0901 000D 0048
The conventional wisdom I've read on this site says changing 727-01-01 XX** to 00 or 01 will send full range to rear speakers. In my internet searching and tinkering with ForScan, I can confidently say it doesn't do anything to my rear speakers. And I don't think it does anything for anyone else's either.
My as built front power source and left speaker specs was 2 = internal power, speaker and tweeter (I believe S&T sends the widest range of frequencies from the list of options). I wrote 3 (no front left speaker) just to confirm my cheat sheet was right. It was. When I wrote value 3 in this spot the front left speaker went silent. I changed value back to as built, as it seemed like the right value to use based on the options below.
Front right and center channel specs: my as built was B, which is speaker and tweeter for front right and no signal for center channel (base has no center channel). Again I tinkered to confirm the list below did what it says it does; the as built value seemed appropriate so no change.
Here's where it gets interesting... rear power and left rear speaker specs. As built value was 1 = internal amp, tweeter only. I changed this to 2 = internal amp, speaker and tweeter. I perceived it to get slightly louder and when turned up mid frequencies would break up the stock speakers a little. I think it's sending a wider frequency band, and that's what we want!
Rear right, sub, and rear center specs... as built was 4, I changed it to 8. Both rear speakers now sound like they are getting pushed slightly harder. I have replacement speakers and 150 Hz blockers on order that will be installed next weekend. I'm expecting to hear an even more noticeable change once those are installed and for the midrange slop I hear in the factory speakers to disappear.
moving on to section 727-01-02, this is supposedly the various preset EQ options. I changed mine from 01 to 00 and didn't notice a lot of difference, but that may be due to the crappy stock speakers. I'll try changes at this address again once I get new speakers in. What's not clear is if there are actually different EQs assigned to all the values below or if some of them are simply unused placeholders. My ears couldn't tell with factory speakers. What we do know is some upper trims have as build value of 00 (flat response) here, but my base has value of 01... so there's at least one real EQ preset in the list otherwise every as built would be 00.
Some other things worth noting as I played with these changes in ForScan:
1. I used the fader and balance to isolate changes to the speakers I was tinkering with. Every time I wrote a change the fader and balance would reset to center.
2. I was playing music through CarPlay to listen to these changes so I could repeat the same track over and over. When I was done with my changes and went back to satellite radio I found that it was back to demo mode. I had to call Sirius to push my subscription settings back to the vehicle.
Source for the screen shots is below. I found that the site responds better on mobile that desktop.
https://cyanlabs.net/asbuilt-db/acm3/
3800 mod only changes front speaker settings. You need to also change the middle code block at address 727-01-01 to affect rear speakers. This post contains a list of all the code values you can use and what they do.
FULL POST:
What I have detailed below is applicable to my 2021 4 door Base. YMMV.
My "as built" values in ACM were:
727-01-01 382B 14F1 0098
727-01-02 0901 000D 0048
The conventional wisdom I've read on this site says changing 727-01-01 XX** to 00 or 01 will send full range to rear speakers. In my internet searching and tinkering with ForScan, I can confidently say it doesn't do anything to my rear speakers. And I don't think it does anything for anyone else's either.
My as built front power source and left speaker specs was 2 = internal power, speaker and tweeter (I believe S&T sends the widest range of frequencies from the list of options). I wrote 3 (no front left speaker) just to confirm my cheat sheet was right. It was. When I wrote value 3 in this spot the front left speaker went silent. I changed value back to as built, as it seemed like the right value to use based on the options below.
Front right and center channel specs: my as built was B, which is speaker and tweeter for front right and no signal for center channel (base has no center channel). Again I tinkered to confirm the list below did what it says it does; the as built value seemed appropriate so no change.
Here's where it gets interesting... rear power and left rear speaker specs. As built value was 1 = internal amp, tweeter only. I changed this to 2 = internal amp, speaker and tweeter. I perceived it to get slightly louder and when turned up mid frequencies would break up the stock speakers a little. I think it's sending a wider frequency band, and that's what we want!
Rear right, sub, and rear center specs... as built was 4, I changed it to 8. Both rear speakers now sound like they are getting pushed slightly harder. I have replacement speakers and 150 Hz blockers on order that will be installed next weekend. I'm expecting to hear an even more noticeable change once those are installed and for the midrange slop I hear in the factory speakers to disappear.
moving on to section 727-01-02, this is supposedly the various preset EQ options. I changed mine from 01 to 00 and didn't notice a lot of difference, but that may be due to the crappy stock speakers. I'll try changes at this address again once I get new speakers in. What's not clear is if there are actually different EQs assigned to all the values below or if some of them are simply unused placeholders. My ears couldn't tell with factory speakers. What we do know is some upper trims have as build value of 00 (flat response) here, but my base has value of 01... so there's at least one real EQ preset in the list otherwise every as built would be 00.
Some other things worth noting as I played with these changes in ForScan:
1. I used the fader and balance to isolate changes to the speakers I was tinkering with. Every time I wrote a change the fader and balance would reset to center.
2. I was playing music through CarPlay to listen to these changes so I could repeat the same track over and over. When I was done with my changes and went back to satellite radio I found that it was back to demo mode. I had to call Sirius to push my subscription settings back to the vehicle.
Source for the screen shots is below. I found that the site responds better on mobile that desktop.
https://cyanlabs.net/asbuilt-db/acm3/
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