Well, in my hastiness to mod this phone, I did a couple things, namely Viper Audio FX Magisk module in Magisk downloads within the Magisk app, and dual speaker module for Magisk which you can get here https://forum.xda-developers.com/one...us-6t-t3860041. I'm running the BOOSTED dual speaker now. Decided to see if my magical speaker config on Viper would give me results like it did on my 3T, and boy, it's a real surprise on this phone. The stock audio tuning on the speaker hides what it can actually do.
Now, you'll need the Convolver profiles for Viper Audio to reproduce my settings. You can get the profiles in this zip: https://androidfilehost.com/?fid=457095661767141554. It's under modules > profiles. Just copy the Viper4Android folder you find in there and store it. You will need to install Magisk with Viper Audio FX and the optional dual speaker mod for the 6T.
Once you get the Viper dual speaker modules installed, plug your phone into your PC and copy the Viper4Android folder you copied from the zip with the profiles, into the internal shared storage root. Close when done.
You can now open the Viper4Android app and enable speaker master, convolver, and speaker optimization switches.
If you click on Convolver it will take you to a menu where you can select profiles. Leave the knob that's next to the profile selector @ 0%. Make sure your main volume is down, because when you select the TUBEAMPLIFIER profile, the volume will boost.
Now you can enjoy rich, deep, sound from the very underrated speaker
So I made another interesting discovery. I installed the latest Cleanslate kernel(version 2.7.7 is the latest from the date of this post) which you can get here along with the configuration(2.9.0) and companion(2.5.0) app, and in the configuration app it allows for tuning of the speakers(yes the earpiece speaker as well!).
I boosted the earpiece speaker to level 7 when I was using reduced dual speaker. Backed it down to 5 on boosted dual speaker, on the slider of the Cleanslate configuration app, and hit save. I think the damn earpiece speaker might be almost as meaty as the bottom speaker. It doesn't distort for ****, and the range of sound is astounding! I think we have a true second speaker for our phone, boys and girls! This is pretty awesome!
I paired it with my ViperAudio tweaks and the OnePlus 6T is now like a portable boombox, lol. I love this phone!