Many thanks to slayer69 for this. Basically just a copy/paste of his thread with some other changes for the low volume on the EVO 3D. I take no responsibility for your actions if you brick it or blow your speaker!!!!
Here is the new process for INCREASING the volume on your EVO 3D. Enjoy!!! (NO ROOT REQUIRED)
1. Install HTC Sync if you haven't already.
2. Use the CDMA Method posted Here to get your MSL. Thanks techwerkz - Or Call Sprint.
3. Download QPST: http://www.x-drivers.com/catalog/fla...pst/12051.html
4. Install QPST software
5. Put phone into Diag mode: dial ##diag#
6. Start QPST service programming. If your phone is in diag mode you will see it listed here.
7. Click Read from phone
8. Enter your SPC number (the one obtained from step number 2)
9. Click the Sounds tab.
10. Change each level to whatever you want it to be. Level 4 is the loudest (try not to blow your speaker, thnx!).
11. Write to phone. (You may see some Read Only Errors. This is normal)
12. Reboot phone and you will hear the difference.
To find the COM port your HTC Modem is using:
Go into the control panel and then device manager. Look for the HTC Modem. Right click on the modem and select properties. Select the "Advanced Tab" then "Advanced Port Settings" Button. Com port will be listed there. (Windows 7 Instructions)
If you have Windows 7 x64 and are having issues with the HTC Modem drivers follow these Instructions.
If you're having problems with the above process see, slayer69's thread here