While Serious Sam Fusion 2017 has support for OpenAL which can be replaced with OpenAL Soft for HRTF, it uses a software mixer by default that disables 3D audio. Fortunately, it's possible to disable this software mixer to restore 3D positional audio on headphones and surround sound.

Step 1: Go into your SeriousSam2017.ini located inside Step 2: Look for dsd_iSoftwareProcessing = 1;
Step 3: Change it to dsd_iSoftwareProcessing = 0;

Now that you've disabled the Crossfeed, it's time to install OpenAL Soft in place of the outdated Creative OpenAL32.dll that comes with Serious Sam Fusion 2017. The next set of instructions depends on if you're playing with headphones or surround speakers. If you are simply playing on 2.0 speakers, it might be best to ignore this guide and play with the Crossfeed on.

Step 1: Download the latest build of OpenAL Soft here.[openal-soft.org]
Step 2: Unzip the folder into %APPDATA% (use Windows key + R to find it).
Step 3: Go inside /bin/Win64 and rename soft_oal.dll to OpenAL32.
Step 4: Copy and paste the newly-renamed file into your Serious Sam Fusion 2017 directory, overwriting the old OpenAL32.dll.
Step 5: Go back into your OpenAL Soft folder and double-click alsoft-config.exe inside the relevant folder.
Step 6: Make sure Stereo Mode is set to Headphones under Playback and HRTF is forced on in the HRTF tab.

When you launch Serious Sam Fusion 2017 the next time, you should now be hearing 3D positional audio through your headphones as demonstrated in the video. For people who are not satisfied with the built-in HRTF preset, you can choose a different one that suits the shape of your head. Simply watch this video and read the description for installation instructions.

Step 1: Download the latest build of OpenAL Soft here.[openal-soft.org]
Step 2: Unzip the folder into %APPDATA% (use Windows key + R to find it).
Step 3: Go inside /bin/Win64 and rename soft_oal.dll to OpenAL32.
Step 4: Copy and paste the newly-renamed file into your Serious Sam Fusion 2017 directory, overwriting the old OpenAL32.dll.
Step 5: Go back into your OpenAL Soft folder and double-click alsoft-config.exe inside the relevant folder.
Step 6: Set Channels to Ambisonic, 3rd Order under playback.
Step 7: Select the Renderer tab and make sure all the boxes are ticked.
Step 8: Find your speaker setup and click the Browse box next to it. You must now select one of the following presets from openal-soft-1.19.1-bin/presets
When you launch Serious Sam Fusion 2017 the next time, you should now be hearing 3D positional audio through your surround speakers complete with elevation and depth. If you find that your CPU cannot keep up the load of Ambisonic, 3rd Order playback, reduce it to either 2nd Order or 1st Order playback until your CPU usage stabilizes.

Something in the Windows 8 and Windows 10 audio stack can cause muffled audio when HRTF is used in various games. The below method is known to fix this.

Step 1: Go into your Advanced Speaker Properties.
Step 2: Untick Allow applications to take exclusive control of this device.
Step 3: Find another option that says Disable all enhancements somewhere in your speaker properties and tick it.

Thank you for reading this guide. I hope it may have solved any problems you had regarding OpenAL and Serious Sam Fusion 2017.

Logo is from https://steamcdn-a.akamaihd.net/steam/apps/564310/capsule_231x87.jpg?t=1550749828 and is copyrighted by Croteam. Use of this image falls under fair use laws for non-profit purposes. Thanks to eksha from the 3D Game Audio server on Discord for letting me know there was a console command for the software audio mixer.