EAX[en.wikipedia.org] (Envionmental Audio Extensions) is sound system developed by Creative Technology Ltd. used by many older games for realistic reverb, surround sounds, doppler effect simulation, surround sound and many more. EAX was compatible with Creative and Realtek soundcards.

EAX saw first release in 1999 and over the time, it had 5 versions.

Star Wars : Battlefront II uses EAX 4.0

Here you can see a quick demonstration of EAX enabled and disabled in several games:

Sadly, EAX was discontinued in 2005 due to absence of HAL (Hardware Abstraction Layer) and Directsound in Windows Vista and newer, breaking compatibility with EAX.

EAX support can be restored on modern operation systems using wrappers such as Creative ALChemy and DSOAL. The best solution is DSOAL which works on every soundcard.

Link to DSOAL:
https://www.nexusmods.com/newvegas/mods/65094

• 1. Create a new .txt file
  
• 2. Copy and paste the following inside the newly created .txt file:
  
  Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Classes\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\Software\Classes\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\Software\Classes\WOW6432Node\CLSID\{47D4D946-62E8-11CF-93BC-444553540000}\InprocServer32] @="dsound.dll" [HKEY_CURRENT_USER\Software\Classes\WOW6432Node\CLSID\{3901CC3F-84B5-4FA4-BA35-AA8172B8A09B}\InprocServer32] @="dsound.dll"
• 3. Change the file extension to .reg
  
• 4. Run the file as administrator and click yes when it prompts you to confirm.
  
• 5. Download and unzip DSOAL
  
• 6. Drag and drop dsound.dll, dsound_aldrv.dll and alsoft.ini into your
  Star Wars Battlefront 2/Gamedata directory
  
• 7. Open alsoft.ini in the directory and customise it to your liking, it stores DSOAL settings.

[/h1]

Start up Battlefront II and go into audio settings. Change the mixer config to Hardware and make sure effects are enabled. Set the in game output to 7.1 to prevent issues with disappearing sounds.

This is very important:
MAKE SURE TO DISABLE BASS MANAGEMENT!

There you go!
EAX now works properly on modern operating systems and even non-creative cards!


Special thanks to:
LAGonauta (Creating DSOAL)
I Drink Lava (Introducing me to DSOAL)
ThatFox (For suggesting the registry tweak)