A simple custom asset post processor script which disables '3D Sound' option of an imported sound asset.

CostumeAudioImporter.cs

#if UNITY_EDITOR 
using UnityEngine; 
using UnityEditor; 
using System.Collections; 

public class CostumeAudioImporter : AssetPostprocessor 
{ 
    void  OnPreprocessAudio () 
    { 
        AudioImporter audioImporter = assetImporter as AudioImporter; 
        if (audioImporter == null) 
            return; 
            
        audioImporter.threeD = false; 
        audioImporter.hardware = true; 
    } 
} 
#endif