Applied SoundPropagationMode patch by Boris.

Source/Plugins/SoundPropagationMode/SoundPropagationDomain.cs

@@ -57,27 +57,15 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 				foreach (Sidedef sd in sector.Sidedefs)
 				{
 					bool blocksound = sd.Line.IsFlagSet(General.Map.UDMF ? "blocksound" : "64");
-					bool blockheight = false;
-					Sector oppositesector;
-
 					if (blocksound) blockinglines.Add(sd.Line);
 
 					// If the line is one sided, the sound can travel nowhere, so try the next one
 					if (sd.Line.Back == null || blocksound) continue;
 	
 					// Get the sector on the other side of the line we're checking right now
-					if (sd.Line.Front.Sector == sector)
+					Sector oppositesector = sd.Other.Sector;
-						oppositesector = sd.Line.Back.Sector;
-					else
-						oppositesector = sd.Line.Front.Sector;
 
-					// Check if the sound will be blocked because of sector floor and ceiling heights
+					bool blockheight = IsSoundBlockedByHeight(sd.Line);
-					// (like closed doors, raised lifts etc.)
-					if (sector.CeilHeight <= oppositesector.FloorHeight || sector.FloorHeight >= oppositesector.CeilHeight 
-						|| oppositesector.CeilHeight <= oppositesector.FloorHeight || sector.CeilHeight <= sector.FloorHeight)
-					{
-						blockheight = true;
-					}
 
 					// Try next line if sound will not pass through the current one. The last check makes
 					// sure that the next line is tried if the current line is blocking sound, and the current
@@ -97,8 +85,11 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 
 			foreach (Linedef ld in blockinglines)
 			{
+				// Lines that don't have a back side, or where the sound is blocked due to
+				// the sector heights on each side can be skipped
+				if (ld.Back == null || IsSoundBlockedByHeight(ld)) continue;
 				if (!sectors.Contains(ld.Front.Sector)) adjacentsectors.Add(ld.Front.Sector);
-				if (ld.Back != null && !sectors.Contains(ld.Back.Sector)) adjacentsectors.Add(ld.Back.Sector);
+				if (!sectors.Contains(ld.Back.Sector)) adjacentsectors.Add(ld.Back.Sector);
 			}
 
 			List<FlatVertex> vertices = new List<FlatVertex>();
@@ -118,6 +109,19 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 			}
 		}
 
+		private static bool IsSoundBlockedByHeight(Linedef ld)
+		{
+			if(ld.Back == null) return false;
+
+			Sector s1 = ld.Front.Sector;
+			Sector s2 = ld.Back.Sector;
+
+			// Check if the sound will be blocked because of sector floor and ceiling heights
+			// (like closed doors, raised lifts etc.)
+			return (s1.CeilHeight <= s2.FloorHeight || s1.FloorHeight >= s2.CeilHeight ||
+			       s2.CeilHeight <= s2.FloorHeight || s1.CeilHeight <= s1.FloorHeight);
+		}
+
 		#endregion
 	}
 }

Source/Plugins/SoundPropagationMode/SoundPropagationMode.cs

@@ -119,6 +119,13 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 		private void UpdateSoundPropagation()
 		{
 			huntingThings.Clear();
+
+			BuilderPlug.Me.BlockingLinedefs.Clear();
+
+			foreach (Linedef ld in General.Map.Map.Linedefs)
+				if (ld.IsFlagSet(General.Map.UDMF ? "blocksound" : "64"))
+					BuilderPlug.Me.BlockingLinedefs.Add(ld);
+
 			if (highlighted == null || highlighted.IsDisposed) return;
 
 			if (!sector2domain.ContainsKey(highlighted))
@@ -126,7 +133,6 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 				SoundPropagationDomain spd = new SoundPropagationDomain(highlighted);
 				foreach (Sector s in spd.Sectors) sector2domain[s] = spd;
 				propagationdomains.Add(spd);
-				BuilderPlug.Me.BlockingLinedefs.AddRange(spd.BlockingLines);
 			}
 
 			foreach (Sector adjacent in sector2domain[highlighted].AdjacentSectors)
@@ -135,11 +141,10 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 				{
 					SoundPropagationDomain aspd = new SoundPropagationDomain(adjacent);
 					foreach (Sector s in aspd.Sectors) sector2domain[s] = aspd;
-					BuilderPlug.Me.BlockingLinedefs.AddRange(aspd.BlockingLines);
 				}
 			}
 
-			//mxd. Create the list of sectors, which will be affected by nose made in highlighted sector
+			//mxd. Create the list of sectors, which will be affected by noise made in highlighted sector
 			SoundPropagationDomain curdomain = sector2domain[highlighted];
 			Dictionary<int, Sector> noisysectors = new Dictionary<int, Sector>(curdomain.Sectors.Count);
 			foreach(Sector s in curdomain.Sectors)
@@ -209,6 +214,9 @@ namespace CodeImp.DoomBuilder.SoundPropagationMode
 
 			// Convert geometry selection to sectors only
 			General.Map.Map.ConvertSelection(SelectionType.Sectors);
+
+			UpdateSoundPropagation();
+			General.Interface.RedrawDisplay();
 		}
 
 		// Mode disengages