Added boundary states for correct resonances

Interfaces/Connection.cs

@@ -0,0 +1,15 @@
+namespace FluidSim.Interfaces
+{
+    /// <summary>Pure data link between two ports, with orifice parameters.</summary>
+    public class Connection
+    {
+        public Port PortA { get; }
+        public Port PortB { get; }
+
+        public double Area { get; set; } = 1e-5;          // effective orifice area (m²)
+        public double DischargeCoefficient { get; set; } = 0.62;
+        public double Gamma { get; set; } = 1.4;
+
+        public Connection(Port a, Port b) => (PortA, PortB) = (a, b);
+    }
+}

Interfaces/SoundConnection.cs

@@ -0,0 +1,25 @@
+namespace FluidSim.Interfaces
+{
+    /// <summary>
+    /// A Connection that also produces an audio sample from the pressure drop across it.
+    /// </summary>
+    public class SoundConnection : Connection
+    {
+        /// <summary>Gain applied to the normalised pressure difference.</summary>
+        public float Gain { get; set; } = 1.0f;
+
+        /// <summary>Reference pressure used for normalisation (Pa). Default: 1 atm.</summary>
+        public double ReferencePressure { get; set; } = 101325.0;
+
+        public SoundConnection(Port a, Port b) : base(a, b) { }
+
+        /// <summary>
+        /// Returns a normalised audio sample proportional to the pressure difference.
+        /// </summary>
+        public float GetAudioSample()
+        {
+            double dp = PortA.Pressure - PortB.Pressure;
+            return (float)(dp / ReferencePressure) * Gain;
+        }
+    }
+}