diff --git a/app.js b/app.js
index 040ea809d116faa09c9b1582f0d4d4d771f43ae1..92bda682c6029b1f9736397bb479650cace1ed32 100644
--- a/app.js
+++ b/app.js
@@ -28,6 +28,7 @@ io.on('connection', function(socket){
     io.sockets.emit('updateUserCount', Object.keys(io.engine.clients).length);
     socket.on('disconnect', function(){
       io.sockets.emit('updateUserCount', Object.keys(io.engine.clients).length);
+      io.sockets.emit('clearExternalData');
     });
   	console.log('a user connected');
   	socket.on('bpm', function(newBpm){
diff --git a/public/client.js b/public/client.js
index b3b5dc5674c63888a412e79a6263a3a126c6d122..23948b0afabe0f427e6aac6d29f21926ed7ad2e6 100644
--- a/public/client.js
+++ b/public/client.js
@@ -28,7 +28,10 @@ $(function(){
     iosocket.on('updateExternalGrid', function(data){
         //playExternalSound(data));
         externalGrid = data;
-        
+    });
+
+    iosocket.on('clearExternalData', function(){
+        externalGrid = null;
     });
 
     iosocket.on('updateUserCount', function(userCount){