--- a/content/media/MediaStreamGraph.cpp
+++ b/content/media/MediaStreamGraph.cpp
@@ -843,17 +843,17 @@ MediaStreamGraphImpl::CreateOrDestroyAud
         audioOutputStream->mAudioPlaybackStartTime = aAudioOutputStartTime;
         audioOutputStream->mBlockedAudioTime = 0;
         audioOutputStream->mLastTickWritten = 0;
         audioOutputStream->mStream = new AudioStream();
         // XXX for now, allocate stereo output. But we need to fix this to
         // match the system's ideal channel configuration.
         // NOTE: we presume this is either fast or async-under-the-covers
         audioOutputStream->mStream->Init(2, IdealAudioRate(),
-                                         aStream->mAudioChannelType,
+                                         AudioChannel::Normal,
                                          AudioStream::LowLatency);
         audioOutputStream->mTrackID = tracks->GetID();
 
         LogLatency(AsyncLatencyLogger::AudioStreamCreate,
                    reinterpret_cast<uint64_t>(aStream),
                    reinterpret_cast<int64_t>(audioOutputStream->mStream.get()));
       }
     }

--- a/content/media/MediaStreamGraph.h
+++ b/content/media/MediaStreamGraph.h
@@ -14,17 +14,16 @@
 #include "StreamBuffer.h"
 #include "TimeVarying.h"
 #include "VideoFrameContainer.h"
 #include "VideoSegment.h"
 #include "MainThreadUtils.h"
 #include "nsAutoRef.h"
 #include "speex/speex_resampler.h"
 #include "AudioMixer.h"
-#include "mozilla/dom/AudioChannelBinding.h"
 
 class nsIRunnable;
 
 template <>
 class nsAutoRefTraits<SpeexResamplerState> : public nsPointerRefTraits<SpeexResamplerState>
 {
   public:
   static void Release(SpeexResamplerState* aState) { speex_resampler_destroy(aState); }
@@ -520,20 +519,16 @@ public:
   virtual bool MainThreadNeedsUpdates() const
   {
     return true;
   }
 
   virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
   virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
 
-  void SetAudioChannelType(dom::AudioChannel aType) {
-    mAudioChannelType = aType;
-  }
-
 protected:
   virtual void AdvanceTimeVaryingValuesToCurrentTime(GraphTime aCurrentTime, GraphTime aBlockedTime)
   {
     mBufferStartTime += aBlockedTime;
     mGraphUpdateIndices.InsertTimeAtStart(aBlockedTime);
     mGraphUpdateIndices.AdvanceCurrentTime(aCurrentTime);
     mExplicitBlockerCount.AdvanceCurrentTime(aCurrentTime);
 
@@ -650,18 +645,16 @@ protected:
   DOMMediaStream* mWrapper;
   // Main-thread views of state
   StreamTime mMainThreadCurrentTime;
   bool mMainThreadFinished;
   bool mMainThreadDestroyed;
 
   // Our media stream graph
   MediaStreamGraphImpl* mGraph;
-
-  dom::AudioChannel mAudioChannelType;
 };
 
 /**
  * This is a stream into which a decoder can write audio and video.
  *
  * Audio and video can be written on any thread, but you probably want to
  * always write from the same thread to avoid unexpected interleavings.
  */

--- a/content/media/webaudio/AudioContext.cpp
+++ b/content/media/webaudio/AudioContext.cpp
@@ -72,34 +72,33 @@ static float GetSampleRateForAudioContex
   } else {
     AudioStream::InitPreferredSampleRate();
     return static_cast<float>(AudioStream::PreferredSampleRate());
   }
 }
 
 AudioContext::AudioContext(nsPIDOMWindow* aWindow,
                            bool aIsOffline,
-                           AudioChannel aChannel,
                            uint32_t aNumberOfChannels,
                            uint32_t aLength,
                            float aSampleRate)
   : DOMEventTargetHelper(aWindow)
   , mSampleRate(GetSampleRateForAudioContext(aIsOffline, aSampleRate))
   , mNumberOfChannels(aNumberOfChannels)
   , mNodeCount(0)
   , mIsOffline(aIsOffline)
   , mIsStarted(!aIsOffline)
   , mIsShutDown(false)
 {
   aWindow->AddAudioContext(this);
 
   // Note: AudioDestinationNode needs an AudioContext that must already be
   // bound to the window.
-  mDestination = new AudioDestinationNode(this, aIsOffline, aChannel,
-                                          aNumberOfChannels, aLength, aSampleRate);
+  mDestination = new AudioDestinationNode(this, aIsOffline, aNumberOfChannels,
+                                          aLength, aSampleRate);
   // We skip calling SetIsOnlyNodeForContext during mDestination's constructor,
   // because we can only call SetIsOnlyNodeForContext after mDestination has
   // been set up.
   mDestination->SetIsOnlyNodeForContext(true);
 }
 
 AudioContext::~AudioContext()
 {
@@ -135,34 +134,16 @@ AudioContext::Constructor(const GlobalOb
 
   RegisterWeakMemoryReporter(object);
 
   return object.forget();
 }
 
 /* static */ already_AddRefed<AudioContext>
 AudioContext::Constructor(const GlobalObject& aGlobal,
-                          AudioChannel aChannel,
-                          ErrorResult& aRv)
-{
-  nsCOMPtr<nsPIDOMWindow> window = do_QueryInterface(aGlobal.GetAsSupports());
-  if (!window) {
-    aRv.Throw(NS_ERROR_FAILURE);
-    return nullptr;
-  }
-
-  nsRefPtr<AudioContext> object = new AudioContext(window, false, aChannel);
-
-  RegisterWeakMemoryReporter(object);
-
-  return object.forget();
-}
-
-/* static */ already_AddRefed<AudioContext>
-AudioContext::Constructor(const GlobalObject& aGlobal,
                           uint32_t aNumberOfChannels,
                           uint32_t aLength,
                           float aSampleRate,
                           ErrorResult& aRv)
 {
   nsCOMPtr<nsPIDOMWindow> window = do_QueryInterface(aGlobal.GetAsSupports());
   if (!window) {
     aRv.Throw(NS_ERROR_FAILURE);
@@ -176,17 +157,16 @@ AudioContext::Constructor(const GlobalOb
       aSampleRate >= TRACK_RATE_MAX) {
     // The DOM binding protects us against infinity and NaN
     aRv.Throw(NS_ERROR_DOM_NOT_SUPPORTED_ERR);
     return nullptr;
   }
 
   nsRefPtr<AudioContext> object = new AudioContext(window,
                                                    true,
-                                                   AudioChannel::Normal,
                                                    aNumberOfChannels,
                                                    aLength,
                                                    aSampleRate);
 
   RegisterWeakMemoryReporter(object);
 
   return object.forget();
 }

--- a/content/media/webaudio/AudioContext.h
+++ b/content/media/webaudio/AudioContext.h
@@ -62,17 +62,16 @@ class ScriptProcessorNode;
 class WaveShaperNode;
 class PeriodicWave;
 
 class AudioContext MOZ_FINAL : public DOMEventTargetHelper,
                                public nsIMemoryReporter
 {
   AudioContext(nsPIDOMWindow* aParentWindow,
                bool aIsOffline,
-               AudioChannel aChannel = AudioChannel::Normal,
                uint32_t aNumberOfChannels = 0,
                uint32_t aLength = 0,
                float aSampleRate = 0.0f);
   ~AudioContext();
 
 public:
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(AudioContext,
@@ -91,22 +90,16 @@ public:
   virtual JSObject* WrapObject(JSContext* aCx) MOZ_OVERRIDE;
 
   using DOMEventTargetHelper::DispatchTrustedEvent;
 
   // Constructor for regular AudioContext
   static already_AddRefed<AudioContext>
   Constructor(const GlobalObject& aGlobal, ErrorResult& aRv);
 
-  // Constructor for regular AudioContext. A default audio channel is needed.
-  static already_AddRefed<AudioContext>
-  Constructor(const GlobalObject& aGlobal,
-              AudioChannel aChannel,
-              ErrorResult& aRv);
-
   // Constructor for offline AudioContext
   static already_AddRefed<AudioContext>
   Constructor(const GlobalObject& aGlobal,
               uint32_t aNumberOfChannels,
               uint32_t aLength,
               float aSampleRate,
               ErrorResult& aRv);
 

--- a/content/media/webaudio/AudioDestinationNode.cpp
+++ b/content/media/webaudio/AudioDestinationNode.cpp
@@ -223,17 +223,16 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_
   NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
 NS_INTERFACE_MAP_END_INHERITING(AudioNode)
 
 NS_IMPL_ADDREF_INHERITED(AudioDestinationNode, AudioNode)
 NS_IMPL_RELEASE_INHERITED(AudioDestinationNode, AudioNode)
 
 AudioDestinationNode::AudioDestinationNode(AudioContext* aContext,
                                            bool aIsOffline,
-                                           AudioChannel aChannel,
                                            uint32_t aNumberOfChannels,
                                            uint32_t aLength,
                                            float aSampleRate)
   : AudioNode(aContext,
               aIsOffline ? aNumberOfChannels : 2,
               ChannelCountMode::Explicit,
               ChannelInterpretation::Speakers)
   , mFramesToProduce(aLength)
@@ -248,23 +247,23 @@ AudioDestinationNode::AudioDestinationNo
                             MediaStreamGraph::CreateNonRealtimeInstance() :
                             MediaStreamGraph::GetInstance();
   AudioNodeEngine* engine = aIsOffline ?
                             new OfflineDestinationNodeEngine(this, aNumberOfChannels,
                                                              aLength, aSampleRate) :
                             static_cast<AudioNodeEngine*>(new DestinationNodeEngine(this));
 
   mStream = graph->CreateAudioNodeStream(engine, MediaStreamGraph::EXTERNAL_STREAM);
-  mStream->SetAudioChannelType(aChannel);
   mStream->AddMainThreadListener(this);
   mStream->AddAudioOutput(&gWebAudioOutputKey);
 
-  if (aChannel != AudioChannel::Normal) {
+  AudioChannel channel = AudioChannelService::GetDefaultAudioChannel();
+  if (channel != AudioChannel::Normal) {
     ErrorResult rv;
-    SetMozAudioChannelType(aChannel, rv);
+    SetMozAudioChannelType(channel, rv);
   }
 
   if (!aIsOffline && UseAudioChannelService()) {
     nsCOMPtr<nsIDOMEventTarget> target = do_QueryInterface(GetOwner());
     if (target) {
       target->AddSystemEventListener(NS_LITERAL_STRING("visibilitychange"), this,
                                      /* useCapture = */ true,
                                      /* wantsUntrusted = */ false);

--- a/content/media/webaudio/AudioDestinationNode.h
+++ b/content/media/webaudio/AudioDestinationNode.h
@@ -25,17 +25,16 @@ class AudioDestinationNode : public Audi
                            , public nsSupportsWeakReference
                            , public MainThreadMediaStreamListener
 {
 public:
   // This node type knows what MediaStreamGraph to use based on
   // whether it's in offline mode.
   AudioDestinationNode(AudioContext* aContext,
                        bool aIsOffline,
-                       AudioChannel aChannel = AudioChannel::Normal,
                        uint32_t aNumberOfChannels = 0,
                        uint32_t aLength = 0,
                        float aSampleRate = 0.0f);
 
   virtual void DestroyMediaStream() MOZ_OVERRIDE;
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(AudioDestinationNode, AudioNode)

--- a/content/media/webaudio/test/test_mozaudiochannel.html
+++ b/content/media/webaudio/test/test_mozaudiochannel.html
@@ -61,17 +61,17 @@ function test_permission(aChannel) {
 }
 
 function test_preferences(aChannel) {
   SpecialPowers.pushPrefEnv({"set": [["media.defaultAudioChannel", aChannel ]]},
     function() {
       SpecialPowers.pushPermissions(
         [{ "type": "audio-channel-" + aChannel, "allow": false, "context": document }],
         function() {
-          var ac = new AudioContext(aChannel);
+          var ac = new AudioContext();
           ok(ac, "AudioContext created");
           is(ac.mozAudioChannelType, aChannel, "Default ac channel == '" + aChannel + "'");
           runTest();
         }
       );
     }
   );
 }