diff --git a/src/backends/av_foundation.rs b/src/backends/av_foundation.rs
index 6940e07..445b3c9 100644
--- a/src/backends/av_foundation.rs
+++ b/src/backends/av_foundation.rs
@@ -10,9 +10,10 @@ use objc::runtime::{Object, Sel};
 use objc::{class, declare::ClassDecl, msg_send, sel, sel_impl};
 
 use crate::{Backend, BackendId, Error, Features, UtteranceId, CALLBACKS};
+use crate::voices::Backend as VoiceBackend;
 
 mod voices;
-use voices::AVSpeechSynthesisVoice;
+use voices::*;
 
 pub(crate) struct AvFoundation {
     id: BackendId,
@@ -100,7 +101,7 @@ impl AvFoundation {
                 rate: 0.5,
                 volume: 1.,
                 pitch: 1.,
-                voice: AVSpeechSynthesisVoice::default(),
+                voice: AVSpeechSynthesisVoice::new(""),
             }
         };
         *backend_id += 1;
@@ -222,11 +223,11 @@ impl Backend for AvFoundation {
     }
 
     fn voice(&self) -> Result<String,Error> {
-        Ok(self.voice.identifier())
+        Ok(self.voice.id())
     }
 
     fn list_voices(&self) -> Vec<String> {
-        AVSpeechSynthesisVoice::list().iter().map(|v| {v.identifier()}).collect()
+        AVSpeechSynthesisVoice::list().iter().map(|v| {v.id()}).collect()
     }
 
     fn set_voice(&mut self, voice: &str) -> Result<(),Error> {
diff --git a/src/backends/av_foundation/voices.rs b/src/backends/av_foundation/voices.rs
index b8ee960..32ae9a2 100644
--- a/src/backends/av_foundation/voices.rs
+++ b/src/backends/av_foundation/voices.rs
@@ -11,7 +11,7 @@ use crate::voices;
 use crate::voices::Gender;
 
 #[derive(Copy,Clone)]
-pub struct AVSpeechSynthesisVoice(*const Object);
+pub(crate) struct AVSpeechSynthesisVoice(*const Object);
 
 impl AVSpeechSynthesisVoice {
     pub fn new(identifier: &str) -> Self {
diff --git a/src/voices.rs b/src/voices.rs
new file mode 100644
index 0000000..031fcdd
--- /dev/null
+++ b/src/voices.rs
@@ -0,0 +1,17 @@
+
+pub use unic_langid::LanguageIdentifier;
+
+pub enum Gender {
+    Other,
+    Male,
+    Female,
+}
+
+pub trait Backend: Sized {
+    type Backend: crate::Backend;
+    fn list() -> Vec<Self>;
+    fn name(self) -> String;
+    fn gender(self) -> Gender;
+    fn id(self) -> String;
+    fn language(self) -> LanguageIdentifier;
+}