diff --git a/phsource/ph_vietnam b/phsource/ph_vietnam
index 04301e98..db73f0f9 100644
--- a/phsource/ph_vietnam
+++ b/phsource/ph_vietnam
@@ -18,7 +18,7 @@ endphoneme
 
 phoneme 3   //  sắc Tone(rising
   stress
-  Tone(30, 55, envelope/p_rise, NULL) // 30 60
+  Tone(20, 50, envelope/p_rise, NULL) // 30 60
 endphoneme