新竹市及新豐紅毛港的閩南語同屬新竹老同安腔，但現今聲、韻、調卻有不同的變體分布及演變。聲母方面，新竹市的老年及中年〈入入〉類無［dz］聲母，然而新豐紅毛港老年人的﹝dz﹞聲母超過九成；此外，新豐紅毛港〈入入〉類有少數﹝g﹞變體，但新竹市無此變體。韻母方面，〈關觀〉類新竹市有老泉音變體﹝ũĩ﹞，新豐紅毛港並無﹝ũĩ﹞；新豐紅毛港部分老年層仍保有兩個泉腔央元音﹝ɨ﹞、﹝Ә﹞，然而新竹市的央中元音﹝Ә﹞卻幾近消失，僅〈居艍〉類尚存部分央元音﹝ɨ﹞。由此可知新竹市閩南語已失去老同安腔的重要方音特點。聲調方面，新竹市閩南語陽入原調的泉腔變體有高短調﹝5﹞及升調﹝34﹞兩種，但是新豐紅毛港僅有高短調﹝5﹞。本文的調查結果亦顯示新竹老同安腔的音變趨勢，部分音類的變化已由方言移借取代自然演變

This study investigates sound change and variation in old Tongan-based Southern Min in Hsinchu City and Hsinfong Hongmaogang. The aim is to probe how much, and how pronunciations have diverged from their origins in these areas and through which process divergence takes place, ＂dialect borrowing＂ or ＂natural, internal change.＂ The results reveal that: (1) In the initials, most middle-aged and elderly Hsinfong speakers keep initial [dz], while most Hsinchu City residents do not. (2) In the finals, in ＜關觀＞ word groups [ũĩ] is generally observed in Hsinchu City, while it is not found in Hsinfong. Some elderly Hsinfong speakers still keep [ɨ] and [ǝ] However, in Hsinchu City, while [ǝ] is simply disappear in Hsinchu City. Evidence shows that most characteristics of the old Tongan-based Southern Min has undergone change in Hsinchu City. (3) In the tones, the higher register entering tone [5] and [34] is observed in Hsinchu City, while only [5] is seen in Hsinfong. This research shows that the major mechanism of sound change in these dialects is through dialect borrowing and not through natural or internal change