Why Vietnamese ESL Learners Can't Pronounce Letter X: /ks/ Sound

For many Vietnamese learners of English, the letter "x" is one of the most confusing letters. This is not because it is a new sound, but because one letter has many different sounds, and it often creates a final consonant cluster — a structure that does not exist in Vietnamese.

1. "X" is not one sound, but two sounds

In most English words, "x" is pronounced as /ks/ — a combination of /k/ + /s/. For example: box /bɒks/, six /sɪks/, tax /tæks/.

Research on Vietnamese learners shows that English consonant clusters are one of the most difficult areas because of differences in phonological features between the two languages.

Vietnamese syllables typically end with only one single consonant. There are no final clusters like /ks/, /nd/, or /st/ in Vietnamese. Because of this, learners have a tendency to simplify complex clusters by deleting one or more consonants.

So my Vietnamese students often say /sɪk/ or /sɪs/ for six, /tak/ for tax, /fik/ for fix, /ˈpɒlətɪk/ for politics — the final cluster is omitted.

2. "X" changes its sound based on position and stress.

/ks/ : box, taxi, exercise

/gz/ : exam, exact, example — when the second syllable is stressed, the sound becomes voiced

/z/ : Xerox, xylophone, xenophobia — at the beginning of a word

/kʃ/ : anxious, luxury

Learners who have not studied phonetics often lack knowledge of voiced vs. voiceless sounds and stress rules, so they apply one rule to all words.

3. Final sounds are often omitted in Vietnamese English.

Studies of Vietnamese students found that the most common pronunciation error is omitting final consonants, because speakers do not have to pronounce ending sounds when they speak Vietnamese. The pair /s/ and /z/ are also frequently confused, and sounds like /ʒ, dʒ, tʃ/ that do not exist in Vietnamese are difficult, especially in final position.

The letter "x" combines both problems: it contains /s/ or /z/ AND it is a final cluster.

Teaching Suggestion

Teach "x" in 3 steps:

1. Practice /s/ and /z/ separately: bus vs. buzz

2. Practice joining /k/ + /s/ slowly: k-ssss - ks. This ia what I do in class. I have to type /k/ then /s/ and model the pronunciation.

3. Minimal pairs: sick vs. six, back vs. box, e-sam vs. exam

References:

1. Tran, T. K. L., & Nguyen, A. T. (2022). English consonant clusters: A case study of Vietnamese learners. Can Tho University Journal of Science, 14(3), 32-39.

2. Nguyen, T. T. H. (2024). English consonant clusters in the pronunciation of Vietnamese learners: a study on two students at Ha Long University. VJOL.

3. Bui, M. C. et al. (2021). Pronunciation errors of final consonants — Sound omission is the most common mistake (43%). IOSR Journal of Research & Method in Education, 11(4).

4. Osborne, D. (2022). Word-Final /s/-/z/ Omission in Vietnamese English. Consonant clusters and word-final fricatives are potential areas for negative L1 transfer. Languages (MDPI).