Consonant clusters
Tell when two consonants share a syllable and when they belong to separate syllables.
Two consonants at the start of a syllable can form a cluster, called อักษรควบ. In ปลา, fish, ป and ล share one vowel: don't insert an extra vowel between them. Recognising the cluster helps you divide the word into syllables and apply the right tone rule.
An initial followed by ร, ล or ว
A true cluster takes its tone class from the first consonant. ปลา is mid tone because ป is mid class. ขวา is rising because ข is high class and the syllable is live. ครับ is high tone: ค is low class, the vowel is short and the final sound makes the syllable dead.
Some pairs look like clusters but are pronounced differently. ทร is pronounced s in familiar words such as ทราบ, to know, and ทราย, sand. ร is silent in จริง, true. สร and ศร also have an s sound in several common words. Learn these words with their recordings: สรุป, to summarise, instead has two syllables, and ทร can retain a tr sound in loanwords such as ทรัมเป็ต, trumpet.
Written pairs with a different reading
Not every adjacent pair forms a cluster. ตลาด, market, and ขนม, dessert, each have two syllables. Use the list of ordinary clusters as a guide, then check the whole word. A written vowel attached to the second consonant can indicate a separate syllable: กรุณา, please, has three. Familiar spellings and the recording are more reliable than simply joining every pair.
In casual speech, the second sound of a cluster is often weakened or dropped. You may hear ปลา without a clear l, or ครับ without a clear r. Standard spelling still keeps the consonant. Look up the written form, and use the app's recording to practise the careful pronunciation.
I like fish.
ปล is a cluster in one syllable. ป supplies the mid-class rule, giving a mid tone.
Turn right.
ขว is one cluster; high-class ข gives this live syllable a rising tone.
I don't know.
ไม่ทราบ is a polite alternative to ไม่รู้. ทร has an s sound here.
Thank you.
ครับ has a high tone. In casual speech, its ร is often dropped.
Common mistake
Don't assume ทร sounds like the tr in English. ทราย, sand, begins with s. For a true cluster, don't choose the tone class from the second letter: ขวา uses high-class ข, even though ว is low class.
Practise
Kai says
Each consonant has a word in its name. I'm ก, named with ไก่, chicken. The word helps you identify the letter when another letter has the same sound.