They all have constant sownds, but can have a different Tone.
Tone 1 G H K L M N Y 7 Tone 2 B F J M P R S T X 9 Tone 3 D W Z 3
Tone 1 originate at the back of the mouth - Tone 2 in the centre of the mouth and Tone 3 at the front of the mouth.
The different tones of constanents and the 2 sounds of each vowels and their tome can be useful in translating words to PI where initially it seems that there can be more than one way of spelling them.