This excludes all natural classes of sounds besides voiceless stops.

The voiceless alveolar stop is a type of consonantal sound used in many spoken languages.

You just gave me the two raised vowels before voiceless stops I'd driven 350 miles for.

Plain voiceless stops and affricates are changed to their voiced equivalent.

Its initial sound is an unaspirated voiceless bilabial stop, like an English 'b' at the beginning of words.

The voiceless uvular stop has an affricated release in final position.

Of the coronals, the voiceless stop is dental, while the others are alveolar.

The voiceless palatal stop is a type of consonantal sound used in some vocal languages.

They also all have a voiceless stop after the vowel, which may or may not be significant.

In other words, ஃ assimilates to the following voiceless stop".