Well, I would say "Cool" are Voiceless
as i know (of consonants) produced without moving your vocal cords are "Voiceless". just like the word "Cool"
for Example:
u can just Put ur hand to ur throat and say the word "Cool". and then trying to say the word "Gold". well, i think u can see the different right? When u said the word "Gold" ur vocal cords should have vibrated / Moving. This is because "g" is a voiced consonant. "k" is a voiceless consonant.
Here is the List :
Voiced Consonants (Vocal cords moving):
/b/ = above
/d/ = day
/g/ = gold
/v/ = Very
/ð/ = The / This
/z/ = Zone
/ʒ/ = Measure
/dʒ/ = Jeans
/m/ = Make
/n/ = town
/ŋ/ = Sing
/l/ = Look
/r/ = Red
Voiceless Consonants (Vocal cords not moving) :
/p/ = Pencil
/t/ = Two
/k/ = Cool
/f/ = Find
/ɵ/ = Thin
/s/ = see
/ʃ/ = She
/tʃ/ = change
hope this can help :))