When praying with the siddur and reading Torah, I've asked myself why is the word כל written with Kamatz if it sounds Kol and not Kal. I've also seen other words like this, but with less frequency. Why does the Kamatz sometimes sounds like an O (a completely different vowel)?
*I don't live in the US, so my pronunciation may vary. For example, I pronounce Shabbat with the same a sound as far.
The vowel qamatz comes in two different flavors: qamatz qatan and qamatz gadol. Qamatz qatan is pronounced like "o" in many Hebrew pronunciations. This is the type of qamatz in the word "כל".
Which type of qamatz a word uses depends on various grammatical rules. In fact, the word "כל" is not even always spelled with a qamatz. Depending on how the sentence is stressed, it could be spelled with a holam.
Yehoshua 1:16 is an interesting example that contains the word כל twice, spelled each way once.
וַֽיַּעֲנ֔וּ אֶת־יְהוֹשֻׁ֖עַ לֵאמֹ֑ר כֹּ֤ל אֲשֶׁר־צִוִּיתָ֨נוּ֙ נַֽעֲשֶׂ֔ה וְאֶֽל־כָּל־אֲשֶׁ֥ר תִּשְׁלָחֵ֖נוּ נֵלֵֽךְ
Unfortunately, the trope marks seem to appear just as squares here, but the first instance of the word כל has a mahpakh trope under it which indicates that the word is stressed as its own word. Since it is a stressed, closed syllable, the vowel is a tenuah gedola: in this case a holam. The second instance of כל does not have a trope associated with it; the word is simply attached to the following word אשר. Here כל is an unstressed closed syllable, so it takes a tenuah qetana, here a qamatz qatan.
It's called a kamatz katan and makes the same sound as a cholam according to many pronunciation systems. Without getting too deep into the grammar, a kamatz kattan is the 'small' version of a cholam, and is used in place of a cholam in certain words, mainly when the word has a less important place of the sentence or is attached in phrase to another word.
this is similar to the es ais difference. alone it is ais, but connected it is es. alone it is coal - with cholam, connected it is kawl - with kawmawtz kawtawn. there are a few exceptions where it is with kawmawtz gawdol, but I would have to look them up.
