That name is also used in Germany and it is pronounced ALL-Bert but the A is not pronounced like the English all (ohll). It sounds like the A in staff, like every A in German.
You have to be careful to take accents into account when indicating pronunciation. The "a" in "staff" would have the wrong pronunciation in American English. The "a" in "father" would be better, as this has the sound of German "a" in any accent of English (so far as I know).