Advanced Trap CR

[Snow]

I'm running 3.5 campaign with 13th level characters and I'm trying to calculate the CR of magical traps using the rules from dungeonscape but I don't seem to understand the math behind it.

The magical traps examples:

Four Meteor Swarm at the same time: CR14

4 spell level 9 (CR 10) is a CR 14 according to encounter level table (3-1 in master's guide)
Maximized Meteor Swarm Trap: CR 13

This is easy, it's a level 12 spell +1
Sucking Void Trap: CR 14

This I don't get it how two level 9 spells and a level 7 spell can get that DC
Intelligent Empowered Polar Ray Trap: CR17

This I have no clue how they got that CR

[Tyndmyr]

Use trap rules from SBG instead.

[Snow]

SBG its 3.0. We are playing 3.5. Also the rules in SBG are really simple I'm looking for high level traps. But thanks anyway for the suggestion.