Ye Olde Rocket Forum - View Single Post - Perforations in solid propellant to reduce output

So I was doing a little reading online about MaxQ and I read something on Wikipedia that drew my interest and want to pose a question here, if anyone wants to take it on.

This is what I read about Max Q as it relates to the Space Shuttle.

"During a normal Space Shuttle launch, for example, max Q occurred at an altitude of approximately 11 km (35,000 ft).[1] The three Space Shuttle Main Engines are throttled back to about 70% of their rated thrust as the dynamic pressure approaches max Q;[2] combined with the propellant perforation design of the solid rocket boosters, which reduces the thrust at max Q by 1/3 after 50 sec of burn, the total stresses on the vehicle are kept to a safe level."

Neat huh? This is my question. I can't picture in my mind how they engineered in perforations into the solid propellant to reduce output without creating small combustion chambers deep inside the solid rocket motor that would ordinarily lead to a CATO?

Then my next question of course is, did they engineer in a throttle up on the boosters back to 100% after max Q or did the boosters continue to burn at 1/3 reduced output?

Not that this new found knowledge will make me a better model rocket enthusiast. Just curious. How did they figured out that they could do that?

David