Question about room dimensions when calcualting modes etc

My room is 18.1ft long. The rear quarter of the room I use for storage, and is sectioned off by 1 inch foam hanging from the roof, across the width of the room, about 3/4 of the way to the floor.. Would the length dimension I use for calculations be 18.1 ft, or the distance from the front of the room to the hanging foam sectioning of the rear 1/4 of the room? thanks

Mondo, That depends on the type of foam. But normally you calculate with the acoustic boundaries, which translated means the surfaces which reflect, which in itself assumes they have a certain TL. Since you're most likely interested in the lows you must most likely take the room measures into account.