[sparky77]

In the push pull configuration you could actually go a bit smaller with a 60L enclosure and have pretty flat response depending on your room. I have a garage full of lab12's and have done quite a few experiments, and an isobaric configuration would be a waste fo the available cone area, stick with push pull you put together, and maybe try a few different sizes between 40 and 90L. That is unless you want to go larger and use a long slot port where you can easily dig down to less than 16hz in room response.