If your box is tuned to 33 hz, that means the entire box is resonates or pressurizes the most at 33 hz, not including the cabin gain. Cabin gain can make you peak away from tuning frequency, depending on what it is. There's a certain distance you can play away from tuning frequency. How far away you can play depends on many factors. Generally you can't play as low as you can high away from tuning frequency, because the wavelength of sound get exponentially longer as you go longer in frequency. Determining exacly how low you can play should be determined during tuning. You could probably easily play into the 60 hz region, maybe even strongly into the 70's, but only play down maybe to the high 20's, or mids 20's if you're really lucky and have good equipment. But there's a lot of factors that determine that, such as box size, port size, the nature of your subs, things like that.