In my office I tend to rock out to a 300-watt stereo system. When I go to wash dishes and have to use my iPad's native speaker, well, there's no comparison. Belkin's Thunderstorm case won't crank up to the level of a really large stereo, but it is loud enough to punch through very noisy environments with ease. At CES I tried one on the show floor where the sound level (according to my iPhone) was close to 100 decibels and the Thunderstorm was not only loud enough to hear, the audio actually sounded good. It's not perfect, however, as I'll explain below. It also retails for US$199, so this is not a budget case or speaker.
Like any iPad case that surrounds the iPad, the Thunderstorm cradles your iPad in a large plastic shell and provides a cover somewhat like Apple's Smart Cover -- but with no magnetic actuation of the iPad itself, like the Smart Cover. The iPad slides into the case, and is secured by a 30-pin dock connection which clicks into place, and provides the power and audio output needed.
Of course you simply can't get around physics, so the drivers for the Thunderbolt are heavy. The case is heavy. Your iPad inside will make all of this very heavy, but this is not a case for casual use if you tend to mostly read iBooks on your iPad. This case is designed to stand up and be loud. There's a shockingly small speaker port on the front, along with a small light under the grill to indicate when the charger (included) is plugged in. The case uses ports to enhance the sound, much as a full size speaker would, and they work very well.
I had a little trouble with the charger at first, until I realized there's just a delay from when you plug it in to when the iPad begins to charge. Still, it is a wall wart and not the most convenient AC adapter to carry around. I wouldn't say it charges slowly, but it is not a fast charge by any means.
A bigger problem in the cover flap. It's one of those origami-style flaps that pinches together to provide a "stand" for viewing the iPad mostly upright. You can roll up the case like Apple's cover, which provides a more upright angle, or fold the case into a bit of a triangle, putting the iPad at almost 45 degrees. That viewing angle is a bit odd, as I felt it leaned back a little far, and you cannot adjust it, but there's the other option, which I felt isn't as stable.
The good news is the flap, when folded as a support, is very sturdy and I never really had it fall down. The bad news is it is loosely secured at the hinge, and if you're used to the relatively strong magnets on the Smart Cover, you will find these magnets aren't as strong. Often while closing the flap I would yank the cover off -- and I'm a wimp.
There are pass-through (mechanical) buttons for power, rotation and volume, plus a large hole for headphones and even a speaker vent at the bottom where the iPad's speaker resides.
It's loud. Really loud. Without exception, when I would demonstrate the volume on this thing their eyebrows would raise and they would say "wow." You won't believe so much sound can come from a small package -- unless you've used a Bose Smartwave, which is similar in a way.
Loudness is the distinguishing feature here, however. This is not a protective case, and it's not designed to do much more than cradle your iPad and make it much louder. Luckily it does that job admirably. It's worth noting that audio quality does not suffer at the hands of volume, and even at the highest setting the highs were crystal clear while the bass punched through loud environments admirably.
There's also a companion app which does boring stuff like handle registration and check firmware, but it also allows you to control the stereo separation. That's a neat trick, but unless you have the device pointed at your face, you lose the spread pretty quickly. Sound, again, is bound by the laws of physics.
If you need a very loud speaker for the iPad but don't want something huge like a dock or external stereo, and you want this speaker embedded in a case, the Thunderstorm is perfect. Belkin's Thunderstorm is the loudest iPad case I've ever heard, and the audio quality doesn't suffer as you crank up the volume. The price, at $199, may turn off some customers, but if you compare to large boombox docks (like JBL's OnStage) it's pretty reasonable. I feel that you're getting your money's worth if you frequently need your iPad to be heard in loud environments or you just want ear-blasting noise from your tablet.