In response to viewer questions, was asked to check out voiceover and narration vocal booths while at NAB. I found Vocal Booth and I must say, I am impressed, and found they can build these units large enough for a video studio space.
I talked with KARL SLECHTA, the PRODUCTION MANAGER at VOCALBOOTH.COM. Didn't want the sales guy, and the sales guy was OK with that, which means I liked these guys already.
Although not cheap, you get what you pay for, and the simplicity of one buy and you're good to go cannot be overlooked.
These are used for voiceovers, audiobook narration, music production, vocals - small enough for a simple vocal booth at 4-foot x 4-foot (1.2 x 1.2 meters) and big enough to make an instant all-in-one video and audio studio - 16-foot x 24-foot (4.9 x 7.3 meters), and 9-foot ceilings.
They custom build your booth to your specs, as simple or decked out as you want it, and can even do a full-size studio with greenscreen built in.
The ventilation is completely quiet (I couldn't hear it at all), and uses the outside ambient air or can be hooked up to an AAC system.
The most impressive part I found was they ship it to you and the entire system can be put together with a single Phillips head screwdriver.