It is often better to record vocals very dry, without any ambience or reverb. This is because you can process the recording in any way you want later. You can add reverb, but you can't take it away.
But achieving a dry vocal sound isn't always easy. If your recording room has hard surfaces, whether flat or irregular, then you will have ambience (the word 'ambience' is generally used to mean the reverberation of a small room). This might sound nice on instruments. It might even sound nice on vocals if you get the mic placement exactly right. But being able to achieve a very dry recording should be part of any recordist's technique.
So you could add acoustic treatment to the room. Acoustic treatment in general (which is not the same as sound insulation) comprises both absorption and diffusion. But here we just want absorption. Without going into the lengthy details here, with sufficient budget and materials you could make any room dry as a dead dingo's armpit.
But what if you don't have the budget? Or you don't want to make the whole room dry? Then you might consider a vocal booth. You can buy a vocal booth, but once again we're talking money. You could build one. Bear in mind that the acoustics of very small spaces are difficult. You could build a small booth, put a lot of absorption in, and find that it ends up sounding 'boxy'.
So in the face of these difficulties, a new class of product has emerged - the portable vocal booth. Typified by this example from sE Electronics, the main aim is to prevent excess vocal sound energy flying straight past the microphone and energizing the room. The device will also reduce reflections that would otherwise strike the back and sides of the mic.
This is a noble aim, although one would have to consider whether any of the similar devices on the market might reflect some sound directly back into the mic. Clearly this would be undesirable.
But one thing seems puzzling. Why are portable vocal booths so small? Well they are not exactly small but they could be a lot bigger. Like a Dyson Sphere versus Ringworld. It's weight that is the problem. It's one matter to sell a product that will sit on a mic stand, quite another if it requires a scaffold to hold it in place.
But these products conventionally treat the vocalist and microphone as an entire system. What about just considering the microphone? What if you could reduce the aperture through which sound energy can access the microphone, so that the microphone is screened from the room in all other directions?
Sounds crazy? Well fortunately there are people in the world crazy enough, or inventive enough, to try it out. Here for instance is the Harlan Hogan Porta-Booth (shown in the photo above). And here is how you can make a similar gadget for yourself...
It's an 'over to you moment'. If you use a booth like this, or build one yourself, send us some 'before and after' audio. A lot of people out there are interested.
P.S. What about adding a hood to go over the performer's head like an old style photographer? Just kidding. Or maybe they already have (at 1:50)...